模拟Spring容器管理bean

package com.spring;import java.io.IOException;import java.net.URL;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import org.jdom.Document;import org.jdom.Element;import org.jdom.JDOMException;import org.jdom.input.SAXBuilder;import org.jdom.xpath.XPath;import com.vo.BeanDefinition;/** * 简单模拟spring的ClassPathXmlApplicationContext spring容器管理bean * */@SuppressWarnings("unchecked")public class MyApplicationContext{    private List<BeanDefinition> list = new ArrayList<BeanDefinition>();    private Map<String, Object> sigletons = new HashMap<String, Object>();    public MyApplicationContext(String fileName)    {        this.readXML(fileName);        try        {            instanceBeans();        }        catch (Exception e)        {            e.printStackTrace();        }    }    /**     * 实例化所有bean     *     * @throws InstantiationException     * @throws IllegalAccessException     * @throws ClassNotFoundException     */    private void instanceBeans() throws InstantiationException,            IllegalAccessException, ClassNotFoundException    {        for (BeanDefinition bean : list)        {            if (null != bean.getClassName() && bean.getClassName().length() > 0)                sigletons.put(bean.getId(), Class.forName(bean.getClassName())                        .newInstance());        }    }    /**     * 读取xml配置     *     * @param fileName     */    public void readXML(String fileName)    {        SAXBuilder builder = new SAXBuilder();        URL url = this.getClass().getClassLoader().getResource(fileName);        try        {            Document doc = builder.build(url);            XPath xpath = XPath.newInstance("//ns:beans/ns:bean");            xpath.addNamespace("ns",                    "http://www.springframework.org/schema/beans");            List<Element> beans = xpath.selectNodes(doc);            for (Element bean : beans)            {                String id = bean.getAttributeValue("id");                String className = bean.getAttributeValue("class");                BeanDefinition beanDefinition = new BeanDefinition(id,                        className);                list.add(beanDefinition);            }        }        catch (JDOMException e)        {            e.printStackTrace();        }        catch (IOException e)        {            e.printStackTrace();        }    }    /**     * 得到指定id的bean     *     * @param id     * @return     */    public Object getBean(String id)    {        return sigletons.get(id);    }}    测试：@Test    public void testMyUserService()    {        MyApplicationContext ctx = new MyApplicationContext("beans.xml");        UserService us = (UserService) ctx.getBean("userService");        us.print();    }

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