1. Hibernate Tutorial

2. HIBERNATE TUTORIALSimply Easy Learning by tutorialspoint.comtutorialspoint.com

3. TUTORIALS POINTSimply Easy LearningABOUT THE TUTORIALHibernate TutorialHibernate is a high-performance Object/Relational persistence and query service which is licensed under theopen source GNU Lesser General Public License (LGPL) and is free to download. Hibernate not only takes careof the mapping from Java classes to database tables (and from Java data types to SQL data types), but alsoprovides data query and retrieval facilities.This tutorial will teach you how to use Hibernate to develop your database based web applications in simple andeasy steps.AudienceThis tutorial is designed for Java programmers with a need to understand the Hibernate framework and API. Aftercompleting this tutorial you will find yourself at a moderate level of expertise in using Hibernate from where youcan take yourself to next levels.PrerequisitesWe assume you have good understanding of the Java programming language. A basic understanding ofrelational databases, JDBC and SQL is very helpful.Copyright & Disclaimer Notice All the content and graphics on this tutorial are the property of tutorialspoint.com. Any content fromtutorialspoint.com or this tutorial may not be redistributed or reproduced in any way, shape, or formwithout the written permission of tutorialspoint.com. Failure to do so is a violation of copyright laws.This tutorial may contain inaccuracies or errors and tutorialspoint provides no guarantee regarding theaccuracy of the site or its contents including this tutorial. If you discover that the tutorialspoint.com siteor this tutorial content contains some errors, please contact us at webmaster@tutorialspoint.com

4. TUTORIALS POINTSimply Easy LearningTable of ContentHibernate Tutorial .................................................................... 2Audience.................................................................................. 2Prerequisites............................................................................ 2Copyright & Disclaimer Notice.................................................. 2ORM Overview......................................................................... 8Pros and Cons of JDBC...................................................................................8Why Object Relational Mapping (ORM)?.........................................................8What is ORM? ..............................................................................................9Java ORM Frameworks................................................................................10Hibernate Overview ............................................................... 11Hibernate Advantages.................................................................................11Supported Databases..................................................................................12Supported Technologies..............................................................................12Hibernate Architecture ........................................................... 13Configuration Object...................................................................................14SessionFactory Object .................................................................................14Session Object............................................................................................15Transaction Object......................................................................................15Query Object..............................................................................................15Criteria Object............................................................................................15Hibernate Environment .......................................................... 16Downloading Hibernate:..............................................................................16Installing Hibernate.....................................................................................17Hibernate Prerequisites...............................................................................17Hibernate Configuration ......................................................... 18Hibernate Properties...................................................................................18Hibernate with MySQL Database..................................................................19Hibernate Sessions................................................................ 21Session Interface Methods ..........................................................................22Hibernate Persistent Class..................................................... 24A simple POJO example:..............................................................................24Hibernate Mapping Files ........................................................ 26Hibernate Mapping Types ...................................................... 29Primitive types ...........................................................................................29Date and time types....................................................................................29Binary and large object types.......................................................................30JDK-related types........................................................................................30

5. TUTORIALS POINTSimply Easy LearningHibernate Examples............................................................... 31Create POJO Classes....................................................................................31Create Database Tables...............................................................................32Create Mapping Configuration File ...............................................................32Create Application Class ..............................................................................33Compilation and Execution ..........................................................................35Hibernate O/R Mapping ......................................................... 36Collections Mappings ............................................................................36Hibernate Set Mappings..............................................................................36Define RDBMS Tables ................................................................................37Define POJO Classes...................................................................................37Define Hibernate Mapping File ..................................................................39Create Application Class ............................................................................40Compilation and Execution........................................................................42Hibernate SortedSet Mappings ....................................................................43Define RDBMS Tables ................................................................................43Define POJO Classes...................................................................................44Define Hibernate Mapping File ..................................................................45Create Application Class ............................................................................47Compilation and Execution........................................................................49Hibernate List Mappings..............................................................................50Define RDBMS Tables ................................................................................50Define POJO Classes...................................................................................51Define Hibernate Mapping File ..................................................................52Create Application Class ............................................................................53Compilation and Execution........................................................................55Hibernate Bag Mappings .............................................................................57Define RDBMS Tables ................................................................................57Define POJO Classes...................................................................................57Define Hibernate Mapping File ..................................................................58Create Application Class ............................................................................60Compilation and Execution........................................................................62Hibernate Map Mappings ............................................................................63Define RDBMS Tables ................................................................................63Define POJO Classes...................................................................................63Define Hibernate Mapping File ..................................................................65Create Application Class ............................................................................66Compilation and Execution........................................................................68Hibernate SortedMap Mappings ..................................................................69

6. TUTORIALS POINTSimply Easy LearningDefine RDBMS Tables ................................................................................69Define POJO Classes...................................................................................70Define Hibernate Mapping File ..................................................................71Compilation and Execution........................................................................75Association Mappings ...........................................................................76Hibernate Many-to-One Mappings ...............................................................76Define RDBMS Tables ................................................................................76Define POJO Classes...................................................................................77Define Hibernate Mapping File ..................................................................79Compilation and Execution........................................................................82Hibernate One-to-One Mappings .................................................................83Define RDBMS Tables ................................................................................83Define POJO Classes...................................................................................84Define Hibernate Mapping File ..................................................................86Compilation and Execution........................................................................89Hibernate One-to-Many Mappings ...............................................................90Define RDBMS Tables ................................................................................90Define POJO Classes...................................................................................91Define Hibernate Mapping File ..................................................................92Create Application Class ............................................................................93Compilation and Execution........................................................................95Hibernate Many-to-Many Mappings.............................................................96Define RDBMS Tables ................................................................................97Define POJO Classes...................................................................................97Define Hibernate Mapping File ..................................................................99Create Application Class ..........................................................................100Compilation and Execution......................................................................102Component Mappings...............................................................................103Hibernate Component Mappings................................................................103Define RDBMS Tables ..............................................................................103Define POJO Classes.................................................................................104Define Hibernate Mapping File ................................................................106Create Application Class ..........................................................................107Compilation and Execution......................................................................109Hibernate Annotations.......................................................... 111Environment Setup for Hibernate Annotation..............................................111Annotated Class Example ..........................................................................111@Entity Annotation ..................................................................................112@Table Annotation...................................................................................113

7. TUTORIALS POINTSimply Easy Learning@Id and @GeneratedValue Annotations.....................................................113@Column Annotation ...............................................................................113Create Application Class ............................................................................113Database Configuration.............................................................................115Compilation and Execution ........................................................................116Hibernate Query Language.................................................. 117FROM Clause............................................................................................117AS Clause.................................................................................................117SELECT Clause ..........................................................................................118WHERE Clause..........................................................................................118ORDER BY Clause ......................................................................................118GROUP BY Clause......................................................................................118Using Named Paramters............................................................................119UPDATE Clause.........................................................................................119DELETE Clause ..........................................................................................119INSERT Clause ..........................................................................................119Aggregate Methods ..................................................................................119Pagination using Query .............................................................................120Hibernate Criteria Queries ................................................... 121Restrictions with Criteria ...........................................................................121Pagination using Criteria............................................................................122Sorting the Results....................................................................................123Projections & Aggregations........................................................................123Criteria Queries Example ...........................................................................123Compilation and Execution ........................................................................127Hibernate Native SQL .......................................................... 128Scalar queries...........................................................................................128Entity queries...........................................................................................128Named SQL queries...................................................................................129Native SQL Example ..................................................................................129Compilation and Execution ........................................................................132Hibernate Caching ............................................................... 133First-level cache........................................................................................133Second-level cache ...................................................................................134Query-level cache.....................................................................................134The Second Level Cache ............................................................................134Concurrency strategies..............................................................................134Cache provider .........................................................................................135The Query-level Cache ..............................................................................137

