本教程操作环境：windows7系统、java10版，DELL G3电脑。
1.概念
使用平衡二叉树堆，实现的具有优先级的无界阻塞队列。是一个BlockingQueue，所以它是线程安全的。
2.特点
（1）无边界设计，但容量实际是依靠系统资源影响
（2）添加元素，如果超过1，则进入优先级排序
3.应用实例
有任务要执行，可以对任务加一个优先级的权重，这样队列会识别出来，对该任务优先进行出队。
例子中定义了一个将要放入“优先阻塞队列”的任务类，并且定义了一个任务工场类和一个任务执行类，在任务工场类中产生了各种不同优先级的任务，将其添加到队列中，在任务执行类中，任务被一个个取出并执行。
package com.niuh.queue.priority;
import java.util.ArrayList;
import java.util.List;
import java.util.Queue;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.TimeUnit;
public class PriorityBlockingQueueDemo {
public static void main(String[] args) throws Exception {
Random random = new Random(47);
ExecutorService exec = Executors.newCachedThreadPool();
PriorityBlockingQueue queue = new PriorityBlockingQueue<>();
exec.execute(new PrioritizedTaskProducer(queue, exec)); // 这里需要注意，往PriorityBlockingQueue中添加任务和取出任务的
exec.execute(new PrioritizedTaskConsumer(queue)); // 步骤是同时进行的，因而输出结果并不一定是有序的
}
}
class PrioritizedTask implements Runnable, Comparable {
private Random random = new Random(47);
private static int counter = 0;
private final int id = counter++;
private final int priority;
protected static List sequence = new ArrayList<>();
public PrioritizedTask(int priority) {
this.priority = priority;
sequence.add(this);
}
@Override
public int compareTo(PrioritizedTask o) {
return priority < o.priority ? 1 : (priority > o.priority ? -1 : 0); // 定义优先级计算方式
}
@Override
public void run() {
try {
TimeUnit.MILLISECONDS.sleep(random.nextInt(250));
} catch (InterruptedException e) {
}
System.out.println(this);
}
@Override
public String toString() {
return String.format("[%1$-3d]", priority) + " Task " + id;
}
public String summary() {
return "(" + id + ": " + priority + ")";
}
public static class EndSentinel extends PrioritizedTask {
private ExecutorService exec;
public EndSentinel(ExecutorService exec) {
super(-1);
this.exec = exec;
}
@Override
public void run() {
int count = 0;
for (PrioritizedTask pt : sequence) {
System.out.print(pt.summary());
if (++count % 5 == 0) {
System.out.println();
}
}
System.out.println();
System.out.println(this + " Calling shutdownNow()");
exec.shutdownNow();
}
}
}
class PrioritizedTaskProducer implements Runnable {
private Random random = new Random(47);
private Queue queue;
private ExecutorService exec;
public PrioritizedTaskProducer(Queue queue, ExecutorService exec) {
this.queue = queue;
this.exec = exec;
}
@Override
public void run() {
for (int i = 0; i < 20; i++) {
queue.add(new PrioritizedTask(random.nextInt(10))); // 往PriorityBlockingQueue中添加随机优先级的任务
Thread.yield();
}
try {
for (int i = 0; i < 10; i++) {
TimeUnit.MILLISECONDS.sleep(250);
queue.add(new PrioritizedTask(10)); // 往PriorityBlockingQueue中添加优先级为10的任务
}
for (int i = 0; i < 10; i++) {
queue.add(new PrioritizedTask(i));// 往PriorityBlockingQueue中添加优先级为1-10的任务
}
queue.add(new PrioritizedTask.EndSentinel(exec));
} catch (InterruptedException e) {
}
System.out.println("Finished PrioritizedTaskProducer");
}
}
class PrioritizedTaskConsumer implements Runnable {
private PriorityBlockingQueue queue;
public PrioritizedTaskConsumer(PriorityBlockingQueue queue) {
this.queue = queue;
}
@Override
public void run() {
try {
while (!Thread.interrupted()) {
queue.take().run(); // 任务的消费者，从PriorityBlockingQueue中取出任务执行
}
} catch (InterruptedException e) {
}
System.out.println("Finished PrioritizedTaskConsumer");
}
} 以上就是java中PriorityBlockingQueue的使用，当我们需要有重要任务想提前处理时，可以选择PriorityBlockingQueue这种阻塞队列来优先任务的处理。学会基础内容后，可以就代码部分进行试验了。
