一、實作Runnable介面

public class RunnableDemo implements Runnable {
    public void run() {
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("in runnable demo");
    }
}

非阻塞呼叫

    public static void main(String[] args) throws Exception {
        Thread runnableThread = new Thread(new RunnableDemo());
        runnableThread.start();
        System.out.println("in main");
    }

輸出結果

in main
in runnable demo

可以看到執行緒的運行沒有阻塞當前執行緒

阻塞呼叫

    public static void main(String[] args) throws Exception {
        Thread runnableThread = new Thread(new RunnableDemo());
        runnableThread.start();
        runnableThread.join();
        System.out.println("in main");
    }

輸出結果

in runnable demo
in main

Join會阻塞當前執行緒，一直等待自定義執行緒才回傳，

二、實作Callable介面

在Runnable的例子中，Runnable介面有一個很大的缺陷就是run方法沒有回傳值定義，主執行緒無法獲取到執行緒執行的結果，這個時候就需要Callable介面，

public class CallableDemo implements Callable<CallableDto> {
    public CallableDto call() throws Exception {
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("in callable demo");
        return new CallableDto(1);
    }
}

class CallableDto {
    private int id;

    public CallableDto(int id) {
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }
}

非阻塞呼叫

   public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(10);
        Future<CallableDto> future = executor.submit(new CallableDemo());
        System.out.println("in main");
    }

輸出結果，如下所示，新啟動的執行緒沒有阻塞當前執行緒

in main
in callable demo

阻塞呼叫，且拿到結果

    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(10);
        Future<CallableDto> future = executor.submit(new CallableDemo());
        CallableDto callableDto = future.get();
        System.out.println("in main");
        System.out.println("id from callable is " + callableDto.getId());
    }

get方法首先會阻塞主執行緒，等待當前執行緒執行結束才回傳，且回傳執行緒的執行結果，

三、CompletableFuture方式

CompletableFuture是jdk1.8引入的api，做了進一步的封裝，用戶執行緒無需實作Callable介面也能啟動，且能夠回傳用戶執行緒的執行結果

public static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier, Executor executor) 

一個沒有實作Callable的普通方法

public class CompletableFutureDemo {
    public CompletableFutureDemoDto action() {
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("in CompletableFutureDemo ");
        return new CompletableFutureDemoDto(1);
    }
}

class CompletableFutureDemoDto {
    private int id;

    public CompletableFutureDemoDto(int id) {
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }
}

非阻塞呼叫

    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(10);
        CompletableFuture<CompletableFutureDemoDto> future = CompletableFuture.supplyAsync(() ->
        {
            return new CompletableFutureDemo().action();
        }, executor);
        System.out.println("in main");
    }

執行結果，可以看到，主執行緒沒有被阻塞

in main
in CompletableFutureDemo 

阻塞呼叫且獲取結果

    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(10);
        CompletableFuture<CompletableFutureDemoDto> future = CompletableFuture.supplyAsync(() ->
        {
            return new CompletableFutureDemo().action();
        }, executor);
        CompletableFutureDemoDto demoDto=future.join();
        System.out.println("in main");
        System.out.println("id from demoDto is " + demoDto.getId());
    }

執行結果，主執行緒一直被阻塞，一直等到用戶執行緒回傳

in CompletableFutureDemo 
in main
id from demoDto is 1

標籤：Java

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