springmvc与mybatis整合中的问题

浅浅的花香味﹌ 2022-06-06 05:40 164阅读 0赞

今天在整合SpringMvc+Mybatis时碰到一些问题，网上找了很多资料，一直未找到问题关键点，浪费了不少时间，先将主要碰到的问题与解决方法记录下来。

问题：bean实例化失败，编译启动时问题如下：

严重: Servlet.service() for servlet \[springmvc\] in context with path \[\] threw exception \[Request processing failed; nested exception is java.lang.NullPointerException\] with root cause  
java.lang.NullPointerException

即空指针问题。之前配置文件是这样的。

<?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:p="http://www.springframework.org/schema/p"
        xmlns:context="http://www.springframework.org/schema/context"
        xmlns:mvc="http://www.springframework.org/schema/mvc"
        xsi:schemaLocation="http://www.springframework.org/schema/beans  
                            http://www.springframework.org/schema/beans/spring-beans.xsd  
                            http://www.springframework.org/schema/context  
                            http://www.springframework.org/schema/context/spring-context.xsd  
                            http://www.springframework.org/schema/mvc  
                            http://www.springframework.org/schema/mvc/spring-mvc.xsd
            http://www.springframework.org/schema/tx 
            http://www.springframework.org/schema/tx/spring-tx.xsd
            http://www.springframework.org/schema/util
            http://www.springframework.org/schema/util/spring-util.xsd">
        
        <context:component-scan base-package="cn.zsf.spring.springMaven" />
        
        <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
            <property name="location" value="classpath:jdbc.properties" />
        </bean>
    
        <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
            <property name="driverClassName" value="${jdbc.driverClassName}" />
            <property name="url" value="${jdbc.url}" />
            <property name="username" value="${jdbc.username}" />
            <property name="password" value="${jdbc.password}" />
            
            <property name="initialSize" value="${jdbc.initialSize}" />
            
            <property name="maxActive" value="${jdbc.maxActive}" />
            
            <property name="maxIdle" value="${jdbc.maxIdle}" />
            
            <property name="minIdle" value="${jdbc.minIdle}" />
            
            <property name="maxWait" value="${jdbc.maxWait}" />
        </bean>
    
        
        <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
            <property name="dataSource" ref="dataSource" />
            <property name="configLocation"  value="classpath:sqlMapConfig.xml"/>
            
            <property name="mapperLocations" value="classpath:cn/zsf/spring/springMaven/mapping/*.xml" />
        </bean>
        <bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">  
        	<constructor-arg index="0" ref="sqlSessionFactory"/>  
    	</bean> 
    
        
        <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
            <property name="dataSource" ref="dataSource" />
        </bean>
    </beans>

我在UserService中注入

package cn.zsf.spring.springMaven.service;  
  
import org.apache.log4j.Logger;  
import org.mybatis.spring.SqlSessionTemplate;  
import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.stereotype.Service;  
  
import cn.zsf.spring.springMaven.dao.UserMapper;  
import cn.zsf.spring.springMaven.pojo.User;  
  
@Service  
public class UserService \{  
    private static Logger logger = Logger.getLogger(UserService.class);  
      
    @Autowired  
    private SqlSessionTemplate sqlSession;  
      
    @Autowired  
    private UserMapper userMapper;  
    
      
    public User get(int id)\{  
        logger.info(sqlSession.toString());  
        return  userMapper.selectByPrimaryKey(id);  
    \}  
      
    public void setUserMapper(UserMapper userMapper)\{  
        this.userMapper = userMapper;  
    \}  
      
    public UserMapper getUserMapper()\{  
        return userMapper;  
    \}  
      
      
\}

在启动时就报错，sqlSession注入失败，userMapper也找不到可用的bean，错误信息为：

ERROR \[web.context.ContextLoader\] Context initialization failed  
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'homeController': Unsatisfied dependency expressed through field 'userService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'userService': Unsatisfied dependency expressed through field 'userMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'cn.zsf.spring.springMaven.dao.UserMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: \{@org.springframework.beans.factory.annotation.Autowired(required=true)\}  
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)

