Spring

Spring was developed by "Rod Jonson" in 2003. Spring framework makes the easy development of JEE application. Spring is a lightweight framework. It can be thought of as a framework of frameworks because it provides support to various frameworks. Like, Struts, EJB, JSF, GWT...

The spring framework comprises several modules such as IOC, AOP, DAO, Context, ORM, Web MVC etc.

Advantages of Spring Framework:
There are many advantages of Spring framework.

Predefined Templates:
Spring framework provides templates for JDBC, Hibernate, JPA etc. So, there is no need to write too much code. It hides the basic steps of these technologies.

Let's take the example of JDBC template you no need to write the code exception handling, creating connection, creating statement, committing transaction, closing connection etc. You need to write the code for executing query. Thus it saves lot of JDBC code.

Loose Coupling:
The Spring applications are loosely coupled because of dependency injection.

Easy to test:
The dependency injection makes easier to test the application. The EJB or Struts applications are required server to run applications. But, Spring framework does not require server.

Lightweight:
Spring framework is lightweight because of POJO implementation. The spring framework doesn't force the programmer to inherit any class or implement any interface. That is why this is said non-invasive.

Fast Development:
The Dependency injection of Spring framework and it support various framework makes the easy development of JEE applications.

Powerful abstraction:
It provides powerful abstraction to JEE specification such as JMS, JDBC, JPA and JTA.

Declarative Support:
It provides declarative support for catching , validation and formatting.


Spring Framework:
The below diagram represents about the spring framework modules.

Test:
Test layer provides support of testing with JUnit and TestNG.

Spring Core Container:
Spring core container contains core, beans, context and expression language modules.

Core & Beans:
These modules provides Inversion Of Control (IOC) and Dependency Injection (DI) features.

Context:
This module supports Internationalization (i18n) , EJB , JMS , Basic Remoting.

Expression Language(EL):
It is an extension to the EL defined in JSP. It provides support to setting and getting property values, method invocation, accessing collections and indexers, named variables, logical & arithmetic operations, retrieval of objects by name, etc.

AOP, Aspects & Instrumentation:
These modules supports Aspects Oriented programming implementation where you can use Advice's, point-cut's etc to decouple the code. The Aspects module provides support to integration with AspectJ.

The Instrumentation module provides support to class instrumentation and class loader implementation.

Data Access / Integration:
This group comprises of JDBC, ORM, OXM, JMS and transaction modules. These modules basically provides support to interact with the database.

WEB:
This group comprises of web, web-serlvet, web-struts and web-portlet. These modules support to create web application.


Inversion Of Control (IOC) & Dependency Injection (DI):
Above design patterns are used to remove dependency from the programming code. They make the code easier to test and maintain,
class Student {
     Address address;
     Student(){
         address = new Address();
    }
}
        
In such case there is dependency in between Student and Address (tightly coupling). In the inversion of control scenario.

class Student{
      Address address;
      Student(Address address){
           this.address = address;
      }
}
        
Thus, IOC makes the code loosely coupled, in such case, there is no need to modify the code if our logic is moved to new environment.

In Spring framework, IOC container is responsible to inject the dependency. We provide metadata to the IOC container either by XML files or annotation.

Advantages of Dependency Injection:
  • makes the code loosely coupled so easy to maintain.
  • makes the code easy to test.

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