手写springioc核心代码

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<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();
}

// 读取配置文件信息
public List<Element> 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<Element> 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<Element> 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;
}

}