Java基于Runtime调用外部程序出现阻塞的解决方法

本文实例讲述了Java基于Runtime调用外部程序出现阻塞的解决方法， 是一个很实用的技巧。分享给大家供大家参考。具体分析如下：

有时候在java代码中会调用一些外部程序，比如SwfTools来转换swf、ffmpeg来转换视频等。如果你的代码这样写：Runtime.getRuntime().exec(command)，会发现程序一下就执行完毕，而在命令行里要执行一会，是因为java没有等待外部程序的执行完毕，此时就需要使用阻塞，来等待外部程序执行结果：

InputStream stderr = process.getInputStream();
InputStreamReader isr = new InputStreamReader(stderr, "GBK");
BufferedReader br = new BufferedReader(isr);
String line = null;
while ((line = br.readLine()) != null)
  System.out.println(line);
int exitValue = process.waitFor();

对于一般的外部程序使用上面的阻塞代码就可以，至少pdf2swf.exe是没有问题的。

但是紧接着又发现对于ffmpeg来说，以上代码会让程序卡住不动，需要使用另一种方式，封装成了一个方法，如下：

@SuppressWarnings("static-access")
public static int doWaitFor(Process process) {
  InputStream in = null;
  InputStream err = null;
  int exitValue = -1; // returned to caller when p is finished
  try {
    in = process.getInputStream();
    err = process.getErrorStream();
    boolean finished = false; // Set to true when p is finished
    while (!finished) {
      try {
        while (in.available() > 0) {
          // Print the output of our system call
          Character c = new Character((char) in.read());
          System.out.print(c);
        }
        while (err.available() > 0) {
          // Print the output of our system call
          Character c = new Character((char) err.read());
          System.out.print(c);
        }
        // Ask the process for its exitValue. If the process
        // is not finished, an IllegalThreadStateException
        // is thrown. If it is finished, we fall through and
        // the variable finished is set to true.
        exitValue = process.exitValue();
        finished = true;
      } catch (IllegalThreadStateException e) {
        // Process is not finished yet;
        // Sleep a little to save on CPU cycles
        Thread.currentThread().sleep(500);
      }
    }
  } catch (Exception e) {
    e.printStackTrace();
  } finally {
    try {
      if (in != null) {
        in.close();
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
    if (err != null) {
      try {
        err.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
  return exitValue;
}

希望本文所述对大家Java程序设计的学习有所帮助。