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<User> list = getList();test1(list);
}//假设有500条数据
static List<User> getList() {List<User> 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<User> 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<User> list = getList();test2(list);
}//......省略getList()，上面有//多线程处理
static void test2(List<User> 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;}@Overridepublic 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<User> list = getList();test1(list);test2(list);}//常规的单线程处理方法static void test1(List<User> 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<User> 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<User> getList() {List<User> 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;}@Overridepublic void run() {try {sendRequest(user);} catch (Exception e) {} finally {countDownLatch.countDown();}}}
}@Data
class User {private String idCard;private String name;
}