Sometimes, overwhelming details are underwhelming. I happened to quickly explore Spotless for code formatting and checks. Spotless is the plugin to spot check. It's good that the README of Spotless upfront has separated Gradle and Maven documentation. I was looking to add maven support for a new Java Spring Boot 3.0 GraphQL project. But the Spotless Maven README documentation was overwhelming.
Quickly read through for few minutes to get an essence of it. Though there are so many details, what I wanted to get done seemed simple. Of course, practicality is always different. That's where experience is gained or comes from ;)
Environment: Java 20, Spring Boot 3.2.0, maven 3.9.6 on macOS Catalina 10.15.7
I quickly applied it to the project, and immediately ran into a couple of Gotchas. It took me couple of hours to explore and set it up finding issues and fixing settings. This post is just about those issues that I ran into.
Use Spaces, not Tabs in code
I prefer SPACES to TABS in code. It is good practice to use SPACE instead of TAB in code formatting. This cannot be a personal preference. But most of IDEs still come with TAB as default setting and many developers don't even pay attention to it. In code reviews, the formatting goes off due to SPACESs vs. TABs and is always annoying.
I use IntelliJ IDEA for my development. Whenever I install IntelliJ, the very first thing I would setup is to use spaces instead of tabs (Go to Preferences > Editor > Code Style > Java, and uncheck Use tab character). With that all code that I write will only use spaces and not tabs. The next thing is to setup to show whitespaces (Go to Preferences > Editor > Appearance, and check Show whitespaces), to easily distinguish Tabs and Spaces by this setting on.
Gotcha-1
The Spotless maven plugin documentation describes many details. The setting I wanted for code check was found at a couple of places in there under <indent> tag. At only one place the setting <spaces>true</spaces> is specified. Though I tried few different things like false for <tabs>, and true for <spaces> etc., the spotless:check maven goal was still suggesting to change code with spaces to tabs.
We also have to use google code style settings: eclipse-formatter.xml, that I took from the other project to use. This is described under Java > eclipse jdt in the spotless documentation. It's a google code style Java settings guide in xml format ;)
The setting id that is used for what I wanted was like: <setting id="org.eclipse.jdt.core.formatter.tabulation.char" value="tab"/>. Changing that "tab" to "space" made spotless happy with spaces in code. ;)
Gotcha-2
Binding to maven phase : I should have read it carefully. At the minimum the <executions><execution><goal>check</goal></execution></execution> is required. Without this ./mvnw spotless:check works, but ./mvnw clean install which also runs verify will not run spotless check. So, for spotless check goal to be bound to maven verify goal, the above setting is required.
A sample spotless settings looks like this:
...
<plugins>
<!-- spotless https://github.com/diffplug/spotless -->
<plugin>
<groupId>com.diffplug.spotless</groupId>
<artifactId>spotless-maven-plugin</artifactId>
<version>${spotless-plugin.version}</version>
<executions>
<execution>
<goals>
<goal>check</goal>
</goals>
</execution>
</executions>
<configuration>
<java>
<endWithNewline />
<trimTrailingWhitespace />
<cleanthat>
<version>2.18</version>
<mutators>
<mutator>AvoidInlineConditionals</mutator>
<mutator>LiteralsFirstInComparisons</mutator>
<mutator>UnnecessaryImport</mutator>
<mutator>UnnecessaryModifier</mutator>
<mutator>UseUnderscoresInNumericLiterals</mutator>
<mutator>UseDiamondOperator</mutator>
</mutators>
</cleanthat>
<eclipse>
<version>4.26</version>
<file>${project.basedir}/eclipse-formatter.xml</file>
</eclipse>
</java>
</configuration>
</plugin>
...
</plugins>
💡 TIPS
Spotless handy maven goals
Check: ./mvnw spotless:check
Apply: ./mvnw spotless:apply
Conclusion
Any new exploration in Maven world never goes smooth for me. There are always bumps along the way. I do not like copy and paste at all. After all, if everything works in the first place when quick-copy-paste-tool is used, there is not much left to learn ;) With the Generative AI getting trained to write code, learning will soon become a rare thing!
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