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。