![]() ![]() JRebel, which has been available since 2007 and was formerly called JavaRebel, takes a different approach. The component granularity allows also very small bundles to be reloaded making the experience almost instantaneous.Ī general problem with reloading classes this way is, that the old and new class versions are available at the same time and have to be carefully handled by the framework. ![]() The state for the new component is already available within the framework. That's why reloaded components with new classloaders are not an issue for them. serialized) before and then reapplied or reloaded into the "new" application or module.Ĭurrent component-based frameworks like Grails or RIFE are responsible for handling component state themselves. To restore the application state it must be stored (e.g. Hotdeployment is effectively a restart of the application. So classloader leaks are introduced that lead to increased memory consumption after continuous redeploys. Then the old application is partly still around, it is just not longer used. Often it is not possible to remove all references to instances, classes or classloaders completely from the JVM. If you remove all references to the loaded classes as well as the classloader you can unload the application and reload it completely using a new classloader. You load an application (or part of it) with a dedicated classloader. The redeployment features of most servlet containers, application servers and OSGi implementations each work along the same lines. Otherwise the concerned instances would have to be replaced completely and all references to them updated as well (including cascading changes) Application Server Redeployment/Hotdeployment One problem is that the state of object instances must not be affected. The complexity of the JVM - especially garbage collectors, memory layout and Hotspot make it difficult to provide a general solution for transparent class bytecode replacement. It does not contribute to the actual reloading process. Since Java 5, hotswapping is available through the instrumentation API.The API is also used by JRebel, but only used to instrument infrastructure class loaders and classes. Hotswap is also ignorant of classloaders, it identifies classes only by their name and works only for existing classes. It doesn't allow structural changes or adding or removal of class members. it only works in Debug mode and only handles changes within method bodies. One might argue that JVM Hotswapping which replaces bytecode in place, has been around for some time (since 2002, JDK 1.4). There are several ways to address the problem of updating changed classes within an application without restarting, but all come with different problems. The reduced productivity can contributes to a lower developer motivation due to the lower number of successes and achievements during the workday. But it also applies to the infrastructure induced causes shown earlier. In the available literature the cost of context switching is discussed for workplace interruptions like phone calls, emails and personal requests. Recovering the original context also takes a substantial amount of time. The amount of information that has to be kept in short term memory for development flow is quite high, but it deteriorates quickly when focus is lost. Context switching in a complex task environment like software development is a major problem. They made the data publicly available and used it to calculate average hourly waiting time of of 6 minutes for building and about 10.5 minutes for redeploying applicationīesides the direct costs of the time spent waiting, there are other, hidden costs. To support the discussion of productivity, Zeroturnaround gathered statistical data from over 1100 Java developers. JRebel aims to reduce development turnaround time significantly by adding a specialized javaagent to the JVM's startup parameters that handles the more difficult details of runtime class replacement. ![]() The need to redeploy or restart a Java application during development introduces unecessary delays which reduce productivity. The information in this article is partly distilled from the series and partly taken from our communication. He recently published a series detailing JVM classloading and runtime class replacement. With the recent release of JRebel 3.0 we spoke with Zeroturnaround's CTO Jevgeni Kabanov to detail some of the internal workings of JRebel, applicability and integration issues and understand the benefits a Java developer could gain from this technology. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |