多线程使用的一些例子

一、例子1：　　　　

package com.cy.test.thread;


import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestMultiThread {
    /**
     * n = 核心数*2 + 1
     */
    private static ExecutorService pool = Executors.newFixedThreadPool(5);

    /**
     * 1.模拟，使用多线程，找到每个学生的老师名字，并且打印出来。
     * @param args
     */
    public static void main(String[] args) {
        long begin = System.currentTimeMillis();

        List<String> studentList = new ArrayList<>();
        studentList.add("zhangsan");
        studentList.add("lisi");
        studentList.add("wangwu");

        try {
            CountDownLatch latch = new CountDownLatch(studentList.size());
            doFindTeacher(studentList, latch);
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("执行完毕，耗时：" + (System.currentTimeMillis() - begin) + "ms");
        pool.shutdown();
    }

    private static void doFindTeacher(List<String> studentList, CountDownLatch latch) {
        for(String student : studentList){
            pool.execute(() -> {
                System.out.println("开始处理学生:" + student);
                //模拟查数据库...等操作，查找学生的老师
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("teacher: " + student + "'s teacher");

                latch.countDown();
            });
        }
    }
}

console：

开始处理学生:zhangsan
开始处理学生:lisi
开始处理学生:wangwu
teacher: lisi's teacher
teacher: zhangsan's teacher
teacher: wangwu's teacher
执行完毕，耗时：3081ms

二、例子2：　　　　

package com.cy.test.thread;


import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestMultiThread2 {
    private static int minProcessCnt = 1;
    private static int poolSize = 5;
    private static ExecutorService pool = Executors.newFixedThreadPool(poolSize);

    /**
     * 1.模拟，使用多线程，找到每个学生的老师名字，并且打印出来。
     * @param args
     */
    public static void main(String[] args) {
        long begin = System.currentTimeMillis();

        List<String> studentList = new ArrayList<>();
        studentList.add("zhangsan");
        studentList.add("lisi");
        studentList.add("wangwu");

        int perCnt = studentList.size() / poolSize;             //每个线程处理的数量
        int step = Math.max(perCnt, minProcessCnt);             //每个线程处理的数量，按照step切割list
        int latchNum = (studentList.size() + step - 1) / step;  //处理次数 (和分页计算方法一样：pageCount = (totalCount + pageSize - 1)/pageSize )
        CountDownLatch latch = new CountDownLatch(latchNum);

        //切割studentList，分批查询
        try {
            for (int i = 0, start = 0; i < latchNum; i++) {
                if(i == latchNum - 1){
                    doFindTeacher(studentList.subList(start, studentList.size()), latch);
                }else{
                    doFindTeacher(studentList.subList(start, start+step), latch);
                    start = start + step;
                }
            }

            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("执行完成，耗时：" + (System.currentTimeMillis() - begin) + "ms");

        pool.shutdown();
    }

    private static void doFindTeacher(List<String> studentList, CountDownLatch latch){
        pool.execute(() -> {
            try{
                for(String student : studentList){
                    System.out.println("开始处理学生:" + student);

                    //模拟查数据库...等操作，查找学生的老师
                    Thread.sleep(3000);
                    System.out.println("teacher: " + student + "'s teacher");
                }
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                latch.countDown();
            }
        });
    }


}

开始处理学生:wangwu
开始处理学生:zhangsan
开始处理学生:lisi
teacher: zhangsan's teacher
teacher: wangwu's teacher
teacher: lisi's teacher
执行完成，耗时：3094ms

三、例子3:　　　　

package com.cy.test.thread;


import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;

public class TestMultiThread3 {
    private static int minProcessCnt = 1;
    private static int poolSize = 5;
    private static ExecutorService pool = Executors.newFixedThreadPool(poolSize);

    /**
     * 1.模拟，使用多线程，找到每个学生的老师名字
     * 2.将老师们的名字返回，并且输出
     * @param args
     */
    public static void main(String[] args) {
        long begin = System.currentTimeMillis();

        List<String> studentList = new ArrayList<>();
        studentList.add("zhangsan");
        studentList.add("lisi");
        studentList.add("wangwu");

        int size = studentList.size();
        int perCnt = size / poolSize;
        int step = Math.max(perCnt, minProcessCnt);
        int pollCount = (size + step - 1) / step;       // 列表循环次数

        List<FutureTask<List<String>>> taskList = new ArrayList<>();
        for (int i = 0; i < pollCount; i++) {
            final int start = step * i;
            final int end = (i == pollCount - 1) ? size : step * (i + 1);
            FutureTask<List<String>> task = new FutureTask<>(() -> {
                return doFindTeacher(studentList, start, end);
            });
            taskList.add(task);
            pool.execute(task);
        }

        //拿到返回结果
        List<String> teacherList = new ArrayList<>();
        try {
            for (FutureTask<List<String>> futureTask : taskList) {
                List<String> list = futureTask.get();
                teacherList.addAll(list);
            }
        }catch (Exception e){
            e.printStackTrace();
        }

        System.out.println(teacherList);

        System.out.println("TestMultiThread3 执行完成，耗时：" + (System.currentTimeMillis() - begin) + "ms");
        pool.shutdown();
    }


    private static List<String> doFindTeacher(List<String> studentList, int start, int end) throws InterruptedException {
        List<String> teacherList = new ArrayList<>();
        for(int j=start; j<end; j++){
            String student = studentList.get(j);
            System.out.println("开始处理学生:" + student);

            //模拟查数据库...等操作，查找学生的老师
            Thread.sleep(3000);
            String teacher = student + "'s teacher";
            teacherList.add(teacher);
        }
        return teacherList;
    }
}

console:

开始处理学生:zhangsan
开始处理学生:wangwu
开始处理学生:lisi
[zhangsan's teacher, lisi's teacher, wangwu's teacher]
TestMultiThread3 执行完成，耗时：3080ms