Idea搭建Mybatis入门案例-----遇到的小问题

╰半橙微兮° 2021-12-10 00:45 340阅读 0赞

### 1.创建一个maven项目，学习mybatis的框架功能的话，**建议一个空的maven工程项目。** ###

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### 二，在pom.xml中导入相应的jar包依赖 ###

<?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
    
        <groupId>cn.waggag</groupId>
        <artifactId>MybatisDemo1</artifactId>
        <version>1.0-SNAPSHOT</version>
        <packaging>jar</packaging>
    
        <dependencies>
            
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.4.5</version>
            </dependency>
            
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.16</version>
            </dependency>
            <dependency>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
                <version>1.2.16</version>
            </dependency>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
            </dependency>
        </dependencies>
    </project>

### 三、创建实体类和接口 ###

3.1、实体类

package cn.waggag.domain;
    
    import java.io.Serializable;
    import java.util.Date;
    
    /**
     * @description: User的实体类
     * @author: waggag
     * @time: 2019/7/15 0:14
     * @Company http://www.waggag.cn
     */
    public class User implements Serializable {
    
        private Integer id;
        private String username;
        private Date birthday;
        private String sex;
        private String address;
        //setter和getter方法
    }

3.2、接口

package cn.waggag.mapper;
    import cn.waggag.domain.User;
    import java.util.List;
    /**
     * @description:用户的持久层接口
     * @author: waggag
     * @time: 2019/7/15 0:18
     * @Company http://www.waggag.cn
     */
    public interface UserMapper {
        /**
         * 查询所有用户操作
         */
        List<User> findAll();
    }

3.3、接口的配置文件UserMapper.xml。

<?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="cn.waggag.mapper.UserMapper">
        
        <select id="findAll" resultType="cn.waggag.domain.User">
            select * from user;
        </select>
    </mapper>

四、创建Mybatis的配置文件，放在resources下。

<?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>
        
        <environments default="mysql">
            
            <environment id="mysql">
                
                <transactionManager type="JDBC"></transactionManager>
                
                <dataSource type="POOLED">
                    
                    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/ssm"/>
                    <property name="username" value="username"/>
                    <property name="password" value="password"/>
                </dataSource>
            </environment>
        </environments>
        
        <mappers>
            <mapper resource="cn/waggag/mapper/UserMapper.xml"/>
        </mappers>
    </configuration>

注意： <mapper resource="cn/waggag/mapper/UserMapper.xml"/>的配置为文件的relative Path

五、创建一个测试类进行测试

package cn.waggag.test;
    
    import cn.waggag.mapper.UserMapper;
    import cn.waggag.domain.User;
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import java.io.IOException;
    import java.io.InputStream;
    import java.util.List;
    /**
     * @description: mybatis的入门
     * @author: waggag
     * @time: 2019/7/15 0:43
     * @Company http://www.waggag.cn
     */
    public class MybatisTest {
        /**
         * mybatis的入门
         * @param args
         */
        public static void main(String[] args) throws IOException {
            //1.读取配置文件
            InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
            //2.创建一个SqlSessionFactory工厂
            SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
            SqlSessionFactory sqlSessionFactory = builder.build(inputStream);
            //3.使用工厂生成SqlSession对象
            SqlSession sqlSession = sqlSessionFactory.openSession();
            //4.使用SqlSession创建Dao接口的代理对象
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            //5.使用代理对象执行方法
            List<User> userList = mapper.findAll();
            for (User user : userList) {
                System.out.println(user);
            }
            //6.释放资源
            sqlSession.close();
            inputStream.close();
        }
    }

六、入门案例中碰到的错误

6.1、数据库时区问题。

\#\#\# Error querying database.  Cause: java.sql.SQLException: The server time zone value '�й���׼ʱ��' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the serverTimezone configuration property) to use a more specifc time zone value if you want to utilize time zone support.

解决办法：

//在SqlSessionConfig.xml中配置数据库时区
    <property name="url" value="jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC"/>

6.2、Error Opening Session 空指针问题。

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解决方法：< environments default=”mysql“> 的默认值需要指定下面配置的环境<environment id="mysql">

<configuration>
        
        <environments default="mysql">
            
            <environment id="mysql">
                
                <transactionManager type="JDBC"></transactionManager>
                
                <dataSource type="POOLED">
                    
                    <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC"/>
                    <property name="username" value="waggag"/>
                    <property name="password" value="225514"/>
                </dataSource>
            </environment>
        </environments>
        
        <mappers>
            <mapper resource="cn/waggag/mapper/UserMapper.xml"/>
        </mappers>
    </configuration>

6.3、无法找到接口的映射文件

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解决方法1：

在pom文件中加入下面代码，发布src/main/java和src/main/resources下的资源文件到classes中

<build>
            <resources>
                <resource>
                    <directory>src/main/java</directory>
                    <includes>
                        <include>**/*.xml</include>
                    </includes>
                </resource>
                <resource>
                    <directory>src/main/resources</directory>
                    <includes>
                        <include>**/*.xml</include>
                        <include>**/*.properties</include>
                    </includes>
                </resource>
            </resources>
        </build>

注意：添加src/main/java的resource,,必须配置src/main/resources,否则resources下的配置文件无法正常访问

解决方法2：

在resources下创建和接口相同的路径，放入接口的映射文件，目录结构如下，配置文件可正常发布到classes下。

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