8. TUTORIALS POINTSimply Easy LearningHibernate Batch Processing................................................. 138Batch Processing Example .........................................................................139Compilation and Execution ........................................................................142Hibernate Interceptors.......................................................... 143How to use Interceptors? ..........................................................................144Create Interceptors...................................................................................144Create POJO Classes..................................................................................145Create Database Tables.............................................................................145Create Mapping Configuration File .............................................................146Create Application Class ............................................................................146Compilation and Execution ........................................................................148

9. TUTORIALS POINTSimply Easy LearningORM OverviewJDBC stands for Java Database Connectivity and provides a set of Java API for accessing the relationaldatabases from Java program. These Java APIs enables Java programs to execute SQL statements and interactwith any SQL compliant database.JDBC provides a flexible architecture to write a database independent application that can run on differentplatforms and interact with different DBMS without any modification.Pros and Cons of JDBCPros of JDBC Cons of JDBC Clean and simple SQL processing Good performance with large data Very good for small applications Simple syntax so easy to learn Complex if it is used in large projects Large programming overhead No encapsulation Hard to implement MVC concept Query is DBMS specificWhy Object Relational Mapping (ORM)?When we work with an object-oriented systems, theres a mismatch between the object model and the relationaldatabase. RDBMSs represent data in a tabular format whereas object-oriented languages, such as Java or C#represent it as an interconnected graph of objects. Consider the following Java Class with proper constructors andassociated public function:public class Employee {private int id;private String first_name;private String last_name;private int salary;CHAPTER1

10. TUTORIALS POINTSimply Easy Learningpublic Employee() {}public Employee(String fname, String lname, int salary) {this.first_name = fname;this.last_name = lname;this.salary = salary;}public int getId() {return id;}public String getFirstName() {return first_name;}public String getLastName() {return last_name;}public int getSalary() {return salary;}}Consider above objects need to be stored and retrieved into the following RDBMS table:create table EMPLOYEE (id INT NOT NULL auto_increment,first_name VARCHAR(20) default NULL,last_name VARCHAR(20) default NULL,salary INT default NULL,PRIMARY KEY (id));First problem, what if we need to modify the design of our database after having developed few pages or ourapplication? Second, Loading and storing objects in a relational database exposes us to the following fivemismatch problems.Mismatch DescriptionGranularitySometimes you will have an object model which has more classes than thenumber of corresponding tables in the database.InheritanceRDBMSs do not define anything similar to Inheritance which is a natural paradigmin object-oriented programming languages.IdentityA RDBMS defines exactly one notion of sameness: the primary key. Java,however, defines both object identity (a==b) and object equality (a.equals(b)).AssociationsObject-oriented languages represent associations using object references whereas am RDBMS represents an association as a foreign key column.Navigation The ways you access objects in Java and in a RDBMS are fundamentally different.The Object-Relational Mapping (ORM) is the solution to handle all the above impedance mismatches.What is ORM?ORM stands for Object-Relational Mapping (ORM) is a programming technique for converting data betweenrelational databases and object oriented programming languages such as Java, C# etc. An ORM system hasfollowing advantages over plain JDBC

11. TUTORIALS POINTSimply Easy LearningS.N. Advantages1 Lets business code access objects rather than DB tables.2 Hides details of SQL queries from OO logic.3 Based on JDBC under the hood4 No need to deal with the database implementation.5 Entities based on business concepts rather than database structure.6 Transaction management and automatic key generation.7 Fast development of application.An ORM solution consists of the following four entities:S.N. Solutions1 An API to perform basic CRUD operations on objects of persistent classes.2 A language or API to specify queries that refer to classes and properties of classes.3 A configurable facility for specifying mapping metadata.4A technique to interact with transactional objects to perform dirty checking, lazy associationfetching, and other optimization functions.Java ORM FrameworksThere are several persistent frameworks and ORM options in Java. A persistent framework is an ORM service thatstores and retrieves objects into a relational database. Enterprise JavaBeans Entity Beans Java Data Objects Castor TopLink Spring DAO Hibernate And many more

12. TUTORIALS POINTSimply Easy LearningHibernate OverviewHibernate is an Object-Relational Mapping(ORM) solution for JAVA and it raised as an open sourcepersistent framework created by Gavin King in 2001. It is a powerful, high performance Object-RelationalPersistence and Query service for any Java Application.Hibernate maps Java classes to database tables and from Java data types to SQL data types and relieve thedeveloper from 95% of common data persistence related programming tasks.Hibernate sits between traditional Java objects and database server to handle all the work in persisting thoseobjects based on the appropriate O/R mechanisms and patterns.Hibernate Advantages Hibernate takes care of mapping Java classes to database tables using XML files and without writingany line of code. Provides simple APIs for storing and retrieving Java objects directly to and from the database. If there is change in Database or in any table then the only need to change XML file properties. Abstract away the unfamiliar SQL types and provide us to work around familiar Java Objects. Hibernate does not require an application server to operate. Manipulates Complex associations of objects of your database.CHAPTER2

13. TUTORIALS POINTSimply Easy Learning Minimize database access with smart fetching strategies. Provides Simple querying of data.Supported DatabasesHibernate supports almost all the major RDBMS. Following is list of few of the database engines supported byHibernate. HSQL Database Engine DB2/NT MySQL PostgreSQL FrontBase Oracle Microsoft SQL Server Database Sybase SQL Server Informix Dynamic ServerSupported TechnologiesHibernate supports a variety of other technologies, including the following: XDoclet Spring J2EE Eclipse plug-ins Maven

14. TUTORIALS POINTSimply Easy LearningHibernate ArchitectureThe Hibernate architecture is layered to keep you isolated from having to know the underlying APIs.Hibernate makes use of the database and configuration data to provide persistence services (and persistentobjects) to the application.Following is a very high level view of the Hibernate Application Architecture.Following is a detailed view of the Hibernate Application Architecture with few important core classes.CHAPTER3

15. TUTORIALS POINTSimply Easy LearningHibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java Naming andDirectory Interface (JNDI). JDBC provides a rudimentary level of abstraction of functionality common to relationaldatabases, allowing almost any database with a JDBC driver to be supported by Hibernate. JNDI and JTA allowHibernate to be integrated with J2EE application servers.Following section gives brief description of each of the class objects involved in Hibernate ApplicationArchitecture.Configuration ObjectThe Configuration object is the first Hibernate object you create in any Hibernate application and usually createdonly once during application initialization. It represents a configuration or properties file required by the Hibernate.The Configuration object provides two keys components: Database Connection: This is handled through one or more configuration files supported by Hibernate.These files are hibernate.properties and hibernate.cfg.xml. Class Mapping Setup: This component creates the connection between the Java classes and databasetables.SessionFactory ObjectConfiguration object is used to create a SessionFactory object which inturn configures Hibernate for theapplication using the supplied configuration file and allows for a Session object to be instantiated. TheSessionFactory is a thread safe object and used by all the threads of an application.

16. TUTORIALS POINTSimply Easy LearningThe SessionFactory is heavyweight object so usually it is created during application start up and kept for lateruse. You would need one SessionFactory object per database using a separate configuration file. So if you areusing multiple databases then you would have to create multiple SessionFactory objects.Session ObjectA Session is used to get a physical connection with a database. The Session object is lightweight and designed tobe instantiated each time an interaction is needed with the database. Persistent objects are saved and retrievedthrough a Session object.The session objects should not be kept open for a long time because they are not usually thread safe and theyshould be created and destroyed them as needed.Transaction ObjectA Transaction represents a unit of work with the database and most of the RDBMS supports transactionfunctionality. Transactions in Hibernate are handled by an underlying transaction manager and transaction (fromJDBC or JTA).This is an optional object and Hibernate applications may choose not to use this interface, instead managingtransactions in their own application code.Query ObjectQuery objects use SQL or Hibernate Query Language (HQL) string to retrieve data from the database and createobjects. A Query instance is used to bind query parameters, limit the number of results returned by the query, andfinally to execute the query.Criteria ObjectCriteria object are used to create and execute object oriented criteria queries to retrieve objects.

