spring管理bean原理

1、读取config.xml文件的bean标签放入数组,读取内容包括id和class。
2、循环数组并根据class路径利用反射机制实例化Bean,并放入Map。
3、根据传入的BeanId获取Map中对应的bean实例。

package com.yt.core.yl;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import org.apache.log4j.Logger;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import com.yt.spring.user.UserBean;

/**
 * @Description: Spring管理Bean原理
 * @ClassName: ClassPathXMLApplicationContext
 * @Project: spring-aop
 * @Author: zxf
 * @Date: 2011-6-3
 */
public class ClassPathXMLApplicationContext {

	Logger log = Logger.getLogger(ClassPathXMLApplicationContext.class);

	List<BeanDefinition> beanList = new ArrayList<BeanDefinition>();
	Map<String, Object> sigletions = new HashMap<String, Object>();

	public ClassPathXMLApplicationContext(String fileName) {
		this.readXML(fileName);
		this.instancesBean();
	}

	/**
	 * 读取Bean配置文件
	 * 
	 * @param fileName
	 * @return
	 */
	@SuppressWarnings("unchecked")
	public void readXML(String fileName) {
		Document document = null;
		SAXReader saxReader = new SAXReader();
		try {
			ClassLoader classLoader = Thread.currentThread()
					.getContextClassLoader();
			document = saxReader
					.read(classLoader.getResourceAsStream(fileName));
			Element beans = document.getRootElement();
			for (Iterator<Element> beansList = beans.elementIterator(); beansList
					.hasNext();) {
				Element element = beansList.next();
				BeanDefinition bean = new BeanDefinition(
						element.attributeValue("id"),
						element.attributeValue("class"));
				beanList.add(bean);
			}
		} catch (DocumentException e) {
			log.info("读取配置文件出错....");
		}
	}
	
	/**
	 * 实例化Bean
	 */
	public void instancesBean() {
		for (BeanDefinition bean : beanList) {
			try {
				sigletions.put(bean.getId(), Class.forName(bean.getClassName())
						.newInstance());
			} catch (Exception e) {
				log.info("实例化Bean出错...");
			}
		}
	}
	
	/**
	 * 获取Map中的对应的bean实例
	 * @param beanId
	 * @return
	 */
	public Object getBean(String beanId) {
		return sigletions.get(beanId);
	}


	public static void main(String[] args) {
		ClassPathXMLApplicationContext path = new ClassPathXMLApplicationContext(
				"config.xml");
		UserBean userBean = (UserBean)path.getBean("userBean");
		userBean.setUserName("zxf_noimp");
		System.out.println(userBean.getUserName());
	}
}

 

package com.yt.core.yl;

/**
 * @Description:
 * @ClassName: BeanDefinition
 * @Project: spring-aop
 * @Author: zxf
 * @Date: 2011-6-3
 */
public class BeanDefinition {

	public String id;
	public 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;
	}

}