Technology Overview

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Spring

Spring's main aim is to make enterprise Java easier to use and promote good programming practice. It does this by enabling a POJO-based programming model that is applicable in a wide range of environments. We believe that Spring provides the ultimate programming model for modern enterprise Java.
Spring does not reinvent the wheel. Thus you'll find no logging packages in Spring, no connection pools, no distributed transaction coordinator. All these things are provided by open source projects (such as Commons Logging, which we use for all our log output, or Commons DBCP), or by your application server or web container. For the same reason, we don't provide an O/R mapping layer. There are good solutions to this problem such as TopLink, Hibernate, JPA and JDO.
Spring does aim to make existing technologies easier to use and does aim to provide a unified, simple yet powerful programming model. For example, although we are not in the business of low-level transaction coordination, we provide an abstraction layer over JTA or any other transaction strategy that is more portable, easier to use and makes code easier to test.
Spring benefits from internal consistency. All the developers are singing from the same hymn sheet, whose fundamental ideas remain faithful to those of Expert One-on-One J2EE Design and Development. And we've been able to use some central concepts, such as Inversion of Control, across multiple areas.
Spring is portable between application servers and web containers. (Indeed, its core functionality does not require another container.) Of course ensuring portability is always a challenge, but we avoid anything platform-specific or non-standard in the developer's view, and support users on WebLogic, Tomcat, Resin, JBoss, Jetty, Geronimo, WebSphere and other application servers. Spring's non-invasive, POJO approach enables us to take advantage of environment-specific features without sacrificing portability, as in the case of enhanced WebLogic, WebSphere and OC4J transaction management functionality that uses BEA and IBM proprietary APIs under the covers.

Spring can effectively organize your middle tier objects. Spring takes care of plumbing that would be left up to you if you use only Struts or other frameworks geared to particular J2EE APIs. And Spring's configuration management services can be used in any architectural layer, in whatever runtime environment.
1. Spring can eliminate the proliferation of Singletons seen on many projects. In my experience, this is a major problem, reducing testability and object orientation.
2. Spring eliminates the need to use a variety of custom properties file formats, by handling configuration in a consistent way throughout applications and projects. Ever wondered what magic property keys or system properties a particular class looks for, and had to read the Javadoc or even source code? With Spring you simply look at the class's JavaBean properties or constructor arguments. The use of Inversion of Control and Dependency Injection (discussed below) helps achieve this simplification.
3. Spring facilitates good programming practice by reducing the cost of programming to interfaces, rather than classes, almost to zero.
4. Spring is designed so that applications built with it depend on as few of its APIs as possible. Most business objects in Spring applications have no dependency on Spring.
5. Applications built using Spring are very easy to test. For certain unit testing scenarios, the Spring Framework provides mock objects and testing support classes. Spring also provides unique “integration testing” functionality in the form of the Spring TestContext Framework and legacy JUnit 3.8 support classes that enable you to test your code quickly and easily, even while accessing a staging database.
6. Spring helps you solve problems with the most lightweight possible infrastructure. Spring provides an alternative to EJB that's appropriate for many applications. For example, Spring can use AOP to deliver declarative transaction management without using an EJB container; even without a JTA implementation, if you only need to work with a single database, or want to avoid two phase commit.
7. Spring provides a consistent framework for data access, whether using JDBC or an O/R mapping product such as TopLink, Hibernate or a JPA or JDO implementation.
8. Spring provides a consistent, simple programming model in many areas, making it ideal architectural "glue." You can see this consistency in the Spring approach to JDBC, JMS, JavaMail, JNDI and many other important APIs.