深入理解springioc机制，以下为例子做理解

通过java反射机制来读取applicationContext.xml的内容该xml文件内容如下

<?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:aop="http://www.springframework.org/schema/aop"
   xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
   xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">

</beans>

第一步：

1.创建实体类，实体类有userId，userName属性

2.首先创建一个maevn工程引入依赖

<dependency>
           <groupId>org.apache.commons</groupId>
           <artifactId>commons-lang3</artifactId>
           <version>3.4</version>
       </dependency>
       <dependency>
           <groupId>org.dom4j</groupId>
           <artifactId>dom4j</artifactId>
           <version>2.0.0</version>
       </dependency>

第二步：

编写读取类，内容如下

package com.springioc.main;

import java.lang.reflect.Field;
import java.util.List;

import org.apache.commons.lang3.StringUtils;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import com.springioc.entity.User;

public class ClassPathXmlApplicationContext {

   private static String PATH;
   private static String ID;
   private static String CLASS;
   private static String NAME;
   private static String VALUE;

   public ClassPathXmlApplicationContext(String path){
       init();
       this.PATH = path;

   }

   public void init(){
       this.ID = "id";
       this.CLASS = "class";
       this.NAME = "name";
       this.VALUE = "value";
   }


   public Object getBean(String beanId) throws Exception{
       Object objectUser = null;
       boolean flag = false;   //判断在application.xml中能否找到beanId，如果没有找到则返回false
       //1.解析XML
       if (StringUtils.isEmpty(beanId)) {
           return null;
       }
       SAXReader saxReader = new SAXReader();
       //读取apliction.xml的路径，注意是按照相对路径来读取的this.getClass().getClassLoader()是读取到该项目的路径
       Document read = saxReader.read(this.getClass().getClassLoader().getResource(PATH));
       Element rootElement = read.getRootElement();   //读取根标题，即一级标题
       List<Element> elements = rootElement.elements();   //二级标题
       for (Element el2 : elements) {
           String id = el2.attributeValue(this.ID);   //读取到<bean id="user1" class="com.springioc.entity.User">中的id属性
           if (beanId.equals(id)) {
               flag = true;
           }

           if (flag) {
               //2.查找对应的Class
               String attrClass = el2.attributeValue(this.CLASS);
               if (attrClass != null) {
                   //3.如果找到对应的Class则用java的反射机制
                   Class<?> forName = Class.forName(attrClass);
                   Object newInstance = forName.newInstance();
                   //4.获取对应的class中里的属性
                   List<Element> el3 = el2.elements();//获取二级标题下的三级标题,然后遍历赋值
                   for (Element element : el3) {
                       String attrName = element.attributeValue(this.NAME);//这个是映射bean的<property name="userId" value="0002"></property>中name属性
                       String attrValue = element.attributeValue(this.VALUE);   //这个是映射bean的<property name="userId" value="0002"></property>中value属性
                       Field declaredField = forName.getDeclaredField(attrName);   //对userId进行修改
                       declaredField.setAccessible(true); //设置私有属性可修改，即private修饰也可以修改
                       declaredField.set(newInstance, attrValue);//将id,name修改即类似set方法
                       objectUser = newInstance;
                   }
               }
               flag = false;   //找到之后对应的bean id之后初始化flag 在进入判断
           }else {
               new Exception("未找到bean中所对应的id");
           }
       }

       return objectUser;
   }




   public static void main(String[] args) throws Exception{

       ClassPathXmlApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
       User user = (User) app.getBean("user1");
       if (user != null) {
           System.out.println(user.toString());
       }else {
           System.out.println("user初始化失败");
       }
   }

}

深入理解springioc机制，以下为例子做理解

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