Future/CompletableFuture与Lambda

汤太咸

Future和CompletableFuture

Runnable task = () -> System.out.println("Hello World");
ExecutorService service = Executors.newSingleThreadExecutor();
//直接通过ExecutorService执行
Future<?> future = service.submit(task);
//或者通过CompletableFuture调用ExecutorService执行
CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(task, service);
//还可以写为直接调用task,不通过ExecutorService
CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(task);
//执行完毕后需要关闭,否则线程仍然卡着
service.shutdown();
//输出
Hello World
//Callable方式
Supplier<String> task = () -> {
    System.out.println("Hello World!");
    return "Hello World!";
};
ExecutorService service = Executors.newSingleThreadExecutor();
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(task, service);
//或者写为不通过ExecutorService的方式
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(task);
//获取执行结果
String string = completableFuture.join();
System.out.println(string);
service.shutdown();
//输出
Hello World
Hello World

Future有五个方法

//阻塞等待获取结果
T get()
//设定超时时间获取结果,否则返回excepiton
T get(Long timeout,TimeUnit unit)
//取消该线程
void cancel()
//获取是否已经完成
boolean isDone()
//获取是否被取消了
boolean isCancelled()

CompletableFuture也有五个方法

//同Future的get()方法
T join()
//检测线程的执行状态,如果完成返回结果,未完成则返回默认的valueIfAbsent的值
T getNow(T valueIfAbsent)
//强制返回值方法,如果线程完成了,则返回get或者join的结果,如果未完成,则强制中断线程,并将设置的value返回
boolean complete(V value)
//强制返回值方法,如果线程完成了,则强制设置value为返回值,如果未完成,则强制完成线程,并将设置的value返回
void obtrudeValue(V value)
//强制返回Exception,如果线程未完成,则强制完成
boolean completeExceptionally(Throwable t)
//强制返回Exception,即使线程完成了,也强制完成,强制返回异常状态
void obtrudeException(V value)

complete方法,如果未完成强制完成

Supplier<String> task = () -> {
    try {
        Thread.sleep(500);
    }catch(Exception e){

    }
    return "Hello World!"+Thread.currentThread().getName();
};
ExecutorService service = Executors.newSingleThreadExecutor();
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(task, service);
completableFuture.complete("Too long");
String string = completableFuture.join();
System.out.println(string);
service.shutdown();
//输出
Too long

//但是如果另外一种写法
Supplier<String> task = () -> {
    try {
        Thread.sleep(500);
    }catch(Exception e){

    }
    return "Hello World!"+Thread.currentThread().getName();
};
ExecutorService service = Executors.newSingleThreadExecutor();
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(task, service);
try {
    Thread.sleep(800);
}catch(Exception e){

}
completableFuture.complete("Too long");
String string = completableFuture.join();
System.out.println(string);
service.shutdown();
//输出
Hello World!pool-1-thread-1

obtrudeValue方法,无论线程是否完成都设置value为返回值

Supplier<String> task = () -> {
    try {
        Thread.sleep(500);
    }catch(Exception e){

    }
    return "Hello World!"+Thread.currentThread().getName();
};
ExecutorService service = Executors.newSingleThreadExecutor();
CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(task, service);
try {
    Thread.sleep(800);
}catch(Exception e){

}
completableFuture.obtrudeValue("Too long");
String string = completableFuture.join();
System.out.println(string);
service.shutdown();
//输出
Too long

first task: supplier supplyAsync(),runable runAsync()
seconde task:runable thenRun(),consumer thenAccept(),function thenApply()

//Runable   ()->System.out.println("Person read")    void run()    thenRun()
CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(()-> System.out.println("run first"))
.thenRun(()-> System.out.println("then run"));
//Consumer  n->System.out.println(n+"Person read")    void accept()    thenAccept()
//Function  id -> readPersonFromDB(id)                Person apply()    thenApply()

