Java启动新线程的几种方式（Runnable、Callable、CompletableFuture）

一、实现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");
    }
}

非阻塞调用

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

输出结果

in main
in runnable demo

可以看到线程的运行没有阻塞当前线程

阻塞调用

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

输出结果

in runnable demo
in main

Join会阻塞当前线程，一直等待自定义线程才返回。

二、实现Callable接口

在Runnable的例子中，Runnable接口有一个很大的缺陷就是run方法没有返回值定义，主线程无法获取到线程执行的结果。这个时候就需要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;
    }
}

非阻塞调用

   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");
    }

输出结果，如下所示，新启动的线程没有阻塞当前线程

in main
in callable demo

阻塞调用，且拿到结果

    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方法首先会阻塞主线程，等待当前线程执行结束才返回，且返回线程的执行结果。

三、CompletableFuture方式

CompletableFuture是jdk1.8引入的api，做了进一步的封装，用户线程无需实现Callable接口也能启动，且能够返回用户线程的执行结果

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

一个没有实现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;
    }
}

非阻塞调用

    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");
    }

执行结果，可以看到，主线程没有被阻塞

in main
in CompletableFutureDemo 

阻塞调用且获取结果

    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());
    }

执行结果，主线程一直被阻塞，一直等到用户线程返回

in CompletableFutureDemo 
in main
id from demoDto is 1