Java注解处理器---------编译时注解

﹏ヽ暗。殇╰゛Y 2022-02-22 13:42 396阅读 0赞

注解处理  
在开发中，碰见很多注解，如@Override、@Documented等，还有像现在很多依赖注入库如ARouter,Dagger 2等·，他的内部如何处理自己的注解，通过什么途径获取自己的注解，实现自己的业务逻辑。看一下ARouter,当添加ARouter依赖后，在需要的Activity添加注解，编译就会看到在build文件夹下生成如下图的文件，文件生成是通过在注解处理器中编写解析和生成代码格式。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podWd1YW5nMTA_size_16_color_FFFFFF_t_70]  
注解处理器：  
是一个在javac中的，用来编译时扫描和处理的注解的工具。你可以为特定的注解，注册你自己的注解处理器。  
注解处理器可以生成Java代码，这些生成的Java代码会组成 .java 文件，但不能修改已经存在的Java类（即不能向已有的类中添加方法）。而这些生成的Java文件，会同时与其他普通的手写Java源代码一起被javac编译。  
注解处理器抽象类AbstractProcessor：

> public class AnnotionTest extends AbstractProcessor \{  
> @Override  
> public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) \{  
> return false;  
> \}  
> @Override  
> public Set getSupportedAnnotationTypes() \{  
> return super.getSupportedAnnotationTypes();  
> \}  
> @Override  
> public SourceVersion getSupportedSourceVersion() \{  
> return super.getSupportedSourceVersion();  
> \}  
> @Override  
> public synchronized void init(ProcessingEnvironment processingEnvironment) \{  
> super.init(processingEnvironment);  
> \} \}

init(ProcessingEnvironment processingEnvironment)初始化数据，相当于构造器，初始化一些工具类，如下。

> Map<String, String> getOptions();  
> Messager getMessager();  
> Filer getFiler();  
> Elements getElementUtils();  
> Types getTypeUtils();  
> SourceVersion getSourceVersion();  
> Locale getLocale();

getSupportedAnnotationTypes()必须重写，指明要注解哪个注解，如

> Set setClazzName = new LinkedHashSet<>();  
> setClazzName.add(TestSelfAnnotation.class.getName());  
> return setClazzName;

getSupportedSourceVersion()支持的java版本。  
process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment)业务逻辑的处理。  
如何使用注解处理器：

首先我们需要创建java库，在库中定义自己的注解，如下：

> @Documented @Target(\{ElementType.FIELD\}) @Retention(value =  
> RetentionPolicy.RUNTIME) public @interface TestSelfAnnotation \{  
> int value() default 0; \}

创建一个java库，添加如下依赖，编写自己的注解处理器继承AbstractProcessor,生成代码使用JavaPoet库，生成.java源文件。

> compile ‘com.google.auto.service:auto-service:1.0-rc4’  
> compile ‘com.squareup:javapoet:1.8.0’  
> implementation project(’:annotationLib’)
> 
> @AutoService(Processor.class) public class MyAnnotationProcessor  
> extends AbstractProcessor \{
> 
>     private Map<String, String> getOptions;
>     
>     private Messager getMessagers;
>     
>     private Filer getFilers;
>     
>     private Elements elementUtils;
>     
>     private Types typeUtils;
>     
>     private SourceVersion getSourceVersion;
>     private Locale getLocale;
>     private static final String RANDOM_SUFFIX = "$$BindView";
>     private HashMap<String, HashMap<String, String>> entryKey = new HashMap<>();
>     private HashMap<String, Element> elementIndexMap = new HashMap<>();
>     @Override
>     public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
>     
>         Set<? extends Element> elementsAnnotatedWith = roundEnvironment.getElementsAnnotatedWith(TestSelfAnnotation.class);
>         for (final Element element : elementsAnnotatedWith)
>             if (element.getKind() == ElementKind.FIELD) {
>     
>                 TestSelfAnnotation annotation = element.getAnnotation(TestSelfAnnotation.class);
>                 TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();
>                 ClassName className = ClassName.get(enclosingElement);
>     
>                 if (entryKey.containsKey(className.simpleName())) {
>                     HashMap<String, String> stringStringHashMap = entryKey.get(className.simpleName());
>                     stringStringHashMap.put(element.getSimpleName().toString(),
> 
> annotation.value() + “”); //  
> entryKey.put(element.getEnclosingElement().getSimpleName().toString(),  
> stringStringHashMap);  
> \} else \{  
> HashMap<String, String> hashMap = new HashMap<>();  
> hashMap.put(element.getSimpleName().toString(), annotation.value() + “”);  
> elementIndexMap.put(className.simpleName(), element);  
> entryKey.put(className.simpleName(), hashMap);  
> \}  
> \}  
> writeClazz(entryKey, elementIndexMap);  
> return false;  
> \}  
> private void writeClazz(HashMap<String, HashMap<String, String>> entryKey, HashMap<String, Element> elementIndexMap) \{  
> for (Map.Entry<String, HashMap<String, String>> map : entryKey.entrySet()) \{  
> String key = map.getKey();  
> HashMap<String, String> value = map.getValue();  
> Element element = elementIndexMap.get(key);  
> TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();  
> ClassName className = ClassName.get(enclosingElement);  
> MethodSpec.Builder builder = MethodSpec.constructorBuilder()  
> .addModifiers(Modifier.PUBLIC)  
> .addParameter(className, “activity”);  
> if (value.size() > 0) \{  
> for (HashMap.Entry<String, String> entry : value.entrySet()) \{  
> CodeBlock of = CodeBlock.of(“ N . " + e n t r y . g e t K e y ( ) + " = " + " N." + entry.getKey() + "=" + " N."\+entry.getKey()\+"="\+"N.” + “findViewById(”  
> \+ entry.getValue() + “);\\n”, “activity”, “activity”);  
> builder.addCode(of);  
> \}  
> \}  
> TypeSpec build = TypeSpec.classBuilder(getClazzName(element) + RANDOM\_SUFFIX)  
> .addModifiers(Modifier.PUBLIC)  
> .addMethod(builder.build())  
> .build();  
> try \{  
> JavaFile javaFile = JavaFile.builder(getPackageName(element), build).build();  
> javaFile.writeTo(getFilers);  
> \} catch (IOException e) \{  
> e.printStackTrace();  
> \}  
> \}  
> \}
> 
>     private String getClazzName(Element element) {
>         Element enclosingElement = element.getEnclosingElement();
>         return enclosingElement.getSimpleName().toString();
>     }
>     private String getPackageName(Element element) {
>         PackageElement packageOf = elementUtils.getPackageOf(element);
>         return packageOf.getQualifiedName().toString();
>     }
>     @Override
>     public synchronized void init(ProcessingEnvironment processingEnvironment) {
>         super.init(processingEnvironment);
>         getMessagers = processingEnvironment.getMessager();
>         getFilers = processingEnvironment.getFiler();
>         elementUtils = processingEnvironment.getElementUtils();
>         typeUtils = processingEnvironment.getTypeUtils();
>     }
>     @Override
>     public Set<String> getSupportedAnnotationTypes() {
>         Set<String> setClazzName = new LinkedHashSet<>();
>         System.out.println("   " + TestSelfAnnotation.class.getCanonicalName());
>         setClazzName.add(TestSelfAnnotation.class.getName());
>         return setClazzName;
>     }
>     @Override
>     public SourceVersion getSupportedSourceVersion() {
>         return SourceVersion.RELEASE_7;
>     } }

