Gradle多模块下Java注解处理器生成类报错求助

我正在使用Gradle多模块结构学习Java注解处理器，想要实现类似Lombok @Builder的注解。目前可以在build/generated/sources/annotationProcessor/java目录生成类，但尝试在被注解类的同包下生成类时，构建任务报错提示尝试替换文件。

项目结构 #

ROOT
|
|-sample  # 包含主类
|-annotation # 供处理器读取的注解
|-processor # 用于生成代码的处理器

各模块配置代码 #

sample模块build.gradle #

plugins {
    id("java")
}

group = "br.com.dio"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

dependencies {
    implementation(project(":annotation"))
    compileOnly(project(":annotation"))
    implementation(project(":processor"))
    annotationProcessor(project(":processor"))
}

processor模块build.gradle #

plugins {
    id("java")
}

group = "br.com.dio"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

val autoServiceVersion = "1.1.1"

dependencies {
    compileOnly("com.google.auto.service:auto-service:$autoServiceVersion")
    annotationProcessor("com.google.auto.service:auto-service:$autoServiceVersion")
    implementation("com.squareup:javapoet:1.13.0")
}

annotation模块build.gradle #

plugins {
    id("java")
}

group = "br.com.dio"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

dependencies {
}

settings.gradle.kts #

rootProject.name = "annotation-processor"
include("processor")
include("sample")
include("annotation")

Processor实现代码 #

public class BuilderProcessor extends AbstractProcessor {

    @Override
    public boolean process(final Set<? extends TypeElement> annotations, final RoundEnvironment roundEnv) {
        for (TypeElement annotation : annotations) {
            for (Element element : roundEnv.getElementsAnnotatedWith(annotation)) {
                Map<String, TypeMirror> fields =element.getEnclosedElements().stream()
                        .filter(e -> e.getKind() == FIELD)
                        .collect(Collectors.toMap(e -> e.getSimpleName().toString(), Element::asType));
                final var packageName = processingEnv.getElementUtils().getPackageOf(element).toString();
                final var className = element.getSimpleName().toString();
                final var fullNameClass = packageName + "." + className;
                final var typeSpec = new BuilderCreate().create(packageName, className, fields);
                var javaFile = JavaFile.builder(packageName, typeSpec)
                        .indent("    ")
                        .build();
                try(
                        var out = new PrintWriter(processingEnv.getFiler()
                                .createSourceFile(className)
                                .openWriter()
                        )
                ){
                    out.println(javaFile);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
        return true;
    }

}

错误原因 #

1. 源文件路径定位错误：createSourceFile(className)仅传递了类名，未指定完整限定类名（包名+类名），导致Filer无法在被注解类的对应包路径下生成文件，反而尝试在默认包创建文件，引发路径冲突。
2. 类名重复：生成的类名和原被注解类名完全一致，Filer不允许覆盖已存在的源文件（原类在src/main/java下），因此报错“尝试替换文件”。

修复步骤 #

1. 修改Processor代码，使用完整限定类名创建源文件 #

将createSourceFile(className)改为传递包名+生成类名，同时给生成的Builder类添加后缀（如Builder）避免和原类重名：

public class BuilderProcessor extends AbstractProcessor {

    @Override
    public boolean process(final Set<? extends TypeElement> annotations, final RoundEnvironment roundEnv) {
        for (TypeElement annotation : annotations) {
            for (Element element : roundEnv.getElementsAnnotatedWith(annotation)) {
                Map<String, TypeMirror> fields = element.getEnclosedElements().stream()
                        .filter(e -> e.getKind() == FIELD)
                        .collect(Collectors.toMap(e -> e.getSimpleName().toString(), Element::asType));
                final var packageName = processingEnv.getElementUtils().getPackageOf(element).toString();
                final var className = element.getSimpleName().toString();
                // 定义生成的Builder类名，避免和原类重名
                final var builderClassName = className + "Builder";
                // 完整限定类名
                final var fullBuilderClassName = packageName + "." + builderClassName;
                
                // 传递builderClassName给create方法，确保生成的类名正确
                final var typeSpec = new BuilderCreate().create(packageName, builderClassName, fields);
                var javaFile = JavaFile.builder(packageName, typeSpec)
                        .indent("    ")
                        .build();
                try(
                        var out = new PrintWriter(processingEnv.getFiler()
                                .createSourceFile(fullBuilderClassName)
                                .openWriter()
                        )
                ){
                    // 使用JavaPoet内置方法写入，格式更可靠
                    javaFile.writeTo(out);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
        return true;
    }

}

2. 优化sample模块依赖 #

移除不必要的implementation(project(":processor"))，因为注解处理器不需要被主代码依赖，只需要annotationProcessor声明即可：

plugins {
    id("java")
}

group = "br.com.dio"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

dependencies {
    compileOnly(project(":annotation"))
    annotationProcessor(project(":processor"))
}

关键说明 #

• Filer.createSourceFile必须接收完整限定类名，这样才能在对应的包路径下生成文件，避免路径冲突。
• 生成的辅助类（如Builder）必须和原类名区分开，禁止重名，否则Filer会因为尝试覆盖已有文件而报错。
• 使用javaFile.writeTo(out)替代手动println，能保证生成代码的格式正确，避免额外的格式问题。

内容的提问来源于stack exchange，提问作者Jose Luiz Junior