【问题记录】进行mybatis实例查询测试时Error opening session. Cause: java.lang.NullPointerException

梦里梦外; 2022-10-08 00:56 7阅读 0赞

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 1]  
去查了一下Resources.getResourceAsStream  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 2]  
试图改变xml配置的位置：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 3]  
结果报错：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 4]

尝试启动 DemomybatisApplication  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 5]  
居然没连接数据库，于是连接数据库：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 6]

再启动test文件：仔细看报错是  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 7]  
去查了一下，加上了mapper注解  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 8]  
然而报错还是一样的，又去查资料，在pom.xml中增加了一配置：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 9]

再次运行，成功了：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzU4NTc0_size_16_color_FFFFFF_t_70 10]  
![在这里插入图片描述][20210619145921400.png]  
查到的结果也正常显示了。

以上查询的代码：  
全局配置：  
mybatis-config.xml

<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        <properties>
            <property name="jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
            <property name="jdbc.url" value="jdbc:mysql://localhost:3308/data1?characterEncoding=UTF-8"/>
            <property name="jdbc.username" value="heziyi"/>
            <property name="jdbc.password" value="123456"/>
        </properties>
        
        <environments default="test">
            
            <environment id="test">
                
                <transactionManager type="JDBC"/>
                
                <dataSource type="POOLED">
                    <property name="driver" value="${jdbc.driver}"/>
                    <property name="url" value="${jdbc.url}"/>
                    <property name="username" value="${jdbc.username}"/>
                    <property name="password" value="${jdbc.password}"/>
                </dataSource>
            </environment>
        </environments>
        <mappers>
            <package name="com.example.demomybatis.mapper"/>
        </mappers>
    </configuration>

实体类和接口：  
![在这里插入图片描述][20210619150041565.png]

package com.example.demomybatis.model;
    
    import lombok.AllArgsConstructor;
    import lombok.Builder;
    import lombok.Data;
    import lombok.ToString;
    
    @Data
    @AllArgsConstructor
    @Builder
    @ToString
    public class UserModel { 
        private int id;
        private String name;
        private String pwd;
    }

import java.util.List;
    @Mapper
    public interface UserMapper { 
        List<UserModel>getList();
    }

查询的xml映射文件：

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.example.demomybatis.mapper.UserMapper">
        
        <select id="getList" resultType="com.example.demomybatis.model.UserModel">
    <![CDATA[ SELECT * FROM user ]]>
    </select>
    </mapper>

运行的Test文件：  
![在这里插入图片描述][20210619150216313.png]

@Slf4j
    public class Demo3Test { 
        private SqlSessionFactory sqlSessionFactory;
        @Before
        public void before() throws IOException { 
    //指定mybatis全局配置文件
            String resource = "mybatis-config.xml";
    //读取全局配置文件
            InputStream inputStream =Resources.getResourceAsStream(resource);
    //构建SqlSessionFactory对象
            SqlSessionFactory sqlSessionFactory = new
                    SqlSessionFactoryBuilder().build(inputStream);
            this.sqlSessionFactory = sqlSessionFactory;
        }
        @Test
        public void test() { 
            try (SqlSession sqlSession = this.sqlSessionFactory.openSession(true);) { 
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    //执行查询操作
                List<UserModel> userModelList = userMapper.getList();
               userModelList.forEach(item -> { 
                   log.info("{}", item);
                });
                log.info("----------------------------------");
    
            }
            }
    }

yml数据库配置：

spring:
      datasource:
        url: jdbc:mysql://localhost:3308/data1?useUnicode=true&characterEncoding=UTF8
        username: heziyi
        password: 123456
        driver-class-name: com.mysql.cj.jdbc.Driver

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[20210619145921400.png]: /images/20221005/424ba6d889a840e1ad8b908eca812f7b.png
[20210619150041565.png]: /images/20221005/bf561335b62f4dc89ea801983504ac36.png
[20210619150216313.png]: /images/20221005/1d931359d1444cf4b7bfa477e99d9513.png