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Working with Maven Plugins

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By Alexander Chuev
4 min read

Introduction

Maven is a widely used build automation tool in the Java ecosystem, facilitating project management, build processes, and dependency management. At the core of Maven’s flexibility are its plugins, which enable the customization and extension of Maven’s capabilities. This article explores the configuration and use of standard Maven plugins, how to create and customize your own plugins, and provides examples of utilizing plugins for testing and deployment.

Overview of Standard Maven Plugins

Maven plugins are essential components that enhance the functionality of Maven. Two commonly used standard plugins are the maven-compiler-plugin and the maven-surefire-plugin.

  1. Maven Compiler Plugin
    This plugin is responsible for compiling the source code of the project. It handles both Java source files and test files. The plugin allows you to specify the source and target Java versions, ensuring compatibility across different environments. 
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    <build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.8.1</version>
      <configuration>
        <source>1.8</source>
        <target>1.8</target>
      </configuration>
    </plugin>
  </plugins>
</build>

    Plugins are configured within the pom.xml file of a Maven project. The section of the pom.xml is where build plugins are declared. In this plugin configuration, the `source` and `target` tags specify Java 8. Adjust these values according to the Java version you are using.

  2. Maven Surefire Plugin
    This plugin is designed to run the unit tests of your project. It supports a range of test frameworks and provides options for test configuration and reporting. It allows you to customize the test execution environment, including specifying test classes or patterns. 
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    <build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-surefire-plugin</artifactId>
      <version>3.0.0-M5</version>
      <configuration>
        <includes>
          <include>**/*Test.java</include>
        </includes>
      </configuration>
    </plugin>
  </plugins>
</build>

    Here, the includes tag ensures that only files ending with Test.java are included in the test run.

  3. Maven Failsafe Plugin
    This plugin is used for integration tests, complementing the maven-surefire-plugin. It runs tests in the src/integration-test/java directory and is configured similarly. 
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    <build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-failsafe-plugin</artifactId>
      <version>3.0.0-M5</version>
      <executions>
        <execution>
          <goals>
            <goal>integration-test</goal>
            <goal>verify</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>
  4. Maven Deploy Plugin
    This plugin handles the deployment of artifacts to a remote repository. 
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    <build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-deploy-plugin</artifactId>
      <version>2.8.2</version>
      <configuration>
        <repositoryId>releases</repositoryId>
        <url>https://myrepository.com/releases</url>
      </configuration>
    </plugin>
  </plugins>
</build>

    Configure the repository details to match your remote repository settings.

Managing Plugin Versions

It’s important to define specific versions for each plugin to ensure consistency across builds. Maven supports the <pluginManagement> tag, which allows you to define default versions and configurations for plugins used in your project, without directly binding them to a specific phase.

This is especially useful in multi-module projects, where <pluginManagement> helps centralize plugin configuration in the parent POM, ensuring all modules inherit the same versions and settings. While plugins defined in <pluginManagement> are not automatically executed, their versions and configurations can be referenced in child POMs by adding them to the <plugins> section. This approach helps avoid version conflicts and ensures consistency across different modules and environments.

Here is an example of managing plugin versions globally in your pom.xml:

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<build>
  <pluginManagement>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.8.1</version>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>3.0.0-M5</version>
      </plugin>
    </plugins>
  </pluginManagement>
</build>

This ensures that every module in the project uses the specified versions of the compiler and Surefire plugins.

Creating and Customizing Your Own Plugins

Creating a custom Maven plugin involves several steps. Maven plugins are essentially Java projects that use the Maven Plugin API.

  1. Set Up the Plugin Project
    Create a new Maven project and include the maven-plugin-api dependency. 
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    <dependency>
  <groupId>org.apache.maven</groupId>
  <artifactId>maven-plugin-api</artifactId>
  <version>3.8.4</version>
  <scope>provided</scope>
</dependency>
  2. Implement the Plugin
    Develop a Java class that extends AbstractMojo and implements the execute method. This class defines the plugin’s behavior. 
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    @Mojo(name = "greet")
public class GreetMojo extends AbstractMojo {
    @Parameter(property = "name", defaultValue = "World")
    private String name;
    
    public void execute() throws MojoExecutionException {
         getLog().info("Hello, " + name + "!");
    }
}

    In this example, the plugin prints a greeting message. The @Mojo annotation specifies the name of the goal, and the @Parameter annotation binds the property to a Maven configuration parameter.

  3. Define the Plugin Descriptor
    Create a META-INF/maven/plugin.xml file to describe the plugin, including goals and configuration options. 
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    <plugin>
  <groupId>com.example</groupId>
  <artifactId>my-plugin</artifactId>
  <version>1.0-SNAPSHOT</version>
  <goals>
    <goal>greet</goal>
  </goals>
</plugin>
  4. Deploy and Test the Plugin
    Install or deploy your plugin to a Maven repository, then configure it in your Maven projects like any other plugin. 
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    <plugin>
  <groupId>com.example</groupId>
  <artifactId>my-plugin</artifactId>
  <version>1.0-SNAPSHOT</version>
  <executions>
    <execution>
      <goals>
        <goal>greet</goal>
      </goals>
    </execution>
  </executions>
</plugin>

Conclusion

Maven plugins are powerful tools that can greatly enhance and customize your build process. By understanding the configuration of standard plugins and learning how to create and customize your own, you can tailor Maven to meet your specific project needs. Whether you are handling compilation, testing, or deployment, Maven plugins offer a flexible and robust approach to managing various aspects of the build lifecycle.

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