本文通过结合Java反射机制与DOM4J库，模拟实现Spring框架中的控制反转（IOC）核心功能。该方案能够读取XML配置文件，动态实例化对象，并根据配置自动注入属性值。

1. 配置文件：applicationContext.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-3.0.xsd">

    <bean id="userOne" class="com.example.entity.UserProfile">
        <property name="id" value="U001"/>
        <property name="name" value="李四"/>
    </bean>

    <bean id="userTwo" class="com.example.entity.UserProfile">
        <property name="id" value="U002"/>
        <property name="name" value="王五"/>
    </bean>

</beans>

2. 核心实现类：XmlApplicationContext

使用DOM4J解析XML，结合反射创建对象并注入属性。

package com.example.container;

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

import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

public class XmlApplicationContext {

    private static final String BEAN_ID = "id";
    private static final String BEAN_CLASS = "class";
    private static final String PROPERTY_NAME = "name";
    private static final String PROPERTY_VALUE = "value";

    private final String configPath;

    public XmlApplicationContext(String configPath) {
        this.configPath = configPath;
    }

    public Object getBean(String beanName) throws Exception {
        if (StringUtils.isBlank(beanName)) return null;

        SAXReader reader = new SAXReader();
        Document document = reader.read(getClass().getClassLoader().getResourceAsStream(configPath));
        Element root = document.getRootElement();

        for (Element bean : root.elements("bean")) {
            String id = bean.attributeValue(BEAN_ID);
            if (!beanName.equals(id)) continue;

            String className = bean.attributeValue(BEAN_CLASS);
            Class clazz = Class.forName(className);
            Object instance = clazz.getDeclaredConstructor().newInstance();

            // 注入属性
            for (Element prop : bean.elements("property")) {
                String fieldName = prop.attributeValue(PROPERTY_NAME);
                String fieldValue = prop.attributeValue(PROPERTY_VALUE);

                Field field = clazz.getDeclaredField(fieldName);
                field.setAccessible(true);
                field.set(instance, fieldValue);
            }

            return instance;
        }

        throw new IllegalArgumentException("No bean found with id: " + beanName);
    }
}

3. 测试实体类：UserProfile

package com.example.entity;

public class UserProfile {
    private String id;
    private String name;

    public UserProfile() {
        System.out.println("UserProfile 构造函数被调用");
    }

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "UserProfile{id='" + id + "', name='" + name + "'}";
    }
}

4. 使用示例

public class TestMain {
    public static void main(String[] args) throws Exception {
        XmlApplicationContext context = new XmlApplicationContext("applicationContext.xml");
        UserProfile user = (UserProfile) context.getBean("userOne");
        System.out.println(user);
    }
}