java中的简单超时

Simple timeout in java

提问by Yuvraj

Can anyone guide me on how I can use a simple timeout in java? Basically in my project I'm executing a statement br.readLine(), which is reading a response from a modem. But sometimes the modem isn't responding. For that purpose I want to add a timeout. I'm looking for a code like:

谁能指导我如何在 Java 中使用简单的超时？基本上在我的项目中，我正在执行一个 statement br.readLine()，它正在读取来自调制解调器的响应。但有时调制解调器没有响应。为此，我想添加一个超时。我正在寻找这样的代码：

try {
    String s= br.readLine();
} catch(TimeoutException e) {
    System.out.println("Time out has occurred");
}

回答by Trein

What you are looking for can be found here. It may exist a more elegant way to accomplish that, but one possible approach is

可以在此处找到您要查找的内容。可能存在一种更优雅的方法来实现这一点，但一种可能的方法是

Option 1 (preferred):

选项 1（首选）：

final Duration timeout = Duration.ofSeconds(30);
ExecutorService executor = Executors.newSingleThreadExecutor();

final Future<String> handler = executor.submit(new Callable() {
    @Override
    public String call() throws Exception {
        return requestDataFromModem();
    }
});

try {
    handler.get(timeout.toMillis(), TimeUnit.MILLISECONDS);
} catch (TimeoutException e) {
    handler.cancel(true);
}

executor.shutdownNow();

Option 2:

选项 2：

final Duration timeout = Duration.ofSeconds(30);
ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

final Future<String> handler = executor.submit(new Callable() {
    @Override
    public String call() throws Exception {
        return requestDataFromModem();
    }
});

executor.schedule(new Runnable() {
    @Override
    public void run(){
        handler.cancel(true);
    }      
}, timeout.toMillis(), TimeUnit.MILLISECONDS);

executor.shutdownNow();

Those are only a draft so that you can get the main idea.

这些只是草稿，以便您可以了解主要想法。

回答by Martin

Use this line of code:

使用这行代码：

Thread.sleep(1000);

It will sleep for 1 second.

它将休眠 1 秒钟。

回答by user1332994

The example 1 will not compile. This version of it compiles and runs. It uses lambda features to abbreviate it.

示例 1 将无法编译。它的这个版本编译并运行。它使用 lambda 特性来缩写它。

/*
 * [RollYourOwnTimeouts.java]
 *
 * Summary: How to roll your own timeouts.
 *
 * Copyright: (c) 2016 Roedy Green, Canadian Mind Products, http://mindprod.com
 *
 * Licence: This software may be copied and used freely for any purpose but military.
 *          http://mindprod.com/contact/nonmil.html
 *
 * Requires: JDK 1.8+
 *
 * Created with: JetBrains IntelliJ IDEA IDE http://www.jetbrains.com/idea/
 *
 * Version History:
 *  1.0 2016-06-28 initial version
 */
package com.mindprod.example;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import static java.lang.System.*;

/**
 * How to roll your own timeouts.
 * Based on code at http://stackoverflow.com/questions/19456313/simple-timeout-in-java
 *
 * @author Roedy Green, Canadian Mind Products
 * @version 1.0 2016-06-28 initial version
 * @since 2016-06-28
 */

public class RollYourOwnTimeout
    {

    private static final long MILLIS_TO_WAIT = 10 * 1000L;

    public static void main( final String[] args )
        {
        final ExecutorService executor = Executors.newSingleThreadExecutor();

        // schedule the work
        final Future<String> future = executor.submit( RollYourOwnTimeout::requestDataFromWebsite );

        try
            {
            // where we wait for task to complete
            final String result = future.get( MILLIS_TO_WAIT, TimeUnit.MILLISECONDS );
            out.println( "result: " + result );
            }

        catch ( TimeoutException e )
            {
            err.println( "task timed out" );
            future.cancel( true /* mayInterruptIfRunning */ );
            }

        catch ( InterruptedException e )
            {
            err.println( "task interrupted" );
            }

        catch ( ExecutionException e )
            {
            err.println( "task aborted" );
            }

        executor.shutdownNow();

        }
/**
 * dummy method to read some data from a website
 */
private static String requestDataFromWebsite()
    {
    try
        {
        // force timeout to expire
        Thread.sleep( 14_000L );
        }
    catch ( InterruptedException e )
        {
        }
    return "dummy";
    }

}