010_Mybatis简介

2021年7月12日 5点热度 0条评论 来源: 清风(学习-踏实)

目录


Mybatis简介

什么是 MyBatis?

MyBatis 是一款优秀的持久层框架,它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO(Plain Old Java Objects,普通老式 Java 对象)为数据库中的记录。

  • MyBatis 是一款优秀的持久层框架
  • 它支持自定义 SQL、存储过程以及高级映射。
  • MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。
  • MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO(Plain Old Java Objects,普通老式 Java 对象)为数据库中的记录。
  • MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code,并且改名为MyBatis 。2013年11月迁移到Github

如何获得Mybatis

  • maven仓库
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.7</version>
</dependency>


持久化


持久层


为什么需要Mybatis


第一个Mybatis程序

学习新东西方法:搭建环境-》导入mybatis-》编写代码-》测试

搭建环境

建库建表

CREATE DATABASE `mybatis`CHARACTER SET utf8 COLLATE utf8_general_ci; 
USE `mybatis`;
CREATE TABLE `mybatis`.`user` ( `id` INT(20) NOT NULL COMMENT '主键', `name` VARCHAR(100) NOT NULL COMMENT '用户名', `pwd` VARCHAR(100) NOT NULL COMMENT '密码', PRIMARY KEY (`id`) ) ENGINE=INNODB CHARSET=utf8 COLLATE=utf8_general_ci; 
DESCRIBE `mybatis`.`user`; 
INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) VALUES ('1', 'zhangyq', '123456'); 
INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) VALUES ('2', 'zhangsf', '123456'); 
INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) VALUES ('3', 'zhangdl', '123456'); 

新建父工程

新建普通maven项目


删除src目录,作为父工程


导入maven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>

    <!--父工程-->
    <groupId>com.qing</groupId>
    <artifactId>mybatis-study</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.49</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
        </dependency>

    </dependencies>

</project>

创建第一个子模块


编写mybatis的核心配置文件

官网:https://mybatis.org/mybatis-3/zh/index.html

<?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">

<!--核心配置文件-->
<configuration>
    <!--指定默认数据源-->
    <environments default="development">
        <!--数据源-->
        <environment id="development">
            <!--事务管理器-->
            <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&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

编写mybatis工具类,获取SqlSession

SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。

package com.qing.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;

public class MybatisUtils {

    // 构建 SqlSessionFactory 的实例
    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();
        }
    }

    /**
     * 获取 SqlSession
     * @return
     */
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

编写代码测试

实体类


接口

package com.qing.dao;

import com.qing.pojo.User;

import java.util.List;

/**
 * 接口
 */
public interface UserMapper {

    List<User> getUserList();
}

Mapper

<?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">
<!--命名空间绑定一个对应的接口-->
<mapper namespace="com.qing.dao.UserMapper">
    <!--id对应接口的方法,返回值类型对应接口返回值,参数类型对应接口方法参数,集合类型写集合泛型类型-->
    <select id="getUserList" resultType="com.qing.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

测试

package com.qing.dao;

import com.qing.pojo.User;
import com.qing.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserMapperTest {

    /**
     * 方式一:sqlSession.getMapper(UserMapper.class)
     */
    @Test
    public void test() {
        // 获取sqlSession
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        // 执行SQL
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        // 关闭sqlSession
        sqlSession.close();
    }
}

问题一:Mapper.xml未注册

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

	at org.apache.ibatis.binding.MapperRegistry.getMapper(MapperRegistry.java:47)
	at org.apache.ibatis.session.Configuration.getMapper(Configuration.java:845)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper(DefaultSqlSession.java:288)
	at com.qing.dao.UserMapperTest.test(UserMapperTest.java:20)

解决:mybatis-config.xml中注册Mapper,resource绑定Mapper,必须使用路径/

<?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">

<!--核心配置文件-->
<configuration>
    <!--指定默认数据源-->
    <environments default="development">
        <!--数据源-->
        <environment id="development">
            <!--事务管理器-->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/qing/dao/UserMapper.xml"/>
    </mappers>
</configuration>

问题二:Mapper文件编译后不存在

java.lang.ExceptionInInitializerError
	at com.qing.dao.UserMapperTest.test(UserMapperTest.java:18)
Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### The error may exist in com/qing/dao/UserMapper.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/qing/dao/UserMapper.xml
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)


