线程异常处理及异常传递

可以给线程指定异常处理类来捕获异常进行自定义处理。

线程中的异常可通过线程组异常处理来实现异常传递，线程组 ThreadGroup 实现了 Thread.UncaughtExceptionHandler 接口。

异常处理

在 Java 多线程技术中，可以对多线程中的异常进行捕捉，使用的是 UncaughtExceptionHandler 类，可以对发生的异常进行有效的处理。

1. 创建线程

   public class MyThread extends Thread {
   
       @Override
       public void run() {
           String username = null;
           System.out.println(username.hashCode());
       }
   }

2. 线程异常处理测试

   public class MainCatchException {
       public static void main(String[] args) {
   
           MyThread t1 = new MyThread();
           t1.setName("线程t1");
           t1.start();
   
           MyThread t2 = new MyThread();
           t2.setName("线程t2");
           t2.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
               @Override
               public void uncaughtException(Thread t2, Throwable e) {
                   System.out.println("线程：" + t2.getName() + " 出现了异常");
                   e.printStackTrace();
               }
           });
           t2.start();
   
           MyThread t3 = new MyThread();
           t3.setName("线程t3");
           t3.start();
   
           MyThread t4 = new MyThread();
           MyThread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
               @Override
               public void uncaughtException(Thread t4, Throwable e) {
                   System.out.println("默认线程异常处理：" + t4.getName());
                   e.printStackTrace();
               }
           });
           t4.setName("线程t4");
           t4.start();
       }
   }

异常传递

Java 的线程组实现了 Thread.UncaughtExceptionHandler 接口，在使用线程组时，可以重写 void uncaughtException(Thread t, Throwable e) 方法，使异常可以在线程组中的线程传递，即其中一个线程异常，线程组中的线程都会抛出此异常。

1. 创建线程

   public class MyThread extends Thread {
   
       private String num = "a";
   
       public MyThread() {
           super();
       }
   
       public MyThread(ThreadGroup threadGroup, String name) {
           super(threadGroup, name);
       }
   
       @Override
       public void run() {
           int numInt = Integer.parseInt(num);
           System.out.println("在线程中打印：" + (numInt + 1));
       }
   }

2. 线程组

   public class MyThreadGroup extends ThreadGroup {
   
       public MyThreadGroup(String name) {
           super(name);
       }
   
       @Override
       public void uncaughtException(Thread t, Throwable e) {
           super.uncaughtException(t, e);
           System.out.println("线程组的异常处理");
           e.printStackTrace();
       }
   }

3. 自定义异常处理类

   public class ObjectUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
       @Override
       public void uncaughtException(Thread t, Throwable e) {
           System.out.println("对象的异常处理");
           e.printStackTrace();
       }
   }

   public class StateUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
       @Override
       public void uncaughtException(Thread t, Throwable e) {
           System.out.println("静态的异常处理");
           e.printStackTrace();
       }
   }

4. Main 测试类

   public class MainTest {
   
       public static void main(String[] args) {
           MyThreadGroup group = new MyThreadGroup("我的线程组");
           MyThread myThread1 = new MyThread(group, "我的线程1");
           MyThread myThread2 = new MyThread(group, "我的线程2");
   
   //        myThread.setUncaughtExceptionHandler(new ObjectUncaughtExceptionHandler());
   //        MyThread.setDefaultUncaughtExceptionHandler(new StateUncaughtExceptionHandler());
   
           myThread1.start();
           myThread2.start();
       }
   }

5. 运行输出结果

   线程组的异常处理
   线程组的异常处理
   Exception in thread "我的线程2" Exception in thread "我的线程1" java.lang.NumberFormatException: For input string: "a"
   	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
   	at java.lang.Integer.parseInt(Integer.java:580)
   	at java.lang.Integer.parseInt(Integer.java:615)
   	at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)
   java.lang.NumberFormatException: For input string: "a"
   	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
   	at java.lang.Integer.parseInt(Integer.java:580)
   	at java.lang.Integer.parseInt(Integer.java:615)
   	at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)
   java.lang.NumberFormatException: For input string: "a"
   	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
   	at java.lang.Integer.parseInt(Integer.java:580)
   	at java.lang.Integer.parseInt(Integer.java:615)
   	at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)
   java.lang.NumberFormatException: For input string: "a"
   	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
   	at java.lang.Integer.parseInt(Integer.java:580)
   	at java.lang.Integer.parseInt(Integer.java:615)
   	at com.java.jdk.thread.exception.Demo1.MyThread.run(MyThread.java:17)