CS 160: Software Engineering November 5 Class Meeting Department of Computer Science San Jose State...

CS 160: Software EngineeringNovember 5 Class Meeting

Department of Computer ScienceSan Jose State University

Fall 2014Instructor: Ron Mak

www.cs.sjsu.edu/~mak

http://www.cs.sjsu.edu/~mak

http://www.cs.sjsu.edu/~mak

Computer Science Dept.Fall 2014: November 5

CS 160: Software Engineering© R. Mak

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Unofficial Field Trip

Computer History Museum in Mt. View http://www.computerhistory.org/

Saturday, November 8, 11:30 – closing time

http://www.computerhistory.org/



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Legacy Software Contains necessary functionality.

May be difficult to use. Often the user interface is the command line.

May be difficult to rewrite. Original programmers long gone. May contain many modifications made over time.

Made by different programmers with varying levels of competence.

Written in an archaic programming language that no one knows any more.

Nobody dares touch the code lest it break.



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Reuse

Lower development effort and cost. Don’t reinvent the wheel.

Lower risk. It’s always worked!

Less training. May be difficult to use, but the concepts are familiar.

Take advantage of past expertise and policies. Overcome the NIH (Not Invented Here) syndrome.



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Rewrite

Too difficult or costly to understand the old code.

The old code has become obsolete or dangerous. Example: The Y2K crisis.

New code will be easier to maintain.

Reuse vs. rewrite? Similar to the classic Make vs. Buy decision.



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What to Do with Legacy Software

An old command-line program.

Keyboard input (standard in)Terminal output (standard out)

Still has useful functionality. Nobody wants (or dares) to rewrite it.

Example: An old FORTRAN IV program.



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What to Do with Legacy Software, cont’dC SQUARE ROOT PROGRAMC DOUBLE PRECISION NUMBER, ROOTCC READ NUMBERC READ (5,100) NUMBER 100 FORMAT (F5.0)CC COMPUTE SQUARE ROOTC ROOT = DSQRT(NUMBER)CC WRITE SQUARE ROOTC WRITE (6,200) NUMBER, ROOT 200 FORMAT ('THE SQUARE ROOT OF ', F5.1, ' IS ', F15.10)C STOP END



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What to Do with Legacy Software

One solution: Wrap it inside a modern Java program.

If the Java program is a servlet, you can deploy the legacy app to the web!

Use a web form to supply input to the app. Display the app's output on a web page.

LegacyDemo

Javaservletprocess

Legacyapplication

processstandard out

standard in



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Shortcomings of JDBC

Java programmers must understandrelational databases.

The database is very visible. The Java programmer must know SQL.

JDBC is not fully object-oriented.

A Java program accesses field values individually from a result set.

You need statements to create Java objects from the result set values.



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Object-Relational Mapping

Goal: Overcome the paradigm mismatch between relational data from an RDBMS and object-oriented programming.

Object-oriented languages such as Java would much rather deal with classes and objects.

Java programmers do not want to write SQL. Java programmers do not want to want to deal

with database concepts such as one-to-many, one-to-many, many-to-many, etc.

Java programmers do not want to understand normalization.



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Solution: Add a layer of software between the database and the Java application that does object-relational mapping.

Relational data being read from the database are automatically converted to objects.

Objects being persisted (saved) to the database are automatically converted to relational data.



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The Java application manipulates objects (create, update, search, delete) and these operations are automatically translated into the corresponding database operations.

The Java programmer can mostly forget that there is an underlying database.

Database platform independence.



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Hibernate

A very popular open-source object-relational persistence and query service for Java. Download from http://www.hibernate.org/

Replace the JDBC API with the Hibernate API.

Java annotations describe in detail the mapping between the Java classes and the relational database tables. _

http://www.hibernate.org/



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Hibernate, cont’d

Import Java packages: Hibernate Hibernate annotations Log4J

import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Column;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import org.hibernate.tool.hbm2ddl.SchemaExport;

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hibernate.cfg.xml

Hibernate configuration file Modify as necessary. Must be in your application’s classpath.

<?xml version='1.0' encoding='utf-8'?><!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration> <session-factory>

 <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="connection.url">jdbc:mysql://localhost/school_demo</property> <property name="connection.username">root</property> <property name="connection.password">sesame</property> <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>

 <property name="show_sql">true</property> </session-factory></hibernate-configuration>



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Hibernate: Student

@Entitypublic class Student { private long id; private String firstName; private String lastName; public Student() {} public Student(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } ...}

The annotations provide metadata for the Java compiler and the Java run time.



