java多线程遍历处理list集合

开发过程中经常遇到如下需求，拿到一个list数据，需要遍历它然后请求第三方接口，然后根据返回结果做一些事

常规写法

public static void main(String[] args) {
    List list = getList();
    test1(list);
}

//假设有500条数据
static List getList() {
    List list = new ArrayList<>();
    for (int i = 1; i < 501; i++) {
        User user = new User();
        user.setIdCard(i + "");
        list.add(user);
    }
    return list;
}

//常规的单线程处理方法
static void test1(List list) {
    long start = System.currentTimeMillis();
    for (User user : list) {
        sendRequest(user);
    }
    long end = System.currentTimeMillis();
    System.out.println("单线程方法，耗时：" + (end - start) + "ms");
}

//模拟请求第三方接口：根据身份证号获取姓名
static void sendRequest(User user){
    //模拟接口请求耗时
    try {
        Thread.sleep(10);
    } catch (Exception e){}
    //模拟获取请求结果后做的一些事
    user.setName("张三-" + user.getIdCard());
    System.out.println("=====> 发送请求： name=" + user.getName());
}

@Data
class User {
    private String idCard;
    private String name;
}

我们使用模拟数据造了 500 条数据，然后for循环列表去请求第三方接口获取数据，总共耗时大约为10 * 500 = 5000ms 以上

使用多线程改造后：

public static void main(String[] args) {
    List list = getList();
    test2(list);
}

//......省略getList()，上面有

//多线程处理
static void test2(List list) {
    long start = System.currentTimeMillis();
    ExecutorService executor = Executors.newFixedThreadPool(10);
    final CountDownLatch countDownLatch = new CountDownLatch(list.size());
    for (User user : list) {
        executor.execute(new Task(user, countDownLatch));
    }
    try {
        countDownLatch.await();
    } catch (Exception e) {

    } finally {
        executor.shutdown();
    }
    long end = System.currentTimeMillis();
    System.out.println("多线程方法，耗时：" + (end - start) + "ms");
}

//实现Runnable的多线程类
static class Task implements  Runnable {

        private User user;
        private CountDownLatch countDownLatch;

        public Task(User user, CountDownLatch countDownLatch) {
            this.user = user;
            this.countDownLatch = countDownLatch;
        }

        @Override
        public void run() {
            try {
                sendRequest(user);
            } catch (Exception e) {

            } finally {
                countDownLatch.countDown();
            }
        }
    }

结果：

注意事项：

1. 正常情况下，我们需要等多线程处理完，获取list数据，再去做一些业务操作（如入库，导出数据等），如果不需要等待结果，可以去掉countDownLatch，速度会更快
2. Task的run方法最好使用try...catch...finally，保证无论sendRequest()方法执行成功与否，countDownLatch都能减1，防止多线程无法终止

完整Demo

public class ForThreadTest {

    public static void main(String[] args) {
        List list = getList();
        test1(list);
        test2(list);
    }

    //常规的单线程处理方法
    static void test1(List list) {
        long start = System.currentTimeMillis();
        for (User user : list) {
            sendRequest(user);
        }
        long end = System.currentTimeMillis();
        System.out.println("单线程方法，耗时：" + (end - start) + "ms");
    }

    //多线程
    static void test2(List list) {
        long start = System.currentTimeMillis();
        ExecutorService executor = Executors.newFixedThreadPool(10);
        final CountDownLatch countDownLatch = new CountDownLatch(list.size());
        for (User user : list) {
            executor.execute(new Task(user, countDownLatch));
        }
        try {
            countDownLatch.await();
        } catch (Exception e) {
    
        } finally {
            executor.shutdown();
        }
        long end = System.currentTimeMillis();
        System.out.println("多线程方法，耗时：" + (end - start) + "ms");
    }


    //假设有500条数据
    static List getList() {
        List list = new ArrayList<>();
        for (int i = 1; i < 501; i++) {
            User user = new User();
            user.setIdCard(i + "");
            list.add(user);
        }
        return list;
    }

    //模拟请求第三方接口：根据身份证号获取姓名
    static void sendRequest(User user){
        //模拟接口请求耗时
        try {
            Thread.sleep(10);
        } catch (Exception e){}
        //模拟获取请求结果后做的一些事
        user.setName("张三-" + user.getIdCard());
        System.out.println("=====> 发送请求： name=" + user.getName());
    }

    static class Task implements  Runnable {

        private User user;
        private CountDownLatch countDownLatch;

        public Task(User user, CountDownLatch countDownLatch) {
            this.user = user;
            this.countDownLatch = countDownLatch;
        }

        @Override
        public void run() {
            try {
                sendRequest(user);
            } catch (Exception e) {

            } finally {
                countDownLatch.countDown();
            }
        }
    }
}

@Data
class User {
    private String idCard;
    private String name;
}