Exec Maven Plugin

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To use the org.codehaus.mojo Exec Maven Plugin in your Maven project, you need to configure it in your pom.xml file and decide how you want to execute programs—either external commands or Java programs—during your build process. The plugin provides two main goals: exec:exec for running external programs and exec:java for executing Java classes. Below, I’ll guide you through the steps to set it up and use it effectively.

Step 1: Add the Plugin to Your `pom.xml`

First, include the Exec Maven Plugin in the <build><plugins> section of your pom.xml. Specify the groupId, artifactId, and a version (the latest as of now is 3.1.0):

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
        </plugin>
    </plugins>
</build>

This adds the plugin to your project, but it won’t do anything yet until you configure it or run its goals manually.

Step 2: Choose Your Goal

The plugin offers two primary goals:

exec:exec: Executes any external program (e.g., shell scripts, binaries, or even the java command).
exec:java: Runs a Java class with a main method from your project in the same JVM as Maven.

You can use these goals either by running them manually from the command line (e.g., mvn exec:exec) or by binding them to a specific phase in the Maven build lifecycle.

Option 1: Running a Java Program with `exec:java`

If you want to execute a Java class from your project, use the exec:java goal. This is ideal for running a main method in a class that’s part of your project, leveraging the project’s runtime classpath (including dependencies) automatically.

Manual Execution

Add a configuration to specify the main class:

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
            <configuration>
                <mainClass>com.example.Main</mainClass>
            </configuration>
        </plugin>
    </plugins>
</build>

Then, run it from the command line:

mvn exec:java

This executes com.example.Main in the same JVM as Maven, inheriting Maven’s JVM settings.

Automatic Execution During Build

To run it automatically during a build phase (e.g., test), use the <executions> section:

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
            <executions>
                <execution>
                    <id>run-my-java</id>
                    <phase>test</phase>
                    <goals>
                        <goal>java</goal>
                    </goals>
                    <configuration>
                        <mainClass>com.example.Main</mainClass>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Now, when you run mvn test, the com.example.Main class will execute during the test phase.

Passing Arguments or System Properties

You can pass arguments to the main method or set system properties:

<configuration>
    <mainClass>com.example.Main</mainClass>
    <arguments>
        <argument>arg1</argument>
        <argument>arg2</argument>
    </arguments>
    <systemProperties>
        <systemProperty>
            <key>propertyName</key>
            <value>propertyValue</value>
        </systemProperty>
    </systemProperties>
</configuration>

Note that exec:java runs in the same JVM as Maven, so JVM options (e.g., -Xmx) are inherited from how Maven is invoked (e.g., mvn -Xmx512m exec:java).

Option 2: Running an External Program with `exec:exec`

For executing external programs like shell scripts or commands, use the exec:exec goal.

Manual Execution

Configure the plugin to run a script:

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
            <configuration>
                <executable>myScript.sh</executable>
                <workingDirectory>/path/to/dir</workingDirectory>
                <arguments>
                    <argument>param1</argument>
                    <argument>param2</argument>
                </arguments>
            </configuration>
        </plugin>
    </plugins>
</build>

Run it with:

mvn exec:exec

This executes myScript.sh with the specified arguments in the given working directory.

Automatic Execution During Build

Bind it to a phase, such as starting and stopping a server for integration tests:

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
            <executions>
                <execution>
                    <id>start-server</id>
                    <phase>pre-integration-test</phase>
                    <goals>
                        <goal>exec</goal>
                    </goals>
                    <configuration>
                        <executable>startServer.sh</executable>
                    </configuration>
                </execution>
                <execution>
                    <id>stop-server</id>
                    <phase>post-integration-test</phase>
                    <goals>
                        <goal>exec</goal>
                    </goals>
                    <configuration>
                        <executable>stopServer.sh</executable>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Running mvn integration-test will start the server before tests and stop it afterward.

Running Java with Custom JVM Options

If you need a separate JVM with specific options (unlike exec:java), use exec:exec with the java executable. You’ll need to manage the classpath manually. Here’s an example:

<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
            <configuration>
                <executable>java</executable>
                <arguments>
                    <argument>-Xmx512m</argument>
                    <argument>-classpath</argument>
                    <argument>${project.build.outputDirectory}</argument>
                    <argument>com.example.Main</argument>
                </arguments>
            </configuration>
        </plugin>
    </plugins>
</build>

To include dependencies in the classpath, you can use the maven-dependency-plugin to generate it:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <version>3.2.0</version>
            <executions>
                <execution>
                    <id>build-classpath</id>
                    <phase>generate-resources</phase>
                    <goals>
                        <goal>build-classpath</goal>
                    </goals>
                    <configuration>
                        <outputProperty>project.classpath</outputProperty>
                    </configuration>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.1.0</version>
            <executions>
                <execution>
                    <id>run-java</id>
                    <phase>test</phase>
                    <goals>
                        <goal>exec</goal>
                    </goals>
                    <configuration>
                        <executable>java</executable>
                        <arguments>
                            <argument>-Xmx512m</argument>
                            <argument>-classpath</argument>
                            <argument>${project.classpath}:${project.build.outputDirectory}</argument>
                            <argument>com.example.Main</argument>
                        </arguments>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Adjust the classpath separator (: for Unix, ; for Windows) as needed.

Additional Configuration Options

Environment Variables (for exec:exec):

<configuration>
    <executable>myScript.sh</executable>
    <environmentVariables>
        <MY_VAR>value</MY_VAR>
    </environmentVariables>
</configuration>

Working Directory: Use <workingDirectory> to set where the command runs.

Summary

The Exec Maven Plugin is versatile:

Use exec:java to run Java classes from your project easily, leveraging the project’s classpath, but it runs in Maven’s JVM.
Use exec:exec for external programs or Java with custom JVM options, requiring manual classpath management if needed.
Configure it in pom.xml and either run it manually (mvn exec:java or mvn exec:exec) or bind it to build phases with <executions>.

This setup allows you to integrate custom executions seamlessly into your Maven build process!

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