Process is a fiddly class to work with at the best of times. I can't say I've ever come across the exec of a Process not returning, when I've used it it will return immediatly from the exec() and you have to use Process.waitFor() if you want to wait for the program to terminate.
A common problem doing this is that the standard output stream from the process fills up and blocks the waitFor() from ever returning as the process will not terminate until it's standard output is consumed. To do this I fork a separate thread just before calling waitFor() to read the standard output and error streams. This fixes the problem for me. Another not-so amusing problem is that if you don't explicitly close the input/output/error streams that Process returns they will get left hanging around and eventually you'll blow the OS limit on open file handles, so remember to close them. My code looks something like the following (I use a ProcessBuilder), needs a bit of work with try/finally to close the streams in all cases. If you need the output the external program generates then have the StreamGobbler store the output in a StringBuilder or something. You should also read this article which I where I got some of my info from originally. http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html HTH // create and start the process - redirect stderr to stdout ProcessBuilder processBuilder = new ProcessBuilder( commands ); processBuilder.redirectErrorStream( true ); // this call does not block Process process = processBuilder.start(); // create the gobbler to read the stdout/stderr from the process StreamGobbler outputGobbler = new StreamGobbler( process.getInputStream() ); // kick off the separate stream gobbler thread outputGobbler.start(); // wait for the process to terminate - blocks int exitCode = process.waitFor(); // wait for the gobbler to terminate - blocks outputGobbler.join(); // close all the process IO streams try { process.getInputStream().close(); } catch ( IOException e ) { // ignore error } try { process.getOutputStream().close(); } catch ( IOException e ) { // ignore error } try { process.getErrorStream().close(); } catch ( IOException e ) { // ignore error } return exitCode; -----Original Message----- From: Zack Grafton [mailto:[EMAIL PROTECTED] Sent: 15 January 2007 05:39 To: Tomcat Users List Subject: Re: Runtime.getRuntime.exec() problem hui zhang wrote: > Zack Grafton wrote: >> hui zhang wrote: >>> Zack Grafton wrote: >>>> hui zhang wrote: >>>>> Hi Everybody, >>>>> >>>>> Now I am trying to launch an external application, for example, >>>>> "top" ,in my web application, and killing it by PID after a while. >>>>> But when I execute Runtime.getRuntime.exec("top") in my JSP page >>>>> or Servlet, Tomcat is stuck in that page and do not display >>>>> anything because it can not stop running until that "commnad" is >>>>> terminated, which means it waiting for the response from >>>>> Runtime.getRuntime.exec("top"). It seems that it will run forever. >>>>> Is there any solution to solve this problem? I mean that JSP page >>>>> can execute the following code no matter if it finish the process >>>>> is done. >>>>> >>>>> BTW, I do not use System.exit() in my program. It may cause >>>>> Security Manager problem. >>>>> Thanks and best regards, >>>>> >>>>> Hui >>>>> >>>>> ------------------------------------------------------------------ >>>>> --- To start a new topic, e-mail: users@tomcat.apache.org To >>>>> unsubscribe, e-mail: [EMAIL PROTECTED] >>>>> For additional commands, e-mail: [EMAIL PROTECTED] >>>>> >>>>> >>>> Hey, >>>> >>>> I'm new to the list and all, but you might want to try executing >>>> "top" in batch mode. The command line option is -b on my gentoo >>>> linux box. Also, be careful of executing commands from applets and >>>> such. Another thing might be user permissions as well. You could >>>> try executing the command and redirecting the output to a file and >>>> parsing the file instead. >>>> >>>> Zack Grafton >>>> >>>> ------------------------------------------------------------------- >>>> -- To start a new topic, e-mail: users@tomcat.apache.org To >>>> unsubscribe, e-mail: [EMAIL PROTECTED] >>>> For additional commands, e-mail: [EMAIL PROTECTED] >>> Hi, >>> >>> "TOP" is only an example in this case. Actually I am running some >>> program which can not stop running until terminating it by "Control >>> + C". In this case, Tomcat can not run the following code if the >>> external application does not stop. I need a solution to make my >>> webapp running in this case. Thank you. >>> >>> Regards, >>> >>> Hui >>> >>> >>> >>> >>> -------------------------------------------------------------------- >>> - To start a new topic, e-mail: users@tomcat.apache.org To >>> unsubscribe, e-mail: [EMAIL PROTECTED] >>> For additional commands, e-mail: [EMAIL PROTECTED] >>> >> Hui, >> >> You could check out the javadoc for the java.lang.Process class. You >> would need to do something like: >> >> Process process = Runtime.getRuntime().exec("command"); >> >> process.getInputStream(); >> process.getOutputStream(); >> >> Just remember to wrap the streams appropriately and you should be >> able to read the stdin and stdout of the program. That should allow >> you to send the <control>+C signal to the program. >> >> >> Zack Grafton >> >> >> --------------------------------------------------------------------- >> To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, >> e-mail: [EMAIL PROTECTED] >> For additional commands, e-mail: [EMAIL PROTECTED] > Hi, > > I can get the InputStream from process object. How can I send > Control+C to the console next? I can not send another command to > console until this command is terminated. > > BTW, what is the string format of "Control + C"? > > Thanks! > > Regards, > > Hui > > --------------------------------------------------------------------- > To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, > e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > Hui, You might also want to look at the destroy method of the Process class. Zack --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] This e-mail is bound by the terms and conditions described at http://www.subexazure.com/mail-disclaimer.html --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
