java的反射机制+Dom4j 实现Spring IOC的原理

àì夳堔傛蜴生んèń 2023-05-29 13:28 17阅读 0赞

## 测试工程的目录结构 ##

![20191106170844940.png][]

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
      <modelVersion>4.0.0</modelVersion>
      <groupId>spring-ioc</groupId>
      <artifactId>spring-ioc</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      
      <dependencies>
    		
    		<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>
    	</dependencies>
    </project>

User.java

package com.sunj.entity;
    
    import java.util.List;
    
    public class User {
    	private String id;
    	private String name;
    	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 "User [id=" + id + ", name=" + name + "]";
    	}
    	public User(String id, String name) {
    		super();
    		this.id = id;
    		this.name = name;
    	}
    	public User() {
    		super();
    	}
    	
    	
    }

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.sunj.entity.User">
    		<property name="id" value="0001"></property>
    		<property name="name" value="张三"></property>
    	</bean>
    	<bean id="user2" class="com.sunj.entity.User">
    		<property name="id" value="0002"></property>
    		<property name="name" value="李四"></property>
    	</bean>
    </beans>

位重写ClassPathXmlApplicationContext类之前，spring获取bean对象是这样的

import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class Test {
    	public static void main(String[] args) {
    		//读取spring配置
    		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
    		User user = (User) context.getBean("user1");
    		System.out.println(user);
    		User user2 = (User) context.getBean("user2");
    		System.out.println(user2);
    	}
    }

重新的ClassPathXmlApplicationContext类

package com.sunj.test;
    
    import java.lang.reflect.Field;
    import java.util.List;
    
    import org.apache.commons.lang3.StringUtils;
    import org.dom4j.Document;
    import org.dom4j.DocumentException;
    import org.dom4j.Element;
    import org.dom4j.io.SAXReader;
    
    import com.sunj.entity.User;
    
    public class ClassPathXmlApplicationContext {
    	private String path;
    	private static final String ID = "id";
    	private static final String CLASS = "class";
    	private static final String NAME = "name";
    	private static final String VALUE = "value";
    	
    	
    	public ClassPathXmlApplicationContext(String path) {
    		super();
    		this.path = path;
    	}
    	
    	public Object getBean(String beanId) throws DocumentException, ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchFieldException, SecurityException{
    		//1、解析xml
    		SAXReader saxreader = new SAXReader();
    		Document read = saxreader.read(this.getClass().getClassLoader().getResource(this.path));
    		Element rootElement = read.getRootElement();
    		List<Element> elements = rootElement.elements();
    		for (Element element : elements) {
    			if(StringUtils.isBlank(element.attributeValue(this.ID))){
    				System.out.println("你找的类不存在");
    				return null;
    			}
    			//2、使用bean的id查找对应xml节点，获取class节点属性
    			String pro = element.attributeValue(this.ID);
    			if(!beanId.equals(pro)){
    				continue;
    			}
    			
    			String classValue = element.attributeValue(this.CLASS);
    			if(StringUtils.isBlank(classValue)){
    				return null;
    			}
    			//3、使用java的反射机制初始化类
    			Class forName = Class.forName(classValue);
    			Object instance = forName.newInstance();
    			List<Element> sunElements = element.elements();
    			//使用java的反射机制给私有属性赋值
    			for (Element element2 : sunElements) {
    				String nameV = element2.attributeValue(this.NAME);
    				String valueV = element2.attributeValue(this.VALUE);
    				Field field = forName.getDeclaredField(nameV);
    				field.setAccessible(true);
    				field.set(instance, valueV);
    			}
    			return instance;
    			
    		}
    		return null;
    	}
    	
    	public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchFieldException, SecurityException, DocumentException {
    		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
    		User user = (User) context.getBean("user2");
    		System.out.println(user);
    	}
    }

[20191106170844940.png]: https://img-blog.csdnimg.cn/20191106170844940.png