【CompletableFuture】CompletableFuture中join()和get()方法的区别

一.相同点：

　　join()和get()方法都是用来获取CompletableFuture异步之后的返回值

 

二.区别：

　　1.join()方法抛出的是uncheck异常（即未经检查的异常),不会强制开发者抛出，

　　会将异常包装成CompletionException异常 /CancellationException异常，但是本质原因还是代码内存在的真正的异常，

　　文档说明：

  /**
     * Returns the result value when complete, or throws an
     * (unchecked) exception if completed exceptionally. To better
     * conform with the use of common functional forms, if a
     * computation involved in the completion of this
     * CompletableFuture threw an exception, this method throws an
     * (unchecked) {@link CompletionException} with the underlying
     * exception as its cause.
     *
     * @return the result value
     * @throws CancellationException if the computation was cancelled
     * @throws CompletionException if this future completed
     * exceptionally or a completion computation threw an exception
     */

　　demo：

    public static void main(String[] args) {
        CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(() -> {
            int i =1/0;
            return 1;
        });
        CompletableFuture.allOf(f1).join();
        System.out.println("CompletableFuture Test");
    }

　　异常信息

Exception in thread "main" java.util.concurrent.CompletionException: java.lang.ArithmeticException: / by zero
    at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
    at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
    at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1592)
    at java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1582)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
Caused by: java.lang.ArithmeticException: / by zero
    at com.gabriel.stage.utils.IpAddressUtil.lambda$main$0(IpAddressUtil.java:44)
    at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
    ... 5 more

 

　　2.get()方法抛出的是经过检查的异常，ExecutionException, InterruptedException 需要用户手动处理（抛出或者 try catch）

　　文档说明

 /**
     * Waits if necessary for this future to complete, and then
     * returns its result.
     *
     * @return the result value
     * @throws CancellationException if this future was cancelled
     * @throws ExecutionException if this future completed exceptionally
     * @throws InterruptedException if the current thread was interrupted
     * while waiting
     */

 

　　demo

public static void main(String[] args) throws ExecutionException, InterruptedException {
        CompletableFuture<Integer> f1 = CompletableFuture.supplyAsync(() -> {
            int i =1/0;
            return 1;
        });
        f1.get();
        System.out.println("CompletableFuture Test");
    }