dcevm | Dynamic Code Evolution VM for Java | Continuous Deployment library

I don't know why, but the Class.forName(className) does not resolve to the same Class object that is referenced in object mapper type factory, but seems to create another Class object for the same class. That's why it considers the types equal. Solution for me was to use class from type factory instead.

DCEVM does not patch the original JVM.
It installs a different version of libjvm.so under $JDK_HOME/lib/dcevm

-XXaltjvm option is supported by the regular Java launcher out of the box. When specified, the launcher looks for libjvm.so in the alternate directory:

• if -XXaltjvm value starts with /, it is treated as the absolute path of the alternative JVM;
• otherwise, the directory is relative to the JDK home: $JDK_HOME/lib/

Because this answer is hidden in a closed issue as @papaya said, i leave it here as reference

HotswapAgent core has no plugin except core JVM plugins. Then it is faster since less scanning tasks are necessary to be done, less class copying to target classloaders, there is no need to disable plugins. You choose only what you want.

Loaded plugins are visible in the log, "HOTSWAP AGENT: 15:43:42.059 INFO (org.hotswap.agent.config.PluginRegistry) - Discovered plugins:"

For core: Hotswapper, WatchResources, AnonymousClassPatch, ClassInitPlugin, JdkPlugin

For fatjar: dkPlugin, Hotswapper, WatchResources, ClassInitPlugin, AnonymousClassPatch, Hibernate, Hibernate3JPA, Hibernate3, Spring, Jersey1, Jersey2, Jetty, Tomcat, ZK, Logback, Log4j2, MyFaces, Mojarra, Omnifaces, ELResolver, WildFlyELResolver, OsgiEquinox, Owb, Proxy, WebObjects, Weld, JBossModules, ResteasyRegistry, Deltaspike, GlassFish, Vaadin, Wicket, CxfJAXRS, FreeMarker, Undertow, MyBatis

JRebel does support GraalVM, you can see the press release here: https://www.jrebel.com/blog/jrebel-2020-2-adds-support-java-14

If you are struggling with setting up JRebel with your GraalVM you should email them at support@jrebel.com and they can help you out.

Yes, it's possible to perform Hot Code Replace in a running JVM. This involves several steps.

1. Prepare (compile) the new version of classes you want to replace. Let's say, you want to replace org.pkg.MyClass, and the new version of this class is located at /new/path/org/pkg/MyClass.class

2. Create a Java Agent that uses Instrumentation API to redefine the given class. Here is how the simplest agent may look like:

I don't have an experience of working with this concrete hotswap agent, but in general to answer your question:

1. When you build the docker image, you are supposed to run your own application after all (via maven, with java -jar or in any other way) So, When you start the application process, you're supposed to make the application ready for remote debugging:

Why can't gradlew build command compile and build only the things that have changed and make the process faster?

There's no dependable way how to determine what needs to be recompiled. For example, compile-time constants get inlined and there's no trace of where they come from in the class files (it can be found in the source files, that implies parsing them and losing time; it can be stored in some auxiliary files and some tools do it).

See the "Limitations" section of this for details.

The reason maybe is that they don't go through configure step of gradle.

Sure, but the configure step doesn't usually take that long.

Eclipse knows which files have changed

Good point (in a comment by holwgler).

Some time ago I spent some time trying to make my gradle compilation faster and I gave up. Eclipse is damn fast for many reasons:

• incremental compilation
• multithreading using all cores
• knowing all changed files
• having the whole compiler code optimized by the JIT
• probably caching file dependencies
• ugly highly optimized code

My "solution" is ignoring the problem. I do everything in Eclipse, except for integration tests (which take way longer than the compilation) and production builds (which are rare enough so I don't care).

You may want to read these performance tips.

To find out where the time gets spent, use