模拟兑现Spring框架

模拟实现Spring框架

Spring框架主要就是使用反射机制实现IOC/DI。

applicationContext.xml

<beans><bean id="u" /><bean id="userService" ><property name="userDAO" bean="u"/></bean></beans>

BeanFactory.java

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

ClassPathXmlApplicationContext.java

public class ClassPathXmlApplicationContext implements BeanFactory {private Map<String , Object> beans = new HashMap<String, Object>();public ClassPathXmlApplicationContext() throws Exception {SAXBuilder sb=new SAXBuilder();    Document doc=sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml"));                                       //构造文档对象    Element root=doc.getRootElement(); //获取根元素：beans    List list=root.getChildren("bean");//获取名字为：bean 的所有元素    for(int i=0;i<list.size();i++){   //对元素bean进行遍历       Element element=(Element)list.get(i);       String id=element.getAttributeValue("id");       String clazz=element.getAttributeValue("class");       Object o = Class.forName(clazz).newInstance();//反射机制、对其进行实例化       beans.put(id, o);//放入Spring容器中       List<Element> le = element.getChildren("property");       for(Element propertyElement : le) {       String name = propertyElement.getAttributeValue("name");       String bean = propertyElement.getAttributeValue("bean");       Object beanObject = beans.get(bean);    //从容其中取出对象       String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);                                      //获取set方法名       Method m = o.getClass().getMethod(methodName, beanObject.getClass().getInterfaces()[0]);       m.invoke(o, beanObject);//执行此set方法       }    }  }public Object getBean(String id) {return beans.get(id);}}

?简单Spring框架就完成了，下面就是如何使用了：

BeanFactory applicationContext = new ClassPathXmlApplicationContext();UserService service = (UserService)applicationContext.getBean("userService");

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