measure java object size using jamm

Often when you develop a java application, you want to measure how big the object occupied in the heap. There are many available tool, such as the SizeOf.jar but today we will take a look at jbellis/jamm. What is Jamm? Jamm provides MemoryMeter, a java agent to measure actual object memory use including JVM overhead.

It is very easy to use, get the source and build the jar. Below is the output of building jar .

jason@localhost:~/codes/jamm$ ant jar
Buildfile: /home/jason/codes/jamm/build.xml

ivy-download:
     [echo] Downloading Ivy...
    [mkdir] Created dir: /home/jason/codes/jamm/target
      [get] Getting: http://repo2.maven.org/maven2/org/apache/ivy/ivy/2.1.0/ivy-2.1.0.jar
      [get] To: /home/jason/codes/jamm/target/ivy-2.1.0.jar

ivy-init:
    [mkdir] Created dir: /home/jason/codes/jamm/target/lib

ivy-retrieve-build:
[ivy:retrieve] :: Ivy 2.1.0 - 20090925235825 :: http://ant.apache.org/ivy/ ::
[ivy:retrieve] :: loading settings :: url = jar:file:/home/jason/codes/jamm/target/ivy-2.1.0.jar!/org/apache/ivy/core/settings/ivysettings.xml
[ivy:retrieve] :: resolving dependencies :: jamm#jamm;working@debby.e2e.serveftp.net
[ivy:retrieve] 	confs: [default]
[ivy:retrieve] 	found junit#junit;4.11 in public
[ivy:retrieve] 	found org.hamcrest#hamcrest-core;1.3 in public
[ivy:retrieve] downloading http://repo1.maven.org/maven2/junit/junit/4.11/junit-4.11-javadoc.jar ...
[ivy:retrieve] .................................................................................................................................................................................................................. (370kB)
[ivy:retrieve] .. (0kB)
[ivy:retrieve] 	[SUCCESSFUL ] junit#junit;4.11!junit.jar(javadoc) (2772ms)
[ivy:retrieve] downloading http://repo1.maven.org/maven2/junit/junit/4.11/junit-4.11.jar ...
[ivy:retrieve] ........................................................................................................................................... (239kB)
[ivy:retrieve] .. (0kB)
[ivy:retrieve] 	[SUCCESSFUL ] junit#junit;4.11!junit.jar (1725ms)
[ivy:retrieve] downloading http://repo1.maven.org/maven2/junit/junit/4.11/junit-4.11-sources.jar ...
[ivy:retrieve] ................................................................................................. (147kB)
[ivy:retrieve] .. (0kB)
[ivy:retrieve] 	[SUCCESSFUL ] junit#junit;4.11!junit.jar(source) (1403ms)
[ivy:retrieve] downloading http://repo1.maven.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar ...
[ivy:retrieve] ........................... (43kB)
[ivy:retrieve] .. (0kB)
[ivy:retrieve] 	[SUCCESSFUL ] org.hamcrest#hamcrest-core;1.3!hamcrest-core.jar (1363ms)
[ivy:retrieve] :: resolution report :: resolve 9107ms :: artifacts dl 7338ms
	---------------------------------------------------------------------
	|                  |            modules            ||   artifacts   |
	|       conf       | number| search|dwnlded|evicted|| number|dwnlded|
	---------------------------------------------------------------------
	|      default     |   2   |   2   |   2   |   0   ||   4   |   4   |
	---------------------------------------------------------------------
[ivy:retrieve] :: retrieving :: jamm#jamm [sync]
[ivy:retrieve] 	confs: [default]
[ivy:retrieve] 	3 artifacts copied, 0 already retrieved (431kB/40ms)

init:
    [mkdir] Created dir: /home/jason/codes/jamm/target/classes
    [mkdir] Created dir: /home/jason/codes/jamm/target/test/classes

build:
     [echo] jamm: /home/jason/codes/jamm/build.xml
    [javac] Compiling 3 source files to /home/jason/codes/jamm/target/classes
    [javac] Note: /home/jason/codes/jamm/src/org/github/jamm/AlwaysEmptySet.java uses unchecked or unsafe operations.
    [javac] Note: Recompile with -Xlint:unchecked for details.