17. TUTORIALS POINTSimply Easy LearningHibernate EnvironmentThis chapter will explain how to install Hibernate and other associated packages to prepare a developenvironment for the Hibernate applications. We will work with MySQL database to experiment with Hibernateexamples, so make sure you already have setup for MySQL database. For a more detail on MySQL you cancheck our MySQL Tutorial.Downloading Hibernate:It is assumed that you already have latest version of Java is installed on your machine. Following are the simplesteps to download and install Hibernate on your machine. Make a choice whether you want to install Hibernate on Windows, or Unix and then proceed to the nextstep to download .zip file for windows and .tz file for Unix. Download the latest version of Hibernate from http://www.hibernate.org/downloads. At the time of writing this tutorial I downloaded hibernate-distribution-3.6.4.Final and when you unzipthe downloaded file it will give you directory structure as follows.CHAPTER4

18. TUTORIALS POINTSimply Easy LearningInstalling HibernateOnce you downloaded and unzipped the latest version of the Hibernate Installation file, you need to performfollowing two simple steps. Make sure you are setting your CLASSPATH variable properly otherwise you will faceproblem while compiling your application. Now copy all the library files from /lib into your CLASSPATH, and change your classpath variable toinclude all the JARs: Finally copy hibernate3.jar file into your CLASSPATH. This file lies in the root directory of theinstallation and is the primary JAR that Hibernate needs to do its work.Hibernate PrerequisitesFollowing is the list of the packages/libraries required by Hibernate and you should install them before startingwith Hibernate. To install these packages you would have to copy library files from /lib into your CLASSPATH,and change your CLASSPATH variable accordingly.S.N. Packages/Libraries1 dom4j - XML parsing www.dom4j.org/2 Xalan - XSLT Processor http://xml.apache.org/xalan-j/3 Xerces - The Xerces Java Parser http://xml.apache.org/xerces-j/4 cglib - Appropriate changes to Java classes at runtime http://cglib.sourceforge.net/5 log4j - Logging Faremwork http://logging.apache.org/log4j6 Commons - Logging, Email etc. http://jakarta.apache.org/commons7 SLF4J - Logging Facade for Java http://www.slf4j.org

19. TUTORIALS POINTSimply Easy LearningHibernate ConfigurationHibernate requires to know in advance where to find the mapping information that defines how your Javaclasses relate to the database tables. Hibernate also requires a set of configuration settings related to databaseand other related parameters. All such information is usually supplied as a standard Java properties filecalled hibernate.properties, or as an XML file named hibernate.cfg.xml.I will consider XML formatted file hibernate.cfg.xml to specify required Hibernate properties in my examples.Most of the properties take their default values and it is not required to specify them in the property file unless it isreally required. This file is kept in the root directory of your applications classpath.Hibernate PropertiesFollowing is the list of important properties you would require to configure for a databases in a standalonesituation:S.N. Properties and Description1hibernate.dialectThis property makes Hibernate generate the appropriate SQL for the chosen database.2hibernate.connection.driver_classThe JDBC driver class.3hibernate.connection.urlThe JDBC URL to the database instance.4hibernate.connection.usernameThe database username.5hibernate.connection.passwordThe database password.6hibernate.connection.pool_sizeLimits the number of connections waiting in the Hibernate database connection pool.7hibernate.connection.autocommitAllows autocommit mode to be used for the JDBC connection.If you are using a database along with an application server and JNDI then you would have to configure thefollowing properties:CHAPTER5

20. TUTORIALS POINTSimply Easy LearningS.N. Properties and Description1hibernate.connection.datasourceThe JNDI name defined in the application server context you are using for the application.2hibernate.jndi.classThe InitialContext class for JNDI.3hibernate.jndi.Passes any JNDI property you like to the JNDI InitialContext.4hibernate.jndi.urlProvides the URL for JNDI.5hibernate.connection.usernameThe database username.6hibernate.connection.passwordThe database password.Hibernate with MySQL DatabaseMySQL is one of the most popular open-source database systems available today. Let uscreatehibernate.cfg.xml configuration file and place it in the root of your applications classpath. You would haveto make sure that you have testdb database available in your MySQL database and you have auser test available to access the database.The XML configuration file must conform to the Hibernate 3 Configuration DTD, which is available fromhttp://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd.org.hibernate.dialect.MySQLDialectcom.mysql.jdbc.Driverjdbc:mysql://localhost/testrootroot123

21. TUTORIALS POINTSimply Easy LearningThe above configuration file includes tags which are related to hibernate-mapping file and we will seein next chapter what exactly is a hibernate mapping file and how and why do we use it. Following is the list ofvarious important databases dialect property type:Database Dialect PropertyDB2 org.hibernate.dialect.DB2DialectHSQLDB org.hibernate.dialect.HSQLDialectHypersonicSQL org.hibernate.dialect.HSQLDialectInformix org.hibernate.dialect.InformixDialectIngres org.hibernate.dialect.IngresDialectInterbase org.hibernate.dialect.InterbaseDialectMicrosoft SQL Server 2000 org.hibernate.dialect.SQLServerDialectMicrosoft SQL Server 2005 org.hibernate.dialect.SQLServer2005DialectMicrosoft SQL Server 2008 org.hibernate.dialect.SQLServer2008DialectMySQL org.hibernate.dialect.MySQLDialectOracle (any version) org.hibernate.dialect.OracleDialectOracle 11g org.hibernate.dialect.Oracle10gDialectOracle 10g org.hibernate.dialect.Oracle10gDialectOracle 9i org.hibernate.dialect.Oracle9iDialectPostgreSQL org.hibernate.dialect.PostgreSQLDialectProgress org.hibernate.dialect.ProgressDialectSAP DB org.hibernate.dialect.SAPDBDialectSybase org.hibernate.dialect.SybaseDialectSybase Anywhere org.hibernate.dialect.SybaseAnywhereDialectSerial No Class Name Functionality1 Assert A set of assert methods.2 TestCase A test case defines the fixture to run multiple tests.3 TestResultA TestResult collects the results of executing atest case.4 TestSuite A TestSuite is a Composite of Tests.

22. TUTORIALS POINTSimply Easy LearningHibernate SessionsASession is used to get a physical connection with a database. The Session object is lightweight anddesigned to be instantiated each time an interaction is needed with the database. Persistent objects are savedand retrieved through a Session object.The session objects should not be kept open for a long time because they are not usually thread safe and theyshould be created and destroyed them as needed. The main function of the Session is to offer create, read anddelete operations for instances of mapped entity classes. Instances may exist in one of the following three statesat a given point in time: transient: A new instance of a a persistent class which is not associated with a Session and has norepresentation in the database and no identifier value is considered transient by Hibernate. persistent: You can make a transient instance persistent by associating it with a Session. A persistentinstance has a representation in the database, an identifier value and is associated with a Session. detached: Once we close the Hibernate Session, the persistent instance will become a detachedinstance.A Session instance is serializable if its persistent classes are serializable. A typical transaction should use thefollowing idiom:Session session = factory.openSession();Transaction tx = null;try {tx = session.beginTransaction();// do some work...tx.commit();}catch (Exception e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}If the Session throws an exception, the transaction must be rolled back and the session must be discarded.CHAPTER6

