Spring依赖注入 --- 模拟实现
面向接口编程，又称面向抽象编程，
数据库如果发生更改，对应的数据访问层也应该改变
多写几个实现，需要用谁的时候在service里new谁就可以了
面向抽象编程的好处就是灵活。
创建用户实体类，
/ImitateSpring/src/yuki/spring/imitate/pojo/User.java
package yuki.spring.imitate.pojo;
public class User {
private String username;
private String password;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}/ImitateSpring/src/yuki/spring/imitate/service/UserService.java
package yuki.spring.imitate.service;
import yuki.spring.imitate.dao.UserDAO;
import yuki.spring.imitate.pojo.User;
public class UserService {
private UserDAO userDAO/* = new UserDAOImpl()*/;
public UserDAO getUserDAO() {
return userDAO;
}
public void setUserDAO(UserDAO userDAO) {
this.userDAO = userDAO;
}
public void add(User u){
this.userDAO.save(u);
}
}/ImitateSpring/src/yuki/spring/imitate/dao/UserDAO.java
package yuki.spring.imitate.dao;
import yuki.spring.imitate.pojo.User;
/*public class UserDAO {
public void save(User u){
System.out.println("user saved...");
}
}*/
public interface UserDAO {
void save(User u);
}/ImitateSpring/src/yuki/spring/imitate/dao/impl/UserDAOImpl.java
package yuki.spring.imitate.dao.impl;
import yuki.spring.imitate.dao.UserDAO;
import yuki.spring.imitate.pojo.User;
public class UserDAOImpl implements UserDAO {
@Override
public void save(User u) {
System.out.println("user saved...");
}
}之前的new很多DAO的解决方式是写工厂方法
现在，要新建一个总的工厂，把消息写在工厂文件中
用jdom解析xml，反射创建对象
引入jar包，jdom-2.0.5.jar
/ImitateSpring/src/yuki/spring/imitate/xml/test.xml
<?xml version="1.0" encoding="UTF-8"?>
<HD>
<disk name="C">
<capacity>8G</capacity>
<directories>200</directories>
<files>1580</files>
</disk>
<disk name="D">
<capacity>10G</capacity>
<directories>500</directories>
<files>3000</files>
</disk>
</HD>/ImitateSpring/src/yuki/spring/imitate/spring/ClassPathXmlApplicationContext.java
package yuki.spring.imitate.xml;
import java.util.List;
import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.input.SAXBuilder;
public class Sample1 {
public static void main(String[] args) throws Exception {
SAXBuilder saxBuilder = new SAXBuilder();
Document document = saxBuilder.build(
/*Sample1.class.getClassLoader().getResourceAsStream("/text.xml")*/
"D:/Workspaces/Eclipse/ImitateSpring/bin/yuki/spring/imitate/xml/test.xml");
Element root = document.getRootElement();
List<Element> elements = root.getChildren();
for(Element element : elements){
String name = element.getAttributeValue("name");
String capacity = element.getChildText("capacity");
String directories = element.getChildText("directories");
String files = element.getChildText("files");
System.out.println("磁盘信息：");
System.out.println("分区盘符：" + name);
System.out.println("分区容量：" + capacity);
System.out.println("目录数：" + directories);
System.out.println("文件数：" + files);
System.out.println("------------------------------");
}
}
}运行结果如下：
磁盘信息： 分区盘符：C 分区容量：8G 目录数：200 文件数：1580 ------------------------------ 磁盘信息： 分区盘符：D 分区容量：10G 目录数：500 文件数：3000 ------------------------------
可以把bean作为另一个bean的属性注入
/ImitateSpring/src/beans.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans>
<bean id="u" class="yuki.spring.imitate.dao.impl.UserDAOImpl"></bean>
<bean id="userService" class="yuki.spring.imitate.service.UserService">
<property name="userDAO" bean="u"></property>
</bean>
</beans>/ImitateSpring/src/yuki/spring/imitate/spring/BeanFactory.java
package yuki.spring.imitate.spring;
public interface BeanFactory {
Object getBean(String name);
}/ImitateSpring/src/yuki/spring/imitate/spring/ClassPathXmlApplicationContext.java
package yuki.spring.imitate.spring;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.input.SAXBuilder;
public class ClassPathXmlApplicationContext implements BeanFactory {
private Map<String, Object> beans = new HashMap<String, Object>();
public ClassPathXmlApplicationContext() throws Exception {
SAXBuilder saxBuilder = new SAXBuilder();
Document document = saxBuilder.build(
"D:/Workspaces/Eclipse/ImitateSpring/bin/beans.xml");
Element root = document.getRootElement();
List<Element> elements = root.getChildren();
for(Element element : elements){
String id = element.getAttributeValue("id");
String clazz = element.getAttributeValue("class");
System.out.println(id + " : " + clazz);
Object o = Class.forName(clazz).newInstance();
beans.put(id, o);
for(Element propertyElement : element.getChildren("property")){
String name = propertyElement.getAttributeValue("name");
String bean = propertyElement.getAttributeValue("bean");
Object beanObject = beans.get(bean);
String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);
System.out.println("method name = " + methodName);
Method m = o.getClass().getMethod(methodName, beanObject.getClass().getInterfaces()[0]);
m.invoke(o, beanObject);
}
}
}
@Override
public Object getBean(String name){
return beans.get(name);
}
}通过JUnit，可以新建测试类
/ImitateSpring/test/yuki/spring/imitate/service/UserServiceTest.java
package yuki.spring.imitate.service;
import org.junit.Test;
import yuki.spring.imitate.pojo.User;
import yuki.spring.imitate.spring.BeanFactory;
import yuki.spring.imitate.spring.ClassPathXmlApplicationContext;
public class UserServiceTest {
@Test
public void testAdd() throws Exception {
BeanFactory factory = new ClassPathXmlApplicationContext();
UserService service = (UserService) factory.getBean("userService");
/*UserDAO userDAO = (UserDAO) factory.getBean("u");
service.setUserDAO(userDAO);*/
User u = new User();
service.add(u);
}
}运行结果如下：
u : yuki.spring.imitate.dao.impl.UserDAOImpl userService : yuki.spring.imitate.service.UserService method name = setUserDAO user saved...
术语解释：
控制反转(IOC)、依赖注入(DI)
本来应该自己控制的，交给容器控制，可以实现随意装配
本文参考了[尚学堂马士兵_Spring_模拟Spring]的公开课程
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