jar:
      [jar] Building jar: /home/jason/codes/jamm/target/jamm-0.2.7-SNAPSHOT.jar

BUILD SUCCESSFUL
Total time: 26 seconds

The jar is found in target/jamm-0.2.7-SNAPSHOT.jar . You can start testing the built jar using ant test. Below is the output.

jason@localhost:~/codes/jamm$ ant test
Buildfile: /home/jason/codes/jamm/build.xml

ivy-download:

ivy-init:

ivy-retrieve-build:
[ivy:retrieve] :: Ivy 2.1.0 - 20090925235825 :: http://ant.apache.org/ivy/ ::
[ivy:retrieve] :: loading settings :: url = jar:file:/home/jason/codes/jamm/target/ivy-2.1.0.jar!/org/apache/ivy/core/settings/ivysettings.xml
[ivy:retrieve] :: resolving dependencies :: jamm#jamm;working@debby.e2e.serveftp.net
[ivy:retrieve] 	confs: [default]
[ivy:retrieve] 	found junit#junit;4.11 in public
[ivy:retrieve] 	found org.hamcrest#hamcrest-core;1.3 in public
[ivy:retrieve] :: resolution report :: resolve 266ms :: artifacts dl 23ms
	---------------------------------------------------------------------
	|                  |            modules            ||   artifacts   |
	|       conf       | number| search|dwnlded|evicted|| number|dwnlded|
	---------------------------------------------------------------------
	|      default     |   2   |   0   |   0   |   0   ||   4   |   0   |
	---------------------------------------------------------------------
[ivy:retrieve] :: retrieving :: jamm#jamm [sync]
[ivy:retrieve] 	confs: [default]
[ivy:retrieve] 	0 artifacts copied, 3 already retrieved (0kB/18ms)

init:

build:
     [echo] jamm: /home/jason/codes/jamm/build.xml

jar:

build-test:
    [javac] Compiling 2 source files to /home/jason/codes/jamm/target/test/classes
    [javac] Note: /home/jason/codes/jamm/test/org/github/jamm/MemoryMeterTest.java uses or overrides a deprecated API.
    [javac] Note: Recompile with -Xlint:deprecation for details.
    [javac] Note: /home/jason/codes/jamm/test/org/github/jamm/MemoryMeterTest.java uses unchecked or unsafe operations.
    [javac] Note: Recompile with -Xlint:unchecked for details.

checkos:

test-mac:

test:
     [echo] running tests
    [mkdir] Created dir: /home/jason/codes/jamm/target/test/output
     [echo] Testing with default Java
    [junit] Testsuite: org.github.jamm.GuessTest
    [junit] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 5.869 sec
    [junit]
    [junit] Testsuite: org.github.jamm.MemoryMeterTest
    [junit] Tests run: 13, Failures: 0, Errors: 0, Skipped: 3, Time elapsed: 0.813 sec
    [junit]
    [junit] Testcase: testMacOSX_i386(org.github.jamm.MemoryMeterTest):SKIPPED: got: "Linux", expected: is "Mac OS X"
    [junit] Testcase: testMacOSX_x86_64(org.github.jamm.MemoryMeterTest):SKIPPED: got: "Linux", expected: is "Mac OS X"
    [junit] Testcase: testCollections(org.github.jamm.MemoryMeterTest):SKIPPED: These vary quite radically depending on the JVM.

BUILD SUCCESSFUL
Total time: 14 seconds

Very easy and work out of the box. To even start to use, just import the class and start measure the object you interested in,

MemoryMeter meter = new MemoryMeter();
meter.measure(object);

but remember to add "-javaagent:<path to>/jamm.jar" to your classpath when you run your app.