JDK useful commands and tools

jps - see all the PID's of all Java processes running on the machine

$ jps

11767 Jps

6854 Main

8205 Bootstrap

jstat - See how many classes are loaded by JVM for a Java program

$ jstat -class [pid]

Loaded Bytes Unloaded Bytes Time

10271 12074.2 0 0.0 11.10

jstack - Create thread dump

$ jstack [pid]

Useful usage of jmap

See summary of the heap memory

$ jmap -heap [pid]

Dump a heap file

$ jmap -dump:binary=b,file=[filename.dump] [pid]

Dump a heap file with only live objects

$ jmap -dump:live,binary=b,file=

Number of objects of a specific type

$ jmap -histo [pid] | grep org.example.MyClass

jinfo - To see system properties and VM flags

$ jinfo [pid]

Visual tools

jconsole - Graphical management console to see a number of attributes and graphs of a Java program. Simple usage:

$ jconsole [pid]

jvisualvm - This is newer than jconsole. Thread dump and heap dump creator and profiler for heap dump. This is also a monitoring tool like jconsole.

jhat - See the heap created. (probably this is not a very useful one. Some profiler/jvisualvm can be used)

$ jhat -port 8081 now.heap