Spring_加载beans.xml简单模拟

最新推荐文章于 2021-11-19 11:43:40 发布

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#spring beans.xml

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本文通过自定义实现BeanFactory接口的ClassPathXmlApplicationContext类，详细介绍了如何使用JDOM解析XML文件来实例化并注入Bean的过程。

使用spring框架时，都会在xml中配置一些bean。这样spring就会把我们配置的组件进行管理，让我们用起来很方便，但是一直想知道它到底是怎么一回事。上网查找资料，用jdom模拟解析xml。

beans.xml

<beans>
	<bean id="u" class="com.code.dao.impl.UserDAOImpl" />
	<bean id="userService" class="com.code.service.UserService" >
		<property name="userDAO" bean="u"/>
	</bean>
	
</beans>

面向接口编程：

BeanFactory.java

package com.code.spring;

public interface BeanFactory {
	public Object getBean(String id);
}

ClassPathXmlApplicationContext.java

package com.code.spring;


import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.List;


import org.jdom.Document;
import org.jdom.Element;
import org.jdom.input.SAXBuilder;


public class ClassPathXmlApplicationContext implements BeanFactory{


<span style="white-space:pre">	</span>HashMap<String, Object> beans = new HashMap<String, Object>();
<span style="white-space:pre">	</span>
<span style="white-space:pre">	</span>public ClassPathXmlApplicationContext() throws Exception {
<span style="white-space:pre">		</span>
<span style="white-space:pre">		</span>SAXBuilder builder = new SAXBuilder();
<span style="white-space:pre">		</span>Document document = builder.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml"));
<span style="white-space:pre">		</span>Element root = document.getRootElement();
<span style="white-space:pre">		</span>List<Element> list = root.getChildren("bean");


<span style="white-space:pre">		</span>for (int i = 0; i < list.size(); i++) {
<span style="white-space:pre">		</span>
<span style="white-space:pre">			</span>Element element = list.get(i);
<span style="white-space:pre">			</span>String id =  element.getAttributeValue("id");
<span style="white-space:pre">			</span>String clazz = element.getAttributeValue("class");
<span style="white-space:pre">			</span>Object o = Class.forName(clazz).newInstance();
<span style="white-space:pre">			</span>
<span style="white-space:pre">			</span>System.out.println("====id==========> " + id);
<span style="white-space:pre">			</span>System.out.println("====clazz=======> " + clazz);
<span style="white-space:pre">			</span>
<span style="white-space:pre">			</span>beans.put(id, o);
<span style="white-space:pre">			</span>
<span style="white-space:pre">			</span>for (Element propertyEl : (List<Element>)element.getChildren("property")) {
<span style="white-space:pre">				</span>
<span style="white-space:pre">				</span>String name = propertyEl.getAttributeValue("name");
<span style="white-space:pre">				</span>String bean = propertyEl.getAttributeValue("bean");
<span style="white-space:pre">				</span>
<span style="white-space:pre">				</span>System.out.println("====name=========> " + name);
<span style="white-space:pre">				</span>System.out.println("====bean=========> " + bean);
<span style="white-space:pre">				</span>
<span style="white-space:pre">				</span>Object objBean = beans.get(bean);
<span style="white-space:pre">				</span>
<span style="white-space:pre">				</span>String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);
<span style="white-space:pre">				</span>System.out.println("====method name===> " + methodName);
<span style="white-space:pre">				</span>
<span style="white-space:pre">				</span>Method m = o.getClass().getMethod(methodName, objBean.getClass().getInterfaces()[0]);
<span style="white-space:pre">				</span>m.invoke(o, objBean);
<span style="white-space:pre">				</span>
<span style="white-space:pre">			</span>}
<span style="white-space:pre">		</span>}
<span style="white-space:pre">	</span>}


<span style="white-space:pre">	</span>public Object getBean(String id) {
<span style="white-space:pre">		</span>return beans.get(id);
<span style="white-space:pre">	</span>}
}

testParse.java

import com.code.dao.UserDAO;
import com.code.model.User;
import com.code.spring.BeanFactory;
import com.code.spring.ClassPathXmlApplicationContext;


public class TestPrase {

	public static void main(String[] args) throws Exception {
		
		User user = new User();
		user.setUsername("admin");
		user.setPassword("password");
		
		BeanFactory beanFactory = new ClassPathXmlApplicationContext();

		UserDAO userDAO =  (UserDAO) beanFactory.getBean("u");
		
		userDAO.save(user);
		
		System.out.println(userDAO);
	}
}