Install

  1. Download the latest release of JetBrains Runtime 17, 21 or 25 for your platform, unpack it and set JAVA_HOME to its location (or add it as JDK to your IDE). JetBrains Runtime supports enhanced class redefinition. To check it, run java -XX:+AllowEnhancedClassRedefinition -version, it fails if the JVM does not support it.
  2. Download the latest release of the Hotswap agent jar and copy it as <JBR-install-directory>/lib/hotswap/hotswap-agent.jar (create the lib/hotswap folder if it does not exist). The file name must be hotswap-agent.jar, without the version.

Configure

  1. Run your application with JBR using additional options: -XX:+AllowEnhancedClassRedefinition -XX:HotswapAgent=fatjar
  2. (optional) create a file named “hotswap-agent.properties” inside your resources directory, see available properties and default values: https://github.com/HotswapProjects/HotswapAgent/blob/master/hotswap-agent-core/src/main/resources/hotswap-agent.properties
  3. (optional) in case you are not using autoHotswap=true and therefore not using the hotswapping mechanism provided by HotswapAgent, you may want to add -Xlog:redefine+class*=info as an additional JVM argument in order to get feedback about reloaded classes.

-XX:HotswapAgent modes

  • fatjar - the JVM loads <JBR>/lib/hotswap/hotswap-agent.jar with all plugins.
  • core - the JVM loads <JBR>/lib/hotswap/hotswap-agent-core.jar, the agent with core plugins only (e.g. Hotswapper, JDK, anonymous classes), without framework plugins.
  • external - the JVM only prepares the module access for the agent, the agent is added with -javaagent:/path/to/hotswap-agent.jar. Use this mode to use an agent jar from another location.
  • disabled - no agent (default).

Use only one way to load the agent. With -XX:HotswapAgent=fatjar (or core) do not add -javaagent:hotswap-agent.jar, otherwise the agent is loaded twice.

Run

  1. start the application in debug mode, check that the agent and plugins are initialized correctly:

     HOTSWAP AGENT: 9:49:29.548 INFO (org.hotswap.agent.HotswapAgent) - Loading Hotswap agent - unlimited runtime class redefinition.
 HOTSWAP AGENT: 9:49:29.725 INFO (org.hotswap.agent.config.PluginRegistry) - Discovered plugins: [org.hotswap.agent.plugin.hotswapper.HotswapperPlugin, org.hotswap.agent.plugin.jvm.AnonymousClassPatchPlugin, org.hotswap.agent.plugin.hibernate.HibernatePlugin, org.hotswap.agent.plugin.spring.SpringPlugin, org.hotswap.agent.plugin.jetty.JettyPlugin, org.hotswap.agent.plugin.tomcat.TomcatPlugin, org.hotswap.agent.plugin.zk.ZkPlugin, org.hotswap.agent.plugin.logback.LogbackPlugin]
 ...
 HOTSWAP AGENT: 9:49:38.700 INFO (org.hotswap.agent.plugin.spring.SpringPlugin) - Spring plugin initialized - Spring core version '3.2.3.RELEASE'

  2. save a changed resource and/or use the HotSwap feature of your IDE to reload changes