Question

Recently, I was reading book about Erlang which has hot deployment feature. The deployment can be done without bringing the system down. All the existing requests will be handled by old version of code and all the new request after deployment will be served by the new code. In these case, both the versions of code available in runtime for sometime till all the old requests are served. Is there any approach in Java where we can keep 2 versions of jar files? Is there any app/web servers support this?

Answer 1

There are many ways to achieve hot deployment in the Java world, so you’ll probably need to be a bit more specific bout your context and what you are trying to achieve.

Here are some good leads / options to consider:

• OSGi is a general purpose module system that supports hot deployment
• Clojure is a dynamic JVM language that enables a lot of runtime interactivity. Clojure is often used for “live coding” – pretty much anything can be hot-swapped and redefined at runtime. Clojure is a functional language with a strong emphasis on immutability and concurrency, so in some ways has some interesting similarities with Erlang. Clojure has some very nice web frameworks like Noir that are suitable for hot swapping web srever code.
• The Play Framework is designed to enable hot swapping code for productivity reasons (avoiding web server restarts). Might be relevant if you are looking primarily at hot-swapping web applications.
• Most Java applicatio servers such as JBoss support some form of hot-swapping for web applications.