MyBatis 基础搭建(CRUD+模糊查询)+常见问题总结

ps 狂神
思路:搭建环境–>导入Mybatis–>编写代码–>测试

环境搭建

1.搭建数据库

create database `mybatis`;
use `mybatis`;
create table `user`(
`id` int(20) primary KEY,
`name` varchar(30) default null,
`pwd` varchar(30) default NULL
) engine=INNODB default charset utf8;

insert into `user`(`id`,`name`,`pwd`)values
(1,'小张','123'),
(2,'小沈','345'),
(4,'小李','789')

2.创建maven项目(点此链接)

注意：检查是不是用自己的maven

3.创建父级工程，把src目录删掉
4.导入依赖(操作pom.xml)

<?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>
        <!--父工程-->
    <groupId>org.example</groupId>
    <artifactId>Mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>
    	<!--子级工程-->
    <modules>
        <module>mybatis01</module>
    </modules>
     <!--指定javasource和 target-->
    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
		<!--导入依赖-->
    <dependencies>
        <!--MySQL驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.49</version>
        </dependency>
        <!--mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--junit 用于单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
        <!--lombok用于初始化对象jdk15-->
    <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.18</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
</project>

注意:导完后要检查包有没有导入
5.创建子级maven项目

创建mybatis模块

1.在resources下配置db.properties(连接数据库属性配置)

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=false&userUnicode=true&characterEncoding=utf-8&serverTimezone=GMT
username=root

2.在resources下配置mybatis-config.xml(核心配置数据库)

<?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核心配置文件-->
<configuration>
    <!--引入外部配置 注意标签优先级,配置文件和标签都能写-->
    <properties resource="db.properties">
        <property name="password" value="123456"/>
    </properties>
        <!--设置控制台日志-->
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
       <!--完全限定类更改别名-->
    <typeAliases>
        <typeAlias type="com.my.pojo.User" alias="User"/>
    </typeAliases>
                <!--environments环境-->
    <environments default="development">
        <environment id="development">
            <!--transactionManager事务管理-->
            <transactionManager type="JDBC"></transactionManager>
            <!--数据库连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <!--mysql8.0要配置时区-->
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--每一个Mapper.xml都需要在Mybatis核心配置文件中注册-->
    <mappers>
        <!--所有的路径以/结尾-->
        <mapper resource="com/my/dao/UserMapper.xml"/>
    </mappers>
</configuration>

2.编写mybatis工具类
SqlSession完全包含了面向数据库执行SQL命令需要的所有方法。可以通过SqlSession实例来直接执行已映射的SQL语句。

public class MybatisUtil {
    
    
    private static  SqlSessionFactory sqlSessionFactory;
    static{
    
    
        //使用Mybatis获取sqlSessionFactory对象
        try {
    
    
            String resource="mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
             sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }
    //SqlSessionFactory完全包含了面向数据库执行Sql命令所需的所有方法
    public static SqlSession getSqlSession(){
    
    
    //true 为自动提交，没用提交事务
         return   sqlSessionFactory.openSession(true);
    }
}

编写代码

1.实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    
    
    private  int id;
    private  String name;
    private  String pwd;
}

2.Dao接口

public interface UserDao {
    
    
//方法存在多个基本类型参数时候，必须用@Param("")注解
    //查询全部用户
    List <User> getUserList();
    //根据id查询用户
    User getUserById(int id);
    //添加用户
    int insertUser(Map map);
   //根据id删除用户
    int deleteUserById(int id);
    //修改
    int updateUser(User user);
       //模糊查询
    List <User> getLikeUser(String value);
    List <User> getLikeUser1(String value);
}

}

3.接口实现类
由Implement实现类转换为UserMapper.xml配置文件
id就相当于重写接口的方法

<?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">
<!--namespace绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.my.dao.UserDao">
    <!--id对应Dao/Mapper接口方法名字-->
    <!--resultType 返回结果要写全限定类名-->
<select id="getUserList" resultType="User">
    select * from mybatis.user;
</select>
    <!--parameterType参数类型-->
    <select id="getUserById" resultType="User" parameterType="int">
       select * from mybatis.user where id=#{id};
    </select>
    <insert id="insertUser" parameterType="map">
        insert into  mybatis.user (pwd, name, id)values(#{pwd},#{name},#{id});
    </insert>
    <delete id="deleteUserById" parameterType="int">
        delete from mybatis.user where id=#{id};
    </delete>
    <update id="updateUser" parameterType="User">
    update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id};
    </update>
    <!--模糊查询-->
    <select id="getLikeUser" resultType="User">
        select * from mybatis.`user` where name like #{value};
    </select>
    <select id="getLikeUser1" resultType="User">
        select *from mybatis.`user` where  name like "%" #{value} "%";
    </select>
</mapper>

