Develop one of your Maven plug-ins: Hello World

Maven has been used for a long time and various plug-ins are used. However, if you do not have any plug-ins, you still need to write them by yourself. Writing a plug-in is not difficult. Another advantage of writing a plug-in is to learn more about the maven working mechanism. It is helpful for better use of Maven.

Create a Maven project named plugin-example1 first.

The term mojo is Maven plain old Java object, which is a common Java class.
We need the mojo api library, so add a dependency in POM. xml:

  <dependencies>    <dependency>      <groupId>org.apache.maven</groupId>      <artifactId>maven-plugin-api</artifactId>      <version>2.0</version>    </dependency>  </dependencies>

Create an example class that inherits from abstractmojo and implements the execute method.
The code is simple:

public class Example extends AbstractMojo{    public void execute() throws MojoExecutionException, MojoFailureException {        getLog().info("Hello world");    }    }

Getlog () obtains the internal log of abstractmojo. The type is org. Apache. Maven. plugin. Logging. log;
At least in Mojo development, do not use other log infrastructure.

Modify the description of the project:

  <groupId>org.freebird</groupId>  <artifactId>plugin-example1</artifactId>  <version>1.0-SNAPSHOT</version>  <packaging>maven-plugin</packaging>  <name>plugin-example1</name>  <url>http://maven.apache.org</url>  <properties>    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>  </properties>

Note that the value of packaging is Maven-plugin.

Compile it now and you will soon encounter an error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:2.9:descriptor (default-descriptor) on project plugin-example1: Error extracting plugin descriptor: 'No mojo definitions were found for plugin: org.freebird:plugin-example1.' -> [Help 1]org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:2.9:descriptor (default-descriptor) on project plugin-example1: Error extracting plugin descriptor: 'No mojo definitions were found for plugin: org.freebird:plugin-example1.'

You need to add a Maven-plugin to generate a descriptor. I don't know why it is not mentioned in Maven official documentation.

  <build>    <plugins>      <plugin>        <groupId>org.apache.maven.plugins</groupId>        <artifactId>maven-plugin-plugin</artifactId>        <version>3.0</version>        <executions>        </executions>        <configuration>          <!-- Needed for Java 5 annotation based configuration, for some reason. -->          <skipErrorNoDescriptorsFound>true</skipErrorNoDescriptorsFound>        </configuration>      </plugin>    </plugins>  </build>

In this way, the compilation is successful. Or add a descriptor to the class watching:

/** * * @goal sayhi */public class Example extends AbstractMojo{

To deploy maven on a private server, add the following Configuration:

  <distributionManagement>    <snapshotRepository>      <id>snapshots</id>      <url>http://your_server:8080/nexus/content/repositories/snapshots</url>    </snapshotRepository>  </distributionManagement>

Then run MVN clean package deploy

Deployed successfully.