java.lang.Process清空缓冲区问题

**
 * 阻塞（自动清理输出缓冲区）
 * @param p
 * @return
 * @throws IOException
 */
public static String waitFor(Process p) throws IOException{
    String str = null;
    InputStream is1 = p.getInputStream(); 
    InputStream is2 = p.getErrorStream();  
    BufferedReader br = new BufferedReader(new InputStreamReader(is1)); 
    while (true) {
        boolean exitFlag = true; 
        if (is1.available() > 0) {
            Character c = new Character( (char) is1.read());
            System.out.print(c); 
            exitFlag = false;
        }
        if (is2.available() > 0) {
            Character c = new Character( (char) is2.read());
            System.out.print(c); 
            exitFlag = false;
        }
        if(exitFlag){
            try {
                Thread.sleep(100); // Nothing to do, sleep a while...
                p.exitValue(); // ThrowIllegalThreadStateException, if the subprocess represented by this Process object has not yet terminated.
                break;
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            } catch (IllegalThreadStateException ex) {
                // Process still alive
            }
        }
    }
    br.close();
    is1.close();
    p.destroy();
    return str;
}