Callable Future FutureTask

你的名字 2023-06-08 06:08 17阅读 0赞

并发包下边的三个可以异步计算的工具类  
**Callable**  
实现线程的一种方式，带有返回值  
**Future**  
带有返回值的的接口  
**FutureTask**  
具体的实现类

--------------------

**1.Callable和Runnable的区别**

**Callable**

public interface Callable<V> {
    　　V call() throws Exception;
    }

**Runnable**

interface Runnable {
    　　public abstract void run();
    }

很明显能看到区别：  
1.Callable能接受一个泛型，然后在call方法中返回一个这个类型的值。而Runnable的run方法没有返回值  
2.Callable的call方法可以抛出异常，而Runnable的run方法不会抛出异常。

**2.Future**  
返回值Future也是一个接口，通过他可以获得任务执行的返回值。

public interface Future<V> {
    　　boolean cancel(boolean var1);
    
    　　boolean isCancelled();
    
    　　boolean isDone();
    
    　　V get() throws InterruptedException, ExecutionException;
    
    　　V get(long var1, TimeUnit var3) throws InterruptedException, ExecutionException, TimeoutException;
    }

**Callable和Future的实践**

package coding.multiThread;
    
    import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.concurrent.*;
    
    public class Main {
    
        public static void main(String[] args) throws InterruptedException, ExecutionException {
            //固定大小线程池使用
            ExecutorService executor = Executors.newFixedThreadPool(2);
            //创建一个Callable，3秒后返回String类型
            Callable myCallable = new Callable() {
    
                @Override
                public String call() throws Exception {
                    Thread.sleep(3000);
                    System.out.println("calld方法执行了");
                    return "我是call方法返回值";
                }
    
            };
            System.out.println("提交任务之前 " + getStringDate());
            Future future = executor.submit(myCallable);
            System.out.println("提交任务之后，获取结果之前 " + getStringDate());
            System.out.println("获取返回值: " + future.get());
            System.out.println("获取到结果之后 " + getStringDate());
            //执行完毕关闭线程池
            executor.shutdown();
        }
        
        public static String getStringDate() {
            Date currentTime = new Date();
            SimpleDateFormat formatter = new SimpleDateFormat("HH:mm:ss");
            String dateString = formatter.format(currentTime);
            return dateString;
        }

**执行结果**

提交任务之前 18:04:58
    提交任务之后，获取结果之前 18:04:58
    calld方法执行了
    获取返回值: 我是call方法返回值
    获取到结果之后 18:05:01

通过上面可以看到get()方法是任务阻塞的，如果有多个任务，阻塞的时间是耗时最多的那个任务的时间。

--------------------

**FutureTask初步Demo,基础知识补充后续补上**

package coding2.review;
    
    import coding.reentrantlock.ThreadPool;
    
    import java.util.ArrayList;
    import java.util.List;
    import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.FutureTask;
    
    /**
     * @Date: 2019/10/16 16:07
     * @Version 1.0
     */
    public class MyTaskDemo implements Callable<Object> {
    
        private String args1;
        private String args2;
        private MyTaskDemo(String args1, String args2) {
            this.args1 = args1;
            this.args2 = args2;
        }
    
        @Override
        public Object call() throws Exception {
    
            StringBuilder result = new StringBuilder("hello");
            for (int i = 0; i < 10; i++) {
                 result.append(i);
            }
            return result;
        }
    
        //多个计算任务 使用线程池实现
        public static void main(String[] args) {
            List<FutureTask<Object>> futureTasks = new ArrayList<>();
            
            for (Integer i = 0; i < 10; i++) {
                MyTaskDemo myTaskDemo = new MyTaskDemo(i.toString(), i.toString());
                futureTasks.add(new FutureTask<>(myTaskDemo));
            }
    
            ExecutorService executorService = Executors.newCachedThreadPool();
    
            for (FutureTask<Object> futureTask : futureTasks) {
                executorService.submit(futureTask);
            }
    
            executorService.shutdown();
    
            for (Integer i = 0; i < 10; i++) {
                try {
                    StringBuilder flag = (StringBuilder) futureTasks.get(i).get();
                    System.out.println(flag);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    
        //单个计算任务 使用Threadsh实现
        /*public static void main(String[] args) {
            MyTaskDemo myTaskDemo = new MyTaskDemo("11","22");
            FutureTask<Object> futureTask = new FutureTask<>(myTaskDemo);
    
            Thread thread = new Thread(futureTask);
    
            thread.start();
            try {
                boolean result = (boolean) futureTask.get();
                System.out.println(result);
            }catch (Exception e){
                e.printStackTrace();
            }
        }*/
    }

执行结果

"C:\Program Files\Java\jdk1.8.0_161\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.1\lib\idea_rt.jar=65450:C:\Program Files\JetBrains\IntelliJ IDEA 2019.1.1\bin" -Dfile.encoding=GBK -classpath "C:\Program Files\Java\jdk1.8.0_161\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\rt.jar;E:\Person\CodingOne\out\production\CodingOne" coding2.review.MyTaskDemo
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    hello0123456789
    
    Process finished with exit code 0