import org.apache.tomcat.util.threads.TaskQueue;
import org.apache.tomcat.util.threads.TaskThreadFactory;
import org.apache.tomcat.util.threads.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;public class TomcatThreadPoolExecutorTest {public static void main(String[] args) throws InterruptedException {String namePrefix = "歪歪歪-exec-";boolean daemon = true;TaskQueue taskqueue = new TaskQueue(300);TaskThreadFactory tf = new TaskThreadFactory(namePrefix, daemon, Thread.NORM_PRIORITY);ThreadPoolExecutor executor = new ThreadPoolExecutor(5,150, 60000, TimeUnit.MILLISECONDS, taskqueue, tf);
// taskqueue.setParent(executor);for (int i = 0; i < 305; i++) {try {executor.execute(() -> {logStatus(executor, "创建任务");try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}});} catch (Exception e) {e.printStackTrace();}}Thread.currentThread().join();}private static void logStatus(ThreadPoolExecutor executor, String name) {TaskQueue queue = (TaskQueue) executor.getQueue();System.out.println(Thread.currentThread().getName() + "-" + name + "-:" +"核心线程数:" + executor.getCorePoolSize() +"\t活动线程数:" + executor.getActiveCount() +"\t最大线程数:" + executor.getMaximumPoolSize() +"\t总任务数:" + executor.getTaskCount() +"\t当前排队线程数:" + queue.size() +"\t队列剩余大小:" + queue.remainingCapacity());}
}队列的使用在日常开发中，特别常见，但是对于队列接口中的一些方法可能使用起来有些疑惑，本文简单记录一下关于Queue接口中几种类似方法的区别。
- add() 和 offer()
- add() : 添加元素，如果添加成功则返回true，如果队列是满的，则抛出异常
- offer() : 添加元素，如果添加成功则返回true，如果队列是满的，则返回false
- 区别：对于一些有容量限制的队列，当队列满的时候，用add()方法添加元素，则会抛出异常，用offer()添加元素，则返回false
- remove() 和 poll()
- remove() : 移除队列头的元素并且返回，如果队列为空则抛出异常
- poll() : 移除队列头的元素并且返回，如果队列为空则返回null
- 区别：在移除队列头元素时，当队列为空的时候，用remove()方法会抛出异常，用poll()方法则会返回null
- element() 和 peek()
- element() ：返回队列头元素但不移除，如果队列为空，则抛出异常
- peek() ：返回队列头元素但不移除，如果队列为空，则返回null
- 区别 ：在取出队列头元素时，如果队列为空，用element()方法则会抛出异常，用peek()方法则会返回null
附上源码以及中文注释：
public interface Queue<E> extends Collection<E> {/*** Inserts the specified element into this queue if it is possible to do so* immediately without violating capacity restrictions, returning* {@code true} upon success and throwing an {@code IllegalStateException}* if no space is currently available.* 插入一个具体的元素到队列中如果没有超过容量限制并且返回true。* 如果没有队列已满则抛出IllegalStateException** @param e the element to add* @return {@code true} (as specified by {@link Collection#add})* @throws IllegalStateException if the element cannot be added at this* time due to capacity restrictions* @throws ClassCastException if the class of the specified element* prevents it from being added to this queue* 如果插入的对象不对，则会抛出类型转换ClassCastException* @throws NullPointerException if the specified element is null and* this queue does not permit null elements* 如果插入null，则会抛出空指针异常* @throws IllegalArgumentException if some property of this element* prevents it from being added to this queue* 添加元素，如果添加成功则返回true，如果队列是满的，则抛出异常*/boolean add(E e);/*** Inserts the specified element into this queue if it is possible to do* so immediately without violating capacity restrictions.* When using a capacity-restricted queue, this method is generally* preferable to {@link #add}, which can fail to insert an element only* by throwing an exception.* 插入一个具体的元素到队列中如果没有超过容量限制并且返回true。* 如果没有队列已满则返回false。* 当使用一个有容量限制的队列时，建议使用该方法offer(),因为使用add()方法当队列满时会* 直接抛出异常，则offer()方法则返回false** @param e the element to add* @return {@code true} if the element was added to this queue, else* {@code false}* @throws ClassCastException if the class of the specified element* prevents it from being added to this queue* @throws NullPointerException if the specified element is null and* this queue does not permit null elements* @throws IllegalArgumentException if some property of this element* prevents it from being added to this queue* 添加元素，如果添加成功则返回true，如果队列是满的，则返回false*/boolean offer(E e);/*** Retrieves and removes the head of this queue. This method differs* from {@link #poll poll} only in that it throws an exception if this* queue is empty.** @return the head of this queue* @throws NoSuchElementException if this queue is empty* 移除队列头的元素并且返回，如果队列为空则抛出异常*/E remove();/*** Retrieves and removes the head of this queue,* or returns {@code null} if this queue is empty.** @return the head of this queue, or {@code null} if this queue is empty* 移除队列头的元素并且返回，如果队列为空则返回null*/E poll();/*** Retrieves, but does not remove, the head of this queue. This method* differs from {@link #peek peek} only in that it throws an exception* if this queue is empty.** @return the head of this queue* @throws NoSuchElementException if this queue is empty* 返回队列头元素但不移除，如果队列为空，则抛出异常*/E element();/*** Retrieves, but does not remove, the head of this queue,* or returns {@code null} if this queue is empty.** @return the head of this queue, or {@code null} if this queue is empty* 返回队列头元素但不移除，如果队列为空，则返回null*/E peek();
}
作者：曾泽浩
链接：https://www.jianshu.com/p/c41053d16713/
来源：简书
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