jhat - Java Heap Analysis Tool

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∟jhat - Java Heap Analysis Tool

This section describes the Java heap analysis tool 'jhat' command and its options. 'jhat' can be used browse a Java heap dump file through a Web interface.

Warning: "jhat" has been discontinued since JDK 9. But if you still have JDK 1.8 installed, you can continue to use it to browser heap dump files generated by JDK 9 to JDK 12.

What Is "jhat"? - "jhat" is a Java heap analysis tool or heap dump file browser: Parses a Java heap dump file and launches a Web server. "jhat" enables you to browse heap dump files using your favorite Web browser. "jhat" supports pre-designed queries (such as 'show all instances of a known class "Foo"') as well as OQL (Object Query Language) - a SQL-like query language to query heap dumps. Help on OQL is available from the OQL help page shown by "jhat". With the default port, OQL help is available at http://localhost:7000/oqlhelp/

But the "jmap" tool included in the Windows version of JDK only supports functions to print histogram of Java object heap and generate a heap dump of a given JVM process:

herong> \Progra~1\java\jdk1.8.0\bin\jhat -help

Usage: jhat [-stack <bool>] [-refs <bool>] [-port <port>]
   [-baseline <file>] [-debug <int>] [-version] [-h|-help] <file>

   -stack false     Turn off tracking object allocation call stack.
   -refs false      Turn off tracking of references to objects
   -port <port>     Set the port for the HTTP server. Default is 7000.
   -exclude <file>  Specify a file that lists data members that should
                    be excluded from the reachableFrom query.
   -baseline <file> Specify a baseline object dump.  Objects in
                    both heap dumps with the same ID and same class
                    will be marked as not being "new".
   -debug <int>     Set debug level.
                    0:  No debug output
                    1:  Debug hprof file parsing
                    2:  Debug hprof file parsing, no server
   -version         Report version number
   -h|-help         Print this help and exit
   <file>           The file to read

For a dump file that contains multiple heap dumps,
you may specify which dump in the file
by appending "#<number>" to the file name, i.e. "foo.hprof#3".

All boolean options default to "true"