//具体执行方法
CompletableFuture<List<Person>>  completableFuture = CompletableFuture.supplyAsync(()-> Arrays.asList(1,2,3))
.thenApply(list -> readPerson(list));
completableFuture.thenRun(()-> System.out.println("The list of Person had been read"));
completableFuture.thenAccept(persons -> System.out.println(persons.size()));
public static List<Person> readPerson(List<Integer> list){
    List<Person> personList = new ArrayList();
    for(int i :list ){
        personList.add(new Person("name",i));
    }
    return personList;
}
//输出
The list of Person had been read
3

在哪个线程执行

CompletableFuture<List<Person>> c2 = CompletableFuture.runAsync()//common FJ Pool
c2.thenApplyAsync()//provided pool of threads
c2.thenRun()//the same thread
c2.thenAcceptAsync()//the same pool of thread

CompletableFuture

public class TestCompletableFuture {
    public static void main(String[] args) throws Exception{
        Supplier<List<Long>> supplyIDs = () -> {
            sleep(200);
            return Arrays.asList(1L,2L,3L);
        };
        Function<List<Long>, List<User>> fetchUsers = ids -> {
            sleep(300);
            return ids.stream().map(User::new).collect(Collectors.toList());
        };
        Consumer<List<User>> displayer = users -> users.forEach(System.out::println);
        CompletableFuture<List<Long>> completableFuture = CompletableFuture.supplyAsync(supplyIDs);
        completableFuture.thenApply(fetchUsers).thenAccept(displayer);
        sleep(10000);
    }
    private static void sleep(int time){
        try{
            Thread.sleep(time);
        }catch (Exception e){
        }
    }
}
//输出
User{id=1}
User{id=2}
User{id=3}
//还可增加ExecutorService保持在单独的线程内执行
ExecutorService executorService = Executors.newSingleThreadExecutor();
CompletableFuture<List<Long>> completableFuture = CompletableFuture.supplyAsync(supplyIDs,executorService);
completableFuture.thenApply(fetchUsers).thenAcceptAsync(displayer,executorService);


Function<List<Long>, CompletableFuture<List<User>>>内置CompletableFuture方法
public class TestCompletableFuture {
    public static void main(String[] args) throws Exception{
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        ExecutorService executorService2 = Executors.newSingleThreadExecutor();
        Supplier<List<Long>> supplyIDs = () -> {
            sleep(200);
            System.out.println("supplyIDs=="+Thread.currentThread().getName());
            return Arrays.asList(1L,2L,3L);
        };
        Function<List<Long>, CompletableFuture<List<User>>> fetchUsers = ids -> {
            System.out.println("fetchUsers=="+Thread.currentThread().getName());
            sleep(300);
            Supplier<List<User>> userSuplier = () -> {
                System.out.println("userSuplier=="+Thread.currentThread().getName());
                return ids.stream().map(User::new).collect(Collectors.toList());
            };
            return CompletableFuture.supplyAsync(userSuplier,executorService2);
        };
        Consumer<List<User>> displayer = users -> users.forEach(System.out::println);
        CompletableFuture<List<Long>> completableFuture = CompletableFuture.supplyAsync(supplyIDs,executorService);
        completableFuture.thenComposeAsync(fetchUsers,executorService2).thenAcceptAsync(displayer,executorService);
        sleep(10000);
        executorService.shutdown();
    }
    private static void sleep(int time){
        try{
            Thread.sleep(time);
        }catch (Exception e){
        }
    }
}

