Need to move on after java error when Python script uses subprocess to run a java program

Question

In a python2.7 script, I'm using subprocess.call to run a java program like this:

java_command = "java -jar /path/to/java_program.jar %s %s >> %s" % (infile, outfile, logfile)
subprocess.call(java_command, shell=True)
...
#Do other stuff unrelated to this output

Most of the time, this works fine, but in some cases the java program errs:

Exception in thread "main" java.lang.NullPointerException
    at MyProgram.MainWindow.setProcessing(MainWindow.java:288)

The problem is that my python script is then stalled on the subprocess.call() line and can't do the "other stuff".

Is there a way I can edit either the java_command I'm using or the way I'm using subprocess to continue the python script even when the java program hangs?

_{Note that I can't modify the java program's code.}

Prune · Accepted Answer · 2016-11-10 19:06:40Z

1

I think you want the check_call method from that same package:

try:
    status = subprocess.check_call(java_command, shell=True)
except CalledProcessError as e:
    # The exception object contains the return code and
    # other failure information.
    ... react to the failure and recover

answered Nov 10, 2016 at 19:06

Prune

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3 Comments

Dan Russell Over a year ago

Just tried this, to no avail. I think the java program is not fully exiting somehow after its error. When I run the same java command outside the script, from the command line, it gives the same answer but still doesn't return the command-line prompt until I Ctrl-C.

Dan Russell Over a year ago

Seems like, based on this, that the exception probably doesn't terminate the JVM, which means that I may be stuck here.

Prune Over a year ago

I see what you mean. You're right: the Java program needs a particular flow handling to terminate on the exception. You may want to spawn the process and continue, checking its status occasionally?

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