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Running an application in development mode

It watches for changes in the project tree, and if they match certain conditions, it will recompile and restart the application.

The plugin can handle changes in all the languages supported by Micronaut: Java, Kotlin and Groovy.

Note that this plugin can work with any Micronaut version (and potentially with any Java application), since it only deals with file changes and JVM restarts.

Usage

You can use mn:run to run your application in development mode:

$ mvn clean mn:run

[INFO] Scanning for projects...
[INFO]
[INFO] -----------------< java.maven.junit:java-maven-junit >------------------
[INFO] Building java-maven-junit 0.1
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ java-maven-junit ---
[INFO] Deleting /Users/alvarosanchez/Micronaut/micronaut-maven-plugin/examples/java/target
[INFO]
[INFO] --- mn:4.0.0:run (default-cli) @ java-maven-junit ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 2 resources
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 2 source files to /Users/alvarosanchez/Micronaut/micronaut-maven-plugin/examples/java/target/classes
13:36:32.665 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 919ms. Server Running: http://localhost:8080

Including and excluding options

By default, this plugin watches for changes in the following locations:

  • /pom.xml. Only dependency changes may trigger an application restart.

  • src/main/resources/*/.

  • src/main/java/*/ (if it exists).

  • src/main/groovy/*/ (if it exists).

  • src/main/kotlin/*/ (if it exists).

You can further include or exclude some other locations:

<project>

    <!-- ... -->

    <build>
        <plugins>

            <!-- ... -->

            <plugin>
                <groupId>io.micronaut.maven</groupId>
                <artifactId>micronaut-maven-plugin</artifactId>
                <version>4.7.1</version>
                <configuration>
                    <watches>
                        <watch>
                            <directory>src/main/resources</directory>
                            <excludes>
                                <exclude>application-test.yml</exclude>
                            </excludes>
                        </watch>
                        <watch>
                            <directory>src/main/webapp</directory>
                        </watch>
                    </watches>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Note that exclusions take precedence over inclusions, so if a file change matches both, it will be excluded.

When no includes/excludes rules are specified, a **/* pattern will be included by default.

Debugging

Debugging options can be specified on the command line directly:

  • Running in debug mode: mvn mn:run -Dmn.debug.

  • Changing the debugger port: mvn mn:run -Dmn.debug -Dmn.debug.port=5006.

  • Changing the debugger host: mvn mn:run -Dmn.debug -Dmn.debug.host=192.168.1.8 or mvn mn:run -Dmn.debug -Dmn.debug.host=*

  • Suspending the debugger execution: mn:run -Dmn.debug -Dmn.debug.suspend.

Other options

For a full list of configuration options, check the mn:run goal documentation.