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Java unlimited runtime class and resource redefinition.

The main purpose of this project is to avoid infamous _change -> restart&wait -> check development lifecycle. Save&Reload during development should be standard and many other languages (including C#) contain this feature.


In contrast to standard Java, where the hotswap is limited to in-body code changes, the DCEVM + HotswapAgent allow the following code changes:

  • Add/remove/modify class fields.
  • Add/remove/modify methods. Add/remove/modify method annotations
  • Add/remove/modify classes including anonymous classes. HotswapAgent handless correct anonymous class redefinitions.
  • Add/remove static member of classes. HotswapAgent handles static member initialization.
  • Add/remove enum values
  • Refresh framework and application server settings

The only unsupported operation is hierarchy change (change the superclass or remove an interface).

DCEVM realizes hotswap on JVM level. HotswapAgent does the same on the level of Java frameworks and servlet containers. Both projects used together form an excellent combination for daily development not only in Java but also in another JVM languages.

Easy to start

JDK 11

Hotswap Agent is now bundled with DCEVM. Just download latest release of trava-jdk-11-dcevm JDK, unpack it and set JAVA_HOME to it’s location (or add it as JDK to your IDE).


Download and install latest DCEVM Java patch + agent jar and launch your application server with options -XXaltjvm=dcevm -javaagent:hotswap-agent.jar to get basic setup. You can attach agent jar to the running JVM using the following example code snippet. Optionally add to your application to configure plugins and agent behaviour.


Each application framework (Spring, Hibernate, Logback, …) needs special reloading mechanisms to keep everything up-to-date after class redefinition (e.g. Hibernate configuration reload after a new entity class is introduced). Hotswap agent works as a plugin system and ships preconfigured with all major framework plugins. It is easy to write your own custom plugin for your application, if needed.


This project is very complex due to lot of supported frameworks and various versions. Community contribution is mandatory to keep it alive. You can start by creating a plugin inside your application or by writing an example/integration test. There is always need for documentation improvement :-). Thank you for any help!