Java并发编程实例--8.在线程中处理未检查异常

java中有两类异常：

已检查异常：这类异常编译器要求开发者必须在代码中通过throws去处理。

例如：IOException和ClassNotFoundException。

未检查异常：不必显式的在代码重处理。例如：NumberFormatException。

所有派生自Error和RuntimeException的类,都是未检查异常.其余的是已检查异常.

当一个已检查异常在线程对象的run()方法中抛出，我们就必须去捕捉并处理它，因为run()方法不接受throws条件。

而当一个未检查异常在run()方法中抛出，其默认行为是将异常信息输出到控制台并退出程序。

幸运的是，Java提供了在线程中捕捉和处理未检查异常的机制，以避免程序结束。

本例就来学习一下这一机制。

Task.java

package com.dylan.thread.ch1.c08.task;

/**
 * Runnable class than throws and Exception
 *
 */
public class Task implements Runnable {

	/**
	 * Main method of the class
	 */
	@Override
	public void run() {
		// The next instruction always throws and exception
		int numero=Integer.parseInt("TTT");
	}

}

ExceptionHandler.java

package com.dylan.thread.ch1.c08.handler;

import java.lang.Thread.UncaughtExceptionHandler;

/**
 * Class that process the uncaught exceptions throwed in a Thread
 *
 */
public class ExceptionHandler implements UncaughtExceptionHandler {

	/**
	 * Main method of the class. It process the uncaught excpetions throwed
	 * in a Thread
	 * @param t The Thead than throws the Exception
	 * @param e The Exception throwed
	 */
	@Override
	public void uncaughtException(Thread t, Throwable e) {
		System.out.printf("An exception has been captured\n");
		System.out.printf("Thread: %s\n",t.getId());
		System.out.printf("Exception: %s: %s\n",e.getClass().getName(),e.getMessage());
		System.out.printf("Stack Trace: \n");
		e.printStackTrace(System.out);
		System.out.printf("Thread status: %s\n",t.getState());
	}

}

Main.java

package com.dylan.thread.ch1.c08.core;

import com.dylan.thread.ch1.c08.handler.ExceptionHandler;
import com.dylan.thread.ch1.c08.task.Task;

/**
 * Main class of the example. Initialize a Thread to process the uncaught
 * exceptions and starts a Task object that always throws an exception
 *
 */
public class Main {

	/**
	 * Main method of the example. Initialize a Thread to process the
	 * uncaught exceptions and starts a Task object that always throws an
	 * exception
	 * @param args
	 */
	public static void main(String[] args) {
		// Creates the Task
		Task task=new Task();
		// Creates the Thread
		Thread thread=new Thread(task);
		// Sets de uncaugh exceptio handler
		thread.setUncaughtExceptionHandler(new ExceptionHandler());
		// Starts the Thread
		thread.start();

		try {
			thread.join();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}

		System.out.printf("Thread has finished\n");

	}

}

运行结果：

An exception has been captured
Thread: 10
Exception: java.lang.NumberFormatException: For input string: "TTT"
Stack Trace: 
java.lang.NumberFormatException: For input string: "TTT"
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.dylan.thread.ch1.c08.task.Task.run(Task.java:16)
at java.lang.Thread.run(Thread.java:745)
Thread status: RUNNABLE
Thread has finished