Spotless - an alternative to Checkstyle that applies the formatting

#java #clean code #gradle

Checkstyle is a wonderful tool when we want to enforce the style guidelines in the project. But it has 2 major problems:

  1. It can’t apply the formatting, it can only check whether the code is compatable. You need to rely on alternatives like suggested in this Stack Overflow thread. But there is no programattic way to do it.
  2. It can’t work only on the changes that you have made. For you to only check with the files that you have modified, you need a workaround suggested in this article. (I don’t speak the language but the code snippet is quite evident)

Enter Spotless

Spotless is more or less similar to Checkstyle but with few more features that we need. We will only discuss the differences. The rest is same.

Apply the fixes

While Checkstyle only supports finding out the problems, Spotless can even fix them for you. With Gradle you would end up running

./gradlew spotlessApply

and ta-da!

The regular ./gradlew spotlessCheck will just generate a report for you like Checkstyle does.

Working with only the diff

A very neat feature with Spotless is that it can only work with the diff. So if you are integrating a code formatter for the first time on a legacy project it would become very simple. The spotless configuration looks something like this:

spotless {
    ratchetFrom 'origin/main'
    // more configuration omitted

This will only check and apply against the diff with main branch. Works fine with tags, branches or any other commit for that matter.

Working with an existing code formatter

Onboarding a legacy project to these changes is always challenging because you end up either too many changes or it doesn’t comply with the exact code style that your organization is following. If your project already uses Eclipse code formatter, you can simply re-use that with spotless. No new files or anything is required.

spotless {
    java {
        eclipse().configFile('./.settings/eclipse-formatter.xml')
        // more configurations emitted
    }
}

Well, these are the 3 features I loved about Spotless, which made it easy to integrate with my existing projects.

This is my 10th of 100 post in #100daysToOffload.