线程异常处理

1 子线程异常主线程无法感知

主线程可以轻松发现异常，子线程却不行 

子线程异常无法用传统方法捕获

/**
 * 单线程，抛出，处理，有异常堆栈 多线程，子线程发生异常，会有什么不同？
 */
public class ExceptionInChildThread {
    public static void main(String[] args) {
        new Thread(() -> {
            throw new RuntimeException("子线程出错啦...");
        }).start();
        //依然还在执行
        for (int i = 0; i < 6; i++) {
            System.out.println(i);
        }
    }
}

/**
 * 1. 不加try catch抛出4个异常，都带线程名字
 * 2. 加了try catch,期望捕获到第一个线程的异常，线程234不应该运行，希望看到打印出Caught Exception
 * 3. 执行时发现，根本没有Caught Exception，线程234依然运行并且抛出异常
 * 
 * 说明线程的异常不能用传统方法捕获
 */
public class CantCatchDirectly implements Runnable {
    @Override
    public void run() {
        throw new RuntimeException();
    }
    
    public static void main(String[] args) throws InterruptedException {
        try {
            new Thread(new CantCatchDirectly(), "MyThread-1").start();
            Thread.sleep(300);
            new Thread(new CantCatchDirectly(), "MyThread-2").start();
            Thread.sleep(300);
            new Thread(new CantCatchDirectly(), "MyThread-3").start();
            Thread.sleep(300);
            new Thread(new CantCatchDirectly(), "MyThread-4").start();
        } catch (RuntimeException e) {
            System.out.println("Caught Exception.");
        }
    }
}

---

2 如何处理异常

方案一（不推荐）：手动在每个run方法里进行 try catch

public class CantCatchDirectly implements Runnable {
    @Override
    public void run() {
        try {
            throw new RuntimeException();
        } catch (RuntimeException e) {
            System.out.println("Caught Exception.");
        }
    }
    public static void main(String[] args) throws InterruptedException {
        new Thread(new CantCatchDirectly(), "MyThread-1").start();
        Thread.sleep(300);
        new Thread(new CantCatchDirectly(), "MyThread-2").start();
        Thread.sleep(300);
        new Thread(new CantCatchDirectly(), "MyThread-3").start();
        Thread.sleep(300);
        new Thread(new CantCatchDirectly(), "MyThread-4").start();
    }
}

方案二（推荐）：利用 UncaughtExceptionHandler

//java.lang.Thread.UncaughtExceptionHandler
@FunctionalInterface
public interface UncaughtExceptionHandler {
	void uncaughtException(Thread t, Throwable e);
}

 

自己实现

• 给程序统一设置
• 给每个线程单独设置
• 给线程池设置

 给程序统一设置

/**
 * 自己的MyUncaughtExceptionHanlder
 */
public class MyUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
    private String name;
    public MyUncaughtExceptionHandler(String name) {
        this.name = name;
    }
    @Override
    public void uncaughtException(Thread t, Throwable e) {
        Logger logger = Logger.getAnonymousLogger();
        logger.log(Level.WARNING, "线程异常，终止啦" + t.getName());
        System.out.println(name + "捕获了异常" + t.getName() + "异常");
    }
}

/**
 * 使用刚才自己写的UncaughtExceptionHandler
 */
public class UseOwnUncaughtExceptionHandler {
    public static void main(String[] args) throws InterruptedException {
        Runnable run = () -> {
            throw new RuntimeException();
        };
        Thread.setDefaultUncaughtExceptionHandler(new MyUncaughtExceptionHandler("捕获器1"));
        new Thread(run, "MyThread-1").start();
        Thread.sleep(300);
        new Thread(run, "MyThread-2").start();
        Thread.sleep(300);
        new Thread(run, "MyThread-3").start();
        Thread.sleep(300);
        new Thread(run, "MyThread-4").start();
    }
}