@AutoService(Processor.class)帮我们自动生成生成如下文件。  
![在这里插入图片描述][201904091412045.]  
3. module依赖注解后，使用注解，编译，我们可以看到，在apt文件下生成文件。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podWd1YW5nMTA_size_16_color_FFFFFF_t_70 1]  
文件结构如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podWd1YW5nMTA_size_16_color_FFFFFF_t_70 2]

> @TestSelfAnnotation(R.id.tv\_button)  
> TextView tv\_button;  
> @TestSelfAnnotation(R.id.bt\_ok)  
> Button bt\_button;  
> @Override  
> protected void onCreate(Bundle savedInstanceState) \{  
> super.onCreate(savedInstanceState);  
> setContentView(R.layout.activity\_shop\_main);  
> HelpAnnotation.inject(this);  
> \}

HelpAnnotation工具类：

> public class HelpAnnotation \{  
> private static final String RANDOM\_SUFFIX = “$$BindView”;  
> /\*\*  
> \* 通过反射的方式找到对应的辅助类，并调用对应的方法实现属性的注入  
> \*  
> \* @param object 被注入的对象  
> \*/  
> public static void inject(Object object) \{  
> try \{  
> Class bindingClass = Class.forName(object.getClass().getCanonicalName() + RANDOM\_SUFFIX);  
> //noinspection unchecked  
> Constructor constructor = bindingClass.getConstructor(object.getClass());  
> constructor.newInstance(object);  
> \} catch (ClassNotFoundException e) \{  
> Log.e(“TAG”, “Meaningful Message”, e);  
> \} catch (NoSuchMethodException e) \{  
> Log.e(“TAG”, “Meaningful Message”, e);  
> \} catch (IllegalAccessException e) \{  
> Log.e(“TAG”, “Meaningful Message”, e);  
> \} catch (InstantiationException e) \{  
> Log.e(“TAG”, “Meaningful Message”, e);  
> \} catch (InvocationTargetException e) \{  
> Log.e(“TAG”, “Meaningful Message”, e);  
> \}  
> \} \}

常见的几个API:

> Name simpleName = element.getSimpleName();//注解的元素名称 //如果元素在\{\}内，则返回类名称。  
> 如果这是顶级类型，则返回其包。 如果这是一个包，null则返回。 如果这是一个类型参数， 则返回参数类型。  
> element.getEnclosingElement(); ClassName className =  
> ClassName.get(enclosingElement);//获得类名

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[201904091412045.]: /images/20220222/fdc8acaf44ee45e6a952a81545a87d58.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podWd1YW5nMTA_size_16_color_FFFFFF_t_70 1]: /images/20220222/01206ce1845a40ac8b55b5b9c5a1e8a9.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3podWd1YW5nMTA_size_16_color_FFFFFF_t_70 2]: /images/20220222/852475059daa44e2a5253d101d8a646e.png