测试

测试就要写道测试包下，用junit
规范：测试要与开发包对应
重点：关闭资源,提交事务

public class UserDaoTest {
    
    

    //测试查询所有用户
    @Test
    public  void  getAllUser(){
    
    
        //获取获得SqlSession对象
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        //执行Sql
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        //获取UserDao接口的方法
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
    
    
            System.out.println(user);
        }
        //关闭SqlSession
        sqlSession.close();
    }
    //测试用id查询所有
    @Test
    public void getUserById(){
    
    
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        User user = mapper.getUserById(1);
        System.out.println(user);
         sqlSession.close();
    }
    //添加用户,增删改需要提交事务
    @Test
    public  void  insertUser(){
    
    
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);

        Map map=new HashMap();
        map.put("pwd","123");
        map.put("id","9");
        map.put("name","小黑");
        int i= mapper.insertUser(map);
        if (i>0)
        {
    
    
            System.out.println(i);
        }
        sqlSession.close();

    }
    //通过id删除用户,记得提交事务
    @Test
    public void deleteUserById(){
    
    
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        int i = mapper.deleteUserById(0);
       if (i>0)
       {
    
    
           System.out.println(i);
       }
       sqlSession.close();
    }
    //通过id，修改用户,提交事务
    @Test
    public void updateUser(){
    
    
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        int i = mapper.updateUser(new User(5, "小赵", "345"));
        if (i>0){
    
    
            System.out.println(i);
        }
        sqlSession.close();
    }

}
  //模糊查询
    @Test
    public  void getLikeUser(){
    
    
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List<User> user = mapper.getLikeUser("%黑%");
        for (User user1 : user) {
    
    
            System.out.println(user1);
        }
        sqlSession.close();
    }
    @Test
    public  void getLikeUser1(){
    
    
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List<User> user = mapper.getLikeUser1("小");
        for (User user1 : user) {
    
    
            System.out.println(user1);
        }
        sqlSession.close();
    }
}

注解开发

public interface UserMapper {
    //查询全部用户
    @Select(" select * from mybatis.user")
    List <User> getUserList();
    //根据id查询用户
    @Select("select * from mybatis.user where id=#{uid}")
    User getUserById(@Param("uid") int id);
    //添加用户
    @Insert("insert into  mybatis.user (pwd, name, id)values(#{pwd},#{name},#{id})")
    int insertUser(Map map);
   //根据id删除用户
    @Delete(" delete from mybatis.user where id=#{id}")
    int deleteUserById(@Param("id") int id);
    //修改
    @Update("  update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id}")
    int updateUser(User user);
    //模糊查询
    List <User> getLikeUser(String value);
    List <User> getLikeUser1(String value);
}

关于@Param("")注解

基本类型的参数或者String类型，需要加上。
引用类型不需要
Sql中引用的就是@Param("")中设定的属性名
#{}加注解能很大程度防止sql注入。preparedStatement
${}中传入的值会进行拼接，无法防止sql注入 statement

解决遇到的问题

重点
绑定问题：
Exception：Type interface com.my.dao.UserDao is not known to the MapperRegistry
在总配置文件中没有绑定Mapper.xml
资源导出失败问题：
Exception:Could not find resource com/my/dao/UserMapper.xml
解释：maven资源文件配置在resources目录下，由于实现类UserMapper.xml在java目录下,则需要手动配置资源过滤
maven由于他的约定大于配置，配置文件无法解析、
解决方案：
在pom中手动配置

<!--在build中配置resources,来防止资源导出失败-->
    <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>

Error creating document instance. Cause: com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: 1 字节的 UTF-8 序列的字节 1 无效。
解决方案：字符集问题,配置完后，在Maven中clean.

Exception:The last packet successfully received from the server was 533 milliseconds ago.
在总配置文件中，把数据库url，useSSL=true改为useSSL=false。