一、Java多線程的方法

1. 繼承 Thread
2. 實現 Runnable
3. 實現 Callable 可以有返回值

package com.test;import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;class MyTread extends Thread {public void run() {System.out.println(Thread.currentThread().getName());}
}//實現Runable接口，實現run方法；
class MyRunnable implements Runnable {public void run() {System.out.println(Thread.currentThread().getName());}
}class MyCallable implements Callable<String> {private List<String> ids;public MyCallable(List<String> ids) {this.ids = ids;}@Overridepublic String call() throws Exception {// 獲取參數，執行響應的操作for (String id : ids) {// 此處為對數據的操作System.out.println(id);}// 返回改線程的idreturn Thread.currentThread() + "";}
}public class ThreadTest {public static void main(String[] args) throws Exception {MyTread thread = new MyTread();thread.start(); //開啟一個線程MyRunnable myRunnable = new MyRunnable();Thread runnable = new Thread(myRunnable);runnable.start(); //開啟一個線程MyCallable myCallable = new MyCallable(new ArrayList<>());String res = myCallable.call(); // 開啟一個線程System.out.println("res: " + res);}
}

Java多線程，一種是不需要等待結果，一種是需要等待任務執行完成的結果，在執行相關操作。下邊著重介紹第二種；

二、等待執行結果返回在執行后續操作

（1）Future類，Future ExecutorService futureTasks.get(i).get()會阻塞，直到線程執行完有所返回值

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;class MyCallables implements Callable<Integer> {private int num;private String name;public MyCallables(Integer num, String name) {this.num = num;this.name = name;}@Overridepublic Integer call() throws Exception {int sum = 0;for (int i = 0; i < num; i = i + 100) {sum += i;}System.out.println("\t---: " + System.currentTimeMillis() + " " + this.name);Thread.sleep(num / 100);System.out.println("\t---: " + System.currentTimeMillis() + " " + this.name);return sum;}
}@Slf4j
@Component
public class TestThreadWork {public static void main(String[] args) throws Exception {int[] numArr = new int[]{100, 200, 300, 400, 500};long start = System.currentTimeMillis();List<FutureTask<Integer>> futureTasks = new ArrayList<>();for (Integer num : numArr) {// 創建線程處理MyCallables callable = new MyCallables(num, "thread-" + String.valueOf(num));FutureTask<Integer> futureTask = new FutureTask<Integer>(callable);futureTasks.add(futureTask);}//創建線程池后，依次提交任務，執行ExecutorService executorService = Executors.newCachedThreadPool();for (FutureTask<Integer> futureTask : futureTasks) {executorService.submit(futureTask);}executorService.shutdown();//根據任務數，依次去獲取任務返回的結果，獲取結果時會依次返回，若前一個沒返回，則會等待，阻塞for (int i = 0; i < numArr.length; i++) {int sum = futureTasks.get(i).get();System.out.println("sum: " + sum);}log.info("timeConsumer: {}", (System.currentTimeMillis() - start));}
}

（2）ExecutorService、CompletionService pool.take().get()，同樣會阻塞，直到線程執行完返回值

https://blog.csdn.net/qq_36898043/article/details/79733124

（3）countDownLatch 閉鎖

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;/************************************** Class Name: TestCountDownLatch* Description:〈測試countDownLatch鎖🔒〉* @create 2020/8/25* @since 1.0.0************************************/
public class TestCountDownLatch {public static void main(String[] args) {// 創建線程池int[] numArr = new int[]{100, 200, 300, 400, 500};final CountDownLatch countDownLatch = new CountDownLatch(numArr.length);List<Future<Integer>> futureList = new ArrayList<>();ExecutorService executorService = Executors.newCachedThreadPool();for (int num : numArr) {Future<Integer> future = executorService.submit(new Callable<Integer>() {@Overridepublic Integer call() throws Exception {int sum = 0;for (int i = 0; i < num; i++) {sum += num;}countDownLatch.countDown();return sum;}});// 提交任務futureList.add(future);}try {// 等待所有線程執行完畢countDownLatch.await();Integer totalCount = 0;for (Future<Integer> future : futureList) {totalCount += future.get();}System.out.println("--------totalCount: " + totalCount);} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();} finally {if (executorService.isShutdown()) {return;}executorService.shutdown();}}
}

參考：

• http://quanzhan.applemei.com/webStack/TXpRNE13PT0=

• https://blog.csdn.net/qq_36898043/article/details/79733124

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