如何在Maven插件的非Mojo类中使用@Parameter注解

我了解@Parameter注解可直接在Mojo类中使用，根据官方文档说明：注入Mojo参数的Bean由基于JSR330的Sisu容器处理，该注解仅在Mojo类自身的字段上生效，嵌套Bean注入需要使用Sisu或JSR330注解。但我尝试了多种方法（如下方MyParam类示例）均无法让嵌套Bean中的字段获得注入值：

问题代码示例 #

Java代码 #

/* MyParam */
@ToString
@Setter
@Getter
public class MyParam {
    // 无效
    @Parameter(defaultValue = "${project.build.outputDirectory}")
    private String outputDir0;

    // 无效
    @Inject
    @Parameter(defaultValue = "${project.build.outputDirectory}")
    private String outputDir1;

    // 无效
    @Parameters
    @Parameter(defaultValue = "${project.build.outputDirectory}")
    private String outputDir2;
}

/* mojo */
@Getter
@Setter
@Mojo(name = "my-mojo", defaultPhase = LifecyclePhase.PROCESS_RESOURCES, threadSafe = true)
public class MyMojo extends AbstractMojo {
    @Parameter(required = true)
    private MyParam myParam;

    // 有效
    @Parameter(defaultValue = "${project.build.outputDirectory}", required = true)
    protected String outputDirectory;

    public void execute() throws MojoExecutionException {
        getLog().info(String.format("myParam: %s", myParam));
        getLog().info(String.format("outputDirectory: %s", outputDirectory));
    }
}

pom.xml配置 #

<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.xxx</groupId>
    <artifactId>my-mojo-maven-plugin</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>maven-plugin</packaging>

    <name>my-mojo-maven-plugin</name>
    <description>my-mojo-maven-plugin</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <javaVersion>8</javaVersion>
        <maven.compiler.source>${javaVersion}</maven.compiler.source>
        <maven.compiler.target>${javaVersion}</maven.compiler.target>

        <maven-plugin.version>3.8.1</maven-plugin.version>
        <maven-plugin-annotations.version>3.10.2</maven-plugin.version>
        
        <lombok.version>1.18.30</lombok.version>
        <junit.version>4.13.2</junit.version>
        <slf4j.version>2.0.13</slf4j.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.apache.maven</groupId>
                <artifactId>maven-plugin-api</artifactId>
                <version>${maven-plugin.version}</version>
            </dependency>
            <dependency>
                <groupId>org.apache.maven.plugin-tools</groupId>
                <artifactId>maven-plugin-annotations</artifactId>
                <version>${maven-plugin-annotations.version}</version>
            </dependency>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>${junit.version}</version>
            </dependency>
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <version>${lombok.version}</version>
            </dependency>
            <dependency>
                <groupId>org.slf4j</groupId>
                <artifactId>slf4j-simple</artifactId>
                <version>${slf4j.version}</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.apache.maven</groupId>
            <artifactId>maven-plugin-api</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.maven.plugin-tools</groupId>
            <artifactId>maven-plugin-annotations</artifactId>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-plugin-plugin</artifactId>
                <version>3.10.2</version>
                <configuration>
                    <skipErrorNoDescriptorsFound>true</skipErrorNoDescriptorsFound>
                </configuration>
                <executions>
                    <execution>
                        <id>generate-helpgoal</id>
                        <goals>
                            <goal>helpmojo</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

插件使用配置 #

<plugin>
    <groupId>com.xmcx</groupId>
    <artifactId>my-mojo-maven-plugin</artifactId>
    <version>1.0-SNAPSHOT</version>
    <executions>
        <execution>
            <phase>process-resources</phase>
            <goals>
                <goal>my-mojo</goal>
            </goals>
            <id>my-mojo</id>
            <configuration>
                <myParam>
                </myParam>
            </configuration>
        </execution>
    </executions>
</plugin>

解决方法 #

要让嵌套Bean中的@Parameter注解生效，核心是让Sisu容器能识别并管理嵌套Bean，具体步骤如下：

1. 给嵌套Bean添加JSR330注解 #

给MyParam类添加@javax.inject.Named注解，让Sisu容器识别并处理该Bean的参数注入：

@ToString
@Setter
@Getter
@Named // 添加JSR330的Named注解
public class MyParam {
    // 现在可正常注入默认值
    @Parameter(defaultValue = "${project.build.outputDirectory}")
    private String outputDir;
}

2. 移除无效的注解组合 #

不要同时使用@Inject和@Parameter，也无需使用@Parameters注解（该注解用于标记方法参数，而非字段）。

3. 确保依赖完整 #

如果项目中没有JSR330的依赖，需要添加以下依赖（通常Maven插件API会间接依赖，但显式添加更稳妥）：

<dependency>
    <groupId>javax.inject</groupId>
    <artifactId>javax.inject</artifactId>
    <version>1</version>
    <scope>provided</scope>
</dependency>

原理说明 #

• Mojo类本身由Maven插件容器直接处理，所以类中的@Parameter注解可直接生效。
• 嵌套Bean不属于Mojo类的直接字段，需要由Sisu容器管理，因此必须添加JSR330的注解（如@Named）让Sisu识别该Bean。
• Sisu容器接管嵌套Bean后，会处理其中的@Parameter注解，完成Maven参数（包括表达式默认值）的注入。

内容的提问来源于stack exchange，提问作者xmcx