通过读取xml文件，利用反射动态加载类和方法，其实就是spring的注入机制
模拟，可以清晰的看出整个运行流程 1、配置文件 applicationContext.xml
<beans>
<bean id="sd" class="dao.impl.IStudentDaoImpl"/>
<bean id="studentService" class="service.StudentService">
<property name="studentDao" ref="sd"/> </bean>
</beans>
property标签中name 为 StudentService.java的属性 2、dao
package dao;
public interface StudentDao {
public void save();
}
3、daoImpl
1)
package dao.impl;
import dao.StudentDao;public class IStudentDaoImpl implements StudentDao {
public void save() {
System.out.println("IStudentDaoImpl.save()");
}
}
2)
package dao.impl;
import dao.StudentDao;
public class StudentDaoImpl implements StudentDao{
public void save() {
System.out.println("StudentDaoImpl.save()");
}
}
4、service
package service;
import dao.StudentDao;
public class StudentService {
private StudentDao studentDao;
public StudentDao getStudentDao() {
return studentDao;
}
public void setStudentDao(StudentDao studentDao) {
this.studentDao = studentDao;
}
public void save(){
this.studentDao.save();
}
}
5、解析xml文件
package util; 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 {
static Map<String,Object> map=new HashMap<String,Object>();
public void SaxXml() throws Exception{
SAXBuilder sb=new SAXBuilder();
Document doc=sb.build(this.getClass().getClassLoader().getResourceAsStream("applicationContext.xml"));
Element root=doc.getRootElement();
List<Element> list=root.getChildren("bean");
for(int i=0;i<list.size();i++){
Element ele=list.get(i);
String id=ele.getAttributeValue("id");
String obj=ele.getAttributeValue("class");
Object o=Class.forName(obj).newInstance();
map.put(id, o); for(Element elePro:(List<Element>)ele.getChildren("property")){
String name=elePro.getAttributeValue("name");
String bean=elePro.getAttributeValue("ref");
String methodName="set"+name.substring(0, 1).toUpperCase()+name.substring(1);
System.out.println("MethodName:"+methodName);
Method m=o.getClass().getMethod(methodName, map.get(bean).getClass().getInterfaces()[0]);
m.invoke(o, map.get(bean));
}
}
}
public static Object get(String id){
return map.get(id);
}
}
6、创建测试类
package service;
import static org.junit.Assert.*;
import org.junit.Test;
import util.ClassPathXmlApplicationContext;
public class StudentServiceTest {
@Test
public void testSave() throws Exception {
ClassPathXmlApplicationContext cpac=new ClassPathXmlApplicationContext();
cpac.SaxXml();
StudentService ss=(StudentService)ClassPathXmlApplicationContext.get("studentService");
ss.save();
}
}
输出结果：IStudentDaoImpl.save() ，因为在xml文件中配置的是IStudentDaoImpl 没有配置StudentDaoImpl，所以反射加载的只是IStudentImpl