spring依賴注入原理

1.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
           <bean id="personDao" class="cn.zoe.dao.impl.PersonDaoBean"></bean>
          <bean id="personService" class="cn.zoe.service.impl.PersonServiceBean">
          	<property name="personDao" ref="personDao"></property>
		<property name="name" value="zoe"/>
          	<property name="id" value="88"/>
          </bean>
</beans>

2.解析beans.xml

package junit.test;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;

import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.XPath;
import org.dom4j.io.SAXReader;

/**
 * zoe版容器
 *
 */
public class ZoeClassPathXMLApplicationContext {
	private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();
	private Map<String, Object> sigletons = new HashMap<String, Object>();
	
	public ZoeClassPathXMLApplicationContext(String filename){
		this.readXML(filename);
		this.instanceBeans();
		this.injectObject();
	}
	/**
	 * 爲bean對象的屬性注入值
	 */
	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();//獲取屬性的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);//把引用對象注入到屬性
								}
								break;
							}
						}
					}
				} catch (Exception e) {
				}
			}
		}
	}
	/**
	 * 完成bean的實例化
	 */
	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();
			}
		}
		
	}
	/**
	 * 讀取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");//加入命名空間
	         XPath xsub = document.createXPath("//ns:beans/ns:bean");//創建beans/bean查詢路徑
	         xsub.setNamespaceURIs(nsMap);//設置命名空間
	         List<Element> beans = xsub.selectNodes(document);//獲取文檔下所有bean節點 
	         for(Element element: beans){
	            String id = element.attributeValue("id");//獲取id屬性值
	            String clazz = element.attributeValue("class"); //獲取class屬性值        
	            BeanDefinition beanDefine = new BeanDefinition(id, clazz);
	            XPath propertysub =  element.createXPath("ns:property");
	            propertysub.setNamespaceURIs(nsMap);//設置命名空間
	            List<Element> propertys = propertysub.selectNodes(element);
	            for(Element property : propertys){	            	
	            	String propertyName = property.attributeValue("name");
	            	String propertyref = property.attributeValue("ref");
	            	PropertyDefinition propertyDefinition = new PropertyDefinition(propertyName, propertyref);
	            	beanDefine.getPropertys().add(propertyDefinition);
	            }
	            beanDefines.add(beanDefine);
	         } 
	        }catch(Exception e){   
	            e.printStackTrace();
	        }
	}
	/**
	 * 獲取bean實例
	 * @param beanName
	 * @return
	 */
	public Object getBean(String beanName){
		return this.sigletons.get(beanName);
	}
}

3.實體類BeanDefiniton.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;
	}
	
}

4.實體類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;
	}
	
}

5.接口PersonService.java

package cn.zoe.service;
public interface PersonService {
	public void save();
}

6.實現類PersonServiceBean.java

package cn.zoe.service.impl;

import cn.zoe.dao.PersonDao;
import cn.zoe.service.PersonService;

public class PersonServiceBean implements PersonService {
	private PersonDao personDao;
	private String name;	
	private Integer id;
	
	public Integer getId() {
		return id;
	}

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

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public PersonDao getPersonDao() {
		return personDao;
	}

	public void setPersonDao(PersonDao personDao) {
		this.personDao = personDao;
	}
	
	public void save(){
		System.out.println("id"+ id+ ","+ name);
		personDao.add();
	}
}

7.接口PersonDao.java

package cn.zoe.dao;
public interface PersonDao {
	public void add();
}

8.實現類PersonDaoBean.java

package cn.zoe.dao.impl;

import cn.zoe.dao.PersonDao;

public class PersonDaoBean implements PersonDao {
	public void add(){
		System.out.println("執行PersonDaoBean中的add()方法");
	}
}

9.測試類

package junit.test;
import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import cn.zoe.service.PersonService;
public class SpringTest {
	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}
	@Test public void instanceSpring(){
		ZoeClassPathXMLApplicationContext ctx = new ZoeClassPathXMLApplicationContext("beans.xml");
		PersonService personService = (PersonService)ctx.getBean("personService");
		personService.save();		
	}
}