解决:pom.xml中配置编译配置

<?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">
    <parent>
        <artifactId>mybatis-study</artifactId>
        <groupId>com.qing</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>mybatis-01</artifactId>

    <!--配置resources,防止资源导出失败问题-->
    <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>
</project>


问题三:数据库连接SSL错误

org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 2,729 milliseconds ago.  The last packet sent successfully to the server was 2,715 milliseconds ago.
### The error may exist in com/qing/dao/UserMapper.xml
### The error may involve com.qing.dao.UserMapper.getUserList
### The error occurred while executing a query
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Caused by: javax.net.ssl.SSLHandshakeException: java.security.cert.CertificateException: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors

Caused by: java.security.cert.CertificateException: java.security.cert.CertPathValidatorException: Path does not chain with any of the trust anchors

解决:mybatis-config.xml中useSSL=true改为useSSL=false

<?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">

<!--核心配置文件-->
<configuration>
    <!--指定默认数据源-->
    <environments default="development">
        <!--数据源-->
        <environment id="development">
            <!--事务管理器-->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/qing/dao/UserMapper.xml"/>
    </mappers>
</configuration>

测试成功


CRUD

namespace中的包名要和Mapper接口的包名一致

<?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">
<!--命名空间绑定一个对应的接口-->
<mapper namespace="com.qing.dao.UserMapper">
    <!--id对应接口的方法,返回值类型对应接口返回值,参数类型对应接口方法参数,集合类型写集合泛型类型-->
    <select id="getUserList" resultType="com.qing.pojo.User">
        select * from mybatis.user
    </select>
</mapper>
package com.qing.dao;

import com.qing.pojo.User;
import java.util.List;

/**
 * 接口
 */
public interface UserMapper {

    /**
     * 查询全部用户
     * @return
     */
    List<User> getUserList();
}

select 选择,查询语句

id 对应接口中的方法名

parameterType 对应接口中方法的请求参数

resultType 对应接口中方法的返回值

集合类型写集合泛型类型

<?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">
<!--命名空间绑定一个对应的接口-->
<mapper namespace="com.qing.dao.UserMapper">
    <!--查询全部用户-->
    <select id="getUserList" resultType="com.qing.pojo.User">
        select * from mybatis.user
    </select>
    <!--id对应接口的方法,返回值类型对应接口返回值,参数类型对应接口方法参数,集合类型写集合泛型类型-->
    <!--根据ID查询用户-->
    <select id="getUserById" parameterType="int" resultType="com.qing.pojo.User">
        select * from mybatis.user where id=#{id}
    </select>
</mapper>
package com.qing.dao;

import com.qing.pojo.User;
import java.util.List;

/**
 * 接口
 */
public interface UserMapper {

    /**
     * 查询全部用户
     * @return
     */
    List<User> getUserList();

    /**
     * 根据ID查询用户
     * @param id
     * @return
     */
    User getUserById(int id);
}

package com.qing.dao;

import com.qing.pojo.User;
import com.qing.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserMapperTest {

    /**
     * 查询全部用户
     */
    @Test
    public void getUserList() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    /**
     * 根据ID查询用户
     */
    @Test
    public void getUserById() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User user = mapper.getUserById(1);
            System.out.println(user);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }
}

insert/update/delete 增删改必须提交事务

编写接口

package com.qing.dao;

import com.qing.pojo.User;

import java.util.List;

/**
 * 接口
 */
public interface UserMapper {

    /**
     * 查询全部用户
     *
     * @return
     */
    List<User> getUserList();

    /**
     * 根据ID查询用户
     *
     * @param id
     * @return
     */
    User getUserById(int id);

    /**
     * 新增用户
     *
     * @param user
     * @return
     */
    int insert(User user);

    /**
     * 修改用户
     * @param user
     * @return
     */
    int update(User user);

    /**
     * 删除用户
     * @param id
     * @return
     */
    int delete(int id);
}

