Spring Framework has several distinct modules for a specific set of functionalities, and they work more or less independently of the others. This system is very flexible, so the developer can choose only those required for the enterprise application. For example, a developer can just use the Spring DI module and build the rest of the application with non-Spring components. So, Spring provides integration points to work with other frameworks and APIs--for example, you can use the Spring Core DI pattern only with the Struts application. In case the development team is more proficient in using Struts, it can be used instead of Spring MVC while the rest of the application uses Spring components and features, such as JDBC and transactions. So while the developers need to deploy the required dependencies with the Struts application, there is no need to add a whole Spring Framework.
Here is an overview of the entire module structure:
The various modules of the Spring Framework
Let's look at each of Spring's modules and see how each fits in to the bigger picture.
This module of the Spring Framework uses lot of the design pattern such as the Factory method design pattern, DI pattern, Abstract Factory Design pattern, Singleton Design pattern, Prototype Design pattern, and so on. All other Spring modules are dependent on this module. You'll implicitly use these classes when you configure your application. It is also called the IoC container and is central to Spring's support for dependency injection, which manages how the beans in a Spring application are created, configured, and managed. You can create Spring container either by using the implementations of BeanFactory or the implementations of the ApplicationContext. This module contains the Spring bean factory, which is the portion of Spring that provides the DI.
Spring AOP is a Java-based AOP Framework with AspectJ integration. It uses dynamic proxies for aspect weaving and focuses on using AOP to solve enterprise problems. This module is based on Proxy and Decorator Design patterns. This module enables the modularization of cross-cutting concerns to avoid tangling and eliminate scattering. Like DI, it supports loose coupling between the core business service and cross-cutting concerns. You can implement your custom aspects and configure them declaratively in your application without impacting on the code of business objects. It provides much flexibility in the code; you could remove or change the aspect logic without touching the code of the business objects. This is a very important module of the spring framework, so I will discuss it in detail in Chapter 6, Spring Aspect Oriented Programming with Proxy and Decorator Pattern of this book.
Spring DAO and Spring JDBC make life very easy by using templates to remove the common code. The templates implement the GOF template method design pattern and provide suitable extension points to plug in custom code. If you are working with a traditional JDBC application, you have to write lots of boilerplate code to, for example, create a database connection, create a statement, find a result set, handle SQLException, and finally close the connection. If you are working with a Spring JDBC Framework with a DAO layer, then you do not have to write boilerplate code, unlike a traditional JDBC application. That means that Spring allows you to keep your application code clean and simple.
Spring also provides support to ORM solutions, and it provides integration with ORM tools for easy persistence of POJO objects in relational databases. This module actually provides an extension to the Spring DAO module. Like JDBC-based templates, Spring provides ORM templates to work with leading ORM products, such as Hibernate, JPA, OpenJPA, TopLink, iBATIS, and so on.
Spring provides a web and remote module for the enterprise web application. This module helps build highly flexible web applications, leveraging the complete benefits of the Spring IOC container. This module of Spring uses the patterns such as the MVC architectural pattern, Front Controller pattern, and the DispatcherServlet Pattern, and it seamlessly integrates with the servlet API. The Spring web module is very pluggable and flexible. We can add any of the view technologies, such as JSP, FreeMarker, Velocity, and so on. We can also integrate it with other frameworks, such as Struts, Webwork, and JSF, using spring IOC and DI.