MavenProject 注入似乎不起作用

Question

我尝试编写自己的 maven 插件，并尝试使用通常的注释访问 MavenProject。但是，当我执行插件时，项目字段不会被注入并保持为空。这是我的示例代码：

package xyz;

import org.apache.maven.plugin.*;
import org.apache.maven.plugins.annotations.*;
import org.apache.maven.project.*;

/**
 * @goal develop
 *
 */
public class Experiment extends AbstractMojo {

    @Parameter( defaultValue = "${project}", readonly = true, required = true )
    protected MavenProject project;

    @Override
    public void execute() throws MojoExecutionException, MojoFailureException {
        if (project == null) {
            getLog().error("Variable ${project} is null!");
        } else {
            getLog().info("Variable ${project} is filled!");
        }
    }
}

无论我尝试什么，我都无法让它工作，因为 maven 会自动将正确的对象注入项目字段，我总是得到该字段为空的信息。知道我做错了什么吗？

pom 文件似乎不是这里有趣的部分，因为我在构建中使用了多年的大 pom 时会出现这种行为。但即使使用最简单的 pom 文件，我也可以重现它：

 <project>
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.mycompany.app</groupId>
   <artifactId>my-app</artifactId>
   <version>1</version>
 </project>

Answer 1

由于没有pom.xml该maven-plugin项目，请尝试如下：

这pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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>stackoverflow.maven</groupId>
    <artifactId>31111852</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>maven-plugin</packaging>
    <parent>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>mojo-parent</artifactId>
        <version>34</version>
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.apache.maven.plugin-tools</groupId>
            <artifactId>maven-plugin-annotations</artifactId>
            <version>3.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.maven</groupId>
            <artifactId>maven-core</artifactId>
            <version>3.3.1</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-plugin-plugin</artifactId>
                <version>3.2</version>
                <configuration>
                    <skipErrorNoDescriptorsFound>true</skipErrorNoDescriptorsFound>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.codehaus.plexus</groupId>
                <artifactId>plexus-component-metadata</artifactId>
                <version>1.5.5</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>generate-metadata</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

文件stackoveflow.Experiment.java​

package stackoveflow;

import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugin.MojoFailureException;
import org.apache.maven.plugins.annotations.Mojo;
import org.apache.maven.plugins.annotations.Parameter;
import org.apache.maven.project.MavenProject;

@Mojo(name = "develop")
public class Experiment extends AbstractMojo {

    @Parameter( property ="project", defaultValue = "${project}", readonly = true, required = true )
    protected MavenProject project;


    public void execute() throws MojoExecutionException, MojoFailureException {
        if (project == null) {
            getLog().error("Variable ${project} is null!");
        } else {
            getLog().info("Variable ${project} is filled!");
        }
    }
}

在本地安装它maven clean install，

然后运行它mvn stackoverflow.maven:31111852:develop