APT前置知识

注解基础：

1.元注解

• 1.@Target：目标，表示注解修饰的目标

  • ElementType.ANNOTIONS_TYPE: 目标是注解，给注解设置的注解
  • ElementType.CONSTRUCTOR: 构造方法
  • ElementType.FIELD: 属性注解
  • ElementType.METHOD: 方法注解
  • ElementType.Type: 类型如：类，接口，枚举
  • ElementType.PACKAGE: 可以给一个包进行注解
  • ElementType.PARAMETER: 可以给一个方法内的参数进行注解
  • ElementType.LOCAL_VARIABLE: 可以给局部变量进行注解

• 2.@Retention:表示需要在什么级别保存该注解信息

  • RetentionPolicy.SOURCE:在编译阶段有用，编译之后会被丢弃，不会保存到字节码class文件中
  • RetentionPolicy.CLASS：注解在class文件中可用，但是会被VM丢弃，在类加载时会被丢弃，在字节码文件处理中有用，注解默认使用这种方式
  • RetentionPolicy.RUNTIME：运行时有效，可以通过反射获取注解信息

• 3.@Document：将注解包含到javaDoc中

• 4.@Inherit：运行子类继承父类的注解

• 5.@Repeatable:定义注解可重复

2.元注解的使用方式

• 2.1：基本使用方式

java
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@Target(ElementType.METHOD) ://表示作用在方法中
@Retention(RetentionPolicy.SOURCE) ：//表示只在编译器有效
public @interface Demo1 {public int id(); //注解的值，无默认值，在创建注解的时候需要设置该值public String desc() default "no info";//注解默认值
}@Demo1(id=1)
public void getData() {
}

• 2.2：重复注解使用方式

定义Persons：

java
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@Target(ElementType.TYPE)  
@Retention(RetentionPolicy.RUNTIME)
public   @interface Persons {Person[] value();
}

定义Person：

java
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@Repeatable(Persons.class)
public  @interface Person{String role() default "";
}

使用使用：

java
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@Person(role="CEO")
@Person(role="husband")
@Person(role="father")
@Person(role="son")
public   class Man {String name="";
}

调用注解

java
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if(Man.class.isAnnotationPresent(Persons.class)) {先判断是否存在这个注解Persons p2=Man.class.getAnnotation(Persons.class);获取注解for(Person t:p2.value()){System.out.println(t.role());}
} 结果：1CEOhusbandfatherson

3.运行时注解

需要使用反射获取

JAVA
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@Retention(RetentionPolicy.RUNTIME)
public void getAnnoInfo() {Class clazz = GetAnno.class;//获得所有的方法Method[] methods = clazz.getMethods();for (Method method : methods) {method.setAccessible(true);//禁用安全机制if (method.isAnnotationPresent(Demo1.class)) {//检查是否使用了Demo1注解Demo1 demo1 = method.getAnnotation(Demo1.class);//获得注解实例String name = method.getName();//获得方法名称}
}

4.编译时注解

需要使用到APT工具

@Retention(RetentionPolicy.SOURCE)或者CLASS注解的获取 可以使用编译期注解动态生成代码，很多优秀的开源库都是使用这个方式：如Arouter ButterKnife，GreenDao，EventBus3等

APT知识储备

• 1.APT是一种注解解析工具：

在编译期找出源代码中所有的注解信息，如果指定了注解器(继承AbstractProcessor)，那么在编译期会调用这个注解器里面的代码，我们可以在这里面做一些处理， 如根据注解信息动态生成一些代码，并将代码注入到源码中

• 使用到的工具类：

工具类1：Element

表示程序的一个元素，它只在编译期存在。可以是package，class，interface，method,成员变量，函数参数，泛型类型等。

Element的子类介绍：

• ExecutableElement:类或者接口中的方法，构造器或者初始化器等元素
• PackageElement:代表一个包元素程序
• VariableElement:代表一个类或者接口中的属性或者常量的枚举类型，方法或者构造器的参数，局部变量，资源变量或者异常参数
• TypeElement:代表一个类或者接口元素
• TypeParameterElement:代表接口，类或者方法的泛型参数元素

通过Element可以获取什么信息呢？

scss
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1.asType() 返回TypeMirror：TypeMirror是元素的类型信息，包括包名，类(或方法，或参数)名/类型TypeMirror的子类：ArrayType, DeclaredType, DisjunctiveType, ErrorType, ExecutableType, NoType, NullType, PrimitiveType, ReferenceType, TypeVariable, WildcardTypegetKind可以获取类型：
2.equals(Object obj) 比较两个Element利用equals方法。
3.getAnnotation(Class annotationType) 传入注解可以获取该元素上的所有注解。
4.getAnnotationMirrors() 获该元素上的注解类型。
5.getEnclosedElements() 获取该元素上的直接子元素，类似一个类中有VariableElement。
6.getEnclosingElement() 获取该元素的父元素,如果是属性VariableElement，则其父元素为TypeElement，如果是PackageElement则返回null，如果是TypeElement则返回PackageElement，如果是TypeParameterElement则返回泛型Element
7.getKind() 返回值为ElementKind,通过ElementKind可以知道是那种element，具体就是Element的那些子类。
8.getModifiers() 获取修饰该元素的访问修饰符，public，private
9.getSimpleName() 获取元素名，不带包名，如果是变量，获取的就是变量名，如果是定义了int age，获取到的name就是age。如果是TypeElement返回的就是类名
10.getQualifiedName()：获取类的全限定名，Element没有这个方法它的子类有，例如TypeElement，得到的就是类的全类名（包名）。
11.Elements.getPackageOf(enclosingElement).asType().toString()：获取所在的包名:

工具类2： ProcessingEnvironment：

APT运行环境：里面提供了写新文件, 报告错误或者查找其他工具.

scss
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1.getFiler()：返回用于创建新的源，类或辅助文件的文件管理器。
2.getElementUtils():返回对元素进行操作的一些实用方法的实现.
3.getMessager():返回用于报告错误，警告和其他通知的信使。
4.getOptions():返回传递给注解处理工具的处理器特定选项。
5.getTypeUtils():返回一些用于对类型进行操作的实用方法的实现。

