Measure memory footprint of Java objects with Eclipse and Maven

// under java maven profiling

Sometimes I need to know the exact size of a Java object, and that can be tricky to compute by hand. Here is a way within Eclipse and a Maven project.

Download, copy it to e.g. src/test/resources/memory/classmexer.jar and add it to your project, e.g.

<dependency>
  <groupId>classmexer</groupId>
  <artifactId>classmexer</artifactId>
  <version>0.3</version>
  <scope>system</scope>
  <systemPath>${basedir}/src/test/resources/memory/classmexer.jar</systemPath>
</dependency>

Instantiate the agent

Run > Run Configurations...
Select the class or test
Tab "Arguments", box "VM arguments:", add -javaagent:src/test/resources/memory/classmexer.jar

Measure the memory of java objects

import static com.javamex.classmexer.MemoryUtil.deepMemoryUsageOf;

Map<Integer, String> mymap = new HashMap<Integer, String>();
mymap.put(1, "hello");
System.out.println(deepMemoryUsageOf(mymap));
mymap.put(2, "a");
System.out.println(deepMemoryUsageOf(mymap));
mymap.put(3, "world");
System.out.println(deepMemoryUsageOf(mymap));

240
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440

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