spring 解析bean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="personService" class="cn.zoe.service.impl.PersonServiceBean"></bean>
</beans>

2.解析beans.xml

package junit.test;

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();
	}
	/**
	 * 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);
	            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;

public class BeanDefinition {
	private String id;
	private String className;
	
	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;
	}
	
}

4.接口PersonService.java

package cn.zoe.service;

public interface PersonService {

	public void save();

}

5.實現類PersonServiceBean.java 

package cn.zoe.service.impl;

import cn.zoe.service.PersonService;

public class PersonServiceBean implements PersonService {

	public void save(){
		System.out.println("我是save()方法");
	}
}

6.測試類

package junit.test;

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

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();
	}
}