23. TUTORIALS POINTSimply Easy LearningSession Interface MethodsThere are number of methods provided by the Session interface but Im going to list down few important methodsonly, which we will use in this tutorial. You can check Hibernate documentation for a complete list of methodsassociated with Session and SessionFactory.S.N. Session Methods and Description1Transaction beginTransaction()Begin a unit of work and return the associated Transaction object.2void cancelQuery()Cancel the execution of the current query.3void clear()Completely clear the session.4Connection close()End the session by releasing the JDBC connection and cleaning up.5Criteria createCriteria(Class persistentClass)Create a new Criteria instance, for the given entity class, or a superclass of an entity class.6Criteria createCriteria(String entityName)Create a new Criteria instance, for the given entity name.7Serializable getIdentifier(Object object)Return the identifier value of the given entity as associated with this session.8Query createFilter(Object collection, String queryString)Create a new instance of Query for the given collection and filter string.9Query createQuery(String queryString)Create a new instance of Query for the given HQL query string.10SQLQuery createSQLQuery(String queryString)Create a new instance of SQLQuery for the given SQL query string.11void delete(Object object)Remove a persistent instance from the datastore.12void delete(String entityName, Object object)Remove a persistent instance from the datastore.13Session get(String entityName, Serializable id)Return the persistent instance of the given named entity with the given identifier, or null ifthere is no such persistent instance.14SessionFactory getSessionFactory()Get the session factory which created this session.15void refresh(Object object)Re-read the state of the given instance from the underlying database.16Transaction getTransaction()Get the Transaction instance associated with this session.17boolean isConnected()Check if the session is currently connected.18boolean isDirty()Does this session contain any changes which must be synchronized with the database?

24. TUTORIALS POINTSimply Easy Learning19boolean isOpen()Check if the session is still open.20Serializable save(Object object)Persist the given transient instance, first assigning a generated identifier.21void saveOrUpdate(Object object)Either save(Object) or update(Object) the given instance.22void update(Object object)Update the persistent instance with the identifier of the given detached instance.23void update(String entityName, Object object)Update the persistent instance with the identifier of the given detached instance.

25. TUTORIALS POINTSimply Easy LearningHibernate Persistent ClassThe entire concept of Hibernate is to take the values from Java class attributes and persist them to adatabase table. A mapping document helps Hibernate in determining how to pull the values from the classes andmap them with table and associated fields.Java classes whose objects or instances will be stored in database tables are called persistent classes inHibernate. Hibernate works best if these classes follow some simple rules, also known as the Plain Old JavaObject (POJO) programming model. There are following main rules of persistent classes, however, none of theserules are hard requirements. All Java classes that will be persisted need a default constructor. All classes should contain an ID in order to allow easy identification of your objects within Hibernate andthe database. This property maps to the primary key column of a database table. All attributes that will be persisted should be declared private and have getXXX and setXXXmethodsdefined in the JavaBean style. A central feature of Hibernate, proxies, depends upon the persistent class being either non-final, or theimplementation of an interface that declares all public methods. All classes that do not extend or implement some specialized classes and interfaces required by the EJBframework.The POJO name is used to emphasize that a given object is an ordinary Java Object, not a special object, and inparticular not an Enterprise JavaBean.A simple POJO example:Based on the few rules mentioned above we can define a POJO class as follows:public class Employee {private int id;private String firstName;private String lastName;private int salary;public Employee() {}CHAPTER7

26. TUTORIALS POINTSimply Easy Learningpublic Employee(String fname, String lname, int salary) {this.firstName = fname;this.lastName = lname;this.salary = salary;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getFirstName() {return firstName;}public void setFirstName( String first_name ) {this.firstName = first_name;}public String getLastName() {return lastName;}public void setLastName( String last_name ) {this.lastName = last_name;}public int getSalary() {return salary;}public void setSalary( int salary ) {this.salary = salary;}}

27. TUTORIALS POINTSimply Easy LearningHibernate Mapping FilesAn Object/relational mappings are usually defined in an XML document. This mapping file instructsHibernate how to map the defined class or classes to the database tables.Though many Hibernate users choose to write the XML by hand, a number of tools exist to generate the mappingdocument. These include XDoclet, Middlegen and AndroMDA for advanced Hibernate users.Let us consider our previously defined POJO class whose objects will persist in the table defined in next section.public class Employee {private int id;private String firstName;private String lastName;private int salary;public Employee() {}public Employee(String fname, String lname, int salary) {this.firstName = fname;this.lastName = lname;this.salary = salary;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getFirstName() {return firstName;}public void setFirstName( String first_name ) {this.firstName = first_name;}public String getLastName() {return lastName;}public void setLastName( String last_name ) {this.lastName = last_name;}public int getSalary() {return salary;}CHAPTER8

28. TUTORIALS POINTSimply Easy Learningpublic void setSalary( int salary ) {this.salary = salary;}}There would be one table corresponding to each object you are willing to provide persistence. Consider aboveobjects need to be stored and retrieved into the following RDBMS table:create table EMPLOYEE (id INT NOT NULL auto_increment,first_name VARCHAR(20) default NULL,last_name VARCHAR(20) default NULL,salary INT default NULL,PRIMARY KEY (id));Based on the two above entities we can define following mapping file which instructs Hibernate how to map thedefined class or classes to the database tables.This class contains the employee detail.You should save the mapping document in a file with the format .hbm.xml. We saved our mappingdocument in the file Employee.hbm.xml. Let us see little detail about the mapping elements used in the mappingfile: The mapping document is an XML document having as the root element whichcontains all the elements. The elements are used to define specific mappings from a Java classes to the database tables.The Java class name is specified using the name attribute of the class element and the database tablename is specified using the table attribute. The element is optional element and can be used to create the class description. The element maps the unique ID attribute in class to the primary key of the database table.The name attribute of the id element refers to the property in the class and the column attribute refers tothe column in the database table. The type attribute holds the hibernate mapping type, this mappingtypes will convert from Java to SQL data type. The element within the id element is used to automatically generate the primary keyvalues. Set the class attribute of the generator element is set to native to let hibernate pick up

29. TUTORIALS POINTSimply Easy Learningeither identity, sequence or hilo algorithm to create primary key depending upon the capabilities of theunderlying database. The element is used to map a Java class property to a column in the database table.The name attribute of the element refers to the property in the class and the column attribute refers tothe column in the database table. The type attribute holds the hibernate mapping type, this mappingtypes will convert from Java to SQL data type.There are other attributes and elements available which will be used in a mapping document and I would try tocover as many as possible while discussing other Hibernate related topics.

30. TUTORIALS POINTSimply Easy LearningHibernate Mapping TypesWhen you prepare a Hibernate mapping document, we have seen that you map Java data types intoRDBMS data types. The types declared and used in the mapping files are not Java data types; they are not SQLdatabase types either. These types are called Hibernate mapping types, which can translate from Java to SQLdata types and vice versa.This chapter lists down all the basic, date and time, large object, and various other built-in mapping types.Primitive typesMapping type Java type ANSI SQL Typeinteger int or java.lang.Integer INTEGERlong long or java.lang.Long BIGINTshort short or java.lang.Short SMALLINTfloat float or java.lang.Float FLOATdouble double or java.lang.Double DOUBLEbig_decimal java.math.BigDecimal NUMERICcharacter java.lang.String CHAR(1)string java.lang.String VARCHARbyte byte or java.lang.Byte TINYINTboolean boolean or java.lang.Boolean BITyes/no boolean or java.lang.BooleanCHAR(1) (Y orN)true/false boolean or java.lang.BooleanCHAR(1) (T orF)Date and time typesMapping type Java type ANSI SQL Type.CHAPTER9

