How to Hot Deploy Java/Kotlin classes in Dev

How to Hot Deploy Java/Kotlin classes in Dev

Jan Vladimir Mostert

One thing the majority of JVM developers find annoying is having to constantly restart their container. Make a small change, restart Tomcat/Jetty, wait 30+ seconds for code to build / compile (or several minutes in the case of large monolithic projects), see results; repeat.

Compared to Dart which auto-reloads your changes as soon as you hit save, this is very inefficient and kills productivity.

There's a commercial solution available called JRebel that aims to solve this problem, I took it for a test drive for a couple of weeks and managed to cut down several hours rapidly increasing my productivity and leaving me with a lot less time to spend on Hashnode.

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Even though JRebel was saving me a lot of time and pretty much worked out of the box, I just couldn't justify the price tag - at almost $500 a year, converted to Rands, that's about the price of one month's rental in South Africa for a small flat - a bit heavy; all the time I'm saving, I'm paying over to them. Don't get me wrong, I enjoyed using JRebel, but the price tag is just too much when there are other solutions available.

There is an open-source alternative which works just as well for what I'm using it for - it's called Spring Loaded. It probably won't cover everything that JRebel is doing, but I'm mostly busy in Spring, so it's perfect for my needs.

Download the jar file, throw it somewhere where you won't accidentally delete it, open your ~/.bash_profile if you're using OSX or on Linux it would typically be your ~/.bashrc and add the following line followed by restarting your terminal:

export MAVEN_OPTS="-javaagent:/absolute/path/Code/springloaded-1.2.5.RELEASE.jar -noverify"

Now when you run your application using the maven jetty plugin or maven tomcat plugin (mvn jetty:run), every time you compile a class, it will be reloaded for you without having to do Ctrl + C and restarting mvn jetty:run. In Eclipse this will happen automatically if you have auto build turned on, in IntellJ, just assign a shortcut to the compile command (I'm using Cmd + S), once you're done with your changes, simply hit Cmd + S and you can immediately see your changes without restarts.

Happy coding!!