spring中注解的实现原理

@Autowired和@Resource的区别：

 

在Java中使用@Autowired和@Resource注解进行装配，这两个注解分别是：
1、@Autowired按照默认类型(类名称)装配依赖对象，默认情况下它要求依赖对象必须存在，如果允许为null,可以设置它的required属性为false
如果我们按名称装配，可以结合@Qualifie注解一起使用。
如：
@Autowired @qualifie("personDaoBean")
private PersonDaoBean personDaoBean;

@Resource默认按照名称(name="test")进行装配,名称可以通过@resource的name属性设定，当找不到与名称匹配的bean才会按类型装配

注意：如果没有指定name属性，并且安装默认的名称依然找不到依赖对象时，@Resource会回退到按类型装配。但一旦指定了name属性，就只能按名称装配了。

 

下面的示例来简单的讲述spring注解原理：

本例实现了在set方法上和在字段属性上注解的处理解析。

1、定义注解

package com.yt.annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/** * @Description:定义注解 * @ClassName: ZxfResource * @Project: spring-aop * @Author: zxf * @Date: 2011-6-7 */// 在运行时执行@Retention(RetentionPolicy.RUNTIME)// 注解适用地方(字段和方法)@Target({ ElementType.FIELD, ElementType.METHOD })public @interface ZxfResource {//注解的name属性public String name() default "";}

2、带有注解的服务类

package com.yt.annotation;/** * @Description: 带有注解的服务 * @ClassName: UserDaoImpl * @Project: spring-aop * @Author: zxf * @Date: 2011-6-7 */public class UserServiceImpl {public UserDaoImpl userDao;public User1DaoImpl user1Dao;// 字段上的注解,可以配置name属性@ZxfResourcepublic User2DaoImpl user2Dao;// set方法上的注解，带有name属性@ZxfResource(name = "userDao")public void setUserDao(UserDaoImpl userDao) {this.userDao = userDao;}// set方法上的注解，没有配置name属性@ZxfResourcepublic void setUser1Dao(User1DaoImpl user1Dao) {this.user1Dao = user1Dao;}public void show() {userDao.show();user1Dao.show1();user2Dao.show2();System.out.println("这里是Service方法........");}}

 3、要注入的DAO

package com.yt.annotation;/** * @Description: 要注入的DAo类 * @ClassName: UserDaoImpl * @Project: spring-aop * @Author: zxf * @Date: 2011-6-7 */public class UserDaoImpl {String name ;public void show(){System.out.println("这里是dao方法........");}}

<?xml version="1.0" encoding="UTF-8"?><beans><bean id = "userDao" class="com.yt.annotation.UserDaoImpl" /><bean id = "user1Dao" class="com.yt.annotation.User1DaoImpl" /><bean id = "user2Dao" class="com.yt.annotation.User2DaoImpl" /><bean id = "userService" class = "com.yt.annotation.UserServiceImpl" /></beans>

4、注解处理器

package com.yt.annotation;import java.beans.Introspector;import java.beans.PropertyDescriptor;import java.lang.reflect.Field;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import org.apache.log4j.Logger;import org.dom4j.Document;import org.dom4j.DocumentException;import org.dom4j.Element;import org.dom4j.io.SAXReader;/** * @Description: spring中的注解原理 * @ClassName: ClassPathXMLApplicationContext * @Project: spring-aop * @Author: zxf * @Date: 2011-6-3 */public class ClassPathXMLApplicationContext {Logger log = Logger.getLogger(ClassPathXMLApplicationContext.class);List<BeanDefine> beanList = new ArrayList<BeanDefine>();Map<String, Object> sigletions = new HashMap<String, Object>();public ClassPathXMLApplicationContext(String fileName) {//读取配置文件中管理的beanthis.readXML(fileName);//实例化beanthis.instancesBean();//注解处理器this.annotationInject();}/** * 读取Bean配置文件 * @param fileName * @return */@SuppressWarnings("unchecked")public void readXML(String fileName) {Document document = null;SAXReader saxReader = new SAXReader();try {ClassLoader classLoader = Thread.currentThread().getContextClassLoader();document = saxReader.read(classLoader.getResourceAsStream(fileName));Element beans = document.getRootElement();for (Iterator<Element> beansList = beans.elementIterator(); beansList.hasNext();) {Element element = beansList.next();BeanDefine bean = new BeanDefine(element.attributeValue("id"),element.attributeValue("class"));beanList.add(bean);}} catch (DocumentException e) {log.info("读取配置文件出错....");}}/** * 实例化Bean */public void instancesBean() {for (BeanDefine bean : beanList) {try {sigletions.put(bean.getId(), Class.forName(bean.getClassName()).newInstance());} catch (Exception e) {log.info("实例化Bean出错...");}}}/** * 注解处理器 * 如果注解ZxfResource配置了name属性，则根据name所指定的名称获取要注入的实例引用， * 如果注解ZxfResource;没有配置name属性，则根据属性所属类型来扫描配置文件获取要 * 注入的实例引用 *  */public void annotationInject(){for(String beanName:sigletions.keySet()){Object bean = sigletions.get(beanName);if(bean!=null){this.propertyAnnotation(bean);this.fieldAnnotation(bean);}}}/** * 处理在set方法加入的注解 * @param bean 处理的bean */public void propertyAnnotation(Object bean){try {//获取其属性的描述PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();for(PropertyDescriptor proderdesc : ps){//获取所有set方法Method setter = proderdesc.getWriteMethod();//判断set方法是否定义了注解if(setter!=null && setter.isAnnotationPresent(ZxfResource.class)){//获取当前注解，并判断name属性是否为空ZxfResource resource = setter.getAnnotation(ZxfResource.class);String name ="";Object value = null;if(resource.name()!=null&&!"".equals(resource.name())){//获取注解的name属性的内容name = resource.name();value = sigletions.get(name);}else{ //如果当前注解没有指定name属性,则根据类型进行匹配for(String key : sigletions.keySet()){//判断当前属性所属的类型是否在配置文件中存在if(proderdesc.getPropertyType().isAssignableFrom(sigletions.get(key).getClass())){//获取类型匹配的实例对象value = sigletions.get(key);break;}}}//允许访问private方法setter.setAccessible(true);//把引用对象注入属性setter.invoke(bean, value); }}} catch (Exception e) {log.info("set方法注解解析异常..........");}}/** * 处理在字段上的注解 * @param bean 处理的bean */public void fieldAnnotation(Object bean){try {//获取其全部的字段描述Field[] fields = bean.getClass().getFields();for(Field f : fields){if(f!=null && f.isAnnotationPresent(ZxfResource.class)){ZxfResource resource = f.getAnnotation(ZxfResource.class);String name ="";Object value = null;if(resource.name()!=null&&!"".equals(resource.name())){name = resource.name();value = sigletions.get(name);}else{for(String key : sigletions.keySet()){//判断当前属性所属的类型是否在配置文件中存在if(f.getType().isAssignableFrom(sigletions.get(key).getClass())){//获取类型匹配的实例对象value = sigletions.get(key);break;}}}//允许访问private字段f.setAccessible(true);//把引用对象注入属性f.set(bean, value);}}} catch (Exception e) {log.info("字段注解解析异常..........");}}/** * 获取Map中的对应的bean实例 * @param beanId * @return */public Object getBean(String beanId) {return sigletions.get(beanId);}public static void main(String[] args) {ClassPathXMLApplicationContext path = new ClassPathXMLApplicationContext("configAnnotation.xml");UserServiceImpl userService =(UserServiceImpl)path.getBean("userService");userService.show();}}

本文转载自：http://zxf-noimp.iteye.com/blog/1071765