31. TUTORIALS POINTSimply Easy Learningdate java.util.Date or java.sql.Date DATEtime java.util.Date or java.sql.Time TIMEtimestamp java.util.Date or java.sql.Timestamp TIMESTAMPcalendar java.util.Calendar TIMESTAMPcalendar_date java.util.Calendar DATEBinary and large object typesMapping type Java type ANSI SQL Typebinary byte[]VARBINARY (orBLOB)text java.lang.String CLOBserializable any Java class that implements java.io.SerializableVARBINARY (orBLOB)clob java.sql.Clob CLOBblob java.sql.Blob BLOBJDK-related typesMapping type Java type ANSI SQL Typeclass java.lang.Class VARCHARlocale java.util.Locale VARCHARtimezone java.util.TimeZone VARCHARcurrency java.util.Currency VARCHAR

32. TUTORIALS POINTSimply Easy LearningHibernate ExamplesLet us try an example of using Hibernate to provide Java persistence in a standalone application. We willgo through different steps involved in creating Java Application using Hibernate technology.Create POJO ClassesThe first step in creating an application is to build the Java POJO class or classes, depending on the applicationthat will be persisted to the database. Let us consider our Employee class with getXXX andsetXXX methods tomake it JavaBeans compliant class.A POJO (Plain Old Java Object) is a Java object that doesnt extend or implement some specialized classes andinterfaces respectively required by the EJB framework. All normal Java objects are POJO.When you design a classs to be persisted by Hibernate, its important to provide JavaBeans compliant code aswell as one attribute which would work as index like id attribute in the Employee class.public class Employee {private int id;private String firstName;private String lastName;private int salary;public Employee() {}public Employee(String fname, String lname, int salary) {this.firstName = fname;this.lastName = lname;this.salary = salary;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getFirstName() {return firstName;}public void setFirstName( String first_name ) {this.firstName = first_name;}public String getLastName() {CHAPTER10

33. TUTORIALS POINTSimply Easy Learningreturn lastName;}public void setLastName( String last_name ) {this.lastName = last_name;}public int getSalary() {return salary;}public void setSalary( int salary ) {this.salary = salary;}}Create Database TablesSecond step would be creating tables in your database. There would be one table corresponding to each objectyou are willing to provide persistence. Consider above objects need to be stored and retrieved into the followingRDBMS table:create table EMPLOYEE (id INT NOT NULL auto_increment,first_name VARCHAR(20) default NULL,last_name VARCHAR(20) default NULL,salary INT default NULL,PRIMARY KEY (id));Create Mapping Configuration FileThis step is to create a mapping file that instructs Hibernate how to map the defined class or classes to thedatabase tables.This class contains the employee detail.You should save the mapping document in a file with the format .hbm.xml. We saved our mappingdocument in the file Employee.hbm.xml. Let us see little detail about the mapping document: The mapping document is an XML document having as the root element whichcontains all the elements.

34. TUTORIALS POINTSimply Easy Learning The elements are used to define specific mappings from a Java classes to the database tables.The Java class name is specified using the name attribute of the class element and the database tablename is specified using the table attribute. The element is optional element and can be used to create the class description. The element maps the unique ID attribute in class to the primary key of the database table.The name attribute of the id element refers to the property in the class and the column attribute refers tothe column in the database table. The type attribute holds the hibernate mapping type, this mappingtypes will convert from Java to SQL data type. The element within the id element is used to automatically generate the primary keyvalues. Set the class attribute of the generator element is set to native to let hibernate pick upeither identity, sequence or hilo algorithm to create primary key depending upon the capabilities of theunderlying database. The element is used to map a Java class property to a column in the database table.The name attribute of the element refers to the property in the class and the column attribute refers tothe column in the database table. The type attribute holds the hibernate mapping type, this mappingtypes will convert from Java to SQL data type.There are other attributes and elements available which will be used in a mapping document and I would try tocover as many as possible while discussing other Hibernate related topics.Create Application ClassFinally, we will create our application class with the main() method to run the application. We will use thisapplication to save few Employees records and then we will apply CRUD operations on those records.import java.util.List;import java.util.Date;import java.util.Iterator;import org.hibernate.HibernateException;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee {private static SessionFactory factory;public static void main(String[] args) {try{factory = new Configuration().configure().buildSessionFactory();}catch (Throwable ex) {System.err.println("Failed to create sessionFactory object." + ex);throw new ExceptionInInitializerError(ex);}ManageEmployee ME = new ManageEmployee();/* Add few employee records in database */Integer empID1 = ME.addEmployee("Zara", "Ali", 1000);Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);Integer empID3 = ME.addEmployee("John", "Paul", 10000);/* List down all the employees */ME.listEmployees();/* Update employees records */ME.updateEmployee(empID1, 5000);

35. TUTORIALS POINTSimply Easy Learning/* Delete an employee from the database */ME.deleteEmployee(empID2);/* List down new list of the employees */ME.listEmployees();}/* Method to CREATE an employee in the database */public Integer addEmployee(String fname, String lname, int salary){Session session = factory.openSession();Transaction tx = null;Integer employeeID = null;try{tx = session.beginTransaction();Employee employee = new Employee(fname, lname, salary);employeeID = (Integer) session.save(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}return employeeID;}/* Method to READ all the employees */public void listEmployees( ){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();List employees = session.createQuery("FROM Employee").list();for (Iterator iterator =employees.iterator(); iterator.hasNext();){Employee employee = (Employee) iterator.next();System.out.print("First Name: " + employee.getFirstName());System.out.print(" Last Name: " + employee.getLastName());System.out.println(" Salary: " + employee.getSalary());}tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}/* Method to UPDATE salary for an employee */public void updateEmployee(Integer EmployeeID, int salary ){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();Employee employee =(Employee)session.get(Employee.class, EmployeeID);employee.setSalary( salary );session.update(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}/* Method to DELETE an employee from the records */public void deleteEmployee(Integer EmployeeID){Session session = factory.openSession();Transaction tx = null;

36. TUTORIALS POINTSimply Easy Learningtry{tx = session.beginTransaction();Employee employee =(Employee)session.get(Employee.class, EmployeeID);session.delete(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}}Compilation and ExecutionHere are the steps to compile and run the above mentioned application. Make sure you have set PATH andCLASSPATH appropriately before proceeding for the compilation and execution. Create hibernate.cfg.xml configuration file as explained in configuration chapter. Create Employee.hbm.xml mapping file as shown above. Create Employee.java source file as shown above and compile it. Create ManageEmployee.java source file as shown above and compile it. Execute ManageEmployee binary to run the program.You would get following result, and records would be created in EMPLOYEE table.$java ManageEmployee.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Zara Last Name: Ali Salary: 1000First Name: Daisy Last Name: Das Salary: 5000First Name: John Last Name: Paul Salary: 10000First Name: Zara Last Name: Ali Salary: 5000First Name: John Last Name: Paul Salary: 10000If you check your EMPLOYEE table, it should have following records:mysql> select * from EMPLOYEE;+----+------------+-----------+--------+| id | first_name | last_name | salary |+----+------------+-----------+--------+| 29 | Zara | Ali | 5000 || 31 | John | Paul | 10000 |+----+------------+-----------+--------+2 rows in set (0.00 secmysql>

