一、线程池创建
如果需要在项目中使用多线程，那么一定要先创建线程池。因为线程池可以达到线程复用，节省反复创建和销毁的开销。提升性能。就跟平时项目中使用的数据库连接池是一个道理。
首先来看一下线程池创建的方法：
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}int corePoolSize, 核心线程数
int maximumPoolSize, 最大线程数
long keepAliveTime, 线程没有任务时的存活时间
TimeUnit unit, 时间单位
BlockingQueue<Runnable> workQueue 一个阻塞队列，用来存储等待执行的任务，这个参数的选择也很重要，会对线程池的运行过程产生重大影响，一般来说，这里的阻塞队列有以下几种选择 ：
ArrayBlockingQueue;
LinkedBlockingQueue;
SynchronousQueue;ThreadFactory threadFactory, 线程工厂，主要用来创建线程
RejectedExecutionHandler handler 表示当拒绝处理任务时的策略，有以下四种取值： ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。 ThreadPoolExecutor.DiscardPolicy：也是丢弃任务，但是不抛出异常。 ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面的任务，然后重新尝试执行任务（重复此过程）
ThreadPoolExecutor.CallerRunsPolicy：由调用线程处理该任务
根据上面的方法我们就可以开始创建我们的线程池了
//创建有界队列，防止内存溢出
BlockingQueue<Runnable> workQueue = new LinkedBlockingQueue<>(1024);
#使用hutool的NamedThreadFactory hutool是一个非常好用的工具类集合
ThreadFactory threadFactory = new NamedThreadFactory("测试",false);
ThreadPoolExecutor es = new ThreadPoolExecutor(
8,
16,
1, TimeUnit.SECONDS,
workQueue,threadFactory);这样我的线程池就创建完成了。
二、根据业务选择线程的创建
如果有返回值那就实现Callable接口，否则就实现Runnable接口
现在假设我们有一个需要返回结果的业务，那该如何实现呢？接下来直接上代码：
public static class Task implements Callable<String>{
/**
* Computes a result, or throws an exception if unable to do so.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
@Override
public String call() throws Exception {
return Thread.currentThread().getName();
}
}这样就算是实现了Callable接口了，但是正常的业务我们肯定需要处理业务的，那就必定会需要接受参数。所以我们的这个类还必须要添加一个构造方法去接收参数。代码如下：
public static class Task2 implements Callable<String>{
private String name;
private int age;
public Task2(String name, int age) {
this.name = name;
this.age = age;
}
/**
* Computes a result, or throws an exception if unable to do so.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
@Override
public String call() throws Exception {
System.out.println("name = " + name);
System.out.println("age = " + age);
//处理业务逻辑
//返回处理结果
return Thread.currentThread().getName();
}
}注意：Callable<> 返回的参数是可以自定义的
比如：Callable<Student> 返回对象 Callable<String> 返回字符串
三、完整代码
package com.xingli.springlearningdemo.stream;
import cn.hutool.core.thread.NamedThreadFactory;
import java.util.*;
import java.util.concurrent.*;
/**
* description: streamTest <br>
*
* @date: 2021/6/11 0011 下午 1:35 <br>
* @author: William <br>
* version: 1.0 <br>
*/
public class streamTest {
public static void main(String[] args) throws ExecutionException, InterruptedException {
List<Future<String>> futureList = new ArrayList<>();
BlockingQueue<Runnable> workQueue = new LinkedBlockingQueue<>(1024);
ThreadFactory threadFactory = new NamedThreadFactory("测试",false);
ThreadPoolExecutor es = new ThreadPoolExecutor(8,16,3, TimeUnit.SECONDS,workQueue,threadFactory);
for (int i = 0; i < 100; i++) {
try{
futureList.add(es.submit(new Task()));
System.out.println("当前排队线程数：= " + es.getQueue().size());
System.out.println("当前活动线程数：= " + es.getActiveCount());
System.out.println("===============================");
}catch (Exception e){
System.out.println("异常");
}
}
es.shutdown();
System.out.println("线程结束===============================");
for (Future<String> stringFuture : futureList) {
System.out.println(stringFuture.get().toString());
}
}
public static class Task implements Callable<String>{
/**
* Computes a result, or throws an exception if unable to do so.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
@Override
public String call() throws Exception {
Thread.sleep(10);
return Thread.currentThread().getName();
}
}
public static class Task2 implements Callable<String>{
private String name;
private int age;
public Task2(String name, int age) {
this.name = name;
this.age = age;
}
/**
* Computes a result, or throws an exception if unable to do so.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
@Override
public String call() throws Exception {
System.out.println("name = " + name);
System.out.println("age = " + age);
return Thread.currentThread().getName();
}
}
}