工具类3:ElementKind

如何判断Element的类型呢，需要用到ElementKind，ElementKind为元素的类型，元素的类型判断不需要用instanceof去判断，而应该通过getKind()去判断对应的类型

ini
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element.getKind()==ElementKind.CLASS;

工具类4： TypeKind

TypeKind为类型的属性，类型的属性判断不需要用instanceof去判断，而应该通过getKind()去判断对应的属性

scss
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element.asType().getKind() == TypeKind.INT

javapoet:生成java文件

3种生成文件的方式：

• 1.StringBuilder·进行拼接
• 2.模板文件进行字段替换
• 3.javaPoet 生成

StringBuilder进行拼接，模板文件进行字段替换进行简单文件生成还好，如果是复杂文件，拼接起来会相当复杂

所以一般复杂的都使用Square出品的sdk：javapoet

java
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implementation "com.squareup:javapoet:1.11.1"

自己实现自定义APT工具类

步骤：

1.创建一个单独javalib模块lib_annotions：

创建需要的注解类：

less
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@Retention(RetentionPolicy.CLASS)
@Target(ElementType.FIELD)
public @interface BindView {int value();
}

2.再创建一个javalib模块lib_compilers:

在模块中创建一个继承AbstractProcessor的类:

java
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@AutoService(Processor.class)
public class CustomProcessorTest extends AbstractProcessor {public Filer filer;private Messager messager;private List<String> result = new ArrayList<>();private int round;private Elements elementUtils;private Map<String, String> options;@Overridepublic Set<String> getSupportedAnnotationTypes() {Set<String> annotations = new LinkedHashSet<>();annotations.add(CustomBindAnnotation.class.getCanonicalName());return annotations;}@Overridepublic SourceVersion getSupportedSourceVersion() {return SourceVersion.latestSupported();}@Overridepublic synchronized void init(ProcessingEnvironment processingEnvironment) {super.init(processingEnvironment);filer = processingEnvironment.getFiler();messager = processingEnvironment.getMessager();elementUtils = processingEnv.getElementUtils();options = processingEnv.getOptions();}@Overridepublic boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {messager.printMessage(Diagnostic.Kind.NOTE,"process");Map<TypeElement, Map<Integer, VariableElement>> typeElementMap = getTypeElementMap(roundEnv);messager.printMessage(Diagnostic.Kind.NOTE,"2222");for(TypeElement key:typeElementMap.keySet()){Map<Integer, VariableElement> variableElementMap = typeElementMap.get(key);TypeSpec typeSpec = generalTypeSpec(key,variableElementMap);String packetName = elementUtils.getPackageOf(key).getQualifiedName().toString();messager.printMessage(Diagnostic.Kind.NOTE,"packetName:"+packetName);JavaFile javaFile = JavaFile.builder(packetName,typeSpec).build();try {javaFile.writeTo(processingEnv.getFiler());messager.printMessage(Diagnostic.Kind.NOTE,"3333");} catch (IOException e) {e.printStackTrace();}}return true;}private TypeSpec generalTypeSpec(TypeElement key,Map<Integer, VariableElement> variableElementMap) {return TypeSpec.classBuilder(key.getSimpleName().toString()+"ViewBinding").addModifiers(Modifier.PUBLIC).addMethod(generalMethodSpec(key,variableElementMap)).build();}private MethodSpec generalMethodSpec(TypeElement typeElement, Map<Integer, VariableElement> variableElementMap) {ClassName className = ClassName.bestGuess(typeElement.getQualifiedName().toString());String parameter = "_" + toLowerCaseFirstChar(className.simpleName());MethodSpec.Builder builder = MethodSpec.methodBuilder("bind").addModifiers(Modifier.PUBLIC,Modifier.STATIC).returns(void.class).addParameter(className,parameter);messager.printMessage(Diagnostic.Kind.NOTE,"typeElement.getQualifiedName().toString():"+typeElement.getQualifiedName().toString());messager.printMessage(Diagnostic.Kind.NOTE,"typeElement.className():"+className.simpleName().toString());messager.printMessage(Diagnostic.Kind.NOTE,"parameter:"+parameter);for(int viewId:variableElementMap.keySet()){VariableElement variableElement = variableElementMap.get(viewId);String elementName = variableElement.getSimpleName().toString();String elementType = variableElement.asType().toString();messager.printMessage(Diagnostic.Kind.NOTE,"elementName:"+elementName);messager.printMessage(Diagnostic.Kind.NOTE,"elementType:"+elementType);
//            builder.addCode("$L.$L = ($L)$L.findViewById($L);\n",parameter,elementName,elementType,parameter,viewId);builder.addStatement("$L.$L = ($L)$L.findViewById($L)",parameter,elementName,elementType,parameter,viewId);}
//        for (int viewId : varElementMap.keySet()) {
//            VariableElement element = varElementMap.get(viewId);
//            String name = element.getSimpleName().toString();
//            String type = element.asType().toString();
//            String text = "{0}.{1}=({2})({3}.findViewById({4}));";
//            builder.addCode(MessageFormat.format(text, parameter, name, type, parameter, String.valueOf(viewId)));
//        }return builder.build();}private Map<TypeElement, Map<Integer, VariableElement>> getTypeElementMap(RoundEnvironment roundEnv) {Map<TypeElement, Map<Integer, VariableElement>> typeElementMap = new HashMap<>();messager.printMessage(Diagnostic.Kind.NOTE,"1111");Set<? extends Element> variableElements = roundEnv.getElementsAnnotatedWith(CustomBindAnnotation.class);for(Element element:variableElements){VariableElement variableElement = (VariableElement) element;//作用在字段上，可以强制转换为VariableElementTypeElement typeElement = (TypeElement) variableElement.getEnclosingElement();Map<Integer, VariableElement> varElementMap = typeElementMap.get(typeElement);if(varElementMap == null){varElementMap = new HashMap<>();typeElementMap.put(typeElement,varElementMap);}CustomBindAnnotation customBindAnnotation = variableElement.getAnnotation(CustomBindAnnotation.class);int viewId = customBindAnnotation.value();varElementMap.put(viewId,variableElement);}return typeElementMap;}//将首字母转为小写private static String toLowerCaseFirstChar(String text) {if (text == null || text.length() == 0 || Character.isLowerCase(text.charAt(0))) return text;else return String.valueOf(Character.toLowerCase(text.charAt(0))) + text.substring(1);}
}

