java 多线程 线程组ThreadGroup;多线程的异常处理。interrupt批量停止组内线程；线程组异常处理

1，线程组定义：

线程组存在的意义，首要原因是安全。java默认创建的线程都是属于系统线程组，而同一个线程组的线程是可以相互修改对方的数据的。但如果在不同的线程组中，那么就不能“跨线程组”修改数据，可以从一定程度上保证数据安全。默认情况下，我们创建的线程都在系统线程组，不过我们可以自定义自己的线程组。

线程组内部可以有线程组，组中还可以有线程，类似于下图：

线程组创建：

• new ThreadGroup("test线程组")

 常用方法：

• activeGroupCount()

• activeGroupCount()获取子线程组个数

• enumerate(threadGroups) 将线程组内子线程，或子线程组 组复制到数组中
• interrupt(); 批量停止线程组里面所有线程

2，线程加入线程组：

定义两个线程，然后一个线程组，分别把两个线程加入到对应的线程组

public class ThreadGroupTest {
    public static void main(String[] args) {
        Runnable r = () ->{
            String tName = Thread.currentThread().getName();
            System.out.println(tName +":运行中");
        };
        ThreadGroup testGroup = new ThreadGroup("test线程组");
        Thread thread1 = new Thread(testGroup,r,"线程1");
        Thread thread2 = new Thread(testGroup,r,"线程2");
        Thread thread3 = new Thread(testGroup,r,"线程3");
        thread1.start();thread2.start();thread3.start();
        //查看线程组下有多少活跃线程
        System.out.println(testGroup.toString() + "下活跃线程数：" + testGroup.activeCount()); //java.lang.ThreadGroup[name=test线程组,maxpri=10]下活跃线程数：3
    }
}

 

3，线程组多级嵌套：线程组下面还有线程组

/**
 * @ClassName ThreadGroupInThreadGroup
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/26.
 */
public class ThreadGroupInThreadGroup {
    public static void main(String[] args) {
        Runnable runnable = ()-> {
            System.out.println(Thread.currentThread().getName() + "运行中");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };
        ThreadGroup parentGroup = new ThreadGroup("parent");
        ThreadGroup childGroup = new ThreadGroup(parentGroup,"child");
        Thread thread = new Thread(childGroup, runnable, "线程A");
        Thread thread1 = new Thread(childGroup, runnable, "线程B");
        Thread thread2 = new Thread(parentGroup, runnable, "线程C");
        thread.start();thread1.start();thread2.start();
        //常用方法
        System.out.println("parentGroup 下有" + parentGroup.activeGroupCount() + "个活跃线程组"); //activeGroupCount()获取子线程组个数
        ThreadGroup[] threadGroups = new ThreadGroup[parentGroup.activeGroupCount()];
        parentGroup.enumerate(threadGroups);    //enumerate(threadGroups) 将线程组内子线程组复制到数组中
        for (ThreadGroup threadGroup:threadGroups){
            System.out.println(threadGroup.getName()); //child
        }
        Thread[] threads = new Thread[childGroup.activeCount()];
        childGroup.enumerate(threads);
        for (Thread t : threads){
            System.out.println("子线程组中线程：" + t.getName());
        }
    }
}

4、线程组的自动归属特性：

就是说我们新创建一个线程组，这个线程组默认就归属到当前线程所在的线程组中：

public class AutoGroupTest {
    public static void main(String[] args) {
        //首先获取一下当前线程所在的线程组
        System.out.println(Thread.currentThread().getThreadGroup().getName());
        ThreadGroup testGroup = new ThreadGroup("测试线程组");
        System.out.println(testGroup.getParent().getName());
    }
}

5，批量停止线程组里面所有的线程：interrupt

/**
 * @ClassName ThreadExitAllThreadInGroup
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/26.
 */
public class ThreadExitAllThreadInGroup {
    public static void main(String[] args) throws InterruptedException {
        ThreadGroup threadGroup = new ThreadGroup("test线程组");
        Runnable r = () -> {
            String tName = Thread.currentThread().getName();
            System.out.println(tName + "：线程运行中");
            while (!Thread.interrupted()){}
            System.out.println(tName + "：线程运行结束");
        };
        for (int i=0; i<10; i++){
            new Thread(threadGroup,r, "T" + i).start();
        }
        Thread.sleep(1000);
        threadGroup.interrupt();
    }
}

 

 

6，多线程的异常处理：

单个线程设置异常处理：thread.setUncaughtExceptionHandler

/**
 * @ClassName ThreadGroupException
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/26.
 */
public class ThreadGroupException {
    public static void main(String[] args) {
        Runnable r = () ->{
            int a = 1/0;
        };
        Thread thread = new Thread(r,"test");

        thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread thread, Throwable throwable) {
                System.err.println(thread.getName() + "抛出异常：" + throwable.getMessage());
            }
        });
        thread.start();
    }
}

多个线程设置异常处理：Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler）

/**
 * @ClassName ThreadGroupException
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/26.
 */
public class ThreadGroupException {
    public static void main(String[] args) {
        Runnable r = () ->{
            int a = 1/0;
        };
        Thread thread = new Thread(r,"test");
        Thread thread1 = new Thread(r,"test1");
        Thread thread2 = new Thread(r,"test2");
        Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread thread, Throwable throwable) {
                System.err.println(thread.getName() + "抛出异常：" + throwable.getMessage());
            }
        });
//        thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
//            @Override
//            public void uncaughtException(Thread thread, Throwable throwable) {
//                System.err.println(thread.getName() + "抛出异常：" + throwable.getMessage());
//            }
//        });
        thread.start();thread1.start();thread2.start();
    }
}

7，线程组的异常怎么处理：

思路:之定义一个线程组，继承ThreadGroup，然后重写ThreadGroup的uncaughtExceptionHandler方法。

注：

本例threadGroup  线程组实例为 Thread类的匿名子类实例化的写法

/**
 * @ClassName ThreadGroupException
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/26.
 */
public class ThreadGroupException {
    public static void main(String[] args) {
        Runnable r = () -> {
            int a = 1/0;
        };
        ThreadGroup threadGroup = new ThreadGroup("TEST-Group"){
            @Override
            public void uncaughtException(Thread t, Throwable e) {
                System.err.println( "线程组：" + getName() + "下的线程："+ t.getName() + "出现了异常：" + e.getMessage());
            }
        };
        for (int i=0; i<10; i++) {
            new Thread(threadGroup, r, "线程" + i).start();
        }
    }
}