手写springIoc框架

springIoc的底层实现原理

1.读取bean的XML配置文件

2.使用beanId查找bean配置，并获取配置文件中class地址。

3.使用Java反射技术实例化对象

4.获取属性配置，使用反射技术进行赋值

使用人家spring框架读取对象

创建实体

package com.itmayiedu.service;

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

	 public UserEntity(){
		 System.out.println("无参构造函数....");
	 }

	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;
	}

}

创建spring的配置文件 application.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"
	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">

	<bean id="user1" class="com.itmayiedu.service.UserEntity">
		<property name="userId" value="0002"></property>
		<property name="userName" value="张三"></property>
	</bean>
	<bean id="user2" class="com.itmayiedu.service.UserEntity">
		<property name="userId" value="0002"></property>
		<property name="userName" value="张三"></property>
	</bean>
</beans> 

读取配置文件

package com.itmayiedu.service;

import org.springframework.context.support.ClassPathXmlApplicationContext;

@SuppressWarnings("resource")
public class Main {

	public static void main(String[] args) {
        //1.读取springxml配置
		ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext(
				"applicationContext.xml");
		//2.获取bean对象
		UserEntity userEntity = (UserEntity) classPathXmlApplicationContext.getBean("user1");
		System.out.println(userEntity.getUserId()+"----"+userEntity.getUserName());
	}

}

自己手写springIoc框架

编写配置文件user.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans>
	<bean id="user1" class="com.itmayiedu.entity.UserEntity">
		<property name="userId" value="0001"></property>
		<property name="userName" value="张三"></property>
	</bean>
	<bean id="user2" class="com.itmayiedu.entity.UserEntity">
		<property name="userId" value="0002"></property>
		<property name="userName" value="张三"></property>
	</bean>
</beans>

编写读取user.xml的方法

package com.itmayiedu.classFrorm;

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

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import com.itmayiedu.entity.UserEntity;

public class ClassPathXmlApplicationContext {
	private String xmlPath;

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

	public Object getBean(String beanId) throws DocumentException, ClassNotFoundException, NoSuchFieldException,
			SecurityException, IllegalArgumentException, IllegalAccessException, InstantiationException {
		// spring 加载过程 或者spring ioc实现原理
		// 1.读取xml配置文件
		// 获取xml解析器
		SAXReader saxReader = new SAXReader();
		// this.getClass().getClassLoader().getResourceAsStream("xmlPath")
		// 获取当前项目路径
		Document read = saxReader.read(this.getClass().getClassLoader().getResourceAsStream(xmlPath));
		// 获取跟节点对象
		Element rootElement = read.getRootElement();
		List<Element> elements = rootElement.elements();
		Object obj = null;
		for (Element sonEle : elements) {
			// 2.获取到每个bean配置 获取class地址
			String sonBeanId = sonEle.attributeValue("id");
			if (!beanId.equals(sonBeanId)) {
				continue;
			}
			String beanClassPath = sonEle.attributeValue("class");
			// 3.拿到class地址 进行反射实例化对象 ，使用反射api 为私有属性赋值
			Class<?> forName = Class.forName(beanClassPath);
			obj = forName.newInstance();
			// 拿到成员属性
			List<Element> sonSoneleme = sonEle.elements();
			for (Element element : sonSoneleme) {
				String name = element.attributeValue("name");
				String value = element.attributeValue("value");
				// 使用反射api 为私有属性赋值
				Field declaredField = forName.getDeclaredField(name);
				//运行往私有成员赋值
				declaredField.setAccessible(true);
				declaredField.set(obj, value);
			}

		}
		// 3.拿到class地址 进行反射实例化对象 ，使用反射api 为私有属性赋值
		return obj;
	}

	public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, SecurityException,
			IllegalArgumentException, IllegalAccessException, InstantiationException, DocumentException {
		ClassPathXmlApplicationContext appLication = new ClassPathXmlApplicationContext("user.xml");
		Object bean = appLication.getBean("user1");
		UserEntity user = (UserEntity) bean;
		System.out.println(user.getUserId() + "----" + user.getUserName());
	}

}

创建对应的user实体省略了

原文地址：https://www.cnblogs.com/wang66a/p/12069290.html