Spring Introduction

Spring is a unique Java application framework meant to simplify the development of applications. Whereas Enterprise Java Beans are very complex to use, the Spring Framework is an easy to use and understand framework for enterprise applications. Spring focuses on:

  • Providing a simple way to manage an object's lifetime and relationships (through Dependency Injection).
  • A layered architecture. Spring is comprehensive yet modular. You only use what you need. For example, you may only make use of the JDBC support without linking in an entire framework.
  • Promoting best software development practices. For example, Spring is designed to always promote test-driven development and eliminate the need for factories and singletons.
  • Inversion of Control. Spring is an application container supporting interceptions and declarative aspect oriented programming.
Spring is an open source project; however it is not housed at Apache.

Jetspeed + Spring

The Jetspeed portal is configured completely as a Spring application. All services in Jetspeed are constructed and configured as Spring beans. Jetspeed runs in a Spring container. Spring provides a great environment for customization your deployment of Jetspeed. Some of the added benefits of Spring in Jetspeed are:

  • Aspect Oriented Programming in the Spring configuration files.
  • Hot swapping: allows implementation hiding and swapping.
  • Failover: failover to next component when a component fails.
  • Multicasting: multicasting of method invocation to multiple components.
  • Lifecycle management: starting, pausing and resuming components.

Components run in a Spring Container

Jetspeed, as a Spring application, is a collection of components, or services, all assembled together to create a complete working portal. If you look at from this point of view, you can see the major portal components being managed by the container, which is really just a Spring container as shown in the diagram below. Note this is by no way an inclusive list of all Jetspeed services wired in Spring:

Programming to the Jetspeed API

When developing Jetspeed core, Jetspeed extensions, or Jetspeed Administrative Portlets, you should always program to the Jetspeed API. All Jetspeed Components are wired together on interfaces, not class implementations. This contract-by-interface approach to programming makes for a powerful and extensible programming model for developing enterprise portal applications. When you are configuring your Jetspeed Spring components (beans), you will see that components have their dependencies wired in to other Jetspeed components via dependency injection. The injected dependencies are always interfaces. Dependencies are declaratively managed in the Spring configuration. In Jetspeed, we support both constructor and setter dependency injection. Here is an example of a component having its dependencies constructor-injected:

<bean id='PortalAdministrationImpl' init-method="start"
    	<constructor-arg index='0'>
    		<ref bean="org.apache.jetspeed.security.UserManager"/>
        <constructor-arg index='1'>
    		<ref bean="org.apache.jetspeed.security.RoleManager"/>
        <constructor-arg index='2'>
    		<ref bean="org.apache.jetspeed.security.GroupManager"/>
        <constructor-arg index='3'>
    		<ref bean="org.apache.jetspeed.page.PageManager"/>
        <constructor-arg index='4'>
    		<ref bean="org.apache.jetspeed.prefs.PreferencesProvider"/>
        <constructor-arg index='5'>
    		<ref bean="org.apache.jetspeed.profiler.Profiler"/>
        <constructor-arg index='6'>
    		<ref bean="mailSender"/>
        <constructor-arg index='7'>
    		<ref bean="adminVelocityEngine"/>

And here is the Java code constructor matching the Spring configuration. Notice that the dependencies injected are interfaces, not concrete class implementations:

public PortalAdministrationImpl( UserManager userManager,
                                 RoleManager roleManager,
                                 GroupManager groupManager, 
                                 PageManager pageManager,
                                 PreferencesProvider preferences,
                                 Profiler profiler,
                                 JavaMailSender mailSender,
                                 VelocityEngine velocityEngine)