JOL (Java Object Layout) is the tiny toolbox to analyze object layout schemes in JVMs. For example, in HotSpot VM on 64x processor an empty string takes 40 bytes i.e. 24 bytes for String object itself + 16 bytes for an internal empty char array.

The plugin is a GUI for JOL and allows you to make an estimate how much memory the object takes. Thus you can perform a simplest but most efficient performance improvements. Just check your DTOs if they fit into 64 bytes of processor's cache line.

Only HotSpot VM is supported by JOL itself. ATM the plugin supports only basic estimate of class layout in different VM modes i.e. the same as jol-cli estimates command.

NOTE: Your app most likely will use the HotSpot with 64-bit VM, compressed references mode.

Open File / Settings / Plugins then type JOL in search input and press Browse in repositories button.

Set a cursor into a class name and then press Code / Show Object Layout and you'll see a right panel with layout info.

The plugin provides an inspection to see most big classes and it's enabled by default. You can find the inspection by path Java | Memory | JOL: Class has too big memory footprint to configure or disable it.

Please rank the Plugin to make it more searchable.

The plugin uses a patched version of jol-core.jar so you must build it first:

git clone https://github.com/stokito/jol.git
git checkout extend_api
mvn install

Then open the IdeaJol project in IntelliJ and run it.