java多进程中waitFor()的作用

在项目中遇到这样的情况：在项目中引入子进程，发现子进程并没有成功运行完成，看不到输出信息不知道怎么回事。度娘后发现问题在于子进程的标准输出流占满缓冲池导致进程阻塞，需要另开两个进程在waitFor()之前将子进程的标准输出流和错误流从缓冲池中取走。具体原因见http://blog.csdn.net/jimzhai/article/details/7864806

从缓冲池读取子进程标准输出和错误流的线程：

public class StreamGobbler extends Thread {

    InputStream is;
    String type;

    public StreamGobbler(InputStream is, String type) {
        this.is = is;
        this.type = type;
    }

    public void run() {
        try {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line = null;
            while ((line = br.readLine()) != null) {
                if (type.equals("Error")) {
                    System.out.println("Error    :" + line);
                } else {
                    System.out.println("Debug:" + line);
                }
            }
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
    }
}

对子进程p，创建两个读取子进程缓冲区输出流和错误流的线程，并在waitFor()之前读取出来：

public class ClearOutputAndErrorStream {

    public void clearProcessOutputstream(Process p) throws InterruptedException {
        //p.getInputStream() : Returns the input stream connected to the normal output of the subprocess.
        //The stream obtains data piped from the standard output of the process represented by this Process object.
        StreamGobbler outstream = new StreamGobbler(p.getInputStream(), "Output");
        //p.getErrorStream() : Returns the input stream connected to the error output of the subprocess.
        //The stream obtains data piped from the error output of the process represented by this Process object.
        StreamGobbler errorstream = new StreamGobbler(p.getErrorStream(), "Error");
        outstream.start();
        errorstream.start();
        p.waitFor();
    }
}

Process p = Runtime.getRuntime().exec("java -cp ./lib/*;./bin test.TestDemo");
coaes.clearProcessOutputstream(p);