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零、前语
我的学习战略很简单,题海战略+ 费曼学习法。假如能把这100题都仔仔细细自己完结一遍,那意味着 JAVA语言 现已筑基成功了。后面的进阶学习,能够持续跟着我,一同走向架构师之路。
一、标题描述
标题:
Java创立线程的几种办法:
Java运用Thread类代表线程,一切线程目标都必须是Thread类或许其子类的实例。Java能够用以下5种办法来创立线程:
1)承继Thread类创立线程;
2)完结Runnable接口创立线程;
3)完结Callable接口,经过FutureTask包装器来创立Thread线程;
4)运用ExecutorService、Callable(或许Runnable)、Future完结由回来成果的线程。
5)运用CompletableFuture类创立异步线程,且是据有回来成果的线程。 JDK8新支撑的
完结:运用这5种办法创立线程,体会其中的妙处。
二、解题思路
承继Thread类创立线程
Thread类本质上是完结了Runnable接口的一个实例,代表一个线程的实例。发动线程的仅有办法就是经过Thread类的start()实例办法。start()办法是一个native办法,它将发动一个新线程,并履行run()办法。这种办法完结多线程很简单,经过自己的类直接extends Thread,并复写run()办法,就能够发动新线程并履行自己定义的run()办法。
完结Runnable接口创立线程
假如自己的类现已extends另一个类,就无法直接extends Thread,此刻,能够完结一个Runnable接口
完结Callable接口,经过FutureTask包装器来创立Thread线程
完结一个Callable接口(它是一个具有回来值的)
运用ExecutorService、Callable(或许Runnable)、Future完结由回来成果的线程
Executors类,供给了一系列工厂办法用于创立线程池,回来的线程池都完结了ExecutorService接口:
//创立固定数目线程的线程池。
public static ExecutorService newFixedThreadPool(int nThreads) ;
//创立一个可缓存的线程池,调用execute 将重用以前构造的线程(假如线程可用)。假如现有线程没有可用的,则创立一个新线程并添加到池中。终止并从缓存中移除那些已有 60 秒钟未被运用的线程。
public static ExecutorService newCachedThreadPool();
//创立一个单线程化的Executor。
public static ExecutorService newSingleThreadExecutor();
//创立一个支撑定时及周期性的使命履行的线程池,大都情况下可用来代替Timer类。
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize);
ExecutoreService供给了submit()办法,传递一个Callable,或Runnable,回来Future。假如Executor后台线程池还没有完结Callable的核算,这调用回来Future目标的get()办法,会堵塞直到核算完结。
运用CompletableFuture类创立异步线程,且是据有回来成果的线程
Future模式的缺点
Future虽然能够完结获取异步履行成果的需求,但是它没有供给告诉的机制,咱们无法得知Future什么时候完结。
要么运用堵塞,在future.get()的地方等候future回来的成果,这时又变成同步操作。要么运用isDone()轮询地判断Future是否完结,这样会耗费CPU的资源。
CompletableFuture介绍
JDK1.8新参加的一个完结类CompletableFuture,完结了Future, CompletionStage两个接口。
CompletableFuture中4个异步履行使命静态办法:
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier) {
return asyncSupplyStage(asyncPool, supplier);
}
public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier,Executor executor) {
return asyncSupplyStage(screenExecutor(executor), supplier);
}
public static CompletableFuture<Void> runAsync(Runnable runnable) {
return asyncRunStage(asyncPool, runnable);
}
public static CompletableFuture<Void> runAsync(Runnable runnable, Executor executor) {
return asyncRunStage(screenExecutor(executor), runnable);
}
其中supplyAsync用于有回来值的使命,runAsync则用于没有回来值的使命。Executor参数能够手动指定线程池,不然默许ForkJoinPool.commonPool()体系级公共线程池
三、代码详解
第一种:承继Thread类创立线程
package com.xiaoxuzhu;
import java.util.concurrent.CountDownLatch;
/**
* Description:承继Thread类创立线程
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修正记载:
* 修正后版别 修正人 修正日期 修正内容
* 2022/5/15.1 xiaoxuzhu 2022/5/15 Create
* </pre>
* @date 2022/5/15
*/
public class ThreadDemo1 extends Thread {
CountDownLatch countDownLatch;
public ThreadDemo1(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + ":my thread ");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
countDownLatch.countDown();
}
}
public static void main(String[] args) {
// 第一种:运用extends Thread办法
CountDownLatch countDownLatch1 = new CountDownLatch(2);
for (int i = 0; i < 2; i++) {
ThreadDemo1 myThread1 = new ThreadDemo1(countDownLatch1);
myThread1.start();
}
try {
countDownLatch1.await();
System.out.println("thread complete...");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
第二种:完结Runnable接口创立线程
package com.xiaoxuzhu;
import java.util.concurrent.CountDownLatch;
/**
* Description: 完结Runnable接口创立线程
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修正记载:
* 修正后版别 修正人 修正日期 修正内容
* 2022/5/15.1 xiaoxuzhu 2022/5/15 Create
* </pre>
* @date 2022/5/15
*/
public class ThreadDemo2 implements Runnable{
