3.编码剖析Spring管理Bean的原理

一.使用dom4j读取spring 配置文件

package junit.test;

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.DocumentException;
import org.dom4j.Element;
import org.dom4j.XPath;
import org.dom4j.io.SAXReader;

public class ZhkClassPathXMLApplicationContext
{
    private List<BeanDefinition> beanDefinitions = new ArrayList<BeanDefinition>();
    private Map<String,Object> singletones = new HashMap<String,Object>();
    
    public ZhkClassPathXMLApplicationContext(String filename)
    {
        this.readXML(filename);
        this.instanceBeans();
    }
    //完成bean实例化
    private void instanceBeans()
    {
        for(BeanDefinition beanDefine : beanDefinitions)
        {
            try
            {                
                if (null != beanDefine.getClassName() && !"".equals(beanDefine.getClassName().trim()))
                {
                    singletones.put(beanDefine.getId(),
                            Class.forName(beanDefine.getClassName())
                                    .newInstance());
                }
            }
            catch (Exception e)
            {               
                e.printStackTrace();
            }         
        }
    }
    
    /** <读取配置文件>
     * @param filename [参数说明]
     */
    private void readXML(String filename)
    {
        SAXReader saxReader = new SAXReader();
        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 className = element.attributeValue("class"); //获取class属性值
                BeanDefinition beanDefine = new BeanDefinition(id,className);
                beanDefinitions.add(beanDefine);               
            }            
        }
        catch (DocumentException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }     
    }
    
    
    /** <获取bean实例>
     * @param beanName
     */
    public Object getBean(String beanName)
    {
        return this.singletones.get(beanName);
        
    }
}

package junit.test;

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;
    }
    
}

package junit.test;


import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.spring.service.PersonService;

public class SpringTest
{
    
    @BeforeClass
    public static void setUpBeforeClass() throws Exception
    {
    }
    @Test public void instanceSpring()
    {
        ZhkClassPathXMLApplicationContext ctx = new ZhkClassPathXMLApplicationContext("beans.xml");
        PersonService personservice = (PersonService)ctx.getBean("personService");
        personservice.save();
    }
}