Monthly Archives: May 2013

Instantiate Spring bean with non-default constructor from another bean

twittergoogle_plusrss

Facebooktwittergoogle_plusredditlinkedinmail

I’d like to show how to instantiate Spring bean with non-default constructor (constructor with parameters) from other Spring driven bean because it seems to me that a lot of Java developers don’t know that this is possible.

First of all, simple annotation based Spring configuration. It’s scanning target package for Spring beans.

@Configuration
@ComponentScan("sk.lkrnac.blog.componentwithparams")
public class SpringContext {
}

Here is component with non-default constructor. This component needs to be specified as prototype, because we will be creating new instances of it. It also needs to be named (will clarify why below).

@Component(SpringConstants.COMPONENT_WITH_PARAMS)
@Scope("prototype")
public class ComponentWithParams {
 private String param1;
 private int param2;

 public ComponentWithParams(String param1, int param2) {
  this.param1 = param1;
  this.param2 = param2;
 }

 @Override
 public String toString() {
  return "ComponentWithParams [param1=" + param1 + ", param2=" + param2
    + "]";
 }
}

Next component instantiates ComponentWithParams. It needs to be aware of Spring’s context instance to be able to pass arguments non-default constructor.
getBean(String name, Object... args) method is used for that purpose. First parameter of this method is name of the instantiating component (that is why component needed to be named). Constructor parameters follow.

@Component
public class CreatorComponent implements ApplicationContextAware{
 ApplicationContext context;

 public void createComponentWithParam(String param1, int param2){
  ComponentWithParams component = (ComponentWithParams)
    context.getBean(SpringConstants.COMPONENT_WITH_PARAMS, 
      param1, param2);
  System.out.println(component.toString() + " instanciated...");
 }

 @Override
 public void setApplicationContext(ApplicationContext context)
   throws BeansException {
  this.context = context;
 }
}

Last code snippet is main class which loads Spring context and runs test.

public class Main {

 public static void main(String[] args) {
  AnnotationConfigApplicationContext context = 
    new AnnotationConfigApplicationContext(SpringContext.class);
  CreatorComponent invoker = context.getBean(CreatorComponent.class);

  invoker.createComponentWithParam("First", 1);
  invoker.createComponentWithParam("Second", 2);
  invoker.createComponentWithParam("Third", 3);
  context.close();
 }
}

Console output:

ComponentWithParams [param1=First, param2=1] instantiated...
ComponentWithParams [param1=Second, param2=2] instantiated...
ComponentWithParams [param1=Third, param2=3] instantiated...

And that’s it. You can download source code from Github.

twittergoogle_plusrss