场景
Java中Thread类的常用API以及使用示例:
https://blog.csdn.net/BADAO_LIUMANG_QIZHI/article/details/126596884
上面讲了Thread的常用API,下面记录下线程的一些常用操作。
注:
博客:
https://blog.csdn.net/badao_liumang_qizhi
实现
后台线程
后台线程,是指运行时在后台提供的一种服务线程,这种线程不是属于必须的。
当所有非后台线程结束时,程序就停止了,同时会终止所有的后台线程。
即只要有任何非后台线程还在运行,程序就不会终止。
实现方式:
Thread daemon = new Thread(new SimpleDaemons()); daemon.setDaemon(true);
示例代码:
public class SimpleDaemons implements Runnable{ @Override public void run() { while(true){ try { TimeUnit.MILLISECONDS.sleep(100); System.out.println(Thread.currentThread()+":"+this); } catch (InterruptedException e) { System.out.println("sleep() interrupted"); e.printStackTrace(); } } } public static void main(String[] args) throws InterruptedException { for (int i = 0; i < 10; i++) { Thread daemon = new Thread(new SimpleDaemons()); daemon.setDaemon(true); daemon.start(); } System.out.println("all daemons started"); TimeUnit.MILLISECONDS.sleep(175); } }
说明:
在每次的循环中会创建10个线程,并把每个线程设置为后台线程,然后开始运行,for循环会进行十次,
然后输出信息,随后主线程休眠一段时间后停止运行。在每次run循环中,都会打印当前线程的信息,
主线程运行完毕,程序就执行完毕了。因为daemon是后台线程,无法影响主线程的执行。但是当你把daemon.setDaemon(true)去掉时,
while(true)会进行无限循环,那么主线程一直在执行重要的任务,所以会一直循环下去无法停止。
线程工厂ThreadFactory
按需要创建线程的对象。使用线程工厂替代了Thread或者Runnable接口的硬连接,
使程序能够使用特殊的线程子类,优先级等。ThreadFactory是一个接口,
它只有一个方法就是创建线程的方法。
示例代码一:
上面实现后台线程可以通过线程工厂实现
import java.util.concurrent.ThreadFactory; public class DaemonThreadFactory implements ThreadFactory { @Override public Thread newThread(Runnable r) { Thread thread = new Thread(r); thread.setDaemon(true); return thread; } }
然后新建线程池时传递线程工厂
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public class DaemonFromFactory implements Runnable{ @Override public void run() { while (true){ try { TimeUnit.MILLISECONDS.sleep(100); System.out.println(Thread.currentThread()+":"+this); } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(new DaemonThreadFactory()); for (int i = 0; i < 10; i++) { executorService.execute(new DaemonFromFactory()); } System.out.println("all daemons started"); TimeUnit.MILLISECONDS.sleep(500); } }
示例代码二:
创建线程池时如果不指定线程工厂会使用默认的线程工厂,查看ThreadPoolExecutor的构造方法源码
Executors.defaultThreadFactory()的源码实现
假如我们要自定义线程池的线程名称前缀,可以参考DefaultThreadFactory自定义线程工厂来实现,方便
出现异常时能快速定位。
public class MyThreadFactory implements ThreadFactory { private static final AtomicInteger poolNumber = new AtomicInteger(1); private final ThreadGroup group; private final AtomicInteger threadNumber = new AtomicInteger(1); private final String namePrefix; public MyThreadFactory(String threadName) { SecurityManager s = System.getSecurityManager(); group = (s !=null)?s.getThreadGroup():Thread.currentThread().getThreadGroup(); if(threadName == null || threadName.isEmpty()){ threadName = "pool"; } namePrefix = threadName + poolNumber.getAndIncrement()+"-thread-"; } @Override public Thread newThread(Runnable r) { Thread t = new Thread(group,r,namePrefix+threadNumber.getAndIncrement(),0); if(t.isDaemon()){ t.setDaemon(false); } if(t.getPriority()!= Thread.NORM_PRIORITY){ t.setPriority(Thread.NORM_PRIORITY); } return t; } }
然后在新建线程池时
import java.util.ArrayList; import java.util.List; import java.util.concurrent.ArrayBlockingQueue; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; public class MyThreadFactoryDemo { public static final ThreadPoolExecutor pool = new ThreadPoolExecutor(5,10,5, TimeUnit.SECONDS,new ArrayBlockingQueue<>(100),new MyThreadFactory("badao")); public static void main(String[] args) { pool.execute(()->{ Integer integer = getOrderInfo(); }); } private static Integer getOrderInfo(){ try { List<Integer> list = new ArrayList<>(); for (int i = 0; i < 10; i++) { list.add(i); } return list.get(11); }catch (Exception exception){ throw new IndexOutOfBoundsException("数组越界"); } } }
这样在出现数组越界时,就会以指定前缀提示
join()方法加入一个线程
一个线程可以在其他线程上调用join()方法,其效果是等待一段时间直到第二个线程执行结束才正常执行。
