android studio配置apt 使用Annotation

1、生成类的Processor必须在类型为“Java or Kotlin Library"的module下，如果没有，则需要新建一个[原因是需要引入

[javax.annotation.processing]包，这个包是jre下面的，只有在这种类型的Module下才能引入。

 2、实现

AbstractProcessor的方法，代码示例如下：

@AutoService(Processor.class)
public class HandlerProcessor extends AbstractProcessor {


    @Override
    public synchronized void init(ProcessingEnvironment processingEnv) {
        super.init(processingEnv);
        //注解处理器提供的API
        processingEnv.getMessager().printMessage(Diagnostic.Kind.NOTE, "HandlerProcessor init");
    }

    @Override
    public Set<String> getSupportedAnnotationTypes() {
        Set<String> hashSet = new HashSet<>();
        hashSet.add(Handler.class.getCanonicalName());
        return hashSet;
    }
    /**
     * 编译版本，固定写法就可以
     */
    @Override
    public SourceVersion getSupportedSourceVersion() {
        return processingEnv.getSourceVersion();
    }


    /**
     * 扫描注解回调
     */
    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        //拿到所有添加Handler注解的成员变量
        Set<? extends Element> elements = roundEnv.getElementsAnnotatedWith(Handler.class);
        if(elements.size() == 0 ) {
            return false;
        }
        Element firstEle = elements.stream().findAny().get();
        Handler firstHandler = firstEle.getAnnotation(Handler.class);
        String packageName = firstHandler.pakcageName();
        String pakcage = "com.nhzero.connection.handler";
        String simpleClsName = "ConnectionHandlerRegister";
        String className = "com.nhzero.connection.handler.ConnectionHandlerRegister";
        if(packageName.contains("device")) {
            className = "com.nhzero.device.handler.DeviceHandlerRegister";
            pakcage = "com.nhzero.device.handler";
            simpleClsName = "DeviceHandlerRegister";
        }
        try {
            JavaFileObject fileObject = processingEnv.getFiler().createSourceFile(className);
            Writer writer = fileObject.openWriter();
            writer.write("package " + pakcage + ";\n");
            writer.write("import com.nhzero.connection.HandlerContext;\n");
            writer.write("import com.nhzero.connection.handler.MessageHandler;\n");

            for (Element element : elements) {
                Name simpleName = element.getSimpleName();
                Handler handler = element.getAnnotation(Handler.class);
                writer.write("import " + handler.pakcageName() + "." + simpleName + ";\n");
            }

            writer.write("public class " + simpleClsName + " {\n");
            writer.write("  public static void init() {\n");

            int i = 0;
            for (Element element : elements) {
                //拿到成员变量名
                Name simpleName = element.getSimpleName();
                Handler handler = element.getAnnotation(Handler.class);
                //输出成员变量名
                processingEnv.getMessager().printMessage(Diagnostic.Kind.NOTE, simpleName);
                if(handler.hasGetInstance()) {
                    writer.write("    MessageHandler handler" + i + " = " + simpleName + ".getInstance();\n");
                } else {
                    writer.write("    MessageHandler handler" + i + " = new " + simpleName + "();\n");
                }

                writer.write("    HandlerContext.addHandler(handler" + i + ", MessageHandler.class, " +
                        (handler.isMultiple()? "e -> e.supportTypes())": "e -> e.supportType())") + ";\n");
                i++;
            }
            writer.write("  }\n");
            writer.write("}\n");
            writer.flush();
            writer.close();
        } catch (Exception e) {
        }


        return false;
    }


    
}

3、上述生成类的HandlerProcessor 所在的module的gradle文件

plugins {
    id 'java-library'
}

java {
    sourceCompatibility = JavaVersion.VERSION_17
    targetCompatibility = JavaVersion.VERSION_17
}

dependencies {
    compileOnly 'com.google.auto.service:auto-service:1.0-rc6'
    annotationProcessor 'com.google.auto.service:auto-service:1.0-rc6'
}

//java控制台输出中文乱码
tasks.withType(JavaCompile) {
    options.encoding = "UTF-8"
}

4、其他module引入上述module

implementation project(':base:apt')
annotationProcessor project(path: ':base:apt')

annotationProcessor 是用于注解扫描，

implementation 是用于引入上面module中定义的Handler注解,这个例子是把注解类和Processor类放在了同一个module下面。

5、特别要注意的
module引入annotationProcessor project(path: ':base:apt') 只能扫描当前module下的加注解的类，而不能扫描引入的其他jar包或其他module下带注解的类