Java Mybatis快速入门之基本使用

ゝ一纸荒年。 2021-09-21 15:22 327阅读 0赞

### 目录 ###

*   *  搭建环境
     *  编写 Mybatis 核心配置文件
     *  pom导出资源失败
     *  测试

## 搭建环境 ##

新建Maven项目

导入Maven依赖

<dependencies>
        
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        
        
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

## 编写 Mybatis 核心配置文件 ##

> 1.核心配置文件 `mybatis-config.xml`

注意, 在 `xml` 中 `&` 需要转义, 应该使用 `&`

<?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="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123456"/>
                </dataSource>
            </environment>
        </environments>
    </configuration>

> 2.编写Mybatis工具类

package com.pro.utils;
    
    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;
    
    // SqlSessionFactory --> SqlSession
    public class MybatisUtils { 
        private static SqlSessionFactory sqlSessionFactory;
    
        static { 
            try { 
                // 获取 SqlSessionFactory 对象
                String resource = "mybatis-config.xml";
                InputStream inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            } catch (IOException e) { 
                e.printStackTrace();
            }
        }
    
        // 既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法
        public static SqlSession getSqlSession() { 
            return sqlSessionFactory.openSession();
        }
    }

> 3.编写接口

package com.pro.dao;
    
    import com.pro.pojo.User;
    
    import java.util.List;
    
    public interface UserDao { 
        public List<User> getUserList();
    }

> 4.由原来的实现类转变为一个 Mapper 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="com.pro.dao.UserDao">
    
        
        <select id="getUserList" resultType="com.pro.pojo.User">
            select * from user
        </select>
    </mapper>

## pom导出资源失败 ##

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

## 测试 ##

注意点

org.apache.ibatis.binding.BindingException: Type interface com.pro.dao.UserDao is not known to the MapperRegistry.

**MapperRegistry**

**在核心配置文件中注册 mapper, 每一个 Mapper.xml 都需要在 Mybatis 核心配置文件中注册**

<mappers>
        <mapper resource="com/pro/dao/UserMapper.xml"></mapper>
    </mappers>

**junit测试**

package com.pro.dao;
    
    import com.pro.pojo.User;
    import com.pro.utils.MybatisUtils;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    import java.util.List;
    
    public class UserDaoTest { 
    
        @Test
        public void test() { 
            // 获取 sqlSession 对象
            SqlSession sqlSession = MybatisUtils.getSqlSession();
            // 执行 SQL 方式一: getMapper
            UserDao mapper = sqlSession.getMapper(UserDao.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) { 
                System.out.println(user);
            }
    
            // 关闭资源
            sqlSession.close();
        }
    }