Java啟動新線程的幾種方式（Runnable、Callable、CompletableFuture）

一、實現Runnable接口

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

非阻塞調用

    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

可以看到線程的運行沒有阻塞當前線程

阻塞調用

    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會阻塞當前線程，一直等待自定義線程才返回。

二、實現Callable接口

在Runnable的例子中，Runnable接口有一個很大的缺陷就是run方法沒有返回值定義，主線程無法獲取到線程執行的結果。這個時候就需要Callable接口。

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;
    }
}

非阻塞調用

   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，新啟動的線程沒有阻塞當前線程

in main
in callable demo

阻塞調用，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方法首先會阻塞主線程，等待當前線程執行結束才返回，且返回線程的執行結果。

三、CompletableFuture方式

CompletableFuture是jdk1.8引入的api，做了進一步的封裝，用戶線程無需實現Callable接口也能啟動，且能夠返回用戶線程的執行結果

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

一個沒有實現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;
    }
}

非阻塞調用

    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，主線程沒有被阻塞

in main
in CompletableFutureDemo 

阻塞調用且獲取結果

    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，主線程一直被阻塞，一直等到用戶線程返回

in CompletableFutureDemo 
in main
id from demoDto is 1