Maven Plugin

What are Maven Plugins?

Maven is actually a plugin execution framework where every task is actually done by plugins. Maven Plugins are generally used to −

• create jar file
• create war file
• compile code files
• unit testing of code
• create project documentation
• create project reports

A plugin generally provides a set of goals, which can be executed using the following syntax −

mvn [plugin-name]:[goal-name]

For example, a Java project can be compiled with the maven-compiler-plugin's compile-goal by running the following command.

mvn compiler:compile

Plugin Types

Maven provided the following two types of Plugins −

Sr.No.	Type & Description
1	Build plugins They execute during the build process and should be configured in the <build/> element of pom.xml.
2	Reporting plugins They execute during the site generation process and they should be configured in the <reporting/> element of the pom.xml.

Following is the list of few common plugins −

Sr.No.	Plugin & Description
1	clean Cleans up target after the build. Deletes the target directory.
2	compiler Compiles Java source files.
3	surefire Runs the JUnit unit tests. Creates test reports.
4	jar Builds a JAR file from the current project.
5	war Builds a WAR file from the current project.
6	javadoc Generates Javadoc for the project.
7	antrun Runs a set of ant tasks from any phase mentioned of the build.

Example
We've used maven-antrun-plugin extensively in our examples to print data on console. Refer Build Profiles chapter. Let us understand it in a better way and create a pom.xml in C:\MVN\project folder.

<project xmlns = "http://maven.apache.org/POM/4.0.0"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0
   http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.companyname.projectgroup</groupId>
   <artifactId>project</artifactId>
   <version>1.0</version>
   <build>
      <plugins>
         <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-antrun-plugin</artifactId>
            <version>1.1</version>
            <executions>
               <execution>
                  <id>id.clean</id>
                  <phase>clean</phase>
                  <goals>
                     <goal>run</goal>
                  </goals>
                  <configuration>
                     <tasks>
                        <echo>clean phase</echo>
                     </tasks>
                  </configuration>
               </execution>     
            </executions>
         </plugin>
      </plugins>
   </build>
</project>

Next, open the command console and go to the folder containing pom.xml and execute the following mvn command.

C:\MVN\project>mvn clean

Maven will start processing and displaying the clean phase of clean life cycle.

[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------
[INFO] Building Unnamed - com.companyname.projectgroup:project:jar:1.0
[INFO]    task-segment: [post-clean]
[INFO] ------------------------------------------------------------------
[INFO] [clean:clean {execution: default-clean}]
[INFO] [antrun:run {execution: id.clean}]
[INFO] Executing tasks
     [echo] clean phase
[INFO] Executed tasks
[INFO] ------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------
[INFO] Total time: < 1 second
[INFO] Finished at: Sat Jul 07 13:38:59 IST 2012
[INFO] Final Memory: 4M/44M
[INFO] ------------------------------------------------------------------

The above example illustrates the following key concepts −

• Plugins are specified in pom.xml using plugins element.
• Each plugin can have multiple goals.
• You can define phase from where plugin should starts its processing using its phase element. We've used clean phase.
• You can configure tasks to be executed by binding them to goals of plugin. We've bound echo task with run goal of maven-antrun-plugin.
• Maven will then download the plugin if not available in local repository and start its processing.