Spring、编码剖析Spring管理Bean的原理

引入dom4j jar包

1、新建Person接口和PersonBean

public interface PersonIService {
	public void helloSpring();
}

public class PersonServiceImpl implements PersonIService {

	@Override
	public void helloSpring() {
		System.out.println("Hello Spring!");
	}
}

2、在beans.xml中注入PersonBean

<bean id="personIService" class="cn.server.impl.PersonServiceImpl" />

3、新建BeanDefinition  用于存放从beans.xml中获取的beans

public class BeanDefinition {
	private String id;
	private String className;
	
	public BeanDefinition(){	
	}
	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;
	}
	
}

5、新建 OhterClassPathXMLApplicationContext 用于解析beans.xml

public class OhterClassPathXMLApplicationContext {
	private List<BeanDefinition> list=new ArrayList<BeanDefinition>();
	private Map<String,Object> beans=new HashMap<String, Object>();
	
	public OhterClassPathXMLApplicationContext(String fileName){
		this.readXML(fileName);
		this.instanceBeans();
	}
	private void instanceBeans(){
		for(BeanDefinition bean : list){
			try {
				// 创建Bean实例，并放到Map中
				if(bean.getClassName()!=null && !bean.getClassName().trim().equals("")){
					beans.put(bean.getId(), Class.forName(bean.getClassName()).newInstance());
				}
			} catch (Exception e) {
				e.printStackTrace();
			} 
		}
	}
	private void readXML(String fileName){
		SAXReader saxReader = new SAXReader();
		Document doc=null;
		try{
			// JAVA里面对于类进行调用配置资源的文件数据，以this.getClass().getResourceAsStream()来读取比较合适。
			// 路径采用相对路径直接可以从工程的path路径去找。
			URL xmlpath=this.getClass().getClassLoader().getResource(fileName);
			doc=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=doc.createXPath("//ns:beans/ns:bean"); // 创建 beans/bean的查询路径
			xsub.setNamespaceURIs(nsMap); // 设置命名空间
			List beans=xsub.selectNodes(doc); // 获取文档下的所有bean节点
			for(Object node : beans){
				Element element=(Element)node;
				String id=element.attributeValue("id");
				String className=element.attributeValue("class");
				BeanDefinition bean=new BeanDefinition(id,className);
				list.add(bean);
			}
			
		}catch(Exception e){
			e.printStackTrace();
		}
	}
	// 通过Id名称，获取Bean
	public Object getBean(String name){
		return beans.get(name);
	}
}

6、测试代码

	@Test
	public void test2() {
		OhterClassPathXMLApplicationContext otherContext=new OhterClassPathXMLApplicationContext("beans.xml");
		PersonIService personIService=(PersonIService)otherContext.getBean("personIService");
		personIService.helloSpring();
	}