Sometimes there may be a need to increase the heap size of the integrate weblogic server within JDeveloper. Obviously one can modify the setDomainEnv file in the domain's bin directory -
For Unix, it is in $HOME/.jdeveloper/system12.1.3****/DefaultDomain/bin
For Windows, it is in %APPDATA%\JDeveloper\system12.1.3***/DefaultDomain/bin
But, you can also change it within JDeveloper, you can do this by
Right click on the integratedWebLogicServer in Application Window and select properties->Launch Settings
Click on More Launch Settings and create a new environment variable entry USER_MEM_ARGS with the desired JVM heap size.
You can also enter any Java Options in the parent dialog or use any other environment variable entry.
However, currently there is a caveat of doing this. It will only be effective if you do not have any application open before you start the server.