![]() ![]() Spring Loaded project ( ) works internally probably in a similar way as JRebel does – it instrumentates loaded clases in a way that they could be modified in runtime. hibernate – modifies entities mappings at runtime.Spring MVC – adds/modifies controller mappings.Spring DI – it allows to add/modify beans in DI container.EJB3 – it had some problems with injection of beans, however successfully handled all other bean code changes.EJB2.1 (yes, that’s a legacy pain, especially when a build contains XDoclet code, which takes ages to generate that’s when we really want such tools).HotSwapAgent proved to work for us while developing an application with the use of: Some additional aspects of hot swap configuration could be given in a file named “ hotswap-agent.properties” which should be placed in a resources directory inside your application. It works as an agent and running it is simply a matter of adding: Furthermore, it adds on-code-changed hooks related to various frameworks. HotSwapAgent basically allows for everything that DCEVM does. However, we haven’t tested all of them in development. It has quite many plugins for different popular Java frameworks: And here comes another project accompanying DCEVM. Also application servers, such as JBoss, don’t allow simple class replacing. Sometimes some work should be done on a framework level (just to mention such operations as refreshing spring context after introducing new annotated methods or changing, for example, ORM annotations on fields etc.). ![]() HCR is often not only a matter of pure classes replacement. We successfully tested DCEVM while developing a large Swing-based desktop application which needs a good few seconds to start. introducing new high-level, inner and anonymous classes.changing class hierarchy (although the documentation states that this should be possible for “full” version 1.7).introducing/modifying lambdas in 1.8 code (sometimes randomly fails).adding, removing annotations from classes and methods.changing body of a method (and static method as well) – actually, it doesn’t make any difference from a standard JVM.Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=XYZĪnd you can attach a debugger from IDE to port XYZ and replace the changed code after compilation. You just run an application with remote debug parameters: removing a superclass), however, as I’ll describe it further in this post, it actually seems not to work.Īny type of further described changes could be done simply by attaching a debugger to a JVM and by using standard HCR feature present in most IDE-s. The authors state that the full version can do more advanced operations, such as modifying class hierarchy (e.g. It’s really easy,painless and causes that every program running on JVM is able to do better HCR out of the box.ĭCEVM is precompiled for both java 1.7 and 1.8, however at the time of writing this post, the “full” version is available only for JVM 1.7. Therefore, the installation is a matter of replacing a standard JVM with DCEVM.Īfter starting the installer you simply choose which of current JVM installations you want to replace:Īs on output, you can notice that only jvm.dll-s were replaced with new ones. Instead, it’s actually a modified JVM, which could handle more of dynamic code change types. The significant difference with JRebel-like solutions is that it doesn’t work by dynamically modifying classes loaded by JVM. ![]() It solves most of the limitations of a standard JVM’s HCR. When it comes to pure Hot Code Replace, DCEVM ( ) seems to be one of the most interesting tools. However, over the last few years things started to change and now we have a set of quite nice free tools which allow to reduce necessity of completely rebuilding and restarting our applications during development. For a long time there was no real alternative. Sure, there are commercial solutions available but as users of the Java software development ecosystem we are used to free and opensource solutions. Some containers / application servers offer kind of “hot redeploy” feature, however when it comes to replacing changed Java code, usually, it’s still necessary to restart the whole application, so it doesn’t help much in development. You cannot change a method signature, you cannot add fields, constants etc. The only thing that could be done is changing a method body. A standard JVM Hot Code Replace (HCR) doesn’t allow for too much. ![]()
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