编写Mapper

<?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">
<!--命名空间绑定一个对应的接口-->
<mapper namespace="com.qing.dao.UserMapper">
    <!--查询全部用户-->
    <select id="getUserList" resultType="com.qing.pojo.User">
        select * from mybatis.user
    </select>
    <!--id对应接口的方法,返回值类型对应接口返回值,参数类型对应接口方法参数,集合类型写集合泛型类型-->
    <!--根据ID查询用户-->
    <select id="getUserById" parameterType="int" resultType="com.qing.pojo.User">
        select * from mybatis.user where id=#{id}
    </select>
    <!--新增用户-->
    <insert id="insert" parameterType="com.qing.pojo.User">
        insert into mybatis.user(id,name,pwd) values(#{id},#{name},#{pwd})
    </insert>
    <!--修改用户-->
    <update id="update" parameterType="com.qing.pojo.User">
        update mybatis.user set name=#{name},pwd=#{pwd} where id=#{id}
    </update>
    <!--删除用户-->
    <delete id="delete" parameterType="int">
        delete from mybatis.user where id=#{id}
    </delete>
</mapper>

测试

package com.qing.dao;

import com.qing.pojo.User;
import com.qing.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserMapperTest {

    /**
     * 查询全部用户
     */
    @Test
    public void getUserList() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    /**
     * 根据ID查询用户
     */
    @Test
    public void getUserById() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User user = mapper.getUserById(1);
            System.out.println(user);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    /**
     * 新增用户
     */
    @Test
    public void insert() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User user = new User(4, "张仲景", "123456");
            int rows = mapper.insert(user);
            System.out.println(rows);
            // 提交事务
            sqlSession.commit();
            System.out.println("提交事务");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    /**
     * 修改用户
     */
    @Test
    public void update() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            User user = new User(4, "张仲景二号", "123456");
            int rows = mapper.update(user);
            System.out.println(rows);
            // 提交事务
            sqlSession.commit();
            System.out.println("提交事务");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    /**
     * 删除用户
     */
    @Test
    public void delete() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            int rows = mapper.delete(4);
            System.out.println(rows);
            // 提交事务
            sqlSession.commit();
            System.out.println("提交事务");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }
}

Map的应用

Map传递参数,用key获取即可

对象传递参数,用属性获取即可

只有一个基本类型参数,可以直接获取,可不写parameterType

编写接口

package com.qing.dao;

import com.qing.pojo.User;

import java.util.List;
import java.util.Map;

/**
 * 接口
 */
public interface UserMapper {

    /**
     * 通过Map新增用户
     * @param map
     * @return
     */
    int insertByMap(Map<String,Object> map);

    /**
     * 通过Map查询用户
     * @param map
     * @return
     */
    List<User> getByMap(Map<String,Object> map);
}

编写Mapper

<?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">
<!--命名空间绑定一个对应的接口-->
<mapper namespace="com.qing.dao.UserMapper">
    <!--通过Map新增用户-->
    <insert id="insertByMap" parameterType="map">
        insert into mybatis.user(id,name,pwd) values(#{userId},#{userName},#{password})
    </insert>
    <!--通过Map查询用户-->
    <select id="getByMap" parameterType="map" resultType="com.qing.pojo.User">
        select * from mybatis.user where id=#{userId} and name=#{userName}
    </select>
</mapper>

测试

package com.qing.dao;

import com.qing.pojo.User;
import com.qing.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class UserMapperTest {

    /**
     * 通过Map新增用户
     */
    @Test
    public void insertByMap() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            Map<String,Object> map = new HashMap<String, Object>();
            map.put("userId",4);
            map.put("userName","张仲景");
            map.put("password","123456");
            int rows = mapper.insertByMap(map);
            System.out.println(rows);
            // 提交事务
            sqlSession.commit();
            System.out.println("提交事务");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    /**
     * 通过Map查询用户
     */
    @Test
    public void getByMap() {
        SqlSession sqlSession = null;
        try {
            // 获取sqlSession
            sqlSession = MybatisUtils.getSqlSession();
            // 执行SQL
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            Map<String,Object> map = new HashMap<String, Object>();
            map.put("userId",4);
            map.put("userName","张仲景");
            List<User> userList = mapper.getByMap(map);
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }
}

    原文作者:清风(学习-踏实)
    原文地址: https://www.cnblogs.com/wl3pb/p/14999214.html
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