Spring 简单模拟

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简单的理解Spring的实现过程，模拟了Spring的读取配置文件

项目结构

主要代码如下

User.java

public class User {

private String username;

private String password;

// getter and setter ..

}

beans.xml 配置文件

<beans>

<bean id="u" class="com.demo.dao.impl.UserDAOImpl" />

<bean id="userService" class="com.demo.service.UserService">

<property name="userDAO" bean="u" />

</bean>

</beans>

ClassPathXmlApplicationContext.java

/**

* 管理器

*

* @author jerome_s@qq.com

*/

public class ClassPathXmlApplicationContext implements BeanFactory {

private Map<String, Object> beans = new HashMap<String, Object>();

/**

* 初始化配置文件

* 模拟spring配置文件。模拟大的工厂，把东西都写到大的配置文件，通过代码读取xml文件模拟spring。

*

* @throws Exception

*/

@SuppressWarnings("unchecked")

public ClassPathXmlApplicationContext() throws Exception {

System.out.println("ClassPathXmlApplicationContext init.");

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HD

List<Element> list = root.getChildren("bean");// 取名字为bean的所有元素

// 循环每个bean

for (int i = 0; i < list.size(); i++) {

Element element = list.get(i);

String id = element.getAttributeValue("id");

String clazz = element.getAttributeValue("class");

Object o = Class.forName(clazz).newInstance();

System.out.println("ClassPathXmlApplicationContext bean's id = " + id);

System.out.println("ClassPathXmlApplicationContext bean's class = " + clazz);

beans.put(id, o);

// 循环bean下的property

for (Element propertyElement : (List<Element>) element.getChildren("property")) {

// 调用 setUserDAO 设置 userDao的值

String name = propertyElement.getAttributeValue("name"); // userDAO

String bean = propertyElement.getAttributeValue("bean"); // u

System.out.println("ClassPathXmlApplicationContext bean's property name = " + name);

System.out.println("ClassPathXmlApplicationContext bean's property bean = " + bean);

Object beanObject = beans.get(bean);// UserDAOImpl instance

// userDAO -> setUserDao

String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);

Method m = o.getClass().getMethod(methodName, beanObject.getClass().getInterfaces()[0]);

m.invoke(o, beanObject);

System.out.println("ClassPathXmlApplicationContext bean's property invoke method " + methodName);

}

System.out.println("-------------------------");

}

public Object getBean(String id) {

return beans.get(id);

}

UserService.java

public class UserService {

private UserDAO userDAO;

public void add(User user) {

userDAO.save(user);

}

public UserDAO getUserDAO() {

return userDAO;

}

public void setUserDAO(UserDAO userDAO) {

this.userDAO = userDAO;

}

UserDAOImpl.java

public class UserDAOImpl implements UserDAO {

public void save(User user) {

System.out.println("UserDAOImpl saved()");

System.out.println("user.toString() = " + user.toString());

}

运行 UserServiceTest.java

public class UserServiceTest {

@Test

public void testAdd() throws Exception {

BeanFactory applicationContext = new ClassPathXmlApplicationContext();

UserService service = (UserService) applicationContext.getBean("userService");

User u = new User();

u.setUsername("jerome");

u.setPassword("jeromepwd");

service.add(u);

}

运行结果如下

ClassPathXmlApplicationContext init.

ClassPathXmlApplicationContext bean's id = u

ClassPathXmlApplicationContext bean's class = com.demo.dao.impl.UserDAOImpl

-------------------------

ClassPathXmlApplicationContext bean's id = userService

ClassPathXmlApplicationContext bean's class = com.demo.service.UserService

ClassPathXmlApplicationContext bean's property name = userDAO

ClassPathXmlApplicationContext bean's property bean = u

ClassPathXmlApplicationContext bean's property invoke method name = setUserDAO