專案結構：出錯位置：在UserController中，對介面注入失敗

package controller;

import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import dao.UserDao;
import model.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;

import java.io.IOException;

@Controller
public class UserController {

    @Autowired
    private UserDao userDao;



    @RequestMapping("/create")
    public String create(@ModelAttribute("form")User users,Model model) throws IOException {
        if((userDao.queryUser(users.getName()) == null)){
            userDao.insertUser(users);
            model.addAttribute("User",users);
            return "login";
        }else{
            return "create";
        }
    }

    @RequestMapping("/login")
    public String login(HttpServletRequest request, HttpServletResponse response, @ModelAttribute("form") User User, Model model) throws IOException {
        model.User tmpUser = userDao.queryUser(User.getName());
        if(User.getPwd().equals(tmpUser.getPwd())){
            model.addAttribute(tmpUser);
            if (request.getParameter("save") != null) {
                savePassword(response, tmpUser);
            }
            return "detail";
        }else{
            return "login";
        }
    }

    public void savePassword(HttpServletResponse response, User users){
        Cookie UserCookie = new Cookie("username", users.toString());
        //設定Cookie的有效期為3天
        UserCookie.setMaxAge(60 * 60 * 24 * 3);
        response.addCookie(UserCookie);
    }
}
 

錯誤資訊：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private dao.UserDao controller.UserController.userDao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [dao.UserDao] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

Mybatis版本：3.3.0    根據錯誤提示表明UserDao介面註解失敗。UserDao介面是mybatis的mapper.xml對映介面。一般情況下介面註解失敗的原因是mapper對映檔案配置出錯和spring配置檔案出錯。在spring配置檔案中影響到UserDao介面的只有資料來源配置以及MapperFactoryBean的配置。 mapper.xml

<?xml version="1.0" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"
 
>
<mapper namespace="test">
    <select id="queryUser" resultType="model.User" parameterType="java.lang.String">
select * from user where name=#{value}
    </select>
    <insert id="insertUser" parameterType="model.User">
insert into user(name,pwd,age) values(#{name},#{pwd},#{age})
    </insert>
</mapper>

其中一個錯誤就是namespace的名字問題。mapper的namespace必須是與之對映的介面類全名，由於之前寫的專案是自己new的介面實現類，然後再方法中呼叫sqlSession的方法。例如：

其中test就是mapper的namespace名，insertUser就是對應的insertid。其本質介面實現類和mapper並不是對映關係，因此完全可以執行成功。在本專案中要使介面和mapper出現對映關係，那麼namespace的名字必須是類的全名。即把”test“改為“dao.UserDao”。還有一點值得注意，在UserDao中的方法命名必須和mapper一直。例如：UserDao

package dao;

import model.User;

public interface UserDao {
    public User queryUser(String name);
    public void insertUser(User User);
}

當配置成功後出現左側的綠色箭頭，在mapper檔案中也有。當這個問題改好之後發現專案執行還是和原來一樣的錯誤，那麼現在唯一可能出錯的地方就是spring配置檔案的問題。

ApplicationContext-datasuorce.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.2.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-3.2.xsd ">

    <!-- 載入配置檔案 -->
    <context:property-placeholder location="classpath:META-INF/db.properties"/>
    <!-- 資料庫連線池，使用dbcp -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="${jdbc.driver}"/>
        <property name="url" value="${jdbc.url}"/>
        <property name="username" value="${jdbc.username}"/>
        <property name="password" value="${jdbc.password}"/>
        <property name="maxActive">
            <value>255</value>
        </property>
        <property name="maxIdle">
            <value>2</value>
        </property>
        <property name="maxWait">
            <value>120000</value>
        </property>
    </bean>

    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <!-- 指定資料來源 -->
    <property name="dataSource" ref="dataSource"/>
    <property name="mapperLocations" value="classpath:config/UserDaoMap.xml"/>
    </bean>

    <bean id="userDao" class="org.mybatis.spring.mapper.MapperFactoryBean">
        <property name="mapperInterface" value="dao.UserDao" />
        <property name="sqlSessionFactory" ref="sqlSessionFactory" />
    </bean>

</beans>

在除錯的時候發現UserDao這個介面注入還是失敗，沒辦法只好自己手動載入。

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext-datasource.xml");
        userDao = (UserDao) applicationContext.getBean("userDao");

新增如上程式碼，發現可以執行。那麼說明配置檔案沒有問題，那麼究竟是什麼原因導致的呢？會不會是配置檔案沒有自動載入。web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath*:META-INF/applicationContext-datasource.xml</param-value>
  </context-param>

 <!--<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  -->

  <servlet>
    <servlet-name>smart</servlet-name>
    <servlet-class>
      org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath*:META-INF/applicationContext.xml</param-value>
    </init-param>

    <load-on-startup>3</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>smart</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

可以看到配置檔案我也載入了，經過比對後發現自己沒有新增監聽器（已經註釋），加上後項目執行成功。對於監聽器做了哪些事這裡附上一個連結：詳解contextConfigLocation。   至此針對ssm mapper對映介面注入失敗問題的總結：
    1.mapper的namespcae命名和介面必須一致，介面中的方法名和mapper對映id必須一致。    2.對於spring配置檔案一定要載入，一直要配置監聽器。