这个类中：重写以下方法

typescript
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1.getSupportedAnnotationTypes：该方法主要作用是：返回支持的注解类型public Set<String> getSupportedAnnotationTypes() {Set<String> hashSet = new HashSet<>();hashSet.add(BindView.class.getCanonicalName());return hashSet;}
2.getSupportedSourceVersion：作用：返回支持的jdk版本public SourceVersion getSupportedSourceVersion() {return SourceVersion.latestSupported();}
3.init(ProcessingEnvironment processingEnvironment)作用：返回一个ProcessingEnvironment这个工具内部有很多处理类1.getFiler()：返回用于创建新的源，类或辅助文件的文件管理器。2.getElementUtils():返回对元素进行操作的一些实用方法的实现.3.getMessager():返回用于报告错误，警告和其他通知的信使。4.getOptions():返回传递给注解处理工具的处理器特定选项。5.getTypeUtils():返回一些用于对类型进行操作的实用方法的实现。
4.process(Set<? extends TypeElement> set, RoundEnvironment environment)：作用：apt核心处理方法，可以在这里面对收集到的注解进行处理，生成动态原文件等

3.在模块的build.gradle文件中

java
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implementation "com.google.auto.service:auto-service:1.0-rc6" //使用Auto-Service来自动注册APT
//Android Plugin for Gradle >= 3.4 或者 Gradle Version >=5.0 都要在自己的annotation processor工程里面增加如下的语句
annotationProcessor 'com.google.auto.service:auto-service:1.0-rc6'implementation "com.squareup:javapoet:1.11.1"//辅助生成文件的工具类
implementation project(':lib_annotionss')//该模块是注解存再的库中

4.最后编译会自动生成对应的类。

然后在需要的地方加上注解就可以了。

编译器自动生成的文件：

java
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public class AnnotationActivityViewBinding {public static void bind(AnnotationActivity _annotationActivity) {_annotationActivity.btn1 = (android.widget.Button)_annotationActivity.findViewById(2131296347);_annotationActivity.lv = (android.widget.ListView)_annotationActivity.findViewById(2131296475);_annotationActivity.btn = (android.widget.Button)_annotationActivity.findViewById(2131296346);}
}

ARouter中APT的使用

我们来看ARouter源码框架

• app:是ARouter提供的一个测试Demo
• arouter-annotation：这个lib模块中声明了很多注解信息和一些枚举类
• arouter-api：ARouter的核心api，转换过程的核心操作都在这个模块里面
• arouter-compiler：APT处理器，自动生成路由表的过程就是在这里面实现的
• arouter-gradle-plugin：这是一个编译期使用的Plugin插件，主要作用是用于编译器自动加载路由表，节省应用的启动时间。

我们主要看arouter-annotation和arouter-compiler这两个模块

1.arouter-annotation

可以看到这里面实现了几个注解类

• Autowired：属性注解

java
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@Target({ElementType.FIELD})
@Retention(RetentionPolicy.CLASS)
public @interface Autowired {// 标志我们外部调用使用的keyString name() default "";// 如果有要求，一定要传入，不然app会crash// Primitive type wont be check!boolean required() default false;// 注解字段描述String desc() default "";
}

@Target({ElementType.FIELD})：指定我们注解是使用在属性字段上 @Retention(RetentionPolicy.CLASS)：指定我们注解只在编译期存在

• Interceptor：拦截器注解

java
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@Target({ElementType.TYPE})
@Retention(RetentionPolicy.CLASS)
public @interface Interceptor {/*** The priority of interceptor, ARouter will be excute them follow the priority.*/int priority();/*** The name of interceptor, may be used to generate javadoc.*/String name() default "Default";
}

@Target({ElementType.TYPE})：指定注解是在类上

@Retention(RetentionPolicy.CLASS)：指定注解在编译期存在

• Route：路由注解

java
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@Target({ElementType.TYPE})
@Retention(RetentionPolicy.CLASS)
public @interface Route {/*** Path of route*/String path();/*** Used to merger routes, the group name MUST BE USE THE COMMON WORDS !!!*/String group() default "";/*** Name of route, used to generate javadoc.*/String name() default "";/*** Extra data, can be set by user.* Ps. U should use the integer num sign the switch, by bits. 10001010101010*/int extras() default Integer.MIN_VALUE;/*** The priority of route.*/int priority() default -1;
}

@Target({ElementType.TYPE})：指定注解是使用在类上

@Retention(RetentionPolicy.CLASS)：指定注解是在编译期存在

枚举类：

• RouteType:路由类型

java
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public enum RouteType {ACTIVITY(0, "android.app.Activity"),SERVICE(1, "android.app.Service"),PROVIDER(2, "com.alibaba.android.arouter.facade.template.IProvider"),CONTENT_PROVIDER(-1, "android.app.ContentProvider"),BOARDCAST(-1, ""),METHOD(-1, ""),FRAGMENT(-1, "android.app.Fragment"),UNKNOWN(-1, "Unknown route type");
}
TypeKind
public enum TypeKind {// Base typeBOOLEAN,BYTE,SHORT,INT,LONG,CHAR,FLOAT,DOUBLE,// Other typeSTRING,SERIALIZABLE,PARCELABLE,OBJECT;
}

model类

• RouteMeta：路由元数据

java
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public class RouteMeta {private RouteType type;         // Type of routeprivate Element rawType;        // Raw type of routeprivate Class<?> destination;   // Destinationprivate String path;            // Path of routeprivate String group;           // Group of routeprivate int priority = -1;      // The smaller the number, the higher the priorityprivate int extra;              // Extra dataprivate Map<String, Integer> paramsType;  // Param typeprivate String name;private Map<String, Autowired> injectConfig;  // Cache inject config.
}

