Java Thread 如何处理未捕获的异常？

Java Thread是不允许异常抛出到本线程之外的，Runnable接口的public abstract void run()是不允许throws Exception的，这在编译时就通不过。

线程异常处理方式两种：

1. try/catch
   
   这种方式很简单很暴力，但是代码不太优雅。一般我们只捕获编译时异常。更优雅的做法就是第二种通过UncaughtExceptionHandler接口实现。

2. Thread.UncaughtExceptionHanlder

• • • 在创建线程的时候进行设置　　

public class ThreadExceptionCatch {
    public static void main(String[] args) {
        Thread t = new Thread() {
            @Override
            public void run() {
                //todo something....
                throw new RuntimeException("异常了");
            }
        };
        t.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread t, Throwable e) {
                System.out.println(t.getName()+"发生异常："+e);
            }
        });

        t.start();
    }

}

• • • 使用Executors创建线程时，还可以在ThreadFactory中设置

public class ThreadExceptionCatch {
    public static void main(String[] args) {
        ExecutorService executorService= Executors.newFixedThreadPool(10, new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread thread=new Thread(r);
                //设置异常处理器
                thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
                    @Override
                    public void uncaughtException(Thread t, Throwable e) {
                        System.out.println(e);
                    }
                });
                return thread;
            }
        });
        //执行
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                throw new RuntimeException("异常了");
            }
        });
    }

}

• • • 设置Thread全局默认UnCaughtExceptionHandler

Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread t, Throwable e) {
                System.out.println(e);
            }
        });

defaultUncaughtExceptionHandler是Thread的静态变量：

private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;