如果某个线程在另一个线程t上调用t.join()方法,此线程将被挂起,直到目标线程t结束才恢复,
可以用t.isAlive返回为真假判断。也可以在调用join时带上一个超时参数,来设置到期时间,时间到期,join方法自动返回
对join的调用也可以被中断,做法是在线程上调用interrupted方法,这时需要用到try...catch子句。
示例代码:
public class TestJoinMethod extends Thread{ @Override public void run() { for (int i = 0; i < 5; i++) { try { TimeUnit.MICROSECONDS.sleep(1000); } catch (InterruptedException e) { throw new RuntimeException(e); } System.out.println(Thread.currentThread() +" "+i); } } public static void main(String[] args) throws InterruptedException { TestJoinMethod joinMethod = new TestJoinMethod(); TestJoinMethod joinMethod1 = new TestJoinMethod(); TestJoinMethod joinMethod2 = new TestJoinMethod(); joinMethod.start(); joinMethod.join(); joinMethod1.start(); joinMethod2.start(); } }
上面加了join的运行结果:
//Thread[Thread-0,5,main] 0
//Thread[Thread-0,5,main] 1
//Thread[Thread-0,5,main] 2
//Thread[Thread-0,5,main] 3
//Thread[Thread-0,5,main] 4
//Thread[Thread-1,5,main] 0
//Thread[Thread-2,5,main] 0
//Thread[Thread-2,5,main] 1
//Thread[Thread-1,5,main] 1
//Thread[Thread-2,5,main] 2
//Thread[Thread-1,5,main] 2
//Thread[Thread-1,5,main] 3
//Thread[Thread-2,5,main] 3
//Thread[Thread-1,5,main] 4
//Thread[Thread-2,5,main] 4
如果将join去掉后的运行结果:
//Thread[Thread-0,5,main] 0
//Thread[Thread-1,5,main] 0
//Thread[Thread-2,5,main] 0
//Thread[Thread-0,5,main] 1
//Thread[Thread-1,5,main] 1
//Thread[Thread-2,5,main] 1
//Thread[Thread-0,5,main] 2
//Thread[Thread-2,5,main] 2
//Thread[Thread-1,5,main] 2
//Thread[Thread-0,5,main] 3
//Thread[Thread-1,5,main] 3
//Thread[Thread-2,5,main] 3
//Thread[Thread-0,5,main] 4
//Thread[Thread-1,5,main] 4
//Thread[Thread-2,5,main] 4
可以看到joinMethod.start();当中的所有的内容都执行完后,才轮到后面的joinMethod1.start();和joinMethod2.start();执行。
换句话说,它会导致当前运行的线程停止运行,直到它加入的线程完成其任务。
线程异常捕获
由于线程的本质,使你不能捕获从线程中逃逸的异常,一旦异常逃出任务的run方法,它就会向外传播到控制台,除非你采用特殊的步骤
捕获这种错误的异常。下面的任务会在run方法的执行期间抛出一个异常,并且这个异常会抛出到run方法的外面,
而且main方法无法对它进行捕获。
public class ExceptionThread implements Runnable{ @Override public void run() { throw new RuntimeException(); } public static void main(String[] args) { try { ExecutorService executorService = Executors.newCachedThreadPool(); executorService.execute(new ExceptionThread()); }catch (Exception exception){ System.out.println(exception); } } }
为了解决这个问题,我们需要修改Executor产生线程的方式,java5提供了一个新的接口Thread.UncaughtExceptionHandler,
它允许你在每个Thread上都附着一个异常处理器。Thread.UncaughtExceptionHandler.uncaughtException()会在线程因
未捕获临近死亡时被调用
下面模拟抛出异常
public class ExceptionThread2 implements Runnable{ @Override public void run() { Thread t = Thread.currentThread(); System.out.println("run() by" + t); System.out.println("eh = "+t.getUncaughtExceptionHandler()); //手动抛出异常 //throw new RuntimeException(); int a = 1/0; } }
然后实现Thread.UncaughtExceptionHandler接口,创建异常处理器
public class MyUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler{ @Override public void uncaughtException(Thread t, Throwable e) { System.out.println("caught "+ e); } }
自定义线程工厂
import java.util.concurrent.ThreadFactory; public class HandlerThreadFactory implements ThreadFactory { @Override public Thread newThread(Runnable r) { System.out.println(this +"creating new Thread"); Thread t = new Thread(r); System.out.println("created "+t); t.setUncaughtExceptionHandler(new MyUncaughtExceptionHandler()); System.out.println("ex = "+t.getUncaughtExceptionHandler()); return t; } }
新建线程池并调用
public class CaptureUncaughtException { public static void main(String[] args) { ExecutorService executorService = Executors.newCachedThreadPool(new HandlerThreadFactory()); executorService.execute(new ExceptionThread2()); } }
运行结果
在程序中添加了额外的追踪机制,用来验证工厂创建的线程会传递给UncaughtExceptionHandler,
可以看到未捕获的异常是通过uncaughtException来捕获的。
标签:Java,自定义,Thread,System,线程,new,main,public From: https://www.cnblogs.com/badaoliumangqizhi/p/17325551.html