Mybatis环境配置

深藏阁楼爱情的钟 2023-10-01 16:58 7阅读 0赞

## 搭建环境 ##

> 也可根据官方文档来进行配置https://mybatis.org/mybatis-3/zh/index.html
> 
> 以下的内容配置均为经过实验的

### pom.xml配置 ###

<dependencies>
    
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.15</version>
            </dependency>
    
            
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.5.7</version>
            </dependency>
    
            
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.13.1</version>
                <scope>test</scope>
            </dependency>
        </dependencies>
        
        <build>
            <resources>
                <resource>
                    <directory>src/main/resources</directory>
                    <includes>
                        <include>**/*.properties</include>
                        <include>**/*.xml</include>
                    </includes>
                </resource>
                <resource>
                    <directory>src/main/java</directory>
                    <includes>
                        <include>**/*.properties</include>
                        <include>**/*.xml</include>
                    </includes>
                    <filtering>true</filtering>
                </resource>
            </resources>
        </build>

### 编写xml核心配置文件 ###

> 在**resources包**下创建一个xml文件，**文件名为:mybatis-config.xml**
> 
> 修改配置文件中driver、url、username、password、resource的value
> 
> 如果报错，可以将开头的UTF-8改为UTF8或者删除xml中的注释

<?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?serverTimezone=Asia/Shanghai&useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
    
                    <property name="username" value="root"/>
                    <property name="password" value="root"/>
                </dataSource>
            </environment>
        </environments>
    
        <mappers>
            <mapper resource="com/lzj/dao/UserMapper.xml"/>
        </mappers>
    </configuration>

### 编写Mybatis工具类 ###

//sqlSessionFactory --> sqlSession
    public class MybatisUtils {
        
        private  static SqlSessionFactory sqlSessionFactory;
        static {
        
            try {
        
                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(){
        
    //        SqlSession sqlSession = sqlSessionFactory.openSession();
    //        return sqlSession;//下一行为优化后的结果
            return sqlSessionFactory.openSession();
        }
    
    }

### 编写实体类、Dao接口和接口实现类 ###

#### 实体类User ####

#### Dao接口 ####

public interface UserDao {
        
        List<User> getUserList();
    }

#### 接口实现类 ####

> 由原来的UserDaoImpl转变为一个xml配置文件，文件名：UserMapper.xml
> 
> 如果报错，可以将开头的UTF-8改为UTF8或者删除xml中的注释

<?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.lzj.dao.UserDao">
    
    
        <select id="getUserList" resultType="com.lzj.entity.User">
            select * from mybatis.user
        </select>
    </mapper>

### 测试 ###

public class UserDaoTest {
        
        @Test
        public void test() {
        
            //获得SqlSession对象
            SqlSession sqlSession = MybatisUtils.getSqlSession();
            //方式一:通过getMapper执行SQL
            UserDao mapper = sqlSession.getMapper(UserDao.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
        
                System.out.println(user);
            }
            
            //方式二:不推荐这种方式
            List<User> userList1 = sqlSession.selectList("com.lzj.dao.UserDao.getUserList");
            for (User user : userList1) {
        
                System.out.println(user);
            }
            
            //关闭SqlSession对象
            sqlSession.close();
    
    
        }
    }

### 可能遇到的问题 ###

*  maven资源无法导入xml的问题
    
     *  将xml中首行的的UTF-8改为UTF8
     *  将注释删除
 *  数据库连接不上的问题
    
     *  这个就需要自己排查mybatis-config.xml文件中的配置是否正确，url是否能够读取