Any good Spring threading with a TaskExecutor examples? [closed]

Question

I'm trying to get a handle on how to implement threading in a Java application that uses Spring for transaction management. I've found the TaskExecutor section in the Spring documentation, and ThreadPoolTaskExecutor looks like it would fit my needs;

ThreadPoolTaskExecutor

This implementation can only be used in a Java 5 environment but is also the most commonly used one in that environment. It exposes bean properties for configuring a java.util.concurrent.ThreadPoolExecutor and wraps it in a TaskExecutor. If you need something advanced such as a ScheduledThreadPoolExecutor, it is recommended that you use a ConcurrentTaskExecutor instead.

However I have no idea how to go about using it. I've been searching for good examples for awhile now with no luck. If anyone can help me out I would appreciate it.

Stride

Answer 1

It's pretty simple. The idea is that you have an executor object that's a bean, which is passed into whatever object wants to fire the new task (in a new thread). The nice thing is that you can modify what type of task executor to use just by changing the Spring config. In the example below I'm taking some example class (ClassWithMethodToFire) and wrapping it in a Runnable object to do the fire; you could also actually implement Runnable in a class of your own, and then in the execute method you'd just call classWithMethodToFire.run().

Here's a very simple example.

public class SomethingThatShouldHappenInAThread {
     private TaskExecutor taskExecutor;
     private ClassWithMethodToFire classWithMethodToFire;

     public SomethingThatShouldHappenInAThread(TaskExecutor taskExecutor,
                                               ClassWithMethodToFire classWithMethodToFire) {
          this.taskExecutor = taskExecutor;
          this.classWithMethodToFire = classWithMethodToFire;
     }

     public void fire(final SomeParameterClass parameter) {
          taskExecutor.execute( new Runnable() {
               public void run() {
                    classWithMethodToFire.doSomething( parameter );
               }
          });
     }
}

And here are the Spring beans:

<bean name="somethingThatShouldHappenInAThread" class="package.name.SomethingThatShouldHappenInAThread">
     <constructor-arg type="org.springframework.core.task.TaskExecutor" ref="taskExecutor" />
     <constructor-arg type="package.name.ClassWithMethodToFire" ref="classWithMethodToFireBean"/>
</bean>

<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
     <property name="corePoolSize" value="5" />
     <property name="maxPoolSize" value="10" />
     <property name="queueCapacity" value="25" />
</bean>

Oversweet

I think my problem is thinking this is more complex then it is. I saw docs.huihoo.com/javadoc/spring/2.0/org/springframework/… and I assumed a ThreadPoolTaskExecutor had a built in queuing mechanism. – Stride

Maybe I wasn't mistaken, what is queueCapacity for? I still feel like I am missing something here. – Stride

If the queue capacity is greater than 0, it creates a queue, so that the tasks that are fired by a particular TaskExecutor can wait until a thread is available from the pool. The capacity indicates how many spaces are in the queue. If the queue fills up, the executor will block (i.e. the execute method won't return until a space opens up). Here's the doc on the queue: java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/… – Oversweet

But you don't modify the queue externally, it is all managed by the TaskExecutor implementation right? I think I get it now. I was thinking you could add all the items you wanted to a queue and then pass it in to the TaskExecutor and have that execute it for you. – Stride

Ah. No, it's all handled for you, as you say. You just call execute over and over and the tasks get queued if necessary. – Oversweet

Though the documentation for corePoolSize, maxPoolSize, queueCapacity could be better. I am not sure I understand what that is controlling. – Stride

Wait, got it, just need to look at the documentation for the Java clases that the Spring classes are based on. java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/… – Stride

To ensure blocking on full queue/pool, you need to set rejectedExecutionHandler to java.util.concurrent.ThreadPoolExecutor.CallerRunsPolicy. Default handler, AbortPolicy, (static.springsource.org/spring/docs/3.0.x/javadoc-api/org/…) aborts tasks instead of block the caller. – Nursemaid

About blocking the caller : jroller.com/ndpar/entry/taskexecutor_blocking_queue – Triceps