Java Framework [Spring] @Autowired 와 Java Spring

[출처] http://stackoverflow.com/questions/7405232/why-does-autowiring-not-function-in-a-thread

Why does Autowiring not function in a thread?

 
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I've made a maven project in Spring 3.0, I've made some DAO, services and controllers, in one of mine controller I call a service in which I start a thread, the problem is that in the thread I declare a "service variable" that should be initialized with Autowired annotiation, but it doesn't work and the variable isn't initilized and has the value null.

this is the thread class
package com.project.tasks;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.task.TaskExecutor;
import org.springframework.stereotype.Component;

import com.project.entities.user.User;
import com.project.services.IUserService;

@Component
public class AddFriendInMyFriendListTaskExecutor {
private class AddFriendInMyFriendListTask implements Runnable {

     // HERE IS THE PROBLEM
    @Autowired
    private IUserService uService;

    private User a;
    private User b;

    public AddFriendInMyFriendListTask() {
        ;
    }

    public AddFriendInMyFriendListTask(User aA, User bB) {
        a = aA;
        b = bB;
    }

    public User getA() {
        return a;
    }
    public void setA(User a) {
        this.a = a;
    }
    public User getB() {
        return b;
    }
    public void setB(User b) {
        this.b = b;
    }

    public void run() {
                    // FROM HERE IT PRINTS THE VALUE OF uService THAT IS NULL
        System.out.println("uService:" + uService);
        uService.insertRightUserIntoLeftUserListOfFriends(a, b);
    }
}

private TaskExecutor taskExecutor;

  public AddFriendInMyFriendListTaskExecutor(TaskExecutor taskExecutor) {
    this.taskExecutor = taskExecutor;
  }

  public void doIt(User a, User b) {
      taskExecutor.execute(new AddFriendInMyFriendListTask(a, b));
  }
}

this is the piece of code that calls the thread
    User a = uDao.getUser(hrA.getMyIdApp());
    User b = uDao.getUser(hrA.getOtherIdApp());
    SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
    AddFriendInMyFriendListTaskExecutor tmp = new AddFriendInMyFriendListTaskExecutor(taskExecutor);
    tmp.doIt(a, b);

I'd like to highlight that in all the other tests in which I don't call any threads, the Autowired of a UserService instance functions correctly! The method I call: insertRightUserIntoLeftUserListOfFriends(User a, User b), works correctly.

java multithreading spring task autowired

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edited Sep 13 '11 at 21:04

 
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asked Sep 13 '11 at 16:25

 
user942458
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4 Answers

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For a bean to be autowired by Spring, the bean must be a Spring bean (i.e. be declared in the context.xml file or be annotated with a Spring annotation (@Service, @Component, etc.).

And of course, it must be instantiated by Spring, and not by your code. If you instantiate a Spring bean yourself with new, Spring doesn't know about the bean, and doesn't inject anything into it.

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answered Sep 13 '11 at 16:36

 
JB Nizet
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No. You instantiate AddFriendInMyFriendListTaskExecutor using new AddFriendInMyFriendListTaskExecutor(), the inner class AddFriendInMyFriendListTask (which should be static) is not annotated, and you instanciate it using new as well. ?  JB Nizet Sep 13 '11 at 16:45 
 

   
 
Excuse me probably I don't understand your answer, or I'm not able to explain my problem, the creation of the AddFriendInMyFriendListTaskExecutor instance dosen't give me any problem, infact after the code :"AddFriendInMyFriendListTaskExecutor tmp = new AddFriendInMyFriendListTaskExecutor(taskExecutor);" tmp is not null, the problem is when I use uService into the class AddFriendInMyFriendListTask, there's no problem with the calss and the initilization of AddFriendInMyFriendListTask's instances ?  user942458 Sep 13 '11 at 17:09
 

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Spring must instantiate the spring beans. Not you. You can not use the new operator to instantiate spring beans. They must either be injected in the current bean by Spring, or you must get them from the bean factory. ?  JB Nizet Sep 13 '11 at 17:45
 
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Spring just autowires beans of the context, no instances created by new. But why do you have declared uService in AddFriendInMyFriendListTask and not as a bean property of the outer (bean) class AddFriendInMyFriendListTaskExecutor, that should simply work:
@Component
public class AddFriendInMyFriendListTaskExecutor {

  private class AddFriendInMyFriendListTask implements Runnable {

    private final User a;
    private final User b;

    public AddFriendInMyFriendListTask(User aA, User bB) {
      a = aA;
      b = bB;
    }

    public void run() {
      AddFriendInMyFriendListTaskExecutor.this.uService.insertRightUserIntoLeftUserListOfFriends(a, b);
    }
  }

  @Autowired
  private IUserService uService;

  @Autowired
  private TaskExecutor taskExecutor;

  public void doIt(User a, User b) {
    taskExecutor.execute(new AddFriendInMyFriendListTask(a, b));
  }
}

(removed some unused getter/setter and made taskExecutor also a bean property)

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answered Sep 13 '11 at 21:36

 
Arne Burmeister
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If you need to autowire a newly created instance (without container support) invoke

ctx.getAutowireCapableBeanFactory().autowireBean(instance)

where ctx is your ApplicationContext and instance the newly created instance.

I asked a similar question here

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answered Sep 13 '11 at 20:56

 
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Another solution would be to inject the user IUserService in a spring managed component (service, component, etc.) and pass the injected value to the constructor of the class AddFriendInMyFriendListTask.

Thus, the constructor becomes something like this
public AddFriendInMyFriendListTask(User aA, User bB, IUserService userService) {
    a = aA;
    b = bB;
    this.userService = userService;
}

and remove the @Autowired from the AddFriendInMyFriendListTask class.

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answered Sep 13 '11 at 21:10

 
aseychell
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