Runtime.exec does not work for commands with lengthy outputs

Question

I need to use Runtime.exec to run some custom commands on a Unix box. I have been doing this for quite some time now and had begun to feel comfortable when recently I started facing a problem. The thing is, whenever there is a command which prints a lot of data on to the console, the program is not able to exit from the waitFor method. Is there some thing that can be done about this?
Following is a part of the code I use:
Runtime rt = Runtime.getRuntime();
Process p = rt.exec (command);
System.out.println ("Got the process");
int exitValue = p.waitFor();
System.out.println ("Exit value: " + exitValue);When the output of the "command" is lengthy, it hangs after printing "Got the process".
PS: By lengthy output, I mean that the command results in printing lines to the console which might be more than 100 in number. Say, something like what "ls -R /" would do in Unix / Linux.

Answer 1

From java.lang.Process API doc:
The Runtime.exec methods may not work well for special processes on certain native platforms, such as native windowing processes, daemon processes, Win16/DOS processes on Microsoft Windows, or shell scripts. The created subprocess does not have its own terminal or console. All its standard io (i.e. stdin, stdout, stderr) operations will be redirected to the parent process through three streams (Process.getOutputStream(), Process.getInputStream(), Process.getErrorStream()). The parent process uses these streams to feed input to and get output from the subprocess. Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.
So you need to consume the process' output. Check the StreamGobbler example from this article.
Hope it helps.