手写SpringIOC框架_反射技术+DOM4J解析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:aop="http://www.springframework.org/schema/aop"
       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/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">

    <bean id="user1" class="com.example.demo02.entity.User">
        <property name="userId" value="0003"></property>
        <property name="userName" value="张三"></property>
    </bean>
    <bean id="user2" class="com.example.demo02.entity.User">
        <property name="userId" value="0004"></property>
        <property name="userName" value="李四"></property>
    </bean>

</beans>

package com.example.demo02.entity;

public class User {
    private String userId;
    private String userName;

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    @Override
    public String toString() {
        return "User{" +
                "userId='" + userId + '\'' +
                ", userName='" + userName + '\'' +
                '}';
    }
}

package com.example.demo02.ioc;

import com.example.demo02.entity.User;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.thymeleaf.util.StringUtils;

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

public class ClassPathXmlApplicationContext {
    private String xmlPath;

    public ClassPathXmlApplicationContext(String xmlPath) {
        this.xmlPath = xmlPath;
    }

    public Object getBean(String beanId) throws Exception {

        if (StringUtils.isEmpty(beanId)) {
            throw new Exception("beanId is null");
        }

        SAXReader saxReader = new SAXReader();
        Document document = saxReader.read(this.getClass().getClassLoader().getResource(xmlPath));
        Element rootElement = document.getRootElement();
        List<Element> elements = rootElement.elements();
        for (Element ele:elements) {
            String id= ele.attributeValue("id");

            if (StringUtils.isEmpty(id)) {
                continue;
            }
            if (!id.equals(beanId)) {
                continue;
            }

            String beanClass = ele.attributeValue("class");
            Class<?> clazz = Class.forName(beanClass);
            Object instance = clazz.newInstance();

            List<Element> elementList = ele.elements();
            for (Element element : elementList) {
                String name = element.attributeValue("name");
                String value = element.attributeValue("value");
                Field declaredField = clazz.getDeclaredField(name);
                declaredField.setAccessible(true);
                declaredField.set(instance,value );
            }
            return instance;

        }
        return  null;
    }

    public static void main(String[] args) throws Exception {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        User user1 = (User) applicationContext.getBean("user1");
        System.out.println(user1);
    }

}