无法从Java进程读取InputStream(Runtime.getRuntime().exec()或ProcessBuilder)

Question

我正在尝试使用Java从外部启动一个进程,并且无法从其InputStream中读取任何内容.

如果我用"ls","ps"或"kill"等命令启动进程,一切正常.我可以在InputStream或Process的ErrorStream上启动该过程并获取信息.

如果我尝试使用像"ftp"或"telnet"这样的命令,则在尝试读取时,InputStream和ErrorStream都会阻塞我的程序.任何时候都不会通过这些流传递任何信息.

谁能解释一下这种行为？这些命令是不可能的,还是我的实现有问题？

     String processName = _configuration.getProgramCommand().getCommand();
   ProcessBuilder procBuilder = new ProcessBuilder(processName);   

   System.out.println("Starting process "+processName);   
   _proc = Runtime.getRuntime().exec(processName);// procBuilder.start();            

   if(!procBuilder.redirectErrorStream()) {    
    _errorWorker = new ProcessErrorWorker(_proc);
    _errorWorker.start();   
   }

   String proc_start_answer = _configuration.getNextCommand().getCommand();
   System.out.println("Waiting for process answer '"+proc_start_answer+"'");
   BufferedReader input = new BufferedReader(new InputStreamReader(_proc.getInputStream()));      

   String answer = "";  

   try {         
    System.out.println("inputstream ready: "+input.ready());
    answer+=input.readLine(); 
    System.out.println("process answer:  "+answer);
    input.close();        

   } catch(Exception e) {
    System.out.print(e.getMessage());     
   } 

Answer 1

我意识到这个问题已经过时了,但我只是遇到了同样的问题.为了解决这个问题,我使用了这段代码.

 List<String> commandAndParameters = ...;
 File dir = ...; // CWD for process

 ProcessBuilder builder = new ProcessBuilder();
 builder.redirectErrorStream(true); // This is the important part
 builder.command(commandAndParameters);
 builder.directory(dir);

 Process process = builder.start();

 InputStream is = process.getInputStream();

似乎该过程期望您也从错误流中读取.解决此问题的最佳方法是将输入和错误流合并在一起.

更新

我没有看到你试图从错误流中读取.它可能只是你需要手动合并它们redirectErrorStream(true)

Answer 2

你需要在一个线程中完成这项工作.例如,记录标准输出:

Process process = Runtime.getRuntime().exec(command);
LogStreamReader lsr = new LogStreamReader(process.getInputStream());
Thread thread = new Thread(lsr, "LogStreamReader");
thread.start();


public class LogStreamReader implements Runnable {

    private BufferedReader reader;

    public LogStreamReader(InputStream is) {
        this.reader = new BufferedReader(new InputStreamReader(is));
    }

    public void run() {
        try {
            String line = reader.readLine();
            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

然后你需要第二个线程进行输入处理.你可能想像stdout一样处理stderr.

Answer 3

我有一个C程序打印到stdout这个问题...

redirectErrorStream(true)使用fflush(stdout)C代码的解决方案为我做了诀窍.