[Guava] Futures 예제

Guava Futures와 관련 API

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/util/concurrent/ListeningExecutorService.html

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/util/concurrent/Futures.html

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/util/concurrent/FutureCallback.html

Guava Futures는 Java Future에 비해서

Callback Listener를 사용할 수 있고, 성공/실패 여부를 받을 수 있다. 

(Mina나 Netty를 사용하는 장점을 알 수 있다.)

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

import org.junit.Test;

import com.google.common.util.concurrent.FutureCallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;

public class GuavaTest {

@Test
public void test_ExecutorService() {
System.out.println("====java future===");
ExecutorService executor = Executors.newFixedThreadPool(10);

Callable<String> asyncTask = new Callable<String>() {
@Override
public String call() throws Exception {
Random random = new Random();
int number = random.nextInt(5);
return "async : " + number;
}
};

Future<String> future = executor.submit(asyncTask);

try {
String result = future.get();
System.out.println(result);
} catch (ExecutionException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}

executor.shutdown();
}

@Test
public void test_guava_future() {
System.out.println("===guava future===");

ListeningExecutorService executor = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));

Callable<String> asyncTask = new Callable<String>() {
@Override
public String call() throws Exception {
Random random = new Random();
int number = random.nextInt(5);
return "async : " + number;
}
};

ListenableFuture<String> listenableFuture = executor.submit(asyncTask);

Futures.addCallback(listenableFuture, new FutureCallback<String>() {
@Override
public void onSuccess(String result) {
System.out.println("[success] : " + result);
}

@Override
public void onFailure(Throwable thrown) {
System.out.println("[success] : " + thrown.getMessage());
}
});

try {
String result = listenableFuture.get();
System.out.println(result);
} catch (ExecutionException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}

executor.shutdown();
}
}

결과

===guava future===

[success] : async : 1

async : 1

====java future===

async : 3

Futures 대신 ListenableFuture.addListener()를 활용할 수도 있다. 

@Test
public void test_guava_future_listener() {
System.out.println("===guava future listener===");

ListeningExecutorService executor = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));

Callable<String> asyncTask = new Callable<String>() {
@Override
public String call() throws Exception {
Random random = new Random();
int number = random.nextInt(5);
return "async : " + number;
}
};

final ListenableFuture<String> listenableFuture = executor.submit(asyncTask);

listenableFuture.addListener(new Runnable() {
      @Override
      public void run() {
          try {
              final String contents = listenableFuture.get();
              System.out.println(contents);
          } catch (InterruptedException e) {
              e.printStackTrace();
          } catch (ExecutionException e) {
          e.printStackTrace();
          }
      }
  }, executor);

executor.shutdown();

}

참조할만한 소스 

https://gist.github.com/bbejeck/1387892