Bash ignore exit from Java app

Question

I have a simple BASH script that wraps a java program with the intention of restarting it if that application crashes:

STOP=0
while [ "$STOP" -eq 0 ]
do
        echo "Starting"
        exec java com.site.app.Worker
        echo "Crashed"
        sleep 3
done

However if the Java process exits it also quits the bash script so the process is never started again.

E.g. (pointing at a fake class):

$ ./RestartApp.ksh
Starting
Exception in thread "main" java.lang.NoClassDefFoundError: com/site/app/Worker
Caused by: java.lang.ClassNotFoundException: com.site.app.Worker
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: com.site.app.Worker.  Program will exit.
$

Is there a way I can catch the errors (but still display them) to allow the script to continue running?

Where is bash file? From where you compiled your class?

Sachin
– Sachin

2013-03-18 12:03:05 +00:00
Commented Mar 18, 2013 at 12:03 — Sachin
– Sachin, Commented Mar 18, 2013 at 12:03

Mat · Accepted Answer · 2013-03-18 12:02:25Z

5

Remove the exec. That's completely replacing the current process (your shell) with the Java VM.

Just remove that and it should work fine.

answered Mar 18, 2013 at 12:02

Mat

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Comments

Raúl Salinas-Monteagudo · Accepted Answer · 2013-03-24 19:51:21Z

0

As Mat said, what exec does is to replace the current shell process by the Java process. It it fails, there is no-one waiting for it to relaunch it. exec can be a very useful and professional tool to use, but it is rather advanced.

An example of a right use for it would be a script that sets variables or priorities in the current shell, and then exec's the process you are wrapping.

The variable "STOP" does not seem to be used. I would simply go for:

while ! java com.site.app.Worker
do
    echo Failed: Sleeping and restarting >&2
    sleep 3 
done

answered Mar 24, 2013 at 19:51

Raúl Salinas-Monteagudo

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