Is Spring @autowired not meant for non-singleton containers?

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I have a MyTask class which implements Runnable and there can be many such objects instantiated at any given moment. There are certain properties that I would like to autowire into MyTask class.

But I think that if I mark MyTask with @Component then it will become a spring-managed singleton correct? That's not what I want, I need many independent instances of this class to be run by a TaskExecutor.

So my question(s):

  • a) Am I fundamentally wrong in my understanding of @Component annotation? Does it NOT make MyTask into a spring-managed singleton?
  • b) Is there some other annotation I should use so that spring detects @Autowired and injects the property?
  • c) Is spring autowiring not meant for non-singleton containers/classes like MyTask?

Update # 1 - These don't work:

public class MyTask implements Runnable { // I want this class to be non-singleton
    @Autowired
    public SomeSpecialSpringConfiguredConnectionClass blah; // this is the singleton bean that should be injected
    @Override
    public void run() {
        // BLAH IS NULL, this shouldn't be NULL, that is not what I want
        // which makes sense considering Spring never knew it had to work
        // on this class
    }
}

@Component
public class MyTask implements Runnable { // I want this class to be non-singleton
    @Autowired
    public SomeSpecialSpringConfiguredConnectionClass blah; // this is the singleton bean that should be injected
    @Override
    public void run() {
        // this works BUT now MyTask is singleton :(
    }
}

@Component
@Scope("prototype")
public class MyTask implements Runnable { // I want this class to be non-singleton
    @Autowired
    public SomeSpecialSpringConfiguredConnectionClass blah; // this is the singleton bean that should be injected
    @Override
    public void run() {
        // BLAH IS NULL, again ... this shouldn't be NULL, that is not what I want
    }
}

Update # 2 - While waiting for some more suggestions on how to do it the easy way, I'm looking into: Using AspectJ to dependency inject domain objects with Spring as an alternative.

autowired spring-aop spring singleton
4 Answers

Typically adding @Scope("prototype") should not cause null error for autowired blah bean,you should check how you instantiate MyTask bean. I think the problem is that you manually instantiate MyTask like:

   MyTask task = new MyTask();

and therefor it goes out of Spring's control that is why its dependency, blah bean, is null , instead of manual instantiation, you need to autowire it and let Spring takes care of its dependencies then blah willnot be null. But then there is another issue. Autowiring a prototype bean, MyTask, whithin another singleton object is wrong. Spring container creates a singleton bean only once, and thus only sets the prototype bean once and this causes the prototype scope not to work.Like below, Myactivity is a singleton which autowires MyTask, I also added a constructor for MyTask to print something once a new instance of MyTask gets created. In below case it only prints once, therefore prototype is not working.

@Component
@Scope("prototype")
public class MyTask implements Runnable {

  @Autowired
  public SomeSpecialSpringConfiguredConnectionClass blah;

  public MyTask(){
    System.out.println("New Instance of MyTask");
  }

  @Override
  public void run() {
    assert(blah != null);
  }
}


@Component
public class MyActivity {

  @Autowired
  private MyTask task;

  public MyTask start() {
    return task;
  }
}

@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest(classes = {MyActivity.class, MyTask.class, 
   SomeSpecialSpringConfiguredConnectionClass.class})
public class MyTaskTest {

  @Autowired
  private MyActivity activity;

  @Test
  public void testActivity() {
    for (int i = 0; i < 5; i++) {
        MyTask task = activity.start();
        task.run();
    }
  }
 }

Based on Spring AOP Scoped proxies I changed @Scope("prototype") to @Scope(proxyMode = ScopedProxyMode.TARGET_CLASS, value = "prototype") so the scoped proxy injects a new instance of MyTask every time singleton MyActivity bean gets called.

@Component
@Scope(proxyMode = ScopedProxyMode.TARGET_CLASS, value = "prototype")
public class MyTask implements Runnable {

  @Autowired
  public SomeSpecialSpringConfiguredConnectionClass blah;

  public MyTask(){
    System.out.println("New Instance of MyTask");
  }

  @Override
  public void run() {
    assert(blah != null);
  }
}

and now the prototype is working fine and this was the result printed in console:

New Instance of MyTask
New Instance of MyTask
New Instance of MyTask
New Instance of MyTask
New Instance of MyTask
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