JAVA为多线程场景提供了线程池,下面是一个线程池的构造方法:
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue workQueue,
RejectedExecutionHandler handler) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), handler);
}
这里想对拒绝策略RejectedExecutionHandler做一下详细的介绍。
在使用线程池并且使用有界队列的时候,如果队列满了,任务添加到线程池的时候就会有问题,针对这些问题java线程池提供了以下几种策略:
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
//不做任何处理,直接抛出异常
throw new RejectedExecutionException("Task " + r.toString() +
" rejected from " +
e.toString());
}
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
//就是一个空的方法
}
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
if (!e.isShutdown()) {
//移除队头元素
e.getQueue().poll();
//再尝试入队
e.execute(r);
}
}
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
if (!e.isShutdown()) {
//直接执行run方法
r.run();
}
}
public class MyRejectPolicy implements RejectedExecutionHandler{
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
//Sender是我的Runnable类,里面有message字段
if (r instanceof Sender) {
Sender sender = (Sender) r;
//直接打印
System.out.println(sender.getMessage());
}
}
}