Spring.Net

Steinar Dragsnes

email: steinar.dragsnes at viz.no

Agenda

Dependency Injection (IoC)

Spring.Net Services

AOP

Declarative Transaction Management through AOP

Additional Spring.Net componentsSpring.Web (out of scope)Spring.Integration

- NHibernate

Dependency Injection

Problem: How to put the various components and layers together

without creating a too tightly coupled system? How to allow for flexibility and technology changes (also

plugging in modules/components)?

IoC is not a new concept.

DI is a reaction to the heavyweight complexity in the mainstream J2EE world (such as EJB framework).

Similar patterns; Service Locator, Factory.

Dependency Injection vs. Service Locator

Service Locator forces you to be dependent on the locator.

With service locator the application class asks for a service by an explicit message to the locator.PULL

With injection there is no explicit request, the service appears in the application class. PUSH

Dependency Injection, less/no configuration of dependency in your source.

Sample Application Architecture

Data RepositoryData Repository

DomainDomainobjectsobjects

DAO implementationsDAO implementations

Service implementationsService implementations

Web interfaceWeb interfaceOtherOtherinterfacesinterfaces

PresentationPresentationLayerLayer

ServiceServiceLayerLayer

Data Data AccessAccessLayerLayer

DAO interfacesDAO interfaces

Service interfacesService interfaces

Defining objects in the containter

Spring.Net uses XML to wire dependencies.Programmatic (C#)Annotations

The syntax is quite simple and straigth farwards: <object id=”name” type=”namespace.class, assembly />

Within the object tags you can specify constructor args and properties, just as you would do in a normal factory.

Example, UserService

public class UserService : IUserService

{

private IUserDao dao;

public UserService(IUserDao dao)

{

this.dao = dao;

}

...

}

Defining the service in the IoC container

<?xml version="1.0" encoding="utf-8" ?>

<objects xmlns="http://www.springframework.net">

...

<object id=”userService” type="SpringApp.Services.UserService, SpringApp.Core">

<!-- Injecting the UserDao into the service. -->

<constructor-arg name="dao" ref=”userDao" />

</object>

...

</objects>

public class UserService : IUserService{

private IUserDao dao;

public UserService(IUserDao dao){

this.dao = dao;}

...}

Defining the service in the IoC container

<?xml version="1.0" encoding="utf-8" ?><objects xmlns="http://www.springframework.net">

...

<object id=”userDao" type="SpringApp.Data.NHibernate12.UserDao, SpringApp.Data.NHibernate">

<property name="SessionFactory" ref="SessionFactory"/> </object>

<object id=”userService” type="SpringApp.Services.UserService, SpringApp.Core"><!-- Injecting the UserDao into the service. --><constructor-arg name="dao" ref=”userDao" />

</object>

...

</objects>

Container configuration

<configuration>

<configSections> <sectionGroup name="spring"> <section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/> </sectionGroup> </configSections>

<spring> <context> <resource uri=“file://~/config/objects.xml"/> </context> </spring></configuration>

IApplicationContext context = ContextRegistry.GetContext();

IUserService service = (IUserService) context.GetObject(“userService");

DI and Application Wiring

Through this very basic example you can get an idea on how you can configure and wire your application together.

Tips: Consider when you want to use DI and apply it where it gives

you most ”bang for the buck”. In the beginning, debugging the XML configuration can be

difficult. Whenever experiencing difficulties, do not hesitate to ask for

help at the Spring.Net user forum [http://forum.springframework.net].

DI brings advantages

Easy to switch implementations without the need for a recompile.

Easy to facilitate testing, unit testing, integration testing.

Better separation of concerns.

Less dependencies within your application.

Easier to write plugin modules.

Encourages best practices such as TDD, decoupling, seperation of concerns, design by contract.

Spring.Net Services

Portable Service Abstractions (PSA) Write plain service classes (PONO) Decide later how you will distribute your objects Specify distribution technology through

configuration.• .Net Remoting• .Net Enterprise Services• Web Services

Spring.Net Services

How is this achieved?Spring.Net creates a proxy at runtime that meets the

implementation requirements of a specific distributed technology

<object id="saoUserService" type="Spring.Remoting.SaoExporter, Spring.Services"> <property name=“TargetName" value=“userService"/> <property name=“ServiceName" value=“RemotedUserService"/></object>

<object id=“userService" type="SpringApp.Services.UserService, SpringApp.Core"> <constructor-arg name=“dao" ref=“userDao"/></object>

Enterprise Services<object id=“comUserServiceComponent" type="Spring.EnterpriseServices.ServicedComponentExporter, Spring.Services"> <property name="TargetName" value=“userService" /> <property name="TypeAttributes"> <list> <object type="System.EnterpriseServices.TransactionAttribute, System.EnterpriseServices" /> </list> </property>…</object>

