一、创建一个Module用于存放自定义注解
1 创建Module MyAnnotation

2 添加build.gradle配置

apply plugin: 'java-library'

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
}

sourceCompatibility = "1.7"
targetCompatibility = "1.7"

二、创建一个Module用于存放注解处理类Processor
1 创建Module MyProcessor
2 添加build.gradle配置

apply plugin: 'java-library'

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation project(':MyAnnotation')
    implementation 'com.google.auto.service:auto-service:1.0-rc2' //build的时候会执行注解处理类
    implementation 'com.squareup:javapoet:1.7.0'//辅助生成java文件
}

sourceCompatibility = "1.7"
targetCompatibility = "1.7"

三、app包的build.gradle
添加

implementation project(':MyAnnotation')
annotationProcessor project(':MyProcessor')

四、自定义注解TestAnnotation.java

@Retention(RetentionPolicy.RUNTIME)
public @interface TestAnnotation {
    String name() default "123";
}

五、编写注解处理类

@AutoService(Processor.class)//自动生成 javax.annotation.processing.IProcessor 文件,使得自定义注解处理类可以在编译时执行
@SupportedSourceVersion(SourceVersion.RELEASE_8)//java版本支持
@SupportedAnnotationTypes({"com.example.myannotation.TestAnnotation"})//标注注解处理器支持的注解类型，就是我们刚才定义的接口Test，可以写入多个注解类型。
public class MyProcessor extends AbstractProcessor{

    private Messager messager;
    private Elements elements;
    private Filer filer;

    @Override
    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
        filer = processingEnv.getFiler();
        elements = processingEnv.getElementUtils();
        messager = processingEnv.getMessager();


        MethodSpec.Builder builder = MethodSpec.methodBuilder("Log")//生成方法
                .addModifiers(Modifier.PUBLIC,Modifier.STATIC)
                .addJavadoc("@方法")
                .returns(void.class);

        for(TypeElement e: ElementFilter.typesIn(roundEnvironment.getElementsAnnotatedWith(TestAnnotation.class))){
            messager.printMessage(Diagnostic.Kind.NOTE,"print： "+e.toString());

            TestAnnotation annotation = e.getAnnotation(TestAnnotation.class);
            String name = annotation.name();
            builder.addStatement("$T.out.println($S)", System.class,name);//添加方法体
            messager.printMessage(Diagnostic.Kind.NOTE,"print： add name-->"+name);
        }

        TypeSpec typeSpec = TypeSpec.classBuilder("LogUtils")//生成类
                .addModifiers(Modifier.PUBLIC,Modifier.FINAL)//类的属性
                .addMethod(builder.build())
                .addJavadoc("@类")//类注释
                .build();

        JavaFile javaFile = JavaFile.builder("com.example.apt", typeSpec).build();//设置包名
        try {
            javaFile.writeTo(filer);//生成java文件   路径 在 app module/build/generated/source/apt
            messager.printMessage(Diagnostic.Kind.NOTE,"print： create JavaFile");
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        return true;
    }
}

最后build一下生成java文件