An Introduction to Spring Framework

 

What is Spring ?

Spring is an application framework. Unlike single-tier frameworks such as Struts or Hibernate, Spring aims to help structure whole applications in a consistent, productive manner, pulling together best-of-breed single-tier frameworks to create a coherent architecture.

Why Spring ?

The Spring Framework is an open source application framework that aims to make J2EE development easier. We’ll look at the motivation for Spring, its goals, and how Spring can help you develop high-quality applications quickly. Using J2EE “out of the box” is not an attractive option.

Many J2EE APIs and services are cumbersome to use. J2EE does a great job of standardizing low-level infrastructure, solving such problems as how can Java code access transaction management without dealing with the details of transactions. But J2EE does not provide an easily usable view for application code.That is the role of an application framework, such as Spring.

Spring enables you to enjoy the key benefits of J2EE, while minimizing the complexity encountered by application code. The essence of Spring is in providing enterprise services to Plain Old Java Objects (POJOs). This is particularly valuable in a J2EE environment, but application code delivered as POJOs is naturally reusable in a variety of runtime environments.

Spring - Architecture

Spring could potentially be a one-stop shop for all your enterprise applications. However, Spring is modular, allowing you to pick and choose which modules are applicable to you, without having to bring in the rest. The following section provides details about all the modules available in Spring Framework. The Spring Framework provides about 20 modules which can be used based on an application requirement

 

Enter Spring

                Spring is both the most popular and most ambitious of the lightweight frameworks. It is the only one to address all architectural tiers of a typical J2EE application, and the only one to offer a comprehensive range of services, as well as a lightweight container. We’ll look at Spring’s modules in more detail later, but the following are the key Spring modules :

·         Inversion of Control container: The core “container” Spring provides, enabling sophisticated configuration management for POJOs. The Spring IoC container can manage fine or coarse grained POJOs (object granularity is a matter for developers, not the framework), and work with other parts of Spring to offer services as well as configuration management. This is also called as Dependency Injection

Spring supports several types of Dependency Injection, those are :

o   Setter Injection: The injection of dependencies via JavaBean setter methods. Often, but not necessarily, each setter has a corresponding getter method, in which case the property is set to be writable as well as readable.

o   Constructor Injection: The injection of dependencies via constructor arguments.

o   Method Injection: A more rarely used form of Dependency Injection in which the container is responsible for implementing methods at runtime. For example, an object might define a protected abstract method, and the container might implement it at runtime to return an object resulting from a container lookup. The aim of Method Injection is, again, to avoid dependencies on the container API.

·         Aspect-Oriented Programming (AOP) framework: AOP enables behavior that would otherwise be scattered through different methods to be modularized in a single place. Spring uses AOP under the hood to deliver important out-of-the-box services such as declarative transaction management. Spring AOP can also be used to implement custom code that would otherwise be scattered between application classes.

·         MVC web framework: Spring provides a request-based MVC web framework. Its use of shared instances of multithreaded “controllers” is similar to the approach of Struts, but Spring’s web framework is more flexible, and integrates seamlessly with the Spring IoC container. All other Spring features can also be used with other web frameworks such as Struts or JSF.

·         Lightweight remoting: Spring provides support for POJO-based remoting over a range of protocols, including RMI, IIOP and other web services protocols.

·         Support for a comprehensive testing strategy for application developers: Spring not only helps to facilitate good design, allowing effective unit testing, but provides a comprehensive solution for integration testing outside an application server.

Conclusion

            Spring is a framework that helps you to "wire" different components together. It is most useful in cases where you have a lot of components and you might decide to combine them in different ways, or wish to make it easy to swap out one component for another depending on different settings or environments.

• Spring is light weight and It minimally invasive development with POJO.
• Spring achieves the loose coupling through dependency injection and interface based programming.
• Declarative programming through aspects and common conventions.
• Boilerplate reduction through aspects and templates.