这里有dao、service和Servlet三个地方

通过配过文件xml生成对象，并注入对象类型的属性，降低耦合

dao文件代码：

package com.swift;public class DaoUser {    public void fun() {        System.out.println("I'm  dao's fun()....................");    }}

service文件代码：（提供setter方法，xml文件可通过这种方法配置）

package com.swift;public class ServiceUser {    private DaoUser daoUser;        public void setDaoUser(DaoUser daoUser) {        this.daoUser = daoUser;    }    public String fun() {        System.out.println("I am Service's fun()..............");        return daoUser.fun();    }}

xml文件代码：

Servlet类文件可以绕开dao的文件，直接使用service即可

package com.swift;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;@WebServlet("/duixiang")public class ServletService extends HttpServlet {    private static final long serialVersionUID = 1L;    public ServletService() {        super();    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        response.getWriter().append("Served at: ").append(request.getContextPath());        @SuppressWarnings("resource")        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");        ServiceUser service=(ServiceUser) context.getBean("service");        response.getWriter().append(service.fun());    }    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);    }}

中间因修改属性名字，而忽略修改setter方法名字导致出错，已改好，错误的类型记录了一下：

Caused by: org.springframework.beans.NotWritablePropertyException: Invalid property 'daoUser' of bean class [com.swift.ServiceUser]: Bean property 'daoUser' is not writable or has an invalid setter method. Does the parameter type of the setter match the return type of the getter?

提示的很好，要不自己很难发现。