thenAcceptBoth可以同时完成两个不同的CompletableFuture

ExecutorService executorService = Executors.newSingleThreadExecutor();
ExecutorService executorService2 = Executors.newSingleThreadExecutor();
Supplier<List<Long>> supplyIDs = () -> {
    sleep(200);
    System.out.println("supplyIDs=="+Thread.currentThread().getName());
    return Arrays.asList(1L,2L,3L);
};
Function<List<Long>, CompletableFuture<List<User>>> fetchUsers = ids -> {
    System.out.println("fetchUsers=="+Thread.currentThread().getName());
    sleep(300);
    Supplier<List<User>> userSuplier = () -> {
        System.out.println("userSuplier=="+Thread.currentThread().getName());
        return ids.stream().map(User::new).collect(Collectors.toList());
    };
    return CompletableFuture.supplyAsync(userSuplier,executorService2);
};
Function<List<Long>, CompletableFuture<List<Email>>> fetchEmails = ids -> {
    System.out.println("fetchUsers=="+Thread.currentThread().getName());
    sleep(300);
    Supplier<List<Email>> emailSuplier = () -> {
        System.out.println("userSuplier=="+Thread.currentThread().getName());
        return ids.stream().map(Email::new).collect(Collectors.toList());
    };
    return CompletableFuture.supplyAsync(emailSuplier,executorService2);
};
Consumer<List<User>> displayer = users -> users.forEach(System.out::println);
CompletableFuture<List<Long>> completableFuture = CompletableFuture.supplyAsync(supplyIDs,executorService);
CompletableFuture<List<User>> userComp  = completableFuture.thenComposeAsync(fetchUsers,executorService2);
CompletableFuture<List<Email>> emailComp  = completableFuture.thenComposeAsync(fetchEmails,executorService2);
userComp.thenAcceptBoth(emailComp,
        (user,email) ->{
            System.out.println(user.size()+""+email.size());
        });
sleep(1000);
executorService.shutdown();
executorService2.shutdown();

acceptEither执行完成任何一个后再执行其他操作

public static void main(String[] args) throws Exception{
    Supplier<List<Long>> supplyIDs = () -> {
        sleep(200);
        return Arrays.asList(1L,2L,3L);
    };
    Function<List<Long>, CompletableFuture<List<User>>> fetchUsers1 = ids -> {
        sleep(300);
        Supplier<List<User>> userSuplier = () -> {
            return ids.stream().map(User::new).collect(Collectors.toList());
        };
        return CompletableFuture.supplyAsync(userSuplier);
    };
    Function<List<Long>, CompletableFuture<List<User>>> fetchUsers2 = ids -> {
        sleep(3000);
        Supplier<List<User>> userSuplier = () -> {
            return ids.stream().map(User::new).collect(Collectors.toList());
        };
        return CompletableFuture.supplyAsync(userSuplier);
    };
    Consumer<List<User>> displayer = users -> users.forEach(System.out::println);
    CompletableFuture<List<Long>> completableFuture = CompletableFuture.supplyAsync(supplyIDs);
    CompletableFuture<List<User>> user1  = completableFuture.thenComposeAsync(fetchUsers1);
    CompletableFuture<List<User>> user2  = completableFuture.thenComposeAsync(fetchUsers2);
    user1.thenRun(()-> System.out.println("User1 done"));
    user2.thenRun(()-> System.out.println("User2 done"));
    user1.acceptEither(user2, displayer);
    sleep(100000);
}

CompletableFuture异常处理

exceptionally()
whenComplete()
handle()

CompletableFuture<List<User>> user3 = CompletableFuture.supplyAsync(supplyIDs)
        .thenApply(list -> readUser(list))
        .exceptionally(excetion -> new ArrayList<User>());
user3.thenRun(()-> System.out.println("user3 is run"));
//whenComplete
CompletableFuture<List<User>> user3 = CompletableFuture.supplyAsync(supplyIDs)
        .thenApply(list -> readUser(list))
        .whenComplete(
                (list, exception) -> {
                    if (list !=null)
                        System.out.println("run successfuly");
                    else
                        System.out.println("run exception");
                }
        );
//handle可以吞下异常,返回新的异常或者返回默认结果
CompletableFuture<List<User>> user3 = CompletableFuture.supplyAsync(supplyIDs)
        .thenApply(list -> readUser(list))
        .handle(
                (list, exception) -> {
                    if (list !=null)
                        return list;
                    else
                        return new ArrayList<User>();
                }
        );
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程序员一枚,也爱读书,也爱理财,还喜欢把学到的读到的总结出来写点东西,写的不难,希望大家喜欢。

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