Java – Spring 3: How to call @Async annotated methods from the TaskExecutor

asynchronousjavamultithreadingspringspring-mvc

I'm new to asynchronous task execution in Spring, so please forgive me if this sounds like a silly question.

I read that @Async annotation is introduced from Spring 3.x onward at method level to invocation of that method will occur asynchronously.
I also read that we can configure the ThreadPoolTaskExecutor in the spring config file.

What I'm not able to understand is that how to call a @Async annotated method from a tak executor lets suppose – AsyncTaskExecutor

Earlier we used to do something like in a class:

@Autowired protected AsyncTaskExecutor executor;

And then

executor.submit(<Some Runnable or Callable task>)

I'm not able to understand the relationship between @Async annotated methods and TaskExecutor.

I tried searching a lot over the internet but could not get anything on this.

Can somebody provide an example for the same.

Best Answer

Here's an example of @Async use:

@Async
void doSomething() {
    // this will be executed asynchronously
}

Now call that method from another class and it will run asynchronously. If you want a return value use a Future

@Async
Future<String> returnSomething(int i) {
    // this will be executed asynchronously
}

The relationship between @Async and TaskExecutor is that @Async uses a TaskExecutor behind the scenes. From the docs:

By default when specifying @Async on a method, the executor that will be used is the one supplied to the 'annotation-driven' element as described above. However, the value attribute of the @Async annotation can be used when needing to indicate that an executor other than the default should be used when executing a given method.

So to set up a default executor, add this to your spring config

<task:annotation-driven executor="myExecutor" />

Or to use a particular executor for a single use try

@Async("otherExecutor")

See http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/scheduling.html#scheduling-annotation-support-async

Related Solutions

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Java – How to call one constructor from another in Java

Yes, it is possible:

public class Foo {
    private int x;

    public Foo() {
        this(1);
    }

    public Foo(int x) {
        this.x = x;
    }
}

To chain to a particular superclass constructor instead of one in the same class, use super instead of this. Note that you can only chain to one constructor, and it has to be the first statement in your constructor body.

See also this related question, which is about C# but where the same principles apply.

Best Answer

Related Solutions

Java – How to test a class that has private methods, fields or inner classes

Java – How to call one constructor from another in Java

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