The Spring Framework consists of features organized into about 20 modules. These modules are grouped into Core Container, Data Access/Integration, Web, AOP (Aspect Oriented Programming), Instrumentation, and Test, as shown in the following diagram.
The Core Container consists of the Core, Beans, Context, and Expression Language modules.
- The Core and Beans modules provide the fundamental parts of the framework, including the IoC and Dependency Injection features.
- The Context module builds on the solid base provided by the Core and Beans modules: it is a means to access objects in a framework-style manner that is similar to a JNDI registry. The Context module also supports Java EE features such as EJB, JMX ,and basic remoting.
- The Expression Language module provides a powerful expression language for querying and manipulating an object graph at runtime.
The Data Access/Integration layer consists of the JDBC, ORM, OXM, JMS and Transaction modules.
- The JDBC module provides a JDBC-abstraction layer that removes the need to do tedious JDBC coding and parsing of database-vendor specific error codes.
- The ORM module provides integration layers for popular object-relational mapping APIs, including JPA, JDO, Hibernate, and iBatis.
- The OXM module provides an abstraction layer that supports Object/XML mapping implementations for JAXB, Castor, XMLBeans, JiBX and XStream.
- The Java Messaging Service (JMS) module contains features for producing and consuming messages.
- The Transaction module supports programmatic and declarative transaction management for classes that implement special interfaces and for all your POJOs (plain old Java objects).
The Web layer consists of the Web, Web-Servlet, Web-Struts, and Web-Portlet modules.
- Spring’s Web module provides basic web-oriented integration features such as multipart file-upload functionality and the initialization of the IoC container using servlet listeners and a web-oriented application context. It also contains the web-related parts of Spring’s remoting support.
- The Web-Servlet module contains Spring’s model-view-controller (MVC) implementation for web applications. Spring’s MVC framework provides a clean separation between domain model code and web forms, and integrates with all the other features of the Spring Framework.
- The Web-Struts module contains the support classes for integrating a classic Struts web tier within a Spring application. Note that this support is now deprecated as of Spring 3.0. Consider migrating your application to Struts 2.0 and its Spring integration or to a Spring MVC solution.
- The Web-Portlet module provides the MVC implementation to be used in a portlet environment and mirrors the functionality of Web-Servlet module.
AOP and Instrumentation
- Spring’s AOP module provides an AOP Alliance-compliant aspect-oriented programming implementation allowing you to define, for example, method-interceptors and pointcuts to cleanly decouple code that implements functionality that should be separated.
- The separate Aspects module provides integration with AspectJ.
- The Instrumentation module provides class instrumentation support and classloader implementations to be used in certain application servers.
The Test module supports the testing of Spring components with JUnit or TestNG. It provides consistent loading of Spring ApplicationContexts and caching of those contexts. It also provides mock objects that you can use to test your code in isolation.