总结下arouter-annotation：

• 1.创建了Autowired：属性注解，Interceptor：拦截器注解，Route：路由注解
• 2.创建了RouteType:路由类型枚举，RouteMeta：路由元数据

2.arouter-compiler

• AutowiredProcessor：属性Autowired注解处理器
• InterceptorProcessor：拦截器Interceptor注解处理器
• RouteProcessor：路由Route注解处理器
• BaseProcessor：注解处理器基类，主要获取一些通用参数，上面三个都继承这个基类
• incremental.annotation.processors：拦截器声明，这里将我们需要使用的几个注解处理器做了声明

java
复制代码
com.alibaba.android.arouter.compiler.processor.RouteProcessor,aggregating
com.alibaba.android.arouter.compiler.processor.AutowiredProcessor,aggregating
com.alibaba.android.arouter.compiler.processor.InterceptorProcessor,aggregating

下面依次来看：

AutowiredProcessor：

java
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@AutoService(Processor.class)//使用AutoService可以将处理器自动注册到processors文件中
@SupportedAnnotationTypes({ANNOTATION_TYPE_AUTOWIRED}) //设置需要匹配的注解类："com.alibaba.android.arouter.facade.annotation.Autowired"
public class AutowiredProcessor extends BaseProcessor {private Map<TypeElement, List<Element>> parentAndChild = new HashMap<>();   // Contain field need autowired and his super class.private static final ClassName ARouterClass = ClassName.get("com.alibaba.android.arouter.launcher", "ARouter");private static final ClassName AndroidLog = ClassName.get("android.util", "Log");@Overridepublic synchronized void init(ProcessingEnvironment processingEnvironment) {super.init(processingEnvironment);logger.info(">>> AutowiredProcessor init. <<<");}//这是注解处理器的核心方法@Overridepublic boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {if (CollectionUtils.isNotEmpty(set)) {try {//这里将所有声明Autowired注解的属性包括在parentAndChild中:parentAndChild的key为注解的类TypeElement//parentAndChild{List<Element>{element1,element2,element3...}}categories(roundEnvironment.getElementsAnnotatedWith(Autowired.class));//生成帮助类generateHelper();} catch (Exception e) {logger.error(e);}return true;}return false;}private void generateHelper() throws IOException, IllegalAccessException {//获取com.alibaba.android.arouter.facade.template.ISyringe的TypeElementTypeElement type_ISyringe = elementUtils.getTypeElement(ISYRINGE);//获取com.alibaba.android.arouter.facade.service.SerializationService的TypeElementTypeElement type_JsonService = elementUtils.getTypeElement(JSON_SERVICE);//获取com.alibaba.android.arouter.facade.template.IProvider的TypeMirror:元素的类型信息，包括包名，类(或方法，或参数)名/类型TypeMirror iProvider = elementUtils.getTypeElement(Consts.IPROVIDER).asType();//获取android.app.Activity的TypeMirror:元素的类型信息，包括包名，类(或方法，或参数)名/类型TypeMirror activityTm = elementUtils.getTypeElement(Consts.ACTIVITY).asType();//获取android.app.Fragment的TypeMirror:元素的类型信息，包括包名，类(或方法，或参数)名/类型TypeMirror fragmentTm = elementUtils.getTypeElement(Consts.FRAGMENT).asType();TypeMirror fragmentTmV4 = elementUtils.getTypeElement(Consts.FRAGMENT_V4).asType();// 生成属性参数的辅助类ParameterSpec objectParamSpec = ParameterSpec.builder(TypeName.OBJECT, "target").build();if (MapUtils.isNotEmpty(parentAndChild)) {//遍历parentAndChild：每个entry使用的key为当前类的TypeElement，value为当前类内部所有使用注解Autowired标记的属性for (Map.Entry<TypeElement, List<Element>> entry : parentAndChild.entrySet()) {//MethodSpec生成方法的辅助类 METHOD_INJECT = 'inject'/**方法名：inject方法注解：Override方法权限：public方法参数：前面objectParamSpec生成的：Object target*/MethodSpec.Builder injectMethodBuilder = MethodSpec.methodBuilder(METHOD_INJECT).addAnnotation(Override.class).addModifiers(PUBLIC).addParameter(objectParamSpec);//key为当前类的TypeElementTypeElement parent = entry.getKey();//value为当前类内部所有使用注解Autowired标记的属性List<Element> childs = entry.getValue();//类的全限定名String qualifiedName = parent.getQualifiedName().toString();//类的包名String packageName = qualifiedName.substring(0, qualifiedName.lastIndexOf("."));//类的文件名：NAME_OF_AUTOWIRED = $$ARouter$$Autowired，完整fileName = BaseActivity$$ARouter$$AutowiredString fileName = parent.getSimpleName() + NAME_OF_AUTOWIRED;//TypeSpec生成类的辅助类/**类名：BaseActivity$$ARouter$$Autowired类doc："DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER."父类：com.alibaba.android.arouter.facade.template.ISyringe权限：public*/TypeSpec.Builder helper = TypeSpec.classBuilder(fileName).addJavadoc(WARNING_TIPS).addSuperinterface(ClassName.get(type_ISyringe)).addModifiers(PUBLIC);//生成字段属性辅助类/**字段类型：SerializationService字段名：serializationService字段属性：private*/FieldSpec jsonServiceField = FieldSpec.builder(TypeName.get(type_JsonService.asType()), "serializationService", Modifier.PRIVATE).build();//将字段添加到类：BaseActivity$$ARouter$$Autowired中helper.addField(jsonServiceField);/**给inject方法添加语句：这里parent = BaseActivity1.serializationService = ARouter.getInstance().navigation(SerializationService.class);2.BaseActivity substitute = (BaseActivity)target;*/		injectMethodBuilder.addStatement("serializationService = $T.getInstance().navigation($T.class)", ARouterClass, ClassName.get(type_JsonService));injectMethodBuilder.addStatement("$T substitute = ($T)target", ClassName.get(parent), ClassName.get(parent));/**生成方法内部代码，注入属性*/for (Element element : childs) {//获取当前element注解Autowired的属性：Autowired fieldConfig = element.getAnnotation(Autowired.class);//获取注解的名称String fieldName = element.getSimpleName().toString();//判断是否是iProvider的子类，说明iProvider字段如果使用Autowired注解的话，会单独处理if (types.isSubtype(element.asType(), iProvider)) {  // It's providerif ("".equals(fieldConfig.name())) {    // User has not set service path, then use byType.