Question

I have a spring injected service

 class A{
      List l = new ArrayList();

      public m1(){
           //do some additions in list 
      }

      public m2(){
           //do some new additions in list
      }
 }

Now because creating of objects of A, is in the hands of spring the behavior of program is not what is expected. (I expect list to be available empty always but not initialized by methods for some wired reason)

Will Spring always create only one instance of A, so that list l will keep on growing, I have configured bean as singleton in application context.

If yes, naturally I must initialize the list inside the functions m1 & m2 or callee must past the reference, and in my case callee being struts2 actions they are not singleton so this issue can be solved?

Or

Does spring provide any support in configuration to initialize member variables at every call or something else?

More generally what are best practices to have in writing services injected by spring about using member variables/ local variables for performance & efficiency.

Answer 1

Trying to answer following :
Does spring provide any support in configuration to initialize member variables at every call or something else?

By default Spring beans are singleton. Initialized only once and use the same object again and again.

However, if requirement changes as you asked. You need to understand scope attribute provided by the Spring.

<bean id="id" class="com.test.TP" scope="prototype">
</bean>

Refer following for detail understanding.
Scope Description

• singleton

  Scopes a single bean definition to a single object instance per
  Spring IoC container.

• prototype

  Scopes a single bean definition to any number of object instances.

• request

  Scopes a single bean definition to the lifecycle of a single HTTP
  request; that is each and every HTTP request will have its own
  instance of a bean created off the back of a single bean definition.
  Only valid in the context of a web-aware Spring ApplicationContext.

• session

  Scopes a single bean definition to the lifecycle of a HTTP Session.
  Only valid in the context of a web-aware Spring ApplicationContext.

• global session

  Scopes a single bean definition to the lifecycle of a global HTTP
  Session. Typically only valid when used in a portlet context. Only
  valid in the context of a web-aware Spring ApplicationContext.

http://static.springsource.org/spring/docs/3.0.0.M3/spring-framework-reference/html/ch04s04.html

It is also possible to have user defined scope such as thread scope.