97 Things Every Java Programmer Should Know

Chapter 79. There Are Great Tools in Your bin/ Directory

Rod Hilton

Every Java developer is familiar with javac for compiling, java for running, and probably jar for packaging Java applications. However, many other useful tools come installed with the JDK. They are already on your computer in your JDK’s bin/ directory and are invokable from your PATH. It’s good to get acquainted with some of these tools so you know what’s at your disposal:

jps

If you’ve ever found yourself running ps aux | grep java to find the running JVMs, you probably just want to run jps. This dedicated tool lists all the running JVMs, but instead of showing you a lengthy command with CLASSPATHs and arguments, jps simply lists the process ID and the application’s main class name, making it far easier to figure out which process is which. jps -l will list the fully qualified main class name, jps -m will show the arguments passed to the main method, and jps -v will show all the arguments passed to the JVM itself.

javap

The JDK comes with a Java class file disassembler. Run javap <class file> to see that class file’s fields and methods, which can often be very enlightening for understanding what code written in JVM-based languages such as Scala, Clojure, or Groovy is turned into under the hood. Run javap -c <class file> to see the complete bytecode of those methods.

jmap

Running jmap -heap <process id> will ...