手写Spring IOC

1.手写Spring IOC XML版本

spring xml配置

代码如下：

XML工具类

package com.itmayiedu.spring;

import java.io.InputStream;
import java.util.List;

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

/**
 * 手写Spring专题 XML方式注入bean
 * 
 * @author 作者:余胜军
 *
 */
public class ClassPathXmlApplicationContext {
	// xml路径地址
	private String xmlPath;

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

	public Object getBean(String beanId) throws Exception {
		// 1. 读取配置文件
		List 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();
	}

	// 读取配置文件信息
	public List readerXml() throws DocumentException {
		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 elements = rootElement.elements();
		if (elements == null || elements.isEmpty()) {
			return null;
		}
		return elements;
	}

	// 使用beanid查找该Class地址
	public String findXmlByIDClass(List elements, String beanId) throws Exception {
		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为查找到元素");
			}
			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xml配置文件
	public InputStream getClassXmlInputStream(String xmlPath) {
		InputStream resourceAsStream = getClass().getClassLoader().getResourceAsStream(xmlPath);
		return resourceAsStream;
	}

}

spring IOC 核心类

package com.itmayiedu.spring;

import java.io.InputStream;
import java.util.List;

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

/**
 * 手写Spring专题 XML方式注入bean
 *
 */
public class ClassPathXmlApplicationContext {
	// xml路径地址
	private String xmlPath;

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

	public Object getBean(String beanId) throws Exception {
		// 1. 读取配置文件
		List 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();
	}

	// 读取配置文件信息
	public List readerXml() throws DocumentException {
		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 elements = rootElement.elements();
		if (elements == null || elements.isEmpty()) {
			return null;
		}
		return elements;
	}

	// 使用beanid查找该Class地址
	public String findXmlByIDClass(List elements, String beanId) throws Exception {
		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为查找到元素");
			}
			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xml配置文件
	public InputStream getClassXmlInputStream(String xmlPath) {
		InputStream resourceAsStream = getClass().getClassLoader().getResourceAsStream(xmlPath);
		return resourceAsStream;
	}

}

测试类

package com.itmayiedu.spring;

import org.dom4j.DocumentException;

import com.itmayiedu.spring.entity.User;

public class Test002 {

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

}