37. TUTORIALS POINTSimply Easy LearningHibernate O/R MappingSo far we have seen very basic O/R mapping using hibernate but there are three most important mappingtopics which we have to learn in detail. These are the mapping of collections, the mapping of associationsbetween entity classes and Component Mappings.Collections MappingsIf an entity or class has collection of values for a particular variable, then we can map those values using any oneof the collection interfaces available in java. Hibernate can persist instances ofjava.util.Map, java.util.Set,java.util.SortedMap, java.util.SortedSet, java.util.List, and any array of persistent entities or values.Collection type Mapping and Descriptionjava.util.Set This is mapped with a element and initialized with java.util.HashSetjava.util.SortedSetThis is mapped with a element and initialized with java.util.TreeSet.The sort attribute can be set to either a comparator or natural ordering.java.util.List This is mapped with a element and initialized with java.util.ArrayListjava.util.CollectionThis is mapped with a or element and initialized withjava.util.ArrayListjava.util.MapThis is mapped with a element and initialized withjava.util.HashMapjava.util.SortedMapThis is mapped with a element and initialized withjava.util.TreeMap. The sort attribute can be set to either a comparator ornatural ordering.Arrays are supported by Hibernate with for Java primitive value types and for everythingelse. However, they are rarely used so Im not going to discuss them in this tutorial.If you want to map a user defined collection interfaces which is not directly supported by Hibernate, you need totell Hibernate about the semantics of your custom collections which is not very easy and not recommend to beused.Hibernate Set MappingsA Set is a java collection that does not contain any duplicate element. More formally, sets contain no pair ofelements e1 and e2 such that e1.equals(e2), and at most one null element. So objects to be added to a set mustCHAPTER11

38. TUTORIALS POINTSimply Easy Learningimplement both the equals() and hashCode() methods so that Java can determine whether any twoelements/objects are identical.A Set is mapped with a element in the mapping table and initialized with java.util.HashSet. You can use Setcollection in your class when there is no duplicate element required in the collection.Define RDBMS TablesConsider a situation where we need to store our employee records in EMPLOYEE table which will have followingstructure:create table EMPLOYEE (id INT NOT NULL auto_increment,first_name VARCHAR(20) default NULL,last_name VARCHAR(20) default NULL,salary INT default NULL,PRIMARY KEY (id));Further, assume each employee can have one or more certificate associated with him/her. So we will storecertificate related information in a separate table which has following structure:create table CERTIFICATE (id INT NOT NULL auto_increment,certificate_name VARCHAR(30) default NULL,employee_id INT default NULL,PRIMARY KEY (id));There will be one-to-many relationship between EMPLOYEE and CERTIFICATE objects:Define POJO ClassesLet us implement our POJO class Employee which will be used to persist the objects related to EMPLOYEE tableand having a collection of certificates in Set variable.import java.util.*;public class Employee {private int id;private String firstName;private String lastName;private int salary;private Set certificates;public Employee() {}public Employee(String fname, String lname, int salary) {this.firstName = fname;this.lastName = lname;this.salary = salary;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getFirstName() {

39. TUTORIALS POINTSimply Easy Learningreturn firstName;}public void setFirstName( String first_name ) {this.firstName = first_name;}public String getLastName() {return lastName;}public void setLastName( String last_name ) {this.lastName = last_name;}public int getSalary() {return salary;}public void setSalary( int salary ) {this.salary = salary;}public Set getCertificates() {return certificates;}public void setCertificates( Set certificates ) {this.certificates = certificates;}}Now let us define another POJO class corresponding to CERTIFICATE table so that certificate objects can bestored and retrieved into the CERTIFICATE table. This class should also implement both the equals() andhashCode() methods so that Java can determine whether any two elements/objects are identical.public class Certificate {private int id;private String name;public Certificate() {}public Certificate(String name) {this.name = name;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getName() {return name;}public void setName( String name ) {this.name = name;}public boolean equals(Object obj) {if (obj == null) return false;if (!this.getClass().equals(obj.getClass())) return false;Certificate obj2 = (Certificate)obj;if((this.id == obj2.getId()) && (this.name.equals(obj2.getName()))){return true;}return false;}public int hashCode() {int tmp = 0;tmp = ( id + name ).hashCode();

40. TUTORIALS POINTSimply Easy Learningreturn tmp;}}Define Hibernate Mapping FileLet us develop our mapping file which instructs Hibernate how to map the defined classes to the database tables.The element will be used to define the rule for Set collection used.This class contains the employee detail.This class contains the certificate records.You should save the mapping document in a file with the format .hbm.xml. We saved our mappingdocument in the file Employee.hbm.xml. You are already familiar with most of the mapping detail but let us see allthe elements of mapping file once again: The mapping document is an XML document having as the root element whichcontains two elements corresponding to each class. The elements are used to define specific mappings from a Java classes to the database tables. TheJava class name is specified using the name attribute of the class element and the database table name isspecified using the table attribute. The element is optional element and can be used to create the class description. The element maps the unique ID attribute in class to the primary key of the database table.The name attribute of the id element refers to the property in the class and the column attribute refers to thecolumn in the database table. The type attribute holds the hibernate mapping type, this mapping types willconvert from Java to SQL data type. The element within the id element is used to automatically generate the primary key values. Setthe class attribute of the generator element is set to native to let hibernate pick up either identity,sequence or hilo algorithm to create primary key depending upon the capabilities of the underlying database.

41. TUTORIALS POINTSimply Easy Learning The element is used to map a Java class property to a column in the database table.The name attribute of the element refers to the property in the class and the column attribute refers to thecolumn in the database table. The type attribute holds the hibernate mapping type, this mapping types willconvert from Java to SQL data type. The element is new here and has been introduced to set the relationship between Certificate andEmployee classes. We used the cascade attribute in the element to tell Hibernate to persist theCertificate objects at the same time as the Employee objects. The nameattribute is set to thedefined Set variable in the parent class, in our case it is certificates. For each set variable, we need to define aseparate set element in the mapping file. The element is the column in the CERTIFICATE table that holds the foreign key to the parent object ie.table EMPLOYEE. The element indicates that one Employee object relates to many Certificate objects and, assuch, the Certificate object must have a Employee parent associated with it. You can use either , or elements based on your requirement.Create Application ClassFinally, we will create our application class with the main() method to run the application. We will use thisapplication to save few Employees records alongwith their certificates and then we will apply CRUD operationson those records.import java.util.*;import org.hibernate.HibernateException;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee {private static SessionFactory factory;public static void main(String[] args) {try{factory = new Configuration().configure().buildSessionFactory();}catch (Throwable ex) {System.err.println("Failed to create sessionFactory object." + ex);throw new ExceptionInInitializerError(ex);}ManageEmployee ME = new ManageEmployee();/* Let us have a set of certificates for the first employee */HashSet set1 = new HashSet();set1.add(new Certificate("MCA"));set1.add(new Certificate("MBA"));set1.add(new Certificate("PMP"));/* Add employee records in the database */Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);/* Another set of certificates for the second employee */HashSet set2 = new HashSet();set2.add(new Certificate("BCA"));set2.add(new Certificate("BA"));/* Add another employee record in the database */Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);/* List down all the employees */ME.listEmployees();/* Update employees salary records */ME.updateEmployee(empID1, 5000);/* Delete an employee from the database */

42. TUTORIALS POINTSimply Easy LearningME.deleteEmployee(empID2);/* List down all the employees */ME.listEmployees();}/* Method to add an employee record in the database */public Integer addEmployee(String fname, String lname,int salary, Set cert){Session session = factory.openSession();Transaction tx = null;Integer employeeID = null;try{tx = session.beginTransaction();Employee employee = new Employee(fname, lname, salary);employee.setCertificates(cert);employeeID = (Integer) session.save(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}return employeeID;}/* Method to list all the employees detail */public void listEmployees( ){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();List employees = session.createQuery("FROM Employee").list();for (Iterator iterator1 =employees.iterator(); iterator1.hasNext();){Employee employee = (Employee) iterator1.next();System.out.print("First Name: " + employee.getFirstName());System.out.print(" Last Name: " + employee.getLastName());System.out.println(" Salary: " + employee.getSalary());Set certificates = employee.getCertificates();for (Iterator iterator2 =certificates.iterator(); iterator2.hasNext();){Certificate certName = (Certificate) iterator2.next();System.out.println("Certificate: " + certName.getName());}}tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}/* Method to update salary for an employee */public void updateEmployee(Integer EmployeeID, int salary ){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();Employee employee =(Employee)session.get(Employee.class, EmployeeID);employee.setSalary( salary );session.update(employee);tx.commit();}catch (HibernateException e) {

