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：

public 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。

 

 

 

 

 

 

 

 

 

以上文章从网上转载，当已经找不到出处，在实际过程中，会遇到乱码的情况

    public int doWaitFor(Process process, JobInfo jobInfo) {
      InputStream in = null;
      InputStream err = null;
      int exitValue = -1; // returned to caller when p is finished

		ByteBuffer byteBuffer = ByteBuffer.allocate(512);
      try {
        in = process.getInputStream();
        err = process.getErrorStream();
        boolean finished = false; // Set to true when p is finished
        while (!finished) {
          try {
            while (in.available() > 0) {
            	if(byteBuffer.position() == byteBuffer.capacity()) {
            		ByteBuffer _byteBuffer = ByteBuffer.allocate(byteBuffer.capacity() + 512);
            		_byteBuffer.put(byteBuffer.array(), 0, byteBuffer.capacity());
            		byteBuffer = _byteBuffer;
            	}
              // Print the output of our system call
                byte _byte = (byte) in.read();
                byteBuffer.put(_byte);
              Character c = new Character((char) _byte);
//              logMessage.append(c);
              System.out.print(c);
            }
            while (err.available() > 0) {
            	if(byteBuffer.position() == byteBuffer.capacity()) {
            		ByteBuffer _byteBuffer = ByteBuffer.allocate(byteBuffer.capacity() + 512);
            		_byteBuffer.put(byteBuffer.array(), 0, byteBuffer.capacity());
            		byteBuffer = _byteBuffer;
            	}
              // Print the output of our system call
                byte _byte = (byte) err.read();
                byteBuffer.put(_byte);
                Character c = new Character((char) _byte);
//              logMessage.append(c);
              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();
          }
        }
      }
		try {
		      String logMessage = new String(byteBuffer.array(), 0, byteBuffer.position(), "gbk");
              System.out.print(logMessage);
				jobInfo.setLogMessage(logMessage);
				jobInfo.setExecuteResult(true);
		} catch (UnsupportedEncodingException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
      return exitValue;
    }

 

 

 

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