MethodIntrospector工具类使用

最近在看国内比较优秀的分布式调度框架xxl-job的源码，作者使用了比较多的spring4版本后提供的便捷方法，正好自己工作中有用到xxl-job，就顺带研究下。

xxl-job相关的代码就不细讲了，重点讲下MethodIntrospector这个工具类的使用场景。

先看下源码中的注释：

/*** Defines the algorithm for searching for metadata-associated methods exhaustively* including interfaces and parent classes while also dealing with parameterized methods* as well as common scenarios encountered with interface and class-based proxies.** <p>Typically, but not necessarily, used for finding annotated handler methods.** @author Juergen Hoeller* @author Rossen Stoyanchev* @since 4.2.3*/

大概的意思是，定义了查找指定方法的一些算法，主要可以被用来查找有指定注解的方法

核心方法 selectMethods

 /*** Select methods on the given target type based on the lookup of associated metadata.* <p>Callers define methods of interest through the {@link MetadataLookup} parameter,* allowing to collect the associated metadata into the result map.* @param targetType the target type to search methods on* @param metadataLookup a {@link MetadataLookup} callback to inspect methods of interest,* returning non-null metadata to be associated with a given method if there is a match,* or {@code null} for no match* @return the selected methods associated with their metadata (in the order of retrieval),* or an empty map in case of no match*/public static <T> Map<Method, T> selectMethods(Class<?> targetType, final MetadataLookup<T> metadataLookup) {final Map<Method, T> methodMap = new LinkedHashMap<>();Set<Class<?>> handlerTypes = new LinkedHashSet<>();Class<?> specificHandlerType = null;//判断是否是代理类if (!Proxy.isProxyClass(targetType)) {//如果是代理类，找到实际的类型specificHandlerType = ClassUtils.getUserClass(targetType);handlerTypes.add(specificHandlerType);}handlerTypes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetType));//遍历所有找到的class对象for (Class<?> currentHandlerType : handlerTypes) {final Class<?> targetClass = (specificHandlerType != null ? specificHandlerType : currentHandlerType);ReflectionUtils.doWithMethods(currentHandlerType, method -> {//获取指定的methodMethod specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);//获取方法关联的元数据，一般是指注解T result = metadataLookup.inspect(specificMethod);if (result != null) {Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) {methodMap.put(specificMethod, result);}}}, ReflectionUtils.USER_DECLARED_METHODS);}return methodMap;}

MetadataLookup接口

 /*** A callback interface for metadata lookup on a given method.* @param <T> the type of metadata returned*/@FunctionalInterfacepublic interface MetadataLookup<T> {/*** Perform a lookup on the given method and return associated metadata, if any.* @param method the method to inspect* @return non-null metadata to be associated with a method if there is a match,* or {@code null} for no match*/@NullableT inspect(Method method);}

这样看可能有点抽象，来个实际点的例子

定义一个自定义的注解：

package cn.magicnian.annotation;import java.lang.annotation.*;@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface MagicAround {String value();Class[] releationClazz();
}

然后写一个简单的使用场景：

package cn.magicnian.annotation;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;@Component
public class MyMagicAroudTest {private Logger logger = LoggerFactory.getLogger(MyMagicAroudTest.class);@MagicAround(value = "function1",releationClazz = String.class)public String function1(String key) {logger.info("......pring key:{}......", key);return "success";}
}

使用MethondIntrospector处理

package cn.magicnian.annotation;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.SmartInitializingSingleton;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.core.MethodIntrospector;
import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.stereotype.Component;import java.lang.reflect.Method;
import java.util.Map;@Component
public class AnnotationMethondExecutor implements ApplicationContextAware, SmartInitializingSingleton {private static final Logger logger = LoggerFactory.getLogger(AnnotationMethondExecutor.class);private ApplicationContext applicationContext;@Overridepublic void afterSingletonsInstantiated() {String[] beanDefinitionNames = applicationContext.getBeanNamesForType(Object.class, false, true);for (String beanDefinitionName : beanDefinitionNames) {Object bean = applicationContext.getBean(beanDefinitionName);// referred to ：org.springframework.context.event.EventListenerMethodProcessor.processBeanMap<Method, MagicAround> annotatedMethods = null;try {annotatedMethods = MethodIntrospector.selectMethods(bean.getClass(),new MethodIntrospector.MetadataLookup<MagicAround>() {@Overridepublic MagicAround inspect(Method method) {return AnnotatedElementUtils.findMergedAnnotation(method, MagicAround.class);}});} catch (Throwable ex) {logger.error("MagicAround resolve error for bean [{}]. exception : {}", beanDefinitionName, ex);}if (annotatedMethods == null || annotatedMethods.isEmpty()) {continue;}for (Map.Entry<Method, MagicAround> methodMagicAroundEntry : annotatedMethods.entrySet()) {Method method = methodMagicAroundEntry.getKey();MagicAround magicAround = methodMagicAroundEntry.getValue();if (magicAround == null) {continue;}String name = magicAround.value();if (name.trim().length() == 0) {throw new RuntimeException("magicaround name invalide, for[" + bean.getClass() + "#" + method.getName() + "] .");}method.setAccessible(true);try {//执行该方法Object returnValue = method.invoke(bean, new Object[]{"magicnian"});logger.info("returnValue : {}", returnValue);} catch (Exception e) {e.printStackTrace();}}}}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {this.applicationContext = applicationContext;}
}

看下执行结果：

可以看到，在AnnotationMethodExecutor中顺利的找到了标记有MagicAround注解的方法，并且执行了该方法

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