What is Spring

Spring is the part of Java Enterprise Edition and was developed by Rod Johnson in 2003 and Spring framework is an open source Java platform and Spring is a "Framework" that contains many framework like Hibernate/ JPA (Data Persist-ency), JSF , JMS , EJB and many other framework  and these all makes the easy development of JavaEE application.


What is Framework?
Framework is a collection of API or structure that help you in technical problem and make your work smooth and faster.Framework take the headache of workload from your self into own self for 60% to 70%.

Overview Of Spring
Basically Spring is a framework of 


Modules In Spring
The Spring Framework consists of features organized into about 20 modules. These modules are grouped into Core Container, Data Access/Integration, Web, AOP (Aspect Oriented Programming), Instrumentation, Messaging, and Test, as shown in the following diagram.

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/overview.html

Feature Of Spring

1. Dependency Injection: 
   Dependency Injection is a design pattern that promotes loose coupling between java objects. This is an extension of the Factory pattern where-in objects do not resolve their dependencies themselves but let an external container (like Spring) take the responsibility of resolving the dependencies. 
   The benefits of using dependency injection is that any object of appropriate type can be injected just by changing the spring configuration. This makes the objects loosely coupled to other objects and promotes 'coding to interface' rather than hardcoding dependencies. 
   Dependency Injection is the back-bone of Spring framework.
   
2. Support for Aspect Oriented Programming (a.k.a. AOP): 
   Aspect Oriented Programming is a style of programming used to factor out cross-cutting concerns across many java objects and keep the code for handing the cross-cutting concern in just one place. Examples of cross-cutting concerns could be logging, method tracing, auditing etc. Using AOP, we need not pollute numerous java classes with the same code for handing cross-cutting concerns thereby promoting high cohesion among java classes.
   
3. Integration technology for easier integration with other Java libraries: 
   Spring uses Dependency Injection and AOP to provide integration facility for many java libraries for access database (e.g. JDBC, Hibernate, myBatis, etc.), queues (JMS based queue integration), web access (e.g. Servlets, Struts, etc.) and to virtually all J2EE technologies. 
   Spring has emerged as the de-facto integration technology for the Java/J2EE stack.

Dependency Injection (DI) is a design pattern and Dependency Injection design pattern allows us to remove the hard-coded dependencies and make our application loosely coupled, extendable and maintainable.DI can help make your code architecturally pure.