<object type="Spring.EnterpriseServices.EnterpriseServicesExporter, Spring.Services"> <property name="ApplicationName"><value>Demo App</value></property> <property name="AccessControl"> <object type=“…ApplicationAccessControlAttribute, …"> <property name="AccessChecksLevel"><value>ApplicationComponent</value></property> </object> </property> <property name="Roles"><list><value>Admin : Administrator role</value></list></property> <property name="Components"> <list> <ref object=“comUserServiceComponent" /> </list> </property> <property name="Assembly"><value>SpringApp.Com.UserService</value></property> </object>

Accessing the service from the client

Administrative type registration is performed using the wellknown element in the client configuration section Seperate service interface and implementation in different assembliesThus clients can obtain a proxy to a specific implementation with only a reference to the interface assembly.

<object id=“userService" type="Spring.Remoting.SaoFactoryObject, Spring.Services"> <property name=“ServiceInterface" value=“SpringApp.Services.IUserService, SpringApp.IServices"/> <property name=“ServiceUrl" value=“tcp://localhost:8005/RemotedUserService"/></object>

IApplicationContext context = ContextRegistry.GetContext();

IUserService service = (IUserService) context.GetObject(“userService");

Aspect Oriented Programming

Problem, an operation that is done repeatedly across many classes and in the same class.

Logging, security, transaction management to name a few.

Extract the logic of these operations (aspects) into it’s own class.

Apply this logic at various locations in your code (pointcut).

Terminology ‘what’ = advice, ‘where’ = pointcut

Aspect Oriented Programming

Spring.Net provides an aspect library: Logging ExceptionHandling Caching Transaction Parameter Validation

Easy to create own aspects. Create a class that implements one of the interceptor contracts

(e.g. IMethodInterceptor) Create a custome attribute Either connect attribute and advice programmatic or preferably

in the Spring.Net container.

<object id="transactionInterceptor" type="Spring.Transaction.Interceptor.TransactionInterceptor, Spring.Data"> <property name="TransactionManager" ref="hibernateTransactionManager"/> <property name="TransactionAttributeSource"> <object type="Spring.Transaction.Interceptor.AttributesTransactionAttributeSource, Spring.Data"/> </property></object>

<object id="transactionAdvisor" type="Spring.Transaction.Interceptor.TransactionAttributeSourceAdvisor, Spring.Data"> <property name="TransactionInterceptor" ref="transactionInterceptor"/></object>

Configuring Aspects

Configuring Aspects

<object id="autoProxyCreator" type="SpringApp.Aop.CustomAdvisorAutoProxyCreator, SpringApp.Core"> <property name="AttributeAdviceMap"> <dictionary> <!-- Each entry creates an instance of Spring.Aop.Support.AttributeMatchMethodPointcutAdvisor --> <entry key="Viz.Core.Aop.Attributes.Log4NetLoggingAroundAttribute,Viz.Core” value="Viz.Core.Aop.Advice.Log4NetLoggingAroundAdvice,Viz.Core"/> <entry key="Viz.Core.Security.Attributes.AccessPriviligesAttribute,Viz.Core" value="Viz.Core.Security.Advices.AccessPriviligesAdvice,Viz.Core"/>

<entry key="Viz.Core.Persistence.nHibernate.Session.Attributes.SessionScopeAttribute,Viz.Core.Persistence"

value="Viz.Core.Persistence.nHibernate.Session.Advices.SessionScopeAdvice,Viz.Core.Persistence"/>

</dictionary> </property></object>

How this turns out in code

[Transaction(ReadOnly = true)]public IList LoadAll(Type entityType){ return dao.LoadAll(entityType);}

[Logging][Permission(Permissions = Permission.ContentManager, Permission.PortfolioManager)[Transaction]public object SaveOrUpdate(object entity){ return dao.SaveOrUpdate(entity);}

Spring.Net Data Access API

Provides a consistent programming model across different transaction APIs such as ADO.NET, Enterprise Services, System.Transactions, and NHibernate.

Declarative transaction management with any of the above data access technologies (AOP)

You can keep the same API across different data access technologies.

Changing the underlying transaction implementation is a matter of configuration or a centralized programmatic change as compared to a major overhauling.

Spring.Net NHibernate Integration

Spring.Net provides integration with NHibernate in terms of Resource management

• DbProvider

• SessionFactory

• Sessions, SessionScope, OSIV

DAO implementation support Transaction strategies

You can use Spring's support for NHibernate without using the full Sprting.Net stack or Spring’s transaction management