CountDownLatch countDownLatch;
public ThreadDemo2(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
try {
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() + ":my runnable ");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
countDownLatch.countDown();
}
}
public static void main(String[] args) {
// 第二种:运用implements Runnable办法
CountDownLatch countDownLatch2 = new CountDownLatch(2);
ThreadDemo2 myRunnable = new ThreadDemo2(countDownLatch2);
for (int i = 0; i < 2; i++) {
new Thread(myRunnable).start();
}
try {
countDownLatch2.await();
System.out.println("runnable complete...");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
第三种:完结Callable接口,经过FutureTask包装器来创立Thread线程
核算1~100的叠加
package com.xiaoxuzhu;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
/**
* Description: 完结Callable接口,经过FutureTask包装器来创立Thread线程
* 跟Runnable比,不同点在于它是一个具有回来值的,且会抛出反常
* //用futureTask接纳成果
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修正记载:
* 修正后版别 修正人 修正日期 修正内容
* 2022/5/15.1 xiaoxuzhu 2022/5/15 Create
* </pre>
* @date 2022/5/15
*/
public class ThreadDemo3 implements Callable<Integer> {
public static void main(String[] args) {
ThreadDemo3 threadDemo03 = new ThreadDemo3();
//1、用futureTask接纳成果
FutureTask<Integer> futureTask = new FutureTask<>(threadDemo03);
new Thread(futureTask).start();
//2、接纳线程运算后的成果
try {
//futureTask.get();这个是堵塞性的等候
Integer sum = futureTask.get();
System.out.println("sum="+sum);
System.out.println("-------------------");
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
@Override
public Integer call() throws Exception {
int sum = 0;
for (int i = 0; i <101 ; i++) {
sum+=i;
}
return sum;
}
}
第四种:运用ExecutorService、Callable(或许Runnable)、Future完结由回来成果的线程
package com.xiaoxuzhu;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
/**
* Description: 运用ExecutorService、Callable(或许Runnable)、Future完结由回来成果的线程
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修正记载:
* 修正后版别 修正人 修正日期 修正内容
* 2022/5/15.1 xiaoxuzhu 2022/5/15 Create
* </pre>
* @date 2022/5/15
*/
public class ThreadDemo4 {
static class MyCallable implements Callable<Integer> {
private CountDownLatch countDownLatch;
public MyCallable(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
public Integer call() {
int sum = 0;
try {
for (int i = 0; i <= 100; i++) {
sum += i;
}
System.out.println("线程履行成果:"+sum);
} finally {
countDownLatch.countDown();
}
return sum;
}
}
public static void main(String[] args) throws ExecutionException, InterruptedException {
// 第四种:运用运用线程池办法
// 承受回来参数
List<Future> resultItems2 = new ArrayList<Future>();
// 給线程池初始化5個线程
ExecutorService executorService = Executors.newFixedThreadPool(5);
CountDownLatch countDownLatch4 = new CountDownLatch(10);
for (int i = 0; i < 10; i++) {
MyCallable myCallable = new MyCallable(countDownLatch4);
Future result = executorService.submit(myCallable);
resultItems2.add(result);
}
// 等候线程池中分配的使命完结后才封闭(封闭之后不允许有新的线程参加,但是它并不会等候线程结束),
// 而executorService.shutdownNow();是立即封闭不论是否线程池中是否有其他未完结的线程。
executorService.shutdown();
try {
countDownLatch4.await();
Iterator<Future> iterator = resultItems2.iterator();
System.out.println("----------------------");
while (iterator.hasNext()) {
try {
System.out.println("线程回来成果:"+iterator.next().get());
} catch (ExecutionException e) {
e.printStackTrace();
}
}
System.out.println("callable complete...");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
第五种:运用CompletableFuture类创立异步线程,且是据有回来成果的线程
package com.xiaoxuzhu;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import org.junit.Test;
/**
* Description: 运用CompletableFuture类创立异步线程,且是据有回来成果的线程。
