process.waitfor()超时配置

一、概述

在编写Java程序时，有时候我们需要调用外部的exe，这时可以通过Runtime的exec()方法，

该命令使用比较简单，但是无法对执行做细节的控制。
通过使用ProcessBuilder构建Process可以进行细节的控制，但是默认process是阻塞的。

public abstract int waitFor() throws InterruptedException;public boolean waitFor(long timeout, TimeUnit unit)

不要被boolean waitFor(long timeout, TimeUnit unit)误解，他也是阻塞的，阻塞到process进程执行完，才进行是否超时的判断。
并不是说当超时时他会自动结束。

通过process.destroy()方法可以从外部终止该process。

但是waitFor时主进程阻塞是阻塞的。我们需要在外部开启一条线程，把waitFor这个阻塞操作放到这条线程，同时主线程进行计时，
如果到了限定时间还未执行完毕，那么就调用process.destroy() kill掉该进程。

二、具体代码思路

首先是一个ProcessWorker类，也就是之前说的用来放置waitFor，阻塞的线程，它继承Thread，实现了run方法。
它记录以下几个状态，通过volatile来确保外部线程可见：

private volatile int exitCode = -99;private volatile boolean completed = false;private volatile String output = "";

在run方法中，通过try with resource来读取该进程的输出，

并且设置waitFor，当等待结束时，设置completed为true。

try (InputStreamReader reader = new InputStreamReader(process.getInputStream(), DEFAULT_ENCODING)) {StringBuilder log = new StringBuilder();char[] buffer = new char[BUFFER_SIZE];int length;while ((length = reader.read(buffer)) != -1) {log.append(buffer, 0, length);}output = log.toString();exitCode = process.waitFor();completed = true;} catch (InterruptedException | IOException e) {Thread.currentThread().interrupt();}

三、完整代码如下

package cn.hengyumo.utils;import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;/*** SystemUtil* 系统工具类** @version 1.0* @since 2020/2/4*/
public class SystemUtil {private final static int BUFFER_SIZE = 1024;private final static String DEFAULT_ENCODING = "gbk";private static class ProcessWorker extends Thread {private final Process process;private volatile int exitCode = -99;private volatile boolean completed = false;private volatile String output = "";private ProcessWorker(Process process) {this.process = process;}@Overridepublic void run() {try (InputStreamReader reader = new InputStreamReader(process.getInputStream(), DEFAULT_ENCODING)) {StringBuilder log = new StringBuilder();char[] buffer = new char[BUFFER_SIZE];int length;while ((length = reader.read(buffer)) != -1) {log.append(buffer, 0, length);}output = log.toString();exitCode = process.waitFor();completed = true;} catch (InterruptedException | IOException e) {Thread.currentThread().interrupt();}}public int getExitCode() {return exitCode;}public String getOutput() {return output;}public boolean isCompleted() {return completed;}}public static int execCmd(String command, StringBuilder log, int timeoutSecond) throws IOException, TimeoutException {ProcessBuilder processBuilder = new ProcessBuilder(command.split(" "));// 合并错误输出流processBuilder.redirectErrorStream(true);Process process = processBuilder.start();ProcessWorker processWorker = new ProcessWorker(process);int exitCode = processWorker.getExitCode();processWorker.start();try {processWorker.join(timeoutSecond * 1000);if (processWorker.isCompleted()) {log.append(processWorker.getOutput());exitCode = processWorker.getExitCode();} else {process.destroy();processWorker.interrupt();throw new TimeoutException("进程执行时间超时");}} catch (InterruptedException e) {processWorker.interrupt();}return exitCode;}
}