CompletionService的异常处理

一、采用take()方法时发生异常

    示例代码：

    情况一：异常比另一个正确任务，较晚出现，正确任务的结果会打印出

import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MyCompletionServiceException {

	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		ExecutorService executor=Executors.newCachedThreadPool();
		CompletionService<String> comservice=new ExecutorCompletionService<String>(executor);
		MyException_one callone=new MyException_one();
		MyException_two calltwo=new MyException_two();
		comservice.submit(callone);
		comservice.submit(calltwo);
		
		try {
//			Thread.sleep(3000);
			System.out.println(comservice.take().get());
			System.out.println(comservice.take().get());
//			System.out.println(comservice.poll().get());
//			System.out.println(comservice.poll().get());
		} catch (InterruptedException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		} catch (ExecutionException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		}
	}

}
class MyException_one implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(2000);
		if(true){
			throw new Exception("抛出异常");
		}
		return "one";
	}
	
}
class MyException_two implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(1000);
		return "two";
	}
	
}

运行结果：

import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MyCompletionServiceException {

	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		ExecutorService executor=Executors.newCachedThreadPool();
		CompletionService<String> comservice=new ExecutorCompletionService<String>(executor);
		MyException_one callone=new MyException_one();
		MyException_two calltwo=new MyException_two();
		comservice.submit(callone);
		comservice.submit(calltwo);
		
		try {
//			Thread.sleep(3000);
			System.out.println(comservice.take().get());
			System.out.println(comservice.take().get());
//			System.out.println(comservice.poll().get());
//			System.out.println(comservice.poll().get());
		} catch (InterruptedException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		} catch (ExecutionException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		}
	}

}
class MyException_one implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(2000);
		if(true){
			throw new Exception("抛出异常");
		}
		return "one";
	}
	
}
class MyException_two implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(1000);
		return "two";
	}
	
}

　　

当只采用take()方法，而不使用get()方法时不出现异常，改为：

System.out.println(comservice.take().get());
System.out.println(comservice.take());

　　运行结果：

two
java.util.concurrent.FutureTask@1f96302

　　情况二：

      异常比另一个正确任务较早出现，这时不会打印出另一个正确任务的结果

   示例代码（贴出有修改的地方）：

class MyException_one implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(1000);
		if(true){
			throw new Exception("抛出异常");
		}
		return "one";
	}
	
}
class MyException_two implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(3000);
		return "two";
	}
	
}

　　运行结果：

java.util.concurrent.ExecutionException: java.lang.Exception: 抛出异常
	at java.util.concurrent.FutureTask.report(Unknown Source)
	at java.util.concurrent.FutureTask.get(Unknown Source)
	at mycompletionservice.MyCompletionServiceException.main(MyCompletionServiceException.java:23)
Caused by: java.lang.Exception: 抛出异常
	at mycompletionservice.MyException_one.call(MyCompletionServiceException.java:44)
	at mycompletionservice.MyException_one.call(MyCompletionServiceException.java:1)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

　　

二、采用poll()方法时发生异常

   情况一：异常比另一个正确任务，较晚出现，正确任务的结果会打印出

示例代码：

import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MyCompletionServiceException {

	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		ExecutorService executor=Executors.newCachedThreadPool();
		CompletionService<String> comservice=new ExecutorCompletionService<String>(executor);
		MyException_one callone=new MyException_one();
		MyException_two calltwo=new MyException_two();
		comservice.submit(calltwo);
		comservice.submit(callone);
		
		try {
			Thread.sleep(3000);
//			System.out.println(comservice.take().get());
//			System.out.println(comservice.take().get());
			System.out.println(comservice.poll().get());
			System.out.println(comservice.poll().get());
		} catch (InterruptedException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		} catch (ExecutionException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		}
	}

}
class MyException_one implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(2000);
		if(true){
			throw new Exception("抛出异常");
		}
		return "one";
	}
	
}
class MyException_two implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(1000);
		return "two";
	}
	
}

　　运行结果：

two
java.util.concurrent.ExecutionException: java.lang.Exception: 抛出异常
	at java.util.concurrent.FutureTask.report(Unknown Source)
	at java.util.concurrent.FutureTask.get(Unknown Source)
	at mycompletionservice.MyCompletionServiceException.main(MyCompletionServiceException.java:26)
Caused by: java.lang.Exception: 抛出异常
	at mycompletionservice.MyException_one.call(MyCompletionServiceException.java:44)
	at mycompletionservice.MyException_one.call(MyCompletionServiceException.java:1)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

　　同样不是get()时不会出现异常

情况二：

      异常比另一个正确任务较早出现，这时不会打印出另一个正确任务的结果

示例代码：

class MyException_one implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(1000);
		if(true){
			throw new Exception("抛出异常");
		}
		return "one";
	}
	
}
class MyException_two implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(2000);
		return "two";
	}
	
}

　　运行结果：

class MyException_one implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(1000);
		if(true){
			throw new Exception("抛出异常");
		}
		return "one";
	}
	
}
class MyException_two implements Callable<String>{

	@Override
	public String call() throws Exception {
		// TODO 自动生成的方法存根
		Thread.sleep(2000);
		return "two";
	}
	
}

　　

import java.util.concurrent.Callable;import java.util.concurrent.CompletionService;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorCompletionService;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;
public class MyCompletionServiceException {
public static void main(String[] args) {// TODO 自动生成的方法存根ExecutorService executor=Executors.newCachedThreadPool();CompletionService<String> comservice=new ExecutorCompletionService<String>(executor);MyException_one callone=new MyException_one();MyException_two calltwo=new MyException_two();comservice.submit(calltwo);comservice.submit(callone);try {Thread.sleep(3000);//System.out.println(comservice.take().get());//System.out.println(comservice.take().get());System.out.println(comservice.poll().get());System.out.println(comservice.poll().get());} catch (InterruptedException e) {// TODO 自动生成的 catch 块e.printStackTrace();} catch (ExecutionException e) {// TODO 自动生成的 catch 块e.printStackTrace();}}
}class MyException_one implements Callable<String>{
@Overridepublic String call() throws Exception {// TODO 自动生成的方法存根Thread.sleep(2000);if(true){throw new Exception("抛出异常");}return "one";}}class MyException_two implements Callable<String>{
@Overridepublic String call() throws Exception {// TODO 自动生成的方法存根Thread.sleep(1000);return "two";}}