手写SpringIOC的XML实现方式

妖狐艹你老母 2022-03-20 15:40 272阅读 0赞

### 1.XML文件(Spring.xml) ###

### 2.需要注入的实体Bean类 ###

package com.weichai.entity;
    
    import java.io.Serializable;
    
    /**
     * User实体诶
     * @author linhaiy
     * @date 2019.01.24
     */
    public class User implements Serializable {
    
    	private Integer id;
    	private String name;
    	private String password;
    	private Integer age;
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	public String getPassword() {
    		return password;
    	}
    	public void setPassword(String password) {
    		this.password = password;
    	}
    	public Integer getAge() {
    		return age;
    	}
    	public void setAge(Integer age) {
    		this.age = age;
    	}
    	@Override
    	public String toString() {
    		return "User [id=" + id + ", name=" + name + ", password=" + password + ", age=" + age + "]";
    	}
    	
    }

### 3.Bean注入的实现原理 ###

package com.weichai.spring;
    
    import java.io.File;
    import java.io.InputStream;
    import java.util.List;
    
    import org.apache.commons.lang.StringUtils;
    import org.dom4j.Document;
    import org.dom4j.DocumentException;
    import org.dom4j.Element;
    import org.dom4j.io.SAXReader;
    
    /**
        *     手写SpringIOC注入Bean的XML实现方式
     * @author linhaiy
     * @date 2019.01.24
     */
    public class ClassPathXmlApplicationContext {
    
    	private String xmlPath;           //要读取的xml路径地址
    
    	public ClassPathXmlApplicationContext(String xmlPath) {
    		super();
    		this.xmlPath = xmlPath;
    	}
    	
    	/**
    	   * 依赖注入获取Bean的主体类
    	 * @param beanId
    	 * @return
    	 * @throws Exception
    	 */
    	public Object getBean(String beanId) throws Exception {
    		//1.读取配置文件
    		List<Element> elements = readerXml();
    		if(elements == null) {
    			throw new Exception("该配置文件没有子元素");
    		}
    		//2.使用beanId查找对应的class地址
    		String beanClass = findXmlByIDClass(elements, beanId);
    		if(StringUtils.isEmpty(beanClass)) {
    			throw new Exception("未找到对应的class地址");
    		}
    		//3.使用反射机制初始化，对象
    		Class<?> forName = Class.forName(beanClass);
    		return forName.newInstance();
    	}
    
    	/**
    	    *   使用beanid查找该Class地址
    	 * @param elements
    	 * @param beanId
    	 * @return
    	 */
    	private String findXmlByIDClass(List<Element> elements, String beanId) throws Exception {
    		// TODO Auto-generated method stub
    		for(Element element : elements) {
    			// 读取节点上是否有value
    			String beanIdValue = element.attributeValue("id");
    			if (beanIdValue == null) {
    				throw new Exception("使用该beanId未查找到元素");
    			}
    			if (!beanIdValue.equals(beanId)) {
    				continue;
    			}
    			// 获取Class地址属性
    			String classPath = element.attributeValue("class");
    			if(!StringUtils.isEmpty(classPath)) {
    				return classPath;
    			}
    		}
    		return null;
    	}
    
    	/**
    	   * 读取配置文件信息
    	 * @return
    	 * @throws DocumentException 
    	 */
    	private List<Element> readerXml() throws DocumentException {
    		// TODO Auto-generated method stub
    		SAXReader saxReader = new SAXReader();
    		if(StringUtils.isEmpty(xmlPath)) {
    			new Exception("xml路径为空...");
    		}
    		Document read = saxReader.read(getClassXmlInputStream(xmlPath));
    		//获取根节点信息
    		Element rootElement = read.getRootElement();
    		//获取子节点
    		List<Element> elements = rootElement.elements();
    		if(elements == null || elements.isEmpty()) {
    			return null;
    		}
    		return elements;
    	}
    
    	/**
    	 * 读取xml配置文件
    	 * @param xmlPath
    	 * @return
    	 */
    	public InputStream getClassXmlInputStream(String xmlPath) {
    		// TODO Auto-generated method stub
    		InputStream resourceAsStream = getClass().getClassLoader().getResourceAsStream(xmlPath);
    		return resourceAsStream;
    	}
    }

### 4.测试类 ###

package com.weichai.SpringIocXml;
    
    import com.weichai.entity.User;
    import com.weichai.spring.ClassPathXmlApplicationContext;
    
    /**
     * SpringIOC的XML实现方式测试
     * @author linhaiy
     * @date 2019.01.24
     */
    public class SpringIocTest {
    
    	public static void main(String[] args) throws Exception {
    		// TODO Auto-generated method stub
    		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");
    		User user = (User) applicationContext.getBean("user");
    		System.out.println("Spring获取Bean实体的内容： " + user);
    	}
    
    }