43. TUTORIALS POINTSimply Easy Learningif (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}/* Method to delete an employee from the records */public void deleteEmployee(Integer EmployeeID){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();Employee employee =(Employee)session.get(Employee.class, EmployeeID);session.delete(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}}Compilation and ExecutionHere are the steps to compile and run the above mentioned application. Make sure you have set PATH andCLASSPATH appropriately before proceeding for the compilation and execution. Create hibernate.cfg.xml configuration file as explained in configuration chapter. Create Employee.hbm.xml mapping file as shown above. Create Employee.java source file as shown above and compile it. Create Certificate.java source file as shown above and compile it. Create ManageEmployee.java source file as shown above and compile it. Execute ManageEmployee binary to run the program.You would get following result on the screen, and same time records would be created in EMPLOYEE andCERTIFICATE tables.$java ManageEmployee.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Manoj Last Name: Kumar Salary: 4000Certificate: MBACertificate: PMPCertificate: MCAFirst Name: Dilip Last Name: Kumar Salary: 3000Certificate: BCACertificate: BAFirst Name: Manoj Last Name: Kumar Salary: 5000Certificate: MBACertificate: PMP

44. TUTORIALS POINTSimply Easy LearningCertificate: MCAIf you check your EMPLOYEE and CERTIFICATE tables, they should have following records:mysql> select * from employee;+----+------------+-----------+--------+| id | first_name | last_name | salary |+----+------------+-----------+--------+| 1 | Manoj | Kumar | 5000 |+----+------------+-----------+--------+1 row in set (0.00 sec)mysql> select * from certificate;+----+------------------+-------------+| id | certificate_name | employee_id |+----+------------------+-------------+| 1 | MBA | 1 || 2 | PMP | 1 || 3 | MCA | 1 |+----+------------------+-------------+3 rows in set (0.00 sec)mysql>Hibernate SortedSet MappingsA SortedSet is a java collection that does not contain any duplicate element and elements are ordered using theirnatural ordering or by a comparator provided.A SortedSet is mapped with a element in the mapping table and initialized with java.util.TreeSet.The sort attribute can be set to either a comparator or natural ordering. If we use natural ordering then its iteratorwill traverse the set in ascending element order.Define RDBMS TablesConsider a situation where we need to store our employee records in EMPLOYEE table which will have followingstructure:create table EMPLOYEE (id INT NOT NULL auto_increment,first_name VARCHAR(20) default NULL,last_name VARCHAR(20) default NULL,salary INT default NULL,PRIMARY KEY (id));Further, assume each employee can have one or more certificate associated with him/her. So we will storecertificate related information in a separate table which has following structure:create table CERTIFICATE (id INT NOT NULL auto_increment,certificate_name VARCHAR(30) default NULL,employee_id INT default NULL,PRIMARY KEY (id));There will be one-to-many relationship between EMPLOYEE and CERTIFICATE objects:

45. TUTORIALS POINTSimply Easy LearningDefine POJO ClassesLet us implement our POJO class Employee which will be used to persist the objects related to EMPLOYEE tableand having a collection of certificates in SortedSet variable.import java.util.*;public class Employee {private int id;private String firstName;private String lastName;private int salary;private SortedSet certificates;public Employee() {}public Employee(String fname, String lname, int salary) {this.firstName = fname;this.lastName = lname;this.salary = salary;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getFirstName() {return firstName;}public void setFirstName( String first_name ) {this.firstName = first_name;}public String getLastName() {return lastName;}public void setLastName( String last_name ) {this.lastName = last_name;}public int getSalary() {return salary;}public void setSalary( int salary ) {this.salary = salary;}public SortedSet getCertificates() {return certificates;}public void setCertificates( SortedSet certificates ) {this.certificates = certificates;}}Now let us define another POJO class corresponding to CERTIFICATE table so that certificate objects can bestored and retrieved into the CERTIFICATE table. This class should also implementComparable interfaceand compareTo method which will be used to sort the elements in case you setsort="natural" in your mappingfile (see below mapping file).public class Certificate implements Comparable {

46. TUTORIALS POINTSimply Easy Learningprivate int id;private String name;public Certificate() {}public Certificate(String name) {this.name = name;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getName() {return name;}public void setName( String name ) {this.name = name;}public int compareTo(Certificate that){final int BEFORE = -1;final int AFTER = 1;if (that == null) {return BEFORE;}Comparable thisCertificate = this.getName();Comparable thatCertificate = that.getName();if(thisCertificate == null) {return AFTER;} else if(thatCertificate == null) {return BEFORE;} else {return thisCertificate.compareTo(thatCertificate);}}}Define Hibernate Mapping FileLet us develop our mapping file which instructs Hibernate how to map the defined classes to the database tables.The element will be used to define the rule for SortedSet collection used.This class contains the employee detail.

47. TUTORIALS POINTSimply Easy LearningThis class contains the certificate records.You should save the mapping document in a file with the format .hbm.xml. We saved our mappingdocument in the file Employee.hbm.xml. You are already familiar with most of the mapping detail but let us see allthe elements of mapping file once again: The mapping document is an XML document having as the root element whichcontains two elements corresponding to each class. The elements are used to define specific mappings from a Java classes to the database tables. TheJava class name is specified using the name attribute of the class element and the database table name isspecified using the table attribute. The element is optional element and can be used to create the class description. The element maps the unique ID attribute in class to the primary key of the database table.The name attribute of the id element refers to the property in the class and the column attribute refers to thecolumn in the database table. The type attribute holds the hibernate mapping type, this mapping types willconvert from Java to SQL data type. The element within the id element is used to automatically generate the primary key values. Setthe class attribute of the generator element is set to native to let hibernate pick up either identity,sequence or hilo algorithm to create primary key depending upon the capabilities of the underlyingdatabase. The element is used to map a Java class property to a column in the database table.The name attribute of the element refers to the property in the class and the column attribute refers to thecolumn in the database table. The type attribute holds the hibernate mapping type, this mapping types willconvert from Java to SQL data type. The element is used to set the relationship between Certificate and Employee classes. We usedthe cascade attribute in the element to tell Hibernate to persist the Certificate objects at the same timeas the Employee objects. The name attribute is set to the definedSortedSet variable in the parent class, inour case it is certificates. The sort attribute can be set to natural to have natural sorting or it can be set to acustom class implementingjava.util.Comparator. We have used a class MyClass which implementsjava.util.Comparator to reverse the sorting order implemented in Certificate class. The element is the column in the CERTIFICATE table that holds the foreign key to the parent objectie. table EMPLOYEE. The element indicates that one Employee object relates to many Certificate objects and, assuch, the Certificate object must have a Employee parent associated with it. You can use either , or elements based on your requirement.If we use sort="natural" setting then we do not need to create a separate class because Certificate class alreadyhas implemented Comparable interface and hibernate will use compareTo() method defined in Certificate class tocompare certificate names. But we are using a custom comparator classMyClass in our mapping file so we wouldhave to create this class based on our sorting algorithm. Let us do descending sorting in this class using thisclass.import java.util.Comparator;

