Java exec() of UNIX shell script

Question

I have a java application that uses:
p = Runtime.getRuntime().exec( cmdLine);
to execute a UNIX shell script, for example:
#!/bin/ksh
. /export/pc112477/freeware/work1/wsEnv
export PATH=/opt/sfw/bin:/usr/ccs/bin:/usr/bin:/usr/ucb:$PATH
cd /export/pc112477/freeware/work1/usr/src/pkgdefs/SFWnmap
/usr/ccs/bin/make -e ROOT=$ROOT install
RESULT=$?
if [ $RESULT = 0 ]
then
echo "Package source"
cd /export/pc112477/freeware/work1/usr/src/pkgdefs/SFWnmapS
/usr/ccs/bin/make -e ROOT=$ROOT install
RESULT=$?
fi
exit $RESULT
Some times the running of the script locks up depending on how much work the script has to, eg. if the make calls pkgmk for a small package it runs okay but if its a large package it locks up in pkgmk.
The script itself works okay if run directly
Does anyone have any ideas on why this locks up and how I could stop it doing it.
Thanks

Answer 1

For anyone who stumbles across this and needs an answer:
To empty the standard error and output, you need to use getErrorStream() and getInputStream() on the Process object created when you execed your command. Create new InputStreamReaders with the streams from the process, then wrap those with BufferedReaders and read each line with a while loop. This is the basic thing you need to do:
try{
Process proc = Runtime.getRuntime().exec(command);
InputStreamReader isr = new InputStreamReader(proc.getErrorStream());
BufferedReader errReader = new BufferedReader(isr);
String line;
while((line = errReader.readLine()) != null)
<do something with each line of error>
} //end try
catch(<errors>) {
<do something with errors>
} //end catch
What you really should do is put the stream handling in a separate class that extends Thread, create an instance for the error and output streams, and start each one. There is a class called StreamGobbler that does this sort of thing. Look at http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html to find out more about it and read a detailed explanation of different problems with exec().