未注入 Maven 插件 @Parameter defaultValue

Question

I have a simple Mojo dto class:

public Output
{

  @Parameter(name="target", required=true)
  private File location;
  
  @Parameter(name="encoding", defaultValue="UTF-8")
  private String encoding;
 
// getters and setters 
}  

I expect that the field encoding will contain UTF-8 if not defined otherwise in pom.xml :

        <plugin>
            <!-- my plugin -->
            <configuration>
                <outputs>
                    <output>
                        <target>${basedir}/src/main/resources/target.json</target>
                    </output>
                </outputs>
            </configuration>
        </plugin>

Instead I get null.

Is my expectation wrong or I'm missing something important?

Answer 1

One things looks suspicious in your example:

@Parameter annotation should usually have property (and defaultValue ) and you set the name instead.

Assuming you're using the correct annotation (it should be this one the source code ), make sure you use property link in this example for instance.

Update 1

Take a look at surefire plugin source code here , for example see the parameter definition (line 544):

 @Parameter( property = "forkCount", defaultValue = "1" )
 private String forkCount;

Note, that they use property not the name like you did in the question.

In the pom.xml you'll be able to use it like this:

<plugin>
       <groupId>org.apache.maven.plugins</groupId>
       <artifactId>maven-surefire-plugin</artifactId>
       <version>...</version>
       <configuration>              
          <forkCount>12345</forkCount>
          ...
       </configuration>
    </plugin>

If you want more complex XML (with inner elements) I'm not aware of the way to map it to the DTO like you did (I might be wrong though).

For example fabric8 maven plugin ( see the source code ) doesn't use compound objects (DTOs) and injects values directly:

@Parameter(property = "fabric8.kubernetesManifest", defaultValue = "${basedir}/target/classes/META-INF/fabric8/kubernetes.yml")
private File kubernetesManifest;