48. TUTORIALS POINTSimply Easy Learningpublic class MyClass implements Comparator{public int compare(Certificate o1, Certificate o2) {final int BEFORE = -1;final int AFTER = 1;/* To reverse the sorting order, multiple by -1 */if (o2 == null) {return BEFORE * -1;}Comparable thisCertificate = o1.getName();Comparable thatCertificate = o2.getName();if(thisCertificate == null) {return AFTER * 1;} else if(thatCertificate == null) {return BEFORE * -1;} else {return thisCertificate.compareTo(thatCertificate) * -1;}}}Create Application ClassFinally, we will create our application class with the main() method to run the application. We will use thisapplication to save few Employees records alongwith their certificates and then we will apply CRUD operationson those records.import java.util.*;import org.hibernate.HibernateException;import org.hibernate.Session;import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee {private static SessionFactory factory;public static void main(String[] args) {try{factory = new Configuration().configure().buildSessionFactory();}catch (Throwable ex) {System.err.println("Failed to create sessionFactory object." + ex);throw new ExceptionInInitializerError(ex);}ManageEmployee ME = new ManageEmployee();/* Let us have a set of certificates for the first employee */TreeSet set1 = new TreeSet();set1.add(new Certificate("MCA"));set1.add(new Certificate("MBA"));set1.add(new Certificate("PMP"));/* Add employee records in the database */Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);/* Another set of certificates for the second employee */TreeSet set2 = new TreeSet();set2.add(new Certificate("BCA"));set2.add(new Certificate("BA"));/* Add another employee record in the database */Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);

49. TUTORIALS POINTSimply Easy Learning/* List down all the employees */ME.listEmployees();/* Update employees salary records */ME.updateEmployee(empID1, 5000);/* Delete an employee from the database */ME.deleteEmployee(empID2);/* List down all the employees */ME.listEmployees();}/* Method to add an employee record in the database */public Integer addEmployee(String fname, String lname,int salary, SortedSet cert){Session session = factory.openSession();Transaction tx = null;Integer employeeID = null;try{tx = session.beginTransaction();Employee employee = new Employee(fname, lname, salary);employee.setCertificates(cert);employeeID = (Integer) session.save(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}return employeeID;}/* Method to list all the employees detail */public void listEmployees( ){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();List employees = session.createQuery("FROM Employee").list();for (Iterator iterator1 =employees.iterator(); iterator1.hasNext();){Employee employee = (Employee) iterator1.next();System.out.print("First Name: " + employee.getFirstName());System.out.print(" Last Name: " + employee.getLastName());System.out.println(" Salary: " + employee.getSalary());SortedSet certificates = employee.getCertificates();for (Iterator iterator2 =certificates.iterator(); iterator2.hasNext();){Certificate certName = (Certificate) iterator2.next();System.out.println("Certificate: " + certName.getName());}}tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}/* Method to update salary for an employee */public void updateEmployee(Integer EmployeeID, int salary ){Session session = factory.openSession();Transaction tx = null;try{

50. TUTORIALS POINTSimply Easy Learningtx = session.beginTransaction();Employee employee =(Employee)session.get(Employee.class, EmployeeID);employee.setSalary( salary );session.update(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}/* Method to delete an employee from the records */public void deleteEmployee(Integer EmployeeID){Session session = factory.openSession();Transaction tx = null;try{tx = session.beginTransaction();Employee employee =(Employee)session.get(Employee.class, EmployeeID);session.delete(employee);tx.commit();}catch (HibernateException e) {if (tx!=null) tx.rollback();e.printStackTrace();}finally {session.close();}}}Compilation and ExecutionHere are the steps to compile and run the above mentioned application. Make sure you have set PATH andCLASSPATH appropriately before proceeding for the compilation and execution. Create hibernate.cfg.xml configuration file as explained in configuration chapter. Create Employee.hbm.xml mapping file as shown above. Create Employee.java source file as shown above and compile it. Create Certificate.java source file as shown above and compile it. Create MyClass.java source file as shown above and compile it. Create ManageEmployee.java source file as shown above and compile it. Execute ManageEmployee binary to run the program.You would get following result on the screen, and same time records would be created in EMPLOYEE andCERTIFICATE tables. You can see certificates has been sorted in reverse order. You can try by changing yourmapping file, simply set sort="natural" and execute your program and compare the results.$java ManageEmployee.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Manoj Last Name: Kumar Salary: 4000Certificate: PMPCertificate: MCA

51. TUTORIALS POINTSimply Easy LearningCertificate: MBAFirst Name: Dilip Last Name: Kumar Salary: 3000Certificate: BCACertificate: BAFirst Name: Manoj Last Name: Kumar Salary: 5000Certificate: PMPCertificate: MCACertificate: MBAIf you check your EMPLOYEE and CERTIFICATE tables, they should have following records:mysql> select * from employee;+----+------------+-----------+--------+| id | first_name | last_name | salary |+----+------------+-----------+--------+| 1 | Manoj | Kumar | 5000 |+----+------------+-----------+--------+1 row in set (0.00 sec)mysql> select * from certificate;+----+------------------+-------------+| id | certificate_name | employee_id |+----+------------------+-------------+| 1 | MBA | 1 || 2 | PMP | 1 || 3 | MCA | 1 |+----+------------------+-------------+3 rows in set (0.00 sec)mysql>Hibernate List MappingsA List is a java collection that stores elements in sequence and allow duplicate elements. The user of thisinterface has precise control over where in the list each element is inserted. The user can access elements bytheir integer index, and search for elements in the list. More formally, lists typically allow pairs of elements e1 ande2 such that e1.equals(e2), and they typically allow multiple null elements if they allow null elements at all.A List is mapped with a element in the mapping table and initialized with java.util.ArrayList.Define RDBMS TablesConsider a situation where we need to store our employee records in EMPLOYEE table which will have followingstructure:create table EMPLOYEE (id INT NOT NULL auto_increment,first_name VARCHAR(20) default NULL,last_name VARCHAR(20) default NULL,salary INT default NULL,PRIMARY KEY (id));

52. TUTORIALS POINTSimply Easy LearningFurther, assume each employee can have one or more certificate associated with him/her. A List collectionmapping needs an index column in the collection table. The index column defines the position of the element inthe collection. So we will store certificate related information in a separate table which has following structure:create table CERTIFICATE (id INT NOT NULL auto_increment,certificate_name VARCHAR(30) default NULL,idx INT default NULL,employee_id INT default NULL,PRIMARY KEY (id));There will be one-to-many relationship between EMPLOYEE and CERTIFICATE objects.Define POJO ClassesLet us implement a POJO class Employee which will be used to persist the objects related to EMPLOYEE tableand having a collection of certificates in List variable.import java.util.*;public class Employee {private int id;private String firstName;private String lastName;private int salary;private List certificates;public Employee() {}public Employee(String fname, String lname, int salary) {this.firstName = fname;this.lastName = lname;this.salary = salary;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getFirstName() {return firstName;}public void setFirstName( String first_name ) {this.firstName = first_name;}public String getLastName() {return lastName;}public void setLastName( String last_name ) {this.lastName = last_name;}public int getSalary() {return salary;}public void setSalary( int salary ) {this.salary = salary;}public List getCertificates() {return certificates;

53. TUTORIALS POINTSimply Easy Learning}public void setCertificates( List certificates ) {this.certificates = certificates;}}We need to define another POJO class corresponding to CERTIFICATE table so that certificate objects can bestored and retrieved into the CERTIFICATE table.public class Certificate{private int id;private String name;public Certificate() {}public Certificate(String name) {this.name = name;}public int getId() {return id;}public void setId( int id ) {this.id = id;}public String getName() {return name;}public void setName( String name ) {this.name = name;}}Define Hibernate Mapping FileLet us develop our mapping file which instructs Hibernate how to map the defined classes to the database tables.The element will be used to define the rule for List collection used. The index of list is always of type integerand is mapped using the element.This class contains the employee detail.

54. TUTORIALS POINTSimply Easy LearningThis class contains the certificate records.You