Spring2.5学习3.2_编码剖析@Resource注解的实现原理

首先看一下J2EE提供的@Resource注解：该注解默认安照名称进行装配，名称能够通过name属性进行指定， 假设没有指定name属性，当注解写在字段上时，默认取字段名进行依照名称查找，假设注解写在setter方法上默认取属性名进行装配。

当找不到与名称匹配的bean时才依照类型进行装配。可是须要注意的是，假设name属性一旦指定。就仅仅会依照名称进行装配。

这里我们模拟@Resource注解，便于理解注解的实现原理：

1.首先在前面模拟的容器中加入注入的方法annotationInject()；

XjjClassPathXMLApplicationContext.java

package junit.test;

import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.beanutils.ConvertUtils;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.XPath;
import org.dom4j.io.SAXReader;

	/**
	 * Xjj版容器
	 *
	 */
	public class XjjClassPathXMLApplicationContext {
		private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();
		private Map<String, Object> sigletons = new HashMap<String, Object>();

		public XjjClassPathXMLApplicationContext(String filename){
			this.readXML(filename);
			this.instanceBeans();
			this.annotationInject();
			this.injectObject();
		}
	/**
	 * 通过注解实现注入依赖对象
	 */
	private void annotationInject() {
		for(String beanName : sigletons.keySet()){
			Object bean = sigletons.get(beanName);
			if(bean!=null){
				try {
					PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();
					for(PropertyDescriptor properdesc : ps){
						Method setter = properdesc.getWriteMethod();//获取属性的setter方法
						if(setter!=null && setter.isAnnotationPresent(XjjResource.class)){
							XjjResource resource = setter.getAnnotation(XjjResource.class);
							Object value = null;
							if(resource.name()!=null && !"".equals(resource.name())){
								value = sigletons.get(resource.name());
							}else{
								value = sigletons.get(properdesc.getName());
								if(value==null){
									for(String key : sigletons.keySet()){
										if(properdesc.getPropertyType().isAssignableFrom(sigletons.get(key).getClass())){
											value = sigletons.get(key);
											break;
										}
									}
								}
							}
							setter.setAccessible(true);
							setter.invoke(bean, value);//把引用对象注入到属性
						}
					}
					Field[] fields = bean.getClass().getDeclaredFields();
					for(Field field : fields){
						if(field.isAnnotationPresent(XjjResource.class)){
							XjjResource resource = field.getAnnotation(XjjResource.class);
							Object value = null;
							if(resource.name()!=null && !"".equals(resource.name())){
								value = sigletons.get(resource.name());
							}else{
								value = sigletons.get(field.getName());
								if(value==null){
									for(String key : sigletons.keySet()){
										if(field.getType().isAssignableFrom(sigletons.get(key).getClass())){
											value = sigletons.get(key);
											break;
										}
									}
								}
							}
							field.setAccessible(true);//同意訪问private字段
							field.set(bean, value);
						}
					}
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}
	}

	/**
	 * 为bean对象的属性注入值
	 */
	private void injectObject() {
		for(BeanDefinition beanDefinition : beanDefines){
			Object bean = sigletons.get(beanDefinition.getId());
			if(bean!=null){
				try {
					PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();
					for(PropertyDefinition propertyDefinition : beanDefinition.getPropertys()){
						for(PropertyDescriptor properdesc : ps){
							if(propertyDefinition.getName().equals(properdesc.getName())){
								Method setter = properdesc.getWriteMethod();//获取属性的setter方法 ,private
								if(setter!=null){
									Object value = null;
									if(propertyDefinition.getRef()!=null && !"".equals(propertyDefinition.getRef().trim())){
										value = sigletons.get(propertyDefinition.getRef());
									}else{
										value = ConvertUtils.convert(propertyDefinition.getValue(), properdesc.getPropertyType());
									}
									setter.setAccessible(true);
									setter.invoke(bean, value);//把引用对象注入到属性
								}
								break;
							}
						}
					}
				} catch (Exception e) {
				}
			}
		}
	}
	/**
	 * 完毕bean的实例化
	 */
	private void instanceBeans() {
		for(BeanDefinition beanDefinition : beanDefines){
			try {
				if(beanDefinition.getClassName()!=null && !"".equals(beanDefinition.getClassName().trim()))
					sigletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getClassName()).newInstance());
			} catch (Exception e) {
				e.printStackTrace();
			}
		}