// GetterinjectMethodBuilder.addStatement("substitute." + fieldName + " = $T.getInstance().navigation($T.class)",ARouterClass,ClassName.get(element.asType()));} else {    // use byName// GetterinjectMethodBuilder.addStatement("substitute." + fieldName + " = ($T)$T.getInstance().build($S).navigation()",ClassName.get(element.asType()),ARouterClass,fieldConfig.name());}// Validator 这里如果设置了required为true，则一定要有值，否则会报错if (fieldConfig.required()) {injectMethodBuilder.beginControlFlow("if (substitute." + fieldName + " == null)");injectMethodBuilder.addStatement("throw new RuntimeException("The field '" + fieldName + "' is null, in class '" + $T.class.getName() + "!")", ClassName.get(parent));injectMethodBuilder.endControlFlow();}} else {    // It's normal intent value//普通属性/**假设fieldName = "name"originalValue = "substitute.name"statement = "substitute.name = substitute."*/String originalValue = "substitute." + fieldName;String statement = "substitute." + fieldName + " = " + buildCastCode(element) + "substitute.";boolean isActivity = false;//判断是Activity 则statement += "getIntent()."if (types.isSubtype(parent.asType(), activityTm)) {  // Activity, then use getIntent()isActivity = true;statement += "getIntent().";//判断是Fragment 则statement += "getArguments()."} else if (types.isSubtype(parent.asType(), fragmentTm) || types.isSubtype(parent.asType(), fragmentTmV4)) {   // Fragment, then use getArguments()statement += "getArguments().";} else {//非Activity和Fragment，其他情况抛异常throw new IllegalAccessException("The field [" + fieldName + "] need autowired from intent, its parent must be activity or fragment!");}//statement = "substitute.name = substitute.getIntent().getExtras() == null ? substitute.name : substitute.getIntent().getExtras()statement = buildStatement(originalValue, statement, typeUtils.typeExchange(element), isActivity, isKtClass(parent));if (statement.startsWith("serializationService.")) {   // Not mortalsinjectMethodBuilder.beginControlFlow("if (null != serializationService)");injectMethodBuilder.addStatement("substitute." + fieldName + " = " + statement,(StringUtils.isEmpty(fieldConfig.name()) ? fieldName : fieldConfig.name()),ClassName.get(element.asType()));injectMethodBuilder.nextControlFlow("else");injectMethodBuilder.addStatement("$T.e("" + Consts.TAG + "", "You want automatic inject the field '" + fieldName + "' in class '$T' , then you should implement 'SerializationService' to support object auto inject!")", AndroidLog, ClassName.get(parent));injectMethodBuilder.endControlFlow();} else {//将statement注入到injectMethodBuilder方法中injectMethodBuilder.addStatement(statement, StringUtils.isEmpty(fieldConfig.name()) ? fieldName : fieldConfig.name());}// 添加null判断if (fieldConfig.required() && !element.asType().getKind().isPrimitive()) {  // Primitive wont be check.injectMethodBuilder.beginControlFlow("if (null == substitute." + fieldName + ")");injectMethodBuilder.addStatement("$T.e("" + Consts.TAG + "", "The field '" + fieldName + "' is null, in class '" + $T.class.getName() + "!")", AndroidLog, ClassName.get(parent));injectMethodBuilder.endControlFlow();}}}//将方法inject注入到类中helper.addMethod(injectMethodBuilder.build());//生成java文件JavaFile.builder(packageName, helper.build()).build().writeTo(mFiler);logger.info(">>> " + parent.getSimpleName() + " has been processed, " + fileName + " has been generated. <<<");}logger.info(">>> Autowired processor stop. <<<");}}/*** Categories field, find his papa.** @param elements Field need autowired*/private void categories(Set<? extends Element> elements) throws IllegalAccessException {if (CollectionUtils.isNotEmpty(elements)) {for (Element element : elements) {//获取element的父元素：如果是属性，父元素就是类或者接口：TypeElementTypeElement enclosingElement = (TypeElement) element.getEnclosingElement();//如果element属性是PRIVATE，则直接报错，所以对于需要依赖注入的属性，一定不能为privateif (element.getModifiers().contains(Modifier.PRIVATE)) {throw new IllegalAccessException("The inject fields CAN NOT BE 'private'!!! please check field ["+ element.getSimpleName() + "] in class [" + enclosingElement.getQualifiedName() + "]");}//判断parentAndChild是否包含enclosingElement，第一次循环是空值会走到else分支，第二次才会包含//格式：parentAndChild{List<Element>{element1,element2,element3...}}if (parentAndChild.containsKey(enclosingElement)) { // Has categriesparentAndChild.get(enclosingElement).add(element);} else {List<Element> childs = new ArrayList<>();childs.add(element);parentAndChild.put(enclosingElement, childs);}}logger.info("categories finished.");}}
}

通过在编译器使用注解处理器AutowiredProcessor处理后，自动生成了以下文件 BaseActivity$$ARouter$$Autowired.java

java
复制代码
/*** DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER. */
public class BaseActivity$$ARouter$$Autowired implements ISyringe {private SerializationService serializationService;@Overridepublic void inject(Object target) {serializationService = ARouter.getInstance().navigation(SerializationService.class);BaseActivity substitute = (BaseActivity)target;substitute.name = substitute.getIntent().getExtras() == null ? substitute.name : substitute.getIntent().getExtras().getString("name", substitute.name);}
}

生成过程：

1.使用Map<TypeElement, List> parentAndChild = new HashMap<>()存储所有被Autowired注解的属性 key：每个类的TypeElement value：当前类TypeElement中所有的Autowired注解的属性字段

