This new feature encapsulates the ability to substitute modified code in a running application through the debugger APIs.
– ‘HotSwapping’ using JVM:http://www.jug.mk/blogs/ipenov/entry/hotswapping_using_jvm

Currently, HotSwap only supports the modification of method body, and does not support the modification of class and method signature (such as modifying class name, method name, method parameter, adding or deleting a method, adding or deleting a class file, etc.). HotSwap cannot be deployed to the service hot. ) There is a reason to consider these limitations. Replacing a class definition requires an association between the new class and the old class, where the association is the full name (and perhaps other information) of the class, and the class name has been changed so that you don’t know which class to replace. As for the modification of the method signature, it should allow for the run-time method invocation, replacing the existing method invocation with the method signature.

many people on the Internet misunderstand the concept of hot deployment and hot loading, so the behavior of disorderly configuration, here is a hint.
hot deployment: the container state is in operation to deploy or redeploy the entire project. In this case the entire memory is usually emptied and reloaded. Simply put, Tomcat or some other Web server will help us reload the project.
hot loading: when the container state is run, it reloads the changed compiled class. In this case, memory will not be emptied,sessin will not be lost, but it is easy to cause memory overflow, or no method can be found. Because memory cannot be converted into a pair, there are exceptions to changing the structure and model of a class, and there is no problem with changing variables and methods that already exist. In medium mode, it is best used during debugging to avoid the whole project loading.
debug mode supports hot loading. Very easy to use.
– IDEA TOMCAT WEB development SSH modify classes don’t restart the deployment of hot load IDEA8: http://3000pzj.javaeye.com/blog/503222

deployment is a common occurrence during project development, especially during debug. But if you have to redeploy the entire project every time you fix a bug so you can test fix or continue to debug other bugs, that’s a nightmare for developers. But no one wants a nightmare, and thanks to the JVM’s hotSwap and Intellij Idea’s support for Debug and hotSwap, the dream has stayed true (a bit of an overplay). Today’s article describes the most convenient and efficient debug effects achieved by setting up Intellij Idea for hot deployment. I want to get some background and concepts before going into the specifics of the setup.
HotSwap: “HotSwap” is a feature in JPDA (Java Platform Debugger Architecture), and JPDA enhancement is a new feature from Java 2 SDK1.4. HotSwap allows you to replace class definitions in the JVM with new class definitions, which allows developers to replace the modified class with an older class in the JVM without having to restart the server during debug.