一、Runtime

在运行时（Runtime）通过反射机制运行处理的注解

/**
 * PageName注解
 *
 * @author 胡永城
 * @date 2018/1/23
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface PageName {
    String value();
}

    @Test
    public void test_class() throws Exception {
        Class clazz = Class.forName("com.hualala.supplychain.mendianbao.app.bill.BillActivity");
        Annotation anno = clazz.getAnnotation(PageName.class);
        if (anno != null && anno instanceof PageName) {
            System.out.println(((PageName) anno).value());
        } else {
            System.out.println("没有获取到注解");
        }
    }

二、Compile time

编译时（Compile time）处理注解

2.1 Annotation Processor

  用来在编译时扫描和处理注解（Annotation）

• 2.1.1 annotationProcessor
    annotationProcessor是Google提供的插件，协助Android Studio 处理annotation processors，允许配置只在编译时作为注解处理器的依赖，而不添加到最后的APK或library中
• 2.1.2 android-apt
    android-apt是由一位开发者自己开发的apt框架，随着Android Gradle 插件 2.2 版本的发布，Android Gradle 插件提供了名为 annotationProcessor 的功能来完全代替 android-apt

2.2 com.google.auto.service:auto-service:1.0-rc2

  google 公司出品，用于自动为 JAVA Processor 生成 META-INF 信息 ,注册你自定义的注解器

2.3 com.squareup:javapoet:1.9.0

  squre 公司出品，用于用于生成.java源文件的Java API

三、使用

3.1 定义注解

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.CLASS)
public @interface ActionAnnotation {
    String filter();

    String name();

    String right();

    String categoryName();

    int resIcon();

    int standardIcon();

    int sceneIcon();

    boolean isScm();

    boolean isOnly();

    boolean isDistributionAction();

    boolean isThirdShopAction();

    boolean isShowScene();

    boolean isShowStandard();
}

3.2 使用注解

    @ActionAnnotation(
            filter = "purchase",
            name = "订货",
            right = "mendianbao.mendianbaodinghuodan.add",
            categoryName = STOCK_MANAGEMENT,
            resIcon = R.drawable.ic_action_dinghuo,
            sceneIcon = R.drawable.baohuo,
            isShowScene = true,
            standardIcon = R.drawable.standard_baohuo,
            isShowStandard = true,
            isScm = true,
            isOnly = false,
            isDistributionAction = false,
            isThirdShopAction = true)
    private String purchase;

3.3 获取注解并生成Java文件

@Override
    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
        if (!mIsFirst) {
            return true;
        }
        List<Action> list = new ArrayList<>();
        for (Element element : roundEnvironment.getElementsAnnotatedWith(ActionAnnotation.class)) {
            if (element.getKind() == ElementKind.FIELD) {
                ActionAnnotation actionAnnotation = element.getAnnotation(ActionAnnotation.class);
                Action action = new Action();
                action.setFilter(actionAnnotation.filter());
                action.setName(actionAnnotation.name());
                action.setRight(actionAnnotation.right());
                action.setCategoryName(actionAnnotation.categoryName());
                action.setResIcon(actionAnnotation.resIcon());
                action.setSceneIcon(actionAnnotation.sceneIcon());
                action.setShowScene(actionAnnotation.isShowScene());
                action.setStandardIcon(actionAnnotation.standardIcon());
                action.setShowStandard(actionAnnotation.isShowStandard());
                action.setScm(actionAnnotation.isScm());
                action.setOnly(actionAnnotation.isOnly());
                action.setDistributionAction(actionAnnotation.isDistributionAction());
                action.setThirdShopAction(actionAnnotation.isThirdShopAction());
                list.add(action);
            }
        }
        //sceneIcon
        FieldSpec actionScene = FieldSpec.builder(ParameterizedTypeName.get(Map.class, String.class, Integer.class), "ACTION_ICON")
                .addModifiers(Modifier.PUBLIC, Modifier.STATIC, Modifier.FINAL)
                .initializer("new $T()", HashMap.class)
                .build();
        CodeBlock.Builder codeBlockScene = CodeBlock.builder();

        //循环添加
        for (Action action : list) {
            if (action.isShowScene()) {
                codeBlockScene.addStatement("ACTION_ICON.put($S, $L)", action.getFilter(), action.getSceneIcon());
            }
        }

        TypeSpec finderClass = TypeSpec.classBuilder("IconHelper")
                .addModifiers(Modifier.PUBLIC)
                .addJavadoc("Automatically generated file. DO NOT MODIFY")
                .addField(actionScene)
                .addStaticBlock(codeBlockScene.build())
                .build();
        JavaFile javaFile = JavaFile.builder("com.hualala.mendianbao.injecter", finderClass)
                .build();
        try {
            javaFile.writeTo(mFiler);
            mIsFirst = false;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return true;
    }