Spring is an open-source application framework, introduced and developed in 2004.Spring is a light-weight framework for the development of enterprise-ready applications. Spring can be used to configure declarative transaction management, remote access to your logic using RMI or web services, mailing facilities and various options in persisting your data to a database.
Spring framework can be used in modular fashion, it allows to use in parts and leave the other components which is not required by the application.Unlike other frameworks and APIs, spring does not impose itself wholly on to the design of a project. Spring is modular and has been divided logically into independent packages, which can function independently. The architects of an application have the flexibility to implement just a few spring packages and leave out most of the packages in spring.
The “Spring Framework” would not feel bad with this attitude and on the contrary encourages users to introduce Spring into existing applications in a phased manner. So no matter what kind of framework you are using now Spring will co-exist with it without causing you nightmares and further more Spring will allow you to choose specific packages in Spring.
Why from Struts to Spring :
The “Struts” framework is no doubt a good framework to enhance the ability of the web tier, but the biggest drawback is the fact that it caters only to the web tier and leaves most of the Enterprise tier or middle tier to the fancy of the application architects. The Application architects need to provide an additional framework to deal with the enterprise tier and make sure that the new framework integrates well with the Struts framework. Spring tries to alleviate this problem by providing a comprehensive framework, which includes an MVC framework, an AOP integration framework, a JDBC integration framework, and an EJB integration framework. It also provides integration modules for major O/R mapping tools like Hibernate and JDO. Spring provides all these in a modular fashion without imposing any layer on to the user. Spring is not a take-it-or- leave-it kind of framework.
It tries to seamlessly blend into the existing framework users have without hindrances. Spring also provides transaction management support using Java classes, email support packages using framework classes, web services support through proxies and many more features like the above. As mentioned earlier all these packages are optional and spring does not make any of them mandatory. Spring can seamlessly integrate with existing applications and provide specific functionality that you intend to provide with minimal demands for customization.
A user can continue to use Struts for the web tier and toplink O/R for the database and meanwhile hook spring to provide e-mail services and web services support. Spring is based on the Inversion of Control/Dependency Injection pattern that has been making rounds in message boards all over the Internet.