A better jstack

2 minutes read
Java • JVM

Jstack is the command line tool get thread dumps out of JVM processes. Let’s improve it a bit so that we can call jstack <classFQN>.

Presentation

jstack is a CLI tool that connects to a JVM identified by its PID and creates a thread dump. It is very handy. However I don’t like to type PIDs. Wouldn’t it be much better if it could identify a JVM based on part of the main class name?

Jstack by name

My initial solution was to type something along the lines of jstack $(jps | grep MyClass | cut -d ' ' -f 1). That’s good but not great. Instead, I came up with that simple script that I added before $JAVA_HOME/bin in my PATH.

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#!/bin/bash

if [[ $1 =~ ^[a-zA-Z]+$ ]]
then
    echo "# Trying to get thread dump of Java process with name '$1'"
    pid=`jps | grep "$1" | cut -d ' ' -f 1`
    shift
    echo $JAVA_HOME/bin/jstack $pid $@
    $JAVA_HOME/bin/jstack $pid $@
else
    echo "# Executing regular jstack"
    $JAVA_HOME/bin/jstack $@
fi

That’s it. Now I can use jstack MyClass. It is a simple hack but I have found it very useful over the last months. Even better, it does not prevent using regular jstack command-line parameters.

A word about thread dumps

Reading thread dumps can be cumbersome. To filter them or query them, mjprof can be useful. It is a thread-dump parser written by Haim Yadid (lifey on Github). I find it a bit difficult to use, but once you get your first filters working, it is quite useful.

If you have any question/comment, feel free to send me a tweet at @pingtimeout. And if you enjoyed this article and want to support my work, you can always buy me a coffee ☕️.