Maven编译Kotlin项目时无法引用注解生成Java类求助

我有一个Kotlin项目，部分代码通过Annotation Processing（AbstractProcessor）生成，生成的是Java代码，输出路径为：

./target/generated-sources/annotations

当前Maven构建配置下，生成的Java代码可以正常访问项目中的Kotlin类，Java代码编译完全正常，但当Kotlin代码引用这些生成的Java类时，执行命令：

mvn clean package spring-boot:repackage -Pproduction -DskipTests=true

会出现编译错误：

[ERROR] Failed to execute goal org.jetbrains.kotlin:kotlin-maven-plugin:1.7.22:compile (compile) on project xxx: Compilation failure: Compilation failure:
[ERROR] /path/to/project/src/main/kotlin/com/x/y/z/View.kt:[12,44] Unresolved reference: CRUD
[ERROR] /path/to/project/src/main/kotlin/com/x/y/z/View.kt:[35,38] Unresolved reference: XxxCRUDController

当前使用的Maven构建配置如下：

<build>
    <finalName>xxx</finalName>
    <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
    <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
    <plugins>
        <plugin>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-plugin</artifactId>
            <configuration>
                <args>
                    <arg>-Xjsr305=strict</arg>
                </args>
                <compilerPlugins>
                    <plugin>spring</plugin>
                </compilerPlugins>
            </configuration>
            <dependencies>
                <dependency>
                    <groupId>org.jetbrains.kotlin</groupId>
                    <artifactId>kotlin-maven-allopen</artifactId>
                    <version>${kotlin.version}</version>
                </dependency>
            </dependencies>

            <executions>
                <execution>
                    <id>compile</id>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
                            <sourceDir>${project.build.directory}/generated-sources/annotations</sourceDir>
                        </sourceDirs>
                    </configuration>
                </execution>
                <execution>
                    <id>test-compile</id>
                    <goals>
                        <goal>test-compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
                            <sourceDir>${project.build.directory}/generated-sources/annotations</sourceDir>
                        </sourceDirs>
                    </configuration>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <executions>
                <!-- Replacing default-compile as it is treated specially by maven -->
                <execution>
                    <id>default-compile</id>
                    <phase>none</phase>
                </execution>
                <!-- Replacing default-testCompile as it is treated specially by maven -->
                <execution>
                    <id>default-testCompile</id>
                    <phase>none</phase>
                </execution>
                <execution>
                    <id>java-compile</id>
                    <phase>compile</phase>
                    <goals> <goal>compile</goal> </goals>
                    
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>

        <!--
            Take care of synchronizing java dependencies and imports in
            package.json and main.js files.
            It also creates webpack.config.js if not exists yet.
        -->
        <plugin>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-maven-plugin</artifactId>
            <version>${vaadin.version}</version>
            <executions>
                <execution>
                    <goals>
                        <goal>prepare-frontend</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

问题根源是编译顺序错误：Kotlin编译时，注解处理器生成的Java代码还未就绪，或者Kotlin编译器无法识别生成的代码目录。按照以下步骤修改配置即可解决：

1. 调整注解处理与编译顺序 #

让注解处理器在Kotlin编译前执行，确保生成代码提前就绪。修改maven-compiler-plugin配置：

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.5.1</version>
    <configuration>
        <source>1.8</source> <!-- 根据项目使用的JDK版本调整 -->
        <target>1.8</target>
        <annotationProcessorPaths>
            <!-- 这里添加你的注解处理器依赖，例如： -->
            <!-- <path>
                <groupId>com.your.processor.group</groupId>
                <artifactId>your-processor-artifact</artifactId>
                <version>your-processor-version</version>
            </path> -->
        </annotationProcessorPaths>
        <generatedSourcesDirectory>${project.build.directory}/generated-sources/annotations</generatedSourcesDirectory>
    </configuration>
    <executions>
        <execution>
            <id>default-compile</id>
            <phase>process-sources</phase> <!-- 提前到process-sources阶段执行注解生成 -->
            <goals>
                <goal>compile</goal>
            </goals>
            <configuration>
                <skipMainCompile>true</skipMainCompile> <!-- 仅执行注解处理，不编译主Java源码 -->
            </configuration>
        </execution>
        <execution>
            <id>java-compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
        </execution>
        <execution>
            <id>default-testCompile</id>
            <phase>none</phase>
        </execution>
    </executions>
</plugin>

2. 更新Kotlin插件配置，确保能访问生成代码 #

修改kotlin-maven-plugin，移除生成目录从sourceDirs（避免Kotlin尝试编译Java源码），转而将生成目录加入classpath，同时确保Kotlin编译在Java编译之后执行：

<plugin>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-maven-plugin</artifactId>
    <configuration>
        <args>
            <arg>-Xjsr305=strict</arg>
        </args>
        <compilerPlugins>
            <plugin>spring</plugin>
        </compilerPlugins>
        <!-- 将生成代码目录加入classpath，让Kotlin编译器能找到生成的类 -->
        <classpathElements>
            <classpathElement>${project.build.directory}/generated-sources/annotations</classpathElement>
        </classpathElements>
    </configuration>
    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-allopen</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
    </dependencies>
    <executions>
        <execution>
            <id>compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>
        <execution>
            <id>test-compile</id>
            <goals>
                <goal>test-compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>
    </executions>
</plugin>

3. 标记生成目录为Maven源码目录 #

添加build-helper-maven-plugin，让Maven整体识别生成的代码目录，避免IDE或其他插件无法识别：

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <version>3.3.0</version>
    <executions>
        <execution>
            <id>add-source</id>
            <phase>generate-sources</phase>
            <goals>
                <goal>add-source</goal>
            </goals>
            <configuration>
                <sources>
                    <source>${project.build.directory}/generated-sources/annotations</source>
                </sources>
            </configuration>
        </execution>
    </executions>
</plugin>

关键说明 #

• 注解处理器必须在Kotlin编译前完成代码生成，否则Kotlin编译器找不到生成的类
• 不要让Kotlin插件尝试编译生成的Java源码，而是通过classpath引用已编译的类
• 标记生成目录为源码目录，确保Maven生态中的所有工具都能识别这些代码

内容的提问来源于stack exchange，提问作者tagtraeumer