	}
	/**
	 * 读取xml配置文件
	 * @param filename
	 */
	private void readXML(String filename) {
	       SAXReader saxReader = new SAXReader();
	        Document document=null;
	        try{
	         URL xmlpath = this.getClass().getClassLoader().getResource(filename);
	         document = saxReader.read(xmlpath);
	         Map<String,String> nsMap = new HashMap<String,String>();
	         nsMap.put("ns","http://www.springframework.org/schema/beans");//增加命名空间
	         XPath xsub = document.createXPath("//ns:beans/ns:bean");//创建beans/bean查询路径
	         xsub.setNamespaceURIs(nsMap);//设置命名空间
	         List<Element> beans = xsub.selectNodes(document);//获取文档下全部bean节点
	         for(Element element: beans){
	            String id = element.attributeValue("id");//获取id属性值
	            String clazz = element.attributeValue("class"); //获取class属性值
	            BeanDefinition beanDefine = new BeanDefinition(id, clazz);
	            XPath propertysub =  element.createXPath("ns:property");
	            propertysub.setNamespaceURIs(nsMap);//设置命名空间
	            List<Element> propertys = propertysub.selectNodes(element);
	            for(Element property : propertys){
	            	String propertyName = property.attributeValue("name");
	            	String propertyref = property.attributeValue("ref");
	            	String propertyValue = property.attributeValue("value");
	            	PropertyDefinition propertyDefinition = new PropertyDefinition(propertyName, propertyref, propertyValue);
	            	beanDefine.getPropertys().add(propertyDefinition);
	            }
	            beanDefines.add(beanDefine);
	         }
	        }catch(Exception e){
	            e.printStackTrace();
	        }
	}
	/**
	 * 获取bean实例
	 * @param beanName
	 * @return
	 */
	public Object getBean(String beanName){
		return this.sigletons.get(beanName);
	}
}

实现注解用的类型：@XjjResource

XjjResource.java

package junit.test;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
public @interface XjjResource {
	public String name() default "";
}

BeanDefinition.java

package junit.test;

import java.util.ArrayList;
import java.util.List;

public class BeanDefinition {
	private String id;
	private String className;
	private List<PropertyDefinition> propertys = new ArrayList<PropertyDefinition>();

	public BeanDefinition(String id, String className) {
		this.id = id;
		this.className = className;
	}

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getClassName() {
		return className;
	}

	public void setClassName(String className) {
		this.className = className;
	}

	public List<PropertyDefinition> getPropertys() {
		return propertys;
	}

	public void setPropertys(List<PropertyDefinition> propertys) {
		this.propertys = propertys;
	}
}

PropertyDefinition.java

package junit.test;

public class PropertyDefinition {
	private String name;
	private String ref;
	private String value;

	public String getValue() {
		return value;
	}

	public void setValue(String value) {
		this.value = value;
	}

	public PropertyDefinition(String name, String ref, String value) {
		this.name = name;
		this.ref = ref;
		this.value = value;
	}

	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getRef() {
		return ref;
	}
	public void setRef(String ref) {
		this.ref = ref;
	}

}

PersonServiceBean.java对PersonDao进行注解方式注入

package xjj.service.impl;

import junit.test.XjjResource;
import xjj.dao.PersonDao;
import xjj.service.PersonService;

public class PersonServiceBean implements PersonService {
	@XjjResource private PersonDao personDao;
	private String name;	

	public void setPersonDao(PersonDao personDao) {
		this.personDao = personDao;
	}

	public PersonServiceBean(){}

	public PersonServiceBean(PersonDao personDao, String name) {
		this.personDao = personDao;
		this.name = name;
	}

	public void save(){
		//System.out.println(name);
		personDao.add();
	}
}

beans.xml

<?xml version="1.0" encoding="UTF-8"?

>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
           http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">

          <context:annotation-config/>
          <bean id="personDaoxxxx" class="xjj.dao.impl.PersonDaoBean"></bean>
          <bean id="personService" class="xjj.service.impl.PersonServiceBean">
          </bean>
</beans>

SpringTest2.java

package junit.test;

import org.junit.BeforeClass;
import org.junit.Test;

import xjj.service.PersonService;
public class SpringTest2 {

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}

	@Test public void instanceSpring(){

		XjjClassPathXMLApplicationContext ctx = new XjjClassPathXMLApplicationContext("beans.xml");
		PersonService personService = (PersonService)ctx.getBean("personService");
		personService.save();

	}
}

模拟结果：成功注入了PersonDaoBean