*
* @author xiaoxuzhu
* @version 1.0
*
* <pre>
* 修正记载:
* 修正后版别 修正人 修正日期 修正内容
* 2022/5/15.1 xiaoxuzhu 2022/5/15 Create
* </pre>
* @date 2022/5/15
*/
public class ThreadDemo5 {
/**
* A使命B使命完结后,才履行C使命
* 回来值的处理
* @param
*@return void
**/
@Test
public void completableFuture1(){
CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("future1 finished!");
return "future1 finished!";
});
CompletableFuture<String> future2 = CompletableFuture.supplyAsync(() -> {
System.out.println("future2 finished!");
return "future2 finished!";
});
CompletableFuture<Void> future3 = CompletableFuture.allOf(future1, future2);
try {
future3.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
System.out.println("future1: " + future1.isDone() + " future2: " + future2.isDone());
}
/**
* 在Java8中,CompletableFuture供给了非常强壮的Future的扩展功能,能够协助咱们简化异步编程的复杂性,
* 并且供给了函数式编程的能力,能够经过回调的办法处理核算成果,也供给了转化和组合 CompletableFuture 的办法
*
* 注意: 办法中有Async一般表明另起一个线程,没有表明用当前线程
*/
@Test
public void test01() throws Exception {
ExecutorService service = Executors.newFixedThreadPool(5);
/**
* supplyAsync用于有回来值的使命,
* runAsync则用于没有回来值的使命
* Executor参数能够手动指定线程池,不然默许ForkJoinPool.commonPool()体系级公共线程池
*/
CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "xiaoxuzhu";
}, service);
CompletableFuture<Void> data = CompletableFuture.runAsync(() -> System.out.println("xiaoxuzhu"));
/**
* 核算成果完结回调
*/
future.whenComplete((x,y)-> System.out.println("有推迟3秒:履行当前使命的线程持续履行:"+x+","+y)); //履行当前使命的线程持续履行
data.whenCompleteAsync((x,y)-> System.out.println("交给线程池另起线程履行:"+x+","+y)); // 交给线程池另起线程履行
future.exceptionally(Throwable::toString);
//System.out.println(future.get());
/**
* thenApply,一个线程依靠另一个线程能够运用,出现反常不履行
*/
//第二个线程依靠第一个的成果
CompletableFuture<Integer> future1 = CompletableFuture.supplyAsync(() -> 5).thenApply(x -> x);
/**
* handle 是履行使命完结时对成果的处理,第一个出现反常持续履行
*/
CompletableFuture<Integer> future2 = future1.handleAsync((x, y) -> x + 2);
System.out.println(future2.get());//7
/**
* thenAccept 消费处理成果,不回来
*/
future2.thenAccept(System.out::println);
/**
* thenRun 不关心使命的处理成果。只要上面的使命履行完结,就开始履行
*/
future2.thenRunAsync(()-> System.out.println("持续下一个使命"));
/**
* thenCombine 会把 两个 CompletionStage 的使命都履行完结后,两个使命的成果交给 thenCombine 来处理
*/
CompletableFuture<Integer> future3 = future1.thenCombine(future2, Integer::sum);
System.out.println(future3.get()); // 5+7=12
/**
* thenAcceptBoth : 当两个CompletionStage都履行完结后,把成果一块交给thenAcceptBoth来进行耗费
*/
future1.thenAcceptBothAsync(future2,(x,y)-> System.out.println(x+","+y)); //5,7
/**
* applyToEither
* 两个CompletionStage,谁履行回来的成果快,我就用那个CompletionStage的成果进行下一步的转化操作
*/
CompletableFuture<Integer> future4 = future1.applyToEither(future2, x -> x);
System.out.println(future4.get()); //5
/**
* acceptEither
* 两个CompletionStage,谁履行回来的成果快,我就用那个CompletionStage的成果进行下一步的耗费操作
*/
future1.acceptEither(future2, System.out::println);
/**
* runAfterEither
* 两个CompletionStage,任何一个完结了都会履行下一步的操作(Runnable
*/
future1.runAfterEither(future,()-> System.out.println("有一个完结了,我持续"));
/**
* runAfterBoth
* 两个CompletionStage,都完结了核算才会履行下一步的操作(Runnable)
*/
future1.runAfterBoth(future,()-> System.out.println("都完结了,我持续"));
/**
* thenCompose 办法
* thenCompose 办法允许你对多个 CompletionStage 进行流水线操作,第一个操作完结时,将其成果作为参数传递给第二个操作
* thenApply是承受一个函数,thenCompose是承受一个future实例,更适合处理流操作
*/
future1.thenComposeAsync(x->CompletableFuture.supplyAsync(()->x+1))
.thenComposeAsync(x->CompletableFuture.supplyAsync(()->x+2))
.thenCompose(x->CompletableFuture.runAsync(()-> System.out.println("流操作成果:"+x)));
TimeUnit.SECONDS.sleep(5);//主线程sleep,等候其他线程履行
}
}
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