前言

MyBatis Generator（MBG）是MyBatis 和iBATIS的代码生成器。可以生成简单CRUD操作的XML配置文件、Mapper文件(DAO接口)、实体类。实际开发中能够有效减少程序员的工作量，甚至不用程序员手动写sql。
mybatis-generator有多种用法：命令行、maven插件等。命令行方式通常要把相关jar包下载到本地，再使用java -jar 运行。方便起见，本文演示使用maven插件的方式。

操作步驟

mybatis-generator有三种用法：命令行、eclipse插件、maven插件。个人觉得maven插件最方便，可以在eclipse/intellij idea等ide上可以通用。此处只介绍maven插件的使用方法。

添加依赖

在需要生成代码的模块pom文件中添加如下依赖，一般在在dao模块下生成代码。

  1. <dependency>
  2.         <groupId>mysql</groupId>
  3.         <artifactId>mysql-connector-java</artifactId>
  4.         <version>8.0.17</version>
  5. </dependency>      
  6. <dependency>
  7.         <groupId>org.mybatis.generator</groupId>
  8.         <artifactId>mybatis-generator-core</artifactId>
  9.         <version>1.3.7</version>
  10. </dependency>

这两个依赖下载到本地仓库，备用。
添加maven插件，具体如下。

  1. <build>
  2.         <plugins>
  3.             <plugin>
  4.                 <groupId>org.springframework.boot</groupId>
  5.                 <artifactId>spring-boot-maven-plugin</artifactId>
  6.             </plugin>
  8.             <plugin>
  9.                 <groupId>org.mybatis.generator</groupId>
  10.                 <artifactId>mybatis-generator-maven-plugin</artifactId>
  11.                 <version>1.3.7</version>
  12.                 <configuration>
  13.                     <configurationFile>src/main/resources/mybatis/generator/generatorConfig.xml</configurationFile>
  14.                 </configuration>
  15.             </plugin>
  16.         </plugins>
  17.     </build>

准备generatorConfig.xml

一般放到dao模块或测试模块的单独目录下，如：
image.png

generator.properties

用于抽取公共配置或便于修改的属性Key

generatorConfig.xml

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE generatorConfiguration
  3.         PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
  4.         "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
  6. <generatorConfiguration>
  7.     <!-- 引入配置文件 -->
  8.     <properties resource="mybatis/generator/generator.properties"/>
  10.     <!--需要指定本地Jar,可用当前Maven本地仓库下的Jar, mysql 连接数据库jar 这里选择自己本地位置-->
  11.     <classPathEntry location="/Users/simon/.m2/repository/mysql/mysql-connector-java/5.1.47/mysql-connector-java-5.1.47.jar"/>
  13.     <context id="testTables" targetRuntime="MyBatis3">
  14.         <!-- mysql关键字处理 -->
  15.         <property name="autoDelimitKeywords" value="true"/>
  16.         <property name="beginningDelimiter" value="`"/>
  17.         <property name="endingDelimiter" value="`"/>
  18.         <!--设置生成的Java文件的编码格式-->
  19.         <property name="javaFileEncoding" value="UTF-8"></property>
  20.         <!--格式化java代码-->
  21.         <property name="javaFormatter" value="org.mybatis.generator.api.dom.DefaultJavaFormatter"></property>
  22.         <!--格式化xml代码-->
  23.         <property name="xmlFormatter" value="org.mybatis.generator.api.dom.DefaultXmlFormatter"></property>
  24.         <!--javaBean生成toString() 方法-->
  25.         <plugin type="org.mybatis.generator.plugins.ToStringPlugin"/>
  26.         <!-- 自动生成注释 -->
  27.         <commentGenerator>
  28.             <property name="suppressDate" value="true"/>
  29.             <property name="addRemarkComments" value="true"/>
  30.         </commentGenerator>
  31.         <!--数据库连接的信息：驱动类、连接地址、用户名、密码 -->
  32.         <jdbcConnection driverClass="com.mysql.jdbc.Driver"
  33.                         connectionURL="jdbc:mysql://127.0.0.1:3306/spring_demo?useUnicode=true&amp;characterEncoding=utf-8"
  34.                         userId="root"
  35.                         password="Xiele">
  36.         </jdbcConnection>
  37.         <!-- 默认false，把JDBC DECIMAL 和 NUMERIC 类型解析为 Integer，为 true时把JDBC DECIMAL 和
  38.            NUMERIC 类型解析为java.math.BigDecimal -->
  39.         <javaTypeResolver>
  40.             <property name="forceBigDecimals" value="false"/>
  41.         </javaTypeResolver>
  43.         <!-- targetProject:生成PO类的位置 -->
  44.         <javaModelGenerator targetPackage="com.example.start.springdemo.mybatis.generator"
  45.                             targetProject="src/main/java">
  46.             <!-- enableSubPackages:是否让schema作为包的后缀 -->
  47.             <property name="enableSubPackages" value="false"/>
  48.             <!-- 从数据库返回的值被清理前后的空格 -->
  49.             <property name="trimStrings" value="true"/>
  50.         </javaModelGenerator>
  51.         <!-- targetProject:mapper映射文件生成的位置
  52.            如果maven工程只是单独的一个工程，targetProject="src/main/java"
  53.            若果maven工程是分模块的工程，targetProject="所属模块的名称"，例如：
  54.            targetProject="ecps-manager-mapper"，下同-->
  55.         <sqlMapGenerator targetPackage="mybatis.generator.sqlmap"
  56.                          targetProject="src/main/resources">
  57.             <!-- enableSubPackages:是否让schema作为包的后缀 -->
  58.             <property name="enableSubPackages" value="false"/>
  59.         </sqlMapGenerator>
  60.         <!-- targetPackage：mapper接口生成的位置 -->
  61.         <javaClientGenerator type="XMLMAPPER"
  62.                              targetPackage="com.example.start.springdemo.mybatis.generator"
  63.                              targetProject="src/main/java">
  64.             <!-- enableSubPackages:是否让schema作为包的后缀 -->
  65.             <property name="enableSubPackages" value="false"/>
  66.         </javaClientGenerator>
  67.         <!-- 指定数据库表 -->
  68.         <table tableName="spring_user" mapperName="SpringUserDao" domainObjectName="SpringUserDO"
  69.                enableCountByExample="false"
  70.                enableUpdateByExample="false" enableDeleteByExample="false"
  71.                enableSelectByExample="false" selectByExampleQueryId="false">
  72.         </table>
  74.     </context>
  75. </generatorConfiguration>