2.使用ParameterSpec生成参数

3.使用MethodSpec生成方法：METHOD_INJECT = ‘inject’

java
复制代码
方法名：inject
方法注解：Override
方法权限：public
方法参数：前面objectParamSpec生成的：Object target

4.使用TypeSpec生成类：

java
复制代码
类名：BaseActivity$$ARouter$$Autowired
类doc："DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER."
父类：com.alibaba.android.arouter.facade.template.ISyringe
权限：public

5.使用addStatement给方法添加语句body

6.将方法注入到帮助类中

java
复制代码helper.addMethod(injectMethodBuilder.build());   

7.写入java文件

java
复制代码
JavaFile.builder(packageName, helper.build()).build().writeTo(mFiler);    

RouteProcessor

java
复制代码
@AutoService(Processor.class)
@SupportedAnnotationTypes({ANNOTATION_TYPE_ROUTE, ANNOTATION_TYPE_AUTOWIRED})
//这里表示我们的RouteProcessor可以处理Route和Autowired两种注解
public class RouteProcessor extends BaseProcessor {private Map<String, Set<RouteMeta>> groupMap = new HashMap<>(); // ModuleName and routeMeta.private Map<String, String> rootMap = new TreeMap<>();  // Map of root metas, used for generate class file in order.private TypeMirror iProvider = null;private Writer docWriter;       // Writer used for write doc//初始化@Overridepublic synchronized void init(ProcessingEnvironment processingEnv) {super.init(processingEnv);//这里如果支持generateDoc，则打开docWriter，待写入文件：generateDoc字段由模块中的build.gradle文件传入if (generateDoc) {try {docWriter = mFiler.createResource(StandardLocation.SOURCE_OUTPUT,PACKAGE_OF_GENERATE_DOCS,"arouter-map-of-" + moduleName + ".json").openWriter();} catch (IOException e) {logger.error("Create doc writer failed, because " + e.getMessage());}}//获取IPROVIDER的类型TypeMirroriProvider = elementUtils.getTypeElement(Consts.IPROVIDER).asType();logger.info(">>> RouteProcessor init. <<<");}//核心处理api/*** {@inheritDoc}** @param annotations* @param roundEnv*/@Overridepublic boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {if (CollectionUtils.isNotEmpty(annotations)) {Set<? extends Element> routeElements = roundEnv.getElementsAnnotatedWith(Route.class);try {logger.info(">>> Found routes, start... <<<");//解析Routesthis.parseRoutes(routeElements);} catch (Exception e) {logger.error(e);}return true;}return false;}private void parseRoutes(Set<? extends Element> routeElements) throws IOException {if (CollectionUtils.isNotEmpty(routeElements)) {// prepare the type an so on.logger.info(">>> Found routes, size is " + routeElements.size() + " <<<");rootMap.clear();//获取Activity的TypeMirrorTypeMirror type_Activity = elementUtils.getTypeElement(ACTIVITY).asType();//获取Service的TypeMirrorTypeMirror type_Service = elementUtils.getTypeElement(SERVICE).asType();//获取Fragment的TypeMirrorTypeMirror fragmentTm = elementUtils.getTypeElement(FRAGMENT).asType();TypeMirror fragmentTmV4 = elementUtils.getTypeElement(Consts.FRAGMENT_V4).asType();// Interface of ARouter//获取IRouteGroup的TypeElementTypeElement type_IRouteGroup = elementUtils.getTypeElement(IROUTE_GROUP);获取IProviderGroup的TypeElementTypeElement type_IProviderGroup = elementUtils.getTypeElement(IPROVIDER_GROUP);//获取RouteMeta的ClassName：权限定名ClassName routeMetaCn = ClassName.get(RouteMeta.class);//获取RouteType的ClassName：权限定名ClassName routeTypeCn = ClassName.get(RouteType.class);/*创建Map<String, Class<? extends IRouteGroup>>类型的ParameterizedTypeNameBuild input type, format as :```Map<String, Class<? extends IRouteGroup>>```*/ParameterizedTypeName inputMapTypeOfRoot = ParameterizedTypeName.get(ClassName.get(Map.class),ClassName.get(String.class),ParameterizedTypeName.get(ClassName.get(Class.class),WildcardTypeName.subtypeOf(ClassName.get(type_IRouteGroup))));/*创建Map<String, RouteMeta>类型的ParameterizedTypeName```Map<String, RouteMeta>```*/ParameterizedTypeName inputMapTypeOfGroup = ParameterizedTypeName.get(ClassName.get(Map.class),ClassName.get(String.class),ClassName.get(RouteMeta.class));/*创建参数类型rootParamSpec，groupParamSpec，providerParamSpecBuild input param name.*/ParameterSpec rootParamSpec = ParameterSpec.builder(inputMapTypeOfRoot, "routes").build();ParameterSpec groupParamSpec = ParameterSpec.builder(inputMapTypeOfGroup, "atlas").build();ParameterSpec providerParamSpec = ParameterSpec.builder(inputMapTypeOfGroup, "providers").build();  // Ps. its param type same as groupParamSpec!/*创建loadInto方法的MethodSpecBuild method : 'loadInto'*/MethodSpec.Builder loadIntoMethodOfRootBuilder = MethodSpec.methodBuilder(METHOD_LOAD_INTO).addAnnotation(Override.class).addModifiers(PUBLIC).addParameter(rootParamSpec);//  Follow a sequence, find out metas of group first, generate java file, then statistics them as root.//遍历routeElements所有的path注解对象for (Element element : routeElements) {//获取对象element的TypeMirrorTypeMirror tm = element.asType();//获取element的注解RouteRoute route = element.getAnnotation(Route.class);RouteMeta routeMeta;// Activity or Fragment 如果是Activity或者Fragment：根据不同情况创建不同的routeMeta路由元数据if (types.isSubtype(tm, type_Activity) || types.isSubtype(tm, fragmentTm) || types.isSubtype(tm, fragmentTmV4)) {// Get all fields annotation by @AutowiredMap<String, Integer> paramsType = new HashMap<>();Map<String, Autowired> injectConfig = new HashMap<>();//这里是收集所有的Autowired属性参数injectParamCollector(element, paramsType, injectConfig);if (types.isSubtype(tm, type_Activity)) {// Activitylogger.info(">>> Found activity route: " + tm.toString() + " <<<");routeMeta = new RouteMeta(route, element, RouteType.ACTIVITY, paramsType);} else {// Fragmentlogger.info(">>> Found fragment route: " + tm.toString() + " <<<");routeMeta = new RouteMeta(route, element, RouteType.parse(FRAGMENT), paramsType);}routeMeta.setInjectConfig(injectConfig);} else if (types.isSubtype(tm, iProvider)) {         // IProviderlogger.info(">>> Found provider route: " + tm.toString() + " <<<");routeMeta = new RouteMeta(route, element, RouteType.PROVIDER, null);} else if (types.isSubtype(tm, type_Service)) {           // Servicelogger.info(">>> Found service route: " + tm.toString() + " <<<");routeMeta = new RouteMeta(route, element, RouteType.parse(SERVICE), null);} else {throw new RuntimeException("The @Route is marked on unsupported class, look at [" + tm.toString() + "].");}//收集路由元数据categories(routeMeta);}//创建IProvider注解的loadInto方法MethodSpec.Builder loadIntoMethodOfProviderBuilder = MethodSpec.methodBuilder(METHOD_LOAD_INTO).addAnnotation(Override.class).addModifiers(PUBLIC).addParameter(providerParamSpec);Map<String, List<RouteDoc>> docSource = new HashMap<>();// Start generate java source, structure is divided into upper and lower levels, used for demand initialization.for (Map.Entry<String, Set<RouteMeta>> entry : groupMap.entrySet()) {String groupName = entry.getKey();//创建IGroupRouter的loadInto方法MethodSpec.Builder loadIntoMethodOfGroupBuilder = MethodSpec.methodBuilder(METHOD_LOAD_INTO).addAnnotation(Override.class).addModifiers(PUBLIC).addParameter(groupParamSpec);List<RouteDoc> routeDocList = new ArrayList<>();// 创建 group 方法的 bodySet<RouteMeta> groupData = entry.getValue();for (RouteMeta routeMeta : groupData) {RouteDoc routeDoc = extractDocInfo(routeMeta);ClassName className = ClassName.get((TypeElement) routeMeta.getRawType());switch (routeMeta.getType()) {//创建PROVIDER的loadInto方法体case PROVIDER:  // Need cache provider's super classList<? extends TypeMirror> interfaces = ((TypeElement) routeMeta.getRawType()).getInterfaces();for (TypeMirror tm : interfaces) {routeDoc.addPrototype(tm.toString());if (types.isSameType(tm, iProvider)) {   // Its implements iProvider interface himself.// This interface extend the IProvider, so it can be used for mark providerloadIntoMethodOfProviderBuilder.addStatement("providers.put($S, $T.build($T." + routeMeta.getType() + ", $T.class, $S, $S, null, " + routeMeta.getPriority() + ", " + routeMeta.getExtra() + "))",(routeMeta.getRawType()).toString(),routeMetaCn,routeTypeCn,className,routeMeta.getPath(),routeMeta.getGroup());} else if (types.isSubtype(tm, iProvider)) {// This interface extend the IProvider, so it can be used for mark providerloadIntoMethodOfProviderBuilder.addStatement("providers.put($S, $T.build($T." + routeMeta.getType() + ", $T.class, $S, $S, null, " + routeMeta.getPriority() + ", " + routeMeta.getExtra() + "))",tm.toString(),    // So stupid, will duplicate only save class name.routeMetaCn,routeTypeCn,className,routeMeta.getPath(),routeMeta.getGroup());}}break;default:break;}// Make map body for paramsTypeStringBuilder mapBodyBuilder = new StringBuilder();Map<String, Integer> paramsType = routeMeta.getParamsType();Map<String, Autowired> injectConfigs = routeMeta.getInjectConfig();if (MapUtils.isNotEmpty(paramsType)) {List<RouteDoc.Param> paramList = new ArrayList<>();for (Map.Entry<String, Integer> types : paramsType.entrySet()) {mapBodyBuilder.append("put("").append(types.getKey()).append("", ").append(types.getValue()).append("); ");RouteDoc.Param param = new RouteDoc.Param();Autowired injectConfig = injectConfigs.get(types.getKey());param.setKey(types.getKey());param.setType(TypeKind.values()[types.getValue()].name().toLowerCase());param.setDescription(injectConfig.desc());param.setRequired(injectConfig.required());paramList.add(param);}routeDoc.setParams(paramList);}String mapBody = mapBodyBuilder.toString();//创建IGroupRouter的方法体loadIntoMethodOfGroupBuilder.addStatement("atlas.put($S, $T.build($T." + routeMeta.getType() + ", $T.class, $S, $S, " + (StringUtils.isEmpty(mapBody) ? null : ("new java.util.HashMap<String, Integer>(){{" + mapBodyBuilder.toString() + "}}")) + ", " + routeMeta.getPriority() + ", " + routeMeta.getExtra() + "))",routeMeta.getPath(),routeMetaCn,routeTypeCn,className,routeMeta.getPath().toLowerCase(),routeMeta.getGroup().toLowerCase());routeDoc.setClassName(className.toString());routeDocList.add(routeDoc);}// Generate groups 生成IGroupRrouter的子类文件String groupFileName = NAME_OF_GROUP + groupName;JavaFile.builder(PACKAGE_OF_GENERATE_FILE,TypeSpec.classBuilder(groupFileName).addJavadoc(WARNING_TIPS).addSuperinterface(ClassName.get(type_IRouteGroup)).addModifiers(PUBLIC).addMethod(loadIntoMethodOfGroupBuilder.build()).build()).build().writeTo(mFiler);logger.info(">>> Generated group: " + groupName + "<<<");rootMap.put(groupName, groupFileName);docSource.put(groupName, routeDocList);}if (MapUtils.isNotEmpty(rootMap)) {// Generate root meta by group name, it must be generated before root, then I can find out the class of group.for (Map.Entry<String, String> entry : rootMap.entrySet()) {loadIntoMethodOfRootBuilder.addStatement("routes.put($S, $T.class)", entry.getKey(), ClassName.get(PACKAGE_OF_GENERATE_FILE, entry.getValue()));}}// Output route docif (generateDoc) {//将path关系写入docdocWriter.append(JSON.toJSONString(docSource, SerializerFeature.PrettyFormat));docWriter.flush();docWriter.close();}// Write provider into disk 写入providerString providerMapFileName = NAME_OF_PROVIDER + SEPARATOR + moduleName;JavaFile.builder(PACKAGE_OF_GENERATE_FILE,TypeSpec.classBuilder(providerMapFileName).addJavadoc(WARNING_TIPS).addSuperinterface(ClassName.get(type_IProviderGroup)).addModifiers(PUBLIC).addMethod(loadIntoMethodOfProviderBuilder.build()).build()).build().writeTo(mFiler);logger.info(">>> Generated provider map, name is " + providerMapFileName + " <<<");// Write root meta into disk.写入root metaString rootFileName = NAME_OF_ROOT + SEPARATOR + moduleName;JavaFile.builder(PACKAGE_OF_GENERATE_FILE,TypeSpec.classBuilder(rootFileName).addJavadoc(WARNING_TIPS).addSuperinterface(ClassName.get(elementUtils.getTypeElement(ITROUTE_ROOT))).addModifiers(PUBLIC).addMethod(loadIntoMethodOfRootBuilder.build()).build()).build().writeTo(mFiler);logger.info(">>> Generated root, name is " + rootFileName + " <<<");}}}

