fmt-maven-plugin

Formats your code using open-java-format, a modern, lambda-friendly, 120-character Java formatter.

Documentation: openjavaformat.dev/get-started/maven

This is a fork of spotify/fmt-maven-plugin, which formats with google-java-format. It works the same way, with open-java-format in its place.

The format cannot be configured by design.

If you want your IDE to stick to the same format, open-java-format also has plugins for IntelliJ IDEA and Eclipse.

Usage

Standard pom.xml

To have your sources automatically formatted on each build, add to your pom.xml:

    <build>
        <plugins>
            <plugin>
                <groupId>dev.openjavaformat</groupId>
                <artifactId>fmt-maven-plugin</artifactId>
                <version>2.27.0.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>format</goal>
                        </goals>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>dev.openjavaformat</groupId>
                        <artifactId>open-java-format</artifactId>
                        <version>2.98.0.4</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>

The open-java-format dependency is required. The plugin does not bring a formatter of its own, so it formats with exactly the version you name here: align it with the version in your IDE, pre-commit Git hook, etc. Without it the build stops with a message that says which dependency to add.

If you prefer, you can only check formatting at build time using the check goal:

    <build>
        <plugins>
            <plugin>
                <groupId>dev.openjavaformat</groupId>
                <artifactId>fmt-maven-plugin</artifactId>
                <version>2.27.0.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>check</goal>
                        </goals>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>dev.openjavaformat</groupId>
                        <artifactId>open-java-format</artifactId>
                        <version>2.98.0.4</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>

The examples below leave the <dependencies> element out to stay short, but every configuration needs it.

Overriding the Default Lifecycle Phase

Both goals have a Maven lifecycle phase configured by default.

Goal	Default Phase
format	process-sources
check	verify

You may prefer to run these goals in a different phase instead.
Maven allows you to override the default phase by specifying a <phase> for the <execution>.

For example, you may prefer that the check goal is performed in an earlier phase such as validate:

                    <execution>
                        <phase>validate</phase>
                        <goals>
                            <goal>check</goal>
                        </goals>
                    </execution>

What gets formatted

Every file is formatted the way open-java-format's other integrations format it: the code is laid out, imports are sorted, unused imports are removed and long strings are reflowed. The style, skipSortingImports, skipRemovingUnusedImports and skipReflowingLongStrings options of spotify/fmt-maven-plugin do not exist here.

Options

sourceDirectory represents the directory where your Java sources that need to be formatted are contained. It defaults to ${project.build.sourceDirectory}

testSourceDirectory represents the directory where your test's Java sources that need to be formatted are contained. It defaults to ${project.build.testSourceDirectory}

additionalSourceDirectories represents a list of additional directories that contains Java sources that need to be formatted. It defaults to an empty list.

verbose is whether the plugin should print a line for every file that is being formatted. It defaults to false.

filesNamePattern represents the pattern that filters files to format. The defaults value is set to .*\.java.

skip is whether the plugin should skip the operation.

skipSourceDirectory is whether the plugin should skip formatting/checking the sourceDirectory. It defaults to false.

skipTestSourceDirectory is whether the plugin should skip formatting/checking the testSourceDirectory. It defaults to false.

forkMode lets you specify whether to run open-java-format in a fork or in-process. Also adds JVM arguments to expose JDK internal javac APIs. Value default (which is the default) will fork (to be able to run at all on JDK 16+), never runs in-process, regardless of JDK version and always will always fork. In-process formatting needs the javac exports in .mvn/jvm.config:

--add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
--add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED
--add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED
--add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED
--add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED

example:

<build>
    <plugins>
        <plugin>
            <groupId>dev.openjavaformat</groupId>
            <artifactId>fmt-maven-plugin</artifactId>
            <version>2.27.0.1</version>
            <configuration>
                <sourceDirectory>some/source/directory</sourceDirectory>
                <testSourceDirectory>some/test/directory</testSourceDirectory>
                <verbose>true</verbose>
                <filesNamePattern>.*\.java</filesNamePattern>
                <additionalSourceDirectories>
                    <param>some/dir</param>
                    <param>some/other/dir</param>
                </additionalSourceDirectories>
                <skip>false</skip>
                <skipSourceDirectory>false</skipSourceDirectory>
                <skipTestSourceDirectory>false</skipTestSourceDirectory>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>format</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

check Options

displayFiles default = true. Display the list of the files that are not compliant.

displayLimit default = 100. Number of files to display that are not compliant.

failOnError default = true. Fail the build if non-compliant files are found.

example to not display the non-compliant files:

<build>
    <plugins>
        <plugin>
            <groupId>dev.openjavaformat</groupId>
            <artifactId>fmt-maven-plugin</artifactId>
            <version>2.27.0.1</version>
            <configuration>
                <displayFiles>false</displayFiles>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>check</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

example to limit the display up to 10 files

<build>
    <plugins>
        <plugin>
            <groupId>dev.openjavaformat</groupId>
            <artifactId>fmt-maven-plugin</artifactId>
            <version>2.27.0.1</version>
            <configuration>
                <displayLimit>10</displayLimit>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>check</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

example to only warn about non-compliant files instead of failing the build

<build>
    <plugins>
        <plugin>
            <groupId>dev.openjavaformat</groupId>
            <artifactId>fmt-maven-plugin</artifactId>
            <version>2.27.0.1</version>
            <configuration>
                <failOnError>false</failOnError>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>check</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Command line

You can also use it on the command line

mvn dev.openjavaformat:fmt-maven-plugin:format

The plugin still has to be declared in your pom.xml with its open-java-format dependency: Maven takes a plugin's dependencies from the pom.xml, the command line cannot name them.

You can pass parameters via standard -D syntax. mvn dev.openjavaformat:fmt-maven-plugin:format -Dverbose=true

-Dfmt.skip is whether the plugin should skip the operation.

Requirements

Maven has to run on JDK 21 or newer: open-java-format is compiled for Java 21, and the plugin formats in a JVM started from the same JDK.

Building

mvn verify on JDK 21 runs the unit tests and the integration tests, the projects in src/test/resources.

Releasing

A tag is a release: pushing a four-number tag, X.Y.Z.N, makes release.yml build that version, sign it and publish it to Maven Central. The repository secrets it needs come from 1Password with mise run gh:secrets.

License

MIT, see LICENSE. The plugin was written at Coveo and Spotify, and this fork keeps their copyright notices. Neither Spotify AB nor Coveo endorses, sponsors or is affiliated with this fork.