模拟Spring管理bean

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;

public class ItcastClassPathXMLApplicationContext {
 private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();
 private Map<String, Object> sigletons = new HashMap<String, Object>();
 
 public ItcastClassPathXMLApplicationContext(String filename){
  this.readXML(filename);
  this.instanceBeans();
 }
 /**
  * 完成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");//加入命名空间
          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);//获取文档下所有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);
             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);
 }
}

 

 

 

spring管理bean的三种方式:

 <bean id="personService" class="cn.itcast.service.impl.PersonServiceBean"></bean>
 <bean id="personService2" class="cn.itcast.service.impl.PersonServiceBeanFactory"
          factory-method="createPersonServiceBean"/>
 <bean id="personServiceFactory" class="cn.itcast.service.impl.PersonServiceBeanFactory"/>
  <bean id="personService3" factory-bean="personServiceFactory" factory-method="createPersonServiceBean2"/>

 

bean的作用域：

 <bean id="personService" class="cn.itcast.service.impl.PersonServiceBean" scope="prototype"></bean>