Spring管理Bean的原理

package test.com.css.spring;import java.net.URL;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import org.dom4j.Document;import org.dom4j.Element;import org.dom4j.XPath;import org.dom4j.io.SAXReader;public class ItcastClassPathXMLApplicationContext {private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();private Map<String, Object> sigletons = new HashMap<String, Object>();public ItcastClassPathXMLApplicationContext(String filename) {this.readXML(filename);this.instanceBeans();}/** * 完成bean的实例化 */private void instanceBeans() {for (BeanDefinition beanDefinition : beanDefines) {try {if (beanDefinition.getClassName() != null&& !"".equals(beanDefinition.getClassName().trim()))sigletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getClassName()).newInstance());// 利用java反射机制构造实例} catch (Exception e) {e.printStackTrace();}}}/** * 读取xml配置文件 * * @param filename */private void readXML(String filename) {SAXReader saxReader = new SAXReader(); // 创建一个读取器Document document = null;try {URL xmlpath = this.getClass().getClassLoader().getResource(filename);document = saxReader.read(xmlpath);Map<String, String> nsMap = new HashMap<String, String>();nsMap.put("ns", "http://www.springframework.org/schema/beans");// 加入命名空间XPath xsub = document.createXPath("//ns:beans/ns:bean");// 创建beans/bean查询路径xsub.setNamespaceURIs(nsMap);// 设置命名空间List<Element> beans = xsub.selectNodes(document);// 获取文档下所有bean节点for (Element element : beans) {String id = element.attributeValue("id");// 获取id属性值String clazz = element.attributeValue("class"); // 获取class属性值BeanDefinition beanDefine = new BeanDefinition(id, clazz);beanDefines.add(beanDefine);}} catch (Exception e) {e.printStackTrace();}}/** * 获取bean实例 * * @param beanName * @return */public Object getBean(String beanName) {return this.sigletons.get(beanName);}}package test.com.css.spring;public class BeanDefinition {private String id;private String className;public BeanDefinition(String id, String className) {this.id = id;this.className = className;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getClassName() {return className;}public void setClassName(String className) {this.className = className;}}