生成过程： 和上面生成AutoWried过程类似，都是使用javapoet的api生成对应的java文件

这里我们需要生成三种文件：

• ARouter$$Root$$xxx：xxx是当前模块名的缩写，存储当前模块路由组的信息：value是路由组的类名

java
复制代码/*** DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER. */
public class ARouter$$Root$$modulejava implements IRouteRoot {@Overridepublic void loadInto(Map<String, Class<? extends IRouteGroup>> routes) {routes.put("m2", ARouter$$Group$$m2.class);routes.put("module", ARouter$$Group$$module.class);routes.put("test", ARouter$$Group$$test.class);routes.put("yourservicegroupname", ARouter$$Group$$yourservicegroupname.class);}
}

• ARouter$$Group$$xxx:xxx是当前路由组的组名，存储一个路由组内路由的信息：内部包含多个路由信息

java
复制代码
/*** DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER. */
public class ARouter$$Group$$test implements IRouteGroup {@Overridepublic void loadInto(Map<String, RouteMeta> atlas) {atlas.put("/test/activity1", RouteMeta.build(RouteType.ACTIVITY, Test1Activity.class, "/test/activity1", "test", new java.util.HashMap<String, Integer>(){{put("ser", 9); put("ch", 5); put("fl", 6); put("dou", 7); put("boy", 0); put("url", 8); put("pac", 10); put("obj", 11); put("name", 8); put("objList", 11); put("map", 11); put("age", 3); put("height", 3); }}, -1, -2147483648));atlas.put("/test/activity2", RouteMeta.build(RouteType.ACTIVITY, Test2Activity.class, "/test/activity2", "test", new java.util.HashMap<String, Integer>(){{put("key1", 8); }}, -1, -2147483648));atlas.put("/test/activity3", RouteMeta.build(RouteType.ACTIVITY, Test3Activity.class, "/test/activity3", "test", new java.util.HashMap<String, Integer>(){{put("name", 8); put("boy", 0); put("age", 3); }}, -1, -2147483648));atlas.put("/test/activity4", RouteMeta.build(RouteType.ACTIVITY, Test4Activity.class, "/test/activity4", "test", null, -1, -2147483648));atlas.put("/test/fragment", RouteMeta.build(RouteType.FRAGMENT, BlankFragment.class, "/test/fragment", "test", new java.util.HashMap<String, Integer>(){{put("ser", 9); put("pac", 10); put("ch", 5); put("obj", 11); put("fl", 6); put("name", 8); put("dou", 7); put("boy", 0); put("objList", 11); put("map", 11); put("age", 3); put("height", 3); }}, -1, -2147483648));atlas.put("/test/webview", RouteMeta.build(RouteType.ACTIVITY, TestWebview.class, "/test/webview", "test", null, -1, -2147483648));}
}

• ARouter$$Providers$$xxx，xxx是模块名，存储的是当前模块中的IProvider信息，key是IProvider的名称，value是RouteMeta路由元数据

java
复制代码
/*** DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER. */
public class ARouter$$Providers$$modulejava implements IProviderGroup {@Overridepublic void loadInto(Map<String, RouteMeta> providers) {providers.put("com.alibaba.android.arouter.demo.service.HelloService", RouteMeta.build(RouteType.PROVIDER, HelloServiceImpl.class, "/yourservicegroupname/hello", "yourservicegroupname", null, -1, -2147483648));providers.put("com.alibaba.android.arouter.facade.service.SerializationService", RouteMeta.build(RouteType.PROVIDER, JsonServiceImpl.class, "/yourservicegroupname/json", "yourservicegroupname", null, -1, -2147483648));providers.put("com.alibaba.android.arouter.demo.module1.testservice.SingleService", RouteMeta.build(RouteType.PROVIDER, SingleService.class, "/yourservicegroupname/single", "yourservicegroupname", null, -1, -2147483648));}
}

还有其他比如拦截器的java文件生成方式就不再描述了，和前面两个注解处理器是一样的原理。 自动生成了这些帮助类之后，在编译器或者运行期，通过调用这些类的loadInto方法，可以将路由元信息加载到内存中。

总结

本文在开始主要讲解一些注解和注解处理器的前置知识，且带大家自己实现了一个APT自动生成文件的demo，最后讲解下在ARouter中APT是如何再编译器动态生成几种帮助类的。