项目问题：线程池使用FutureTask得不到抛出的错误

怼烎@ 2023-01-13 10:47 26阅读 0赞

## 线程池使用FutureTask得不到抛出的错误 ##

## 一、使用Thread ##

public static void main(String[] args) { 
            Test test = new Test();
            FutureTask futureTask = new FutureTask<>(test);
    
            Thread thread = new Thread(futureTask);
            thread.start();
            try { 
                futureTask.get();
            }catch (Exception e){ 
                e.printStackTrace();
            }
        }
    
        public static class Test implements Callable<String> { 
    
            @Override
            public String call() throws Exception { 
                System.out.println(100 / 0);
                return "test";
            }
        }

**执行结果：**

java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero
    	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
    	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
    	at com.jkys.drugstore.gwrpc.ActivityInfoServiceTest.main(ActivityInfoServiceTest.java:41)
    Caused by: java.lang.ArithmeticException: / by zero
    	at com.jkys.drugstore.gwrpc.ActivityInfoServiceTest$Test.call(ActivityInfoServiceTest.java:66)
    	at com.jkys.drugstore.gwrpc.ActivityInfoServiceTest$Test.call(ActivityInfoServiceTest.java:62)
    	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    	at java.lang.Thread.run(Thread.java:748)

## 二、使用线程池 ##

public static void main(String[] args) { 
            getFuture();
        }
    
        public static void getFuture() { 
            ExecutorService executorService = Executors.newFixedThreadPool(1);
    
            Future<?> future =  executorService.submit(new FutureTask<>(() -> { 
                System.out.println(100 / 0);
                return "test";
            }));
    
            try { 
                System.out.println(future.get());
            } catch (Exception e) { 
                System.out.println("Error!");
            }
        }

**执行结果：** null，没有异常

objc[9813]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/bin/java (0x10098f4c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x1029c04e0). One of the two will be used. Which one is undefined.
    null

## 三、解析 ##

由上面两个例子可以看出，直接用Thread配合FutureTask是可以得到子线程中的异常的，那么为什么配合线程池却得不到呢？

### 3.1 线程池解析—从submit开始 ###

//AbstractExecutorService 109行
    public Future<?> submit(Runnable task) { 
            if (task == null) throw new NullPointerException();
            RunnableFuture<Void> ftask = newTaskFor(task, null);
            execute(ftask);
            return ftask;
        }
    
    //AbstractExecutorService 86行
    protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { 
            return new FutureTask<T>(runnable, value);
        }
    
    //FutureTask 151行，也就是传进来的Runnable被包装成FutureTask
     public FutureTask(Runnable runnable, V result) { 
            this.callable = Executors.callable(runnable, result);
            this.state = NEW;       // ensure visibility of callable
        }
    
    //Executors 404行
    public static <T> Callable<T> callable(Runnable task, T result) { 
            if (task == null)
                throw new NullPointerException();
            return new RunnableAdapter<T>(task, result);
        }
    
    //Executors 503行
     static final class RunnableAdapter<T> implements Callable<T> { 
            final Runnable task;
            final T result;
            RunnableAdapter(Runnable task, T result) { 
                this.task = task;
                this.result = result;
            }
            public T call() { 
                task.run();
                return result;
            }
        }

从上面代码部分能得到：线程池submit入参是Runnable，但是经过一系列的调用最终到了FutureTask的构造器，即把入参的Runnbale适配成一个新的FutureTask。 但是如果扔到线程池中的已经是一个FutureTask呢？其实也会被当做成Runnablue去继续被包装成FutureTask。

### 3.2包装的FutureTask和自己扔进去的FutureTask关系图 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppYW5nMTgyMzgwMzI4OTE_size_16_color_FFFFFF_t_70]

### 3.3调用时序图 ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppYW5nMTgyMzgwMzI4OTE_size_16_color_FFFFFF_t_70 1]

由上面的关系图和时序图，就能得知为什么扔到线程池中的FutureTask在主线程get的时候得不到异常了。

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ppYW5nMTgyMzgwMzI4OTE_size_16_color_FFFFFF_t_70 1]: /images/20221022/1ceb65c6f685466ab4f7cc6d5ed18e78.png