java8 - fork-join之CompletableFuture 使用总结
CompletableFuture类实现了CompletionStage和Future接口。Future是Java 5添加的类，用来描述一个异步计算的结果，但是获取一个结果时方法较少,要么通过轮询isDone，确认完成后，调用get()获取值，要么调用get()设置一个超时时间。但是这个get()方法会阻塞住调用线程，这种阻塞的方式显然和我们的异步编程的初衷相违背。
为了解决这个问题，JDK吸收了guava的设计思想，加入了Future的诸多扩展功能形成了CompletableFuture。CompletableFuture可以在某个线程完成某任务的时候回调某个函数
CompletableFuture 主要API如下
变换操作
public CompletionStage thenApply(Functionsuper T,? extends U> fn);
public CompletionStage thenApplyAsync(Functionsuper T,? extends U> fn);
public CompletionStage thenApplyAsync(Functionsuper T,? extends U> fn,Executor executor);例如
public void thenApplay() {
String result = CompletableFuture.supplyAsync(() -> "hello").thenApply(s -> s + " world").join();
System.out.println(result);
}运行结果为
hello world消耗操作
public CompletionStage thenAccept(Consumersuper T> action);
public CompletionStage thenAcceptAsync(Consumersuper T> action);
public CompletionStage thenAcceptAsync(Consumersuper T> action,Executor executor); 示例
@Test
public void thenAccept(){
CompletableFuture.supplyAsync(()->"hello").thenAccept(s-> System.out.println(s+" world"));
}运行结果为
hello world对上一步的计算结果不关心，执行下一个操作
public CompletionStage thenRun(Runnable action);
public CompletionStage thenRunAsync(Runnable action);
public CompletionStage thenRunAsync(Runnable action,Executor executor); 示例
public void thenRun(){
CompletableFuture.supplyAsync(()->{
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "Hello World";
}).thenRun(()-> System.out.println("Hello World"));
}运行结果
Hello World结合两个CompletionStage经过转化后返回
public CompletionStage thenCombine(CompletionStage other,BiFunctionsuper T,? super U,? extends V> fn);
public CompletionStage thenCombineAsync(CompletionStage other,BiFunctionsuper T,? super U,? extends V> fn);
public CompletionStage thenCombineAsync(CompletionStage other,BiFunctionsuper T,? super U,? extends V> fn,Executor executor); 示例
public void thenCombine(){
String result=CompletableFuture.supplyAsync(()->{
return "hello ";
}).thenCombine(CompletableFuture.supplyAsync(()->{
return "world";
}),(s1,s2)->s1+s2).join();
System.out.println(result);
}运行结果
hello world在两个CompletionStage都运行完执行
public CompletionStage runAfterBoth(CompletionStage other,Runnable action);
public CompletionStage runAfterBothAsync(CompletionStage other,Runnable action);
public CompletionStage runAfterBothAsync(CompletionStage other,Runnable action,Executor executor); 示例
public void thenAfterRun() {
CompletableFuture.supplyAsync(() -> "Hello")
.runAfterBoth(CompletableFuture.supplyAsync(() -> " World"), () -> System.out.println("Hello World"));
}运行结果
Hello World调用优先执行完的结果进行处理
public <U> CompletionStage<U> applyToEither(CompletionStage extends T> other,Functionsuper T, U> fn);
public CompletionStage applyToEitherAsync(CompletionStage extends T> other,Functionsuper T, U> fn);
public CompletionStage applyToEitherAsync(CompletionStage extends T> other,Functionsuper T, U> fn,Executor executor);示例
public void applyToEither(){
String result=CompletableFuture.supplyAsync(()->"hello").applyToEither(CompletableFuture.supplyAsync(()->" World"),s->s).join();
System.out.println(result);
}运行结果
hello调用优先执行完的结果进行消耗
这个API与上一个API优点像不同点在于上一个API有返回值
public CompletionStage acceptEither(CompletionStage other,Consumersuper T> action);
public CompletionStage acceptEitherAsync(CompletionStage other,Consumersuper T> action);
public CompletionStage acceptEitherAsync(CompletionStage other,Consumersuper T> action,Executor executor); 示例
public void acceptEither(){
CompletableFuture.supplyAsync(()->"Hello")
.acceptEither(CompletableFuture.supplyAsync(()->"World"),System.out::println);
}运行结果
Hello只要有一个完成就执行下一步操作
public CompletionStage runAfterEither(CompletionStage other,Runnable action);
public CompletionStage runAfterEitherAsync(CompletionStage other,Runnable action);
public CompletionStage runAfterEitherAsync(CompletionStage other,Runnable action,Executor executor); 示例
public void runAfterEigher() {
CompletableFuture.supplyAsync(() -> {
while (true) {
}
}).runAfterEither(CompletableFuture.supplyAsync(() -> "s2"), () -> System.out.println("finish"));运行结果
finish异常处理
public CompletionStage exceptionally(Function fn); 示例
public void exceptionally() {
String result = (String) CompletableFuture.supplyAsync(() -> {
throw new RuntimeException("异常");
}).exceptionally(e -> {
System.out.println(e.getMessage());
return "hello world";
}).join();
System.out.println(result);
}结果为
java.lang.RuntimeException: 异常
hello world记录结果
运行完成时,对结果
public CompletionStage whenComplete(BiConsumersuper T, ? super Throwable> action);
public CompletionStage whenCompleteAsync(BiConsumersuper T, ? super Throwable> action);
public CompletionStage whenCompleteAsync(BiConsumersuper T, ? super Throwable> action,Executor executor); 示例
public void whenComplete() {
String result = CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (1 == 1) {
throw new RuntimeException("测试一下异常情况");
}
return "s1";
}).whenComplete((s, t) -> {
System.out.println(s);
System.out.println(t.getMessage());
}).exceptionally(e -> {
System.out.println(e.getMessage());
return "hello world";
}).join();
System.out.println(result);
}运行完成时处理结果
public CompletionStage handle(BiFunctionsuper T, Throwable, ? extends U> fn);
public CompletionStage handleAsync(BiFunctionsuper T, Throwable, ? extends U> fn);
public CompletionStage handleAsync(BiFunctionsuper T, Throwable, ? extends U> fn,Executor executor);示例
public void handle() {
String result = CompletableFuture.supplyAsync(() -> {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//出现异常
if (1 == 1) {
throw new RuntimeException("测试一下异常情况");
}
return "s1";
}).handle((s, t) -> {
if (t != null) {
return "hello world";
}
return s;
}).join();
System.out.println(result);
}结果为
hello world