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Hibernate: Student@Entitypublic class Student { ... @Id @GeneratedValue @Column(name="id") public long getId() { return id; } public void setId(long id) { this.id = id; } @Column(name="first_name") public String getFirstName() { return firstName; } public void setFirstName(String name) { this.firstName = name; } @Column(name="last_name") public String getLastName() { return lastName; } public void setLastName(String name) { this.lastName = name; } ...}



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Student.java

Main method (for testing)

public static void main(String args[]){ // Configure Hibernate and add the Student class. Configuration config = new Configuration(); config.addAnnotatedClass(Student.class); config.configure(); // Create the database table. (new SchemaExport(config)).create(true, true); // Create a session. SessionFactory factory = config.buildSessionFactory(); Session session = factory.openSession(); ...}



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Student.javapublic static void main(String args[]){ ... // Create a session. SessionFactory factory = config.buildSessionFactory(); Session session = factory.openSession(); // Load the Student table in a transaction. Transaction tx = session.beginTransaction(); { session.save(new Student("Mary", "Jane")); session.save(new Student("Kim", "Smith")); session.save(new Student("John", "Doe")); session.save(new Student("Tim", "Novak")); session.save(new Student("Leslie", "Klein")); } tx.commit(); session.close();}

SchoolDemo1



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HibernateContext.java

Goal: Move all the Hibernate bookkeeping code into a shared class.



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HibernateContext.javaimport org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import org.hibernate.tool.hbm2ddl.SchemaExport;

public class HibernateContext { public static Configuration config = null; public static SessionFactory factory = null; /** * Set the configuration if it is null. */ private static void setConfiguration() { if (config == null) { config = new Configuration(); config.configure(); } }

...}



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public class HibernateContext { public static Configuration config = null; public static SessionFactory factory = null;

... /** * Set the factory if it is null. */ private static void setFactory() { if (factory == null) { setConfiguration(); factory = config.buildSessionFactory(); } } ...}



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... /** * Open a session from the factory. * @return a session. */ public static Session getSession() { setFactory(); return factory.openSession(); } ...}



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... /** * Create a new schema (database) from the configuration. */ public static void createSchema() { setConfiguration(); (new SchemaExport(config)).create(true, true); } ...}



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... /** * Add a new class object to the database. * @param klass the class object. */ public static void addClass(Class klass) { setConfiguration(); config.addAnnotatedClass(klass); } ...}



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HibernateContext.javapublic class HibernateContext { public static Configuration config = null; public static SessionFactory factory = null;

... /** * Add a list of class objects to the database. * @param klasses the list of class objects. */ public static void addClasses(Class klasses[]) { for (Class klass : klasses) { addClass(klass); } }}



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Student.java@Entitypublic class Student { ...

public static Student find(long id) { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Student where id = :idvar"); query.setLong("idvar", id); Student student = (Student) query.uniqueResult(); session.close(); return student; }

...}

Hibernate Query Language (HQL)



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Student.java@Entitypublic class Student { ...

public static Student find(String lastName) { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Student where lastName = :name"); query.setString("name", lastName); Student student = (Student) query.uniqueResult(); session.close(); return student; }

...}



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Teacher.java

@Entitypublic class Teacher { private long id; private String firstName; private String lastName; public Teacher () {} public Teacher(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } ...}

Similar to Student.java



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Teacher.java@Entitypublic class Teacher { ... @Id @GeneratedValue @Column(name="id") public long getId() { return id; } public void setId(long id) { this.id = id; } @Column(name="first_name") public String getFirstName() { return firstName; } public void setFirstName(String name) { this.firstName = name; } @Column(name="last_name") public String getLastName() { return lastName; } public void setLastName(String name) { this.lastName = name; } ...}



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Teacher.java@Entitypublic class Teacher { ... /** * Load the Teacher table. */ public static void load() { Session session = HibernateContext.getSession(); Transaction tx = session.beginTransaction(); { session.save(new Teacher("Tom", "Rogers")); session.save(new Teacher("Art", "Thompson")); session.save(new Teacher("John", "Lane")); session.save(new Teacher("Mabel", "Flynn")); } tx.commit(); session.close(); System.out.println("Teacher table loaded."); } ...}



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Teacher.java@Entitypublic class Teacher { ... /** * List all the teachers. */ public static void list() { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Teacher"); System.out.println("All teachers:"); for (Teacher teacher : (List<Teacher>) query.list()) { teacher.print(); } session.close(); }}



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Teacher.java

@Entitypublic class Teacher { ... /** * Print teacher attributes. */ public void print() { System.out.printf("%d: %s %s\n", id, firstName, lastName); } ...}



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SchoolDemo.javaimport java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;

public class SchoolDemo { private static final String HELP_MESSAGE = "*** Commands: create, load, find <n>, students, teachers, quit"; public static void main(String args[]) { BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); String command; Class klasses[] = {Student.class, Teacher.class}; HibernateContext.addClasses(klasses);

... }}



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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ... do { System.out.print("\nCommand? "); try { command = stdin.readLine(); } catch (java.io.IOException ex) { command = "?"; } String parts[] = command.split(" ");

... } while (!command.equalsIgnoreCase("quit")); }}



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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ...

do { ... if (command.equalsIgnoreCase("create")) { HibernateContext.createSchema(); } else if (command.equalsIgnoreCase("load")) { Student.load(); Teacher.load(); }




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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ...

do { ...

else if (command.equalsIgnoreCase("teachers")) { Teacher.list(); } else if (command.equalsIgnoreCase("students")) { Student.list(); }




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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ... do { ... else if (parts[0].equalsIgnoreCase("find") && (parts.length >= 2)) { long id = Long.parseLong(parts[1]); Student student = Student.find(id); if (student != null) { student.print(); } else { System.out.printf("*** No student with id %d\n", id); } } ... } while (!command.equalsIgnoreCase("quit")); }}

SchoolDemo2

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