看几个根底的注解
@AliasFor
@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)@Documentedpublic @interface AliasFor { @AliasFor("attribute") String value() default ""; @AliasFor("value") String attribute() default ""; Class<? extends Annotation> annotation() default Annotation.class;}AliasFor这个注解很奇怪，value的别名是attribute，attribute的别名是value
那么它的行为在哪里被定义的呢？在AnnotationTypeMapping中咱们能够找到答案
// 这里应用了AnnotationsScanner的getDeclaredAnnotation办法来获取所有的AliasFor注解的办法// AnnotationsScanner 是spring中的非公开抽象类，在咱们的代码中不能间接进行应用// Spring中没有提供子类private Map<Method, List<Method>> resolveAliasedForTargets() { Map<Method, List<Method>> aliasedBy = new HashMap<>(); for (int i = 0; i < this.attributes.size(); i++) { Method attribute = this.attributes.get(i); AliasFor aliasFor = AnnotationsScanner.getDeclaredAnnotation(attribute, AliasFor.class); if (aliasFor != null) { Method target = resolveAliasTarget(attribute, aliasFor); aliasedBy.computeIfAbsent(target, key -> new ArrayList<>()).add(attribute); } } return Collections.unmodifiableMap(aliasedBy);}// 为了简洁，我将源代码中其余部分省略掉了，能够看到，这里应用用反射失去的Method的getAnnotation办法失去实例private Method resolveAliasTarget(Method attribute, AliasFor aliasFor, boolean checkAliasPair) { // ... ... Method target = AttributeMethods.forAnnotationType(targetAnnotation).get(targetAttributeName); // ... ... if (isAliasPair(target) && checkAliasPair) { AliasFor targetAliasFor = target.getAnnotation(AliasFor.class); if (targetAliasFor != null) { Method mirror = resolveAliasTarget(target, targetAliasFor, false); if (!mirror.equals(attribute)) { throw new AnnotationConfigurationException(String.format( "%s must be declared as an @AliasFor %s, not %s.", StringUtils.capitalize(AttributeMethods.describe(target)), AttributeMethods.describe(attribute), AttributeMethods.describe(mirror))); } } } return target;}通过学习@AliasFor，咱们晓得了能够通过先流动Method，再或得其润饰的注解的办法。
依据这样的办法，咱们能够应用上面的代码，找到类DockingHandlers中所有被注解@DockIngMessage润饰的办法
// DockIngMessage 是自定义的注解Method[] methods = DockingHandlers.class.getMethods();for (Method method : methods) { DockIngMessage dockIngMessage = method.getAnnotation(DockIngMessage.class); if (dockIngMessage != null) { System.out.println(dockIngMessage.name()); }}@Bean
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface Bean { @AliasFor("name") String[] value() default {}; @AliasFor("value") String[] name() default {}; @Deprecated Autowire autowire() default Autowire.NO; boolean autowireCandidate() default true; String initMethod() default ""; String destroyMethod() default AbstractBeanDefinition.INFER_METHOD;}@Bean注解是Spring中用得比拟宽泛的注解之一，来看看Spring源码中是怎么查找@Bean注解的
public static boolean isBeanAnnotated(Method method) { return AnnotatedElementUtils.hasAnnotation(method, Bean.class);}应用了AnnotatedElementUtils工具类，那么咱们就能够把下面的代码革新一下
Method[] methods = DockingHandlers.class.getMethods();for (Method method : methods) { if (AnnotatedElementUtils.hasAnnotation(method, DockIngMessage.class)) { DockIngMessage dockIngMessage = AnnotatedElementUtils.getMergedAnnotation(method,DockIngMessage.class); System.out.println(dockIngMessage.name()); }}// 相比于判断 != null , 这样的写法绝对优雅了许多至于Bean到底是怎么失效的，咱们须要留到当前钻研Spring容器的时候再探讨
@Controller
@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Componentpublic @interface Controller { @AliasFor(annotation = Component.class) String value() default "";}在Controller的test外面有这么一段代码
@Testpublic void testWithComponentAnnotationOnly() { ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false); provider.addIncludeFilter(new AnnotationTypeFilter(Component.class)); provider.addExcludeFilter(new AnnotationTypeFilter(Repository.class)); provider.addExcludeFilter(new AnnotationTypeFilter(Service.class)); provider.addExcludeFilter(new AnnotationTypeFilter(Controller.class)); Set<BeanDefinition> candidates = provider.findCandidateComponents(TEST_BASE_PACKAGE); assertThat(candidates.size()).isEqualTo(3); assertThat(containsBeanClass(candidates, NamedComponent.class)).isTrue(); assertThat(containsBeanClass(candidates, ServiceInvocationCounter.class)).isTrue(); assertThat(containsBeanClass(candidates, BarComponent.class)).isTrue(); assertThat(containsBeanClass(candidates, FooServiceImpl.class)).isFalse(); assertThat(containsBeanClass(candidates, StubFooDao.class)).isFalse(); assertThat(containsBeanClass(candidates, NamedStubDao.class)).isFalse();}也就是说，能够利用扫包的形式来获取某个包下被某个注解润饰的类。
总结
查找某注解润饰的所有类就应用 ClassPathScanningCandidateComponentProvider 进行扫描。
查找某注解润饰的办法，就先找到那个类，而后失去所有的办法，应用AnnotatedElementUtils.hasAnnotation判断办法是否被某注解润饰即可
上面是一个简略的例子
ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false);provider.addIncludeFilter(new AnnotationTypeFilter(DockingAnnotation.class));Set<BeanDefinition> candidates = provider.findCandidateComponents("package_name");for (BeanDefinition definition : candidates){ try { Class clz = Class.forName(definition.getBeanClassName()); Method[] methods = clz.getMethods(); for (Method method : methods){ if (AnnotatedElementUtils.hasAnnotation(method,DockIngMessage.class)){ DockIngMessage dockIngMessage = AnnotatedElementUtils.getMergedAnnotation(method,DockIngMessage.class); System.out.println(dockIngMessage.name()); } } } catch (ClassNotFoundException e) { e.printStackTrace(); }}炒鸡辣鸡原创文章，转载请注明起源