造成sqlSession、userMapper都无法注入成功，原因是配置错误，未配置mybatis mapper接口，在spring-mybatis.xml中

后面添加

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
            <property name="basePackage" value="cn.zsf.spring.springMaven.**.dao"/>
            <property name="sqlSessionTemplateBeanName" value="sqlSessionTemplate"/>
        </bean>

即可；

另外碰到一个问题，错误提示信息

在HomeController中调用 userService.get(1)方法， 错误原因为：在我直接手动进行service初始化， UserService userService = new UserService();  这是一个低级错误，因UserService中有注入sqlsession和userMapper，并注册为Service，通过手动new的方式，是无法完成这两个属性的注入的，因此调用自然也就错误了。 其必须通过

@Autowired

private UserMapper userMapper

的方式进行注入引用。

这里附上其他的配置文件(可正常使用)：

sqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE configuration PUBLIC  
        "-//mybatis.org//DTD Config 3.0//EN"  
        "http://mybatis.org/dtd/mybatis-3-config.dtd">  
    <configuration>  
        <typeAliases>
            <typeAlias type="cn.zsf.spring.springMaven.pojo.User" alias="UserEntry" />
        </typeAliases>
    </configuration>

applicationContent.xml

spring-mvc.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:p="http://www.springframework.org/schema/p"    
    xmlns:context="http://www.springframework.org/schema/context" 
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xsi:schemaLocation="http://www.springframework.org/schema/beans    http://www.springframework.org/schema/beans/spring-beans.xsd    
    http://www.springframework.org/schema/context    http://www.springframework.org/schema/context/spring-context.xsd 
    http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"
    default-lazy-init="true">
    
    	
        <context:component-scan base-package="cn.zsf.spring.springMaven">  
            
             
        </context:component-scan>
        
        <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
        	<property name="messageConverters">
        		<list>
        			<ref bean="mappingJacksonHttpMessageConverter"/>
        			<ref bean="utf8StringHttpMessageConverter" />
        		</list>
        	</property>
        </bean>
        
        <bean id="mappingJacksonHttpMessageConverter" class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">  
            <property name="supportedMediaTypes">  
                <list>  
                    <value>text/plain;charset=UTF-8</value>
                    <value>text/html;charset=UTF-8</value>  
                    <value>application/json;charset=UTF-8</value>
                </list>  
            </property>  
        </bean>  
        <bean id="utf8StringHttpMessageConverter" class="org.springframework.http.converter.StringHttpMessageConverter">
            <property name="supportedMediaTypes">
                <list>
                    <value>text/plain;charset=UTF-8</value>
                    <value>text/html;charset=UTF-8</value>
                    <value>application/json;charset=UTF-8</value>
                </list>
            </property>
        </bean>
         
        <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        	<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
            <property name="prefix" value="/WEB-INF/views/"/>
            <property name="suffix" value=".jsp"/>
        </bean>
        
        <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"></bean>
        
        
        
        
    
    </beans>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
    <web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
    
      <display-name>Zsf Web Application</display-name>
     
      
        <context-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath*:applicationContext.xml,
            classpath*:spring-mybatis.xml,
            </param-value>
        </context-param>
        
        
        <listener>
            <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
        </listener>
        
          
        <filter>
            <filter-name>encodingFilter</filter-name>
            <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
            <init-param>
                <param-name>encoding</param-name>
                <param-value>UTF-8</param-value>
            </init-param>
        </filter>
        <filter-mapping>
            <filter-name>encodingFilter</filter-name>
            <url-pattern>/*</url-pattern>
        </filter-mapping>
        
        
        
        <servlet>
            <servlet-name>springmvc</servlet-name>
            <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
            <init-param>  
                <param-name>contextConfigLocation</param-name>  
                
                <param-value>/WEB-INF/classes/spring-mvc.xml</param-value>
            </init-param>  
            <load-on-startup>1</load-on-startup>  
        </servlet>
        <servlet-mapping>
            <servlet-name>springmvc</servlet-name>
            <url-pattern>/</url-pattern>
        </servlet-mapping>
        
        <welcome-file-list>  
            <welcome-file>index.jsp</welcome-file>  
        </welcome-file-list>
        
        
    </web-app>