Java 未捕获异常处理

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发布于: 2020 年 10 月 13 日
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思考：
实际工作中：如何全局处理异常？为什么要全局处理？不处理行不行？
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UncaughtException﻿
线程的异常不能用传统方法捕获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
不能直接捕获的后果、提高健壮性
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方式一：不加  try catch抛出 4 个异常，都带线程名字
public class CantCatchDirectly implements Runnable {
    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();
    }
    @Override
    public void run() {
        throw new RuntimeException();
    }
}
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方式二：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，执行时发现，根本没有 Caught Exception，线程 234 依然运行并且抛出异常
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public class CantCatchDirectly implements Runnable {
    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.");
        }
    }
    @Override
    public void run() {
        throw new RuntimeException();
    }
}
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 为什么需要使用 UncaughtExceptionHandler﻿
方案一（不推荐）：手动在每个 run 方法里进行 try catch
public class CantCatchDirectly implements Runnable {
    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.");
        }
    }
    @Override
    public void run() {
        try {
            throw new RuntimeException();
        } catch (RuntimeException e) {
            System.out.println("Caught Exception.");
        }
    }
}
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方案二（推荐）：利用 UncaughtExceptionHandler
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UncaughtExceptionHandler 接口
void uncaughtException(Thread t, Throwable e);
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异常处理器的调用策略
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实现给程序统一设置
给每个线程单独设置
给线程池设置
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/**
 * 描述：     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");
    }
}
﻿
public class UseOwnUncaughtExceptionHandler implements Runnable {
    public static void main(String[] args) throws InterruptedException {
        Thread.setDefaultUncaughtExceptionHandler(new MyUncaughtExceptionHandler("捕获器"));
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-1").start();
        Thread.sleep(300);
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-2").start();
        Thread.sleep(300);
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-3").start();
        Thread.sleep(300);
        new Thread(new UseOwnUncaughtExceptionHandler(), "MyThread-4").start();
    }
    @Override
    public void run() {
        throw new RuntimeException();
    }
}
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思考：run 方法是否可以抛出异常？如果抛出异常，线程的状态会怎么样？
线程中如何处理某个未处理异常？
发布于: 2020 年 10 月 13 日阅读数: 14
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