替换mybatis-generator-core.jar包

如果没有特殊需要，可以忽略这一步。
由于mybatis generator在生成XML文件时，会默认生成jdbcType和parameterType，而且在脚本语言中也带有jdbcType，本身来讲这个不是什么问题，但是如果遇到传入的对象是parameterType的子类对象，并且在脚本语言中用到了子类对象特有属性时，就会出现找不到属性的异常了。并且生成的DO文件注释也不符合规范。所以通过反编译重新打包的方式，对源码做了简单的修改，去掉了jdbcType和parameterType，将DO文件注释改为符合规范的风格。
只需用下文附件中的mybatis-generator-core-1.3.7.jar 替换本地仓库 org/mybatis/generator/mybatis-generator-core/1.3.7 目录下的 mybatis-generator-core-1.3.7.jar 即可。
mybatis-generator-core-1.3.7.jar

运行maven插件

通过IDEA执行
image.png

自动生成的代码示例

DAO&DO

  1. package com.example.start.springdemo.mybatis.generator;
  3. public interface SpringUserDao {
  4.     /**
  5.      * This method was generated by MyBatis Generator.
  6.      * This method corresponds to the database table spring_user
  7.      */
  8.     int deleteByPrimaryKey(Long id);
  10.     /**
  11.      * This method was generated by MyBatis Generator.
  12.      * This method corresponds to the database table spring_user
  13.      */
  14.     int insert(SpringUserDO record);
  16.     /**
  17.      * This method was generated by MyBatis Generator.
  18.      * This method corresponds to the database table spring_user
  19.      */
  20.     int insertSelective(SpringUserDO record);
  22.     /**
  23.      * This method was generated by MyBatis Generator.
  24.      * This method corresponds to the database table spring_user
  25.      */
  26.     SpringUserDO selectByPrimaryKey(Long id);
  28.     /**
  29.      * This method was generated by MyBatis Generator.
  30.      * This method corresponds to the database table spring_user
  31.      */
  32.     int updateByPrimaryKeySelective(SpringUserDO record);
  34.     /**
  35.      * This method was generated by MyBatis Generator.
  36.      * This method corresponds to the database table spring_user
  37.      */
  38.     int updateByPrimaryKey(SpringUserDO record);
  39. }
  1. package com.example.start.springdemo.mybatis.generator;
  3. /**
  4.  * @author wb-jc582827
  5.  * @version 1.0: com.example.start.springdemo.mybatis.generator.SpringUserDao.java, v 0.1 2020-06-04 17:51:18 wb-jc582827 Exp $
  6.  *
  7.  * This class was generated by MyBatis Generator.
  8.  * This class corresponds to the database table spring_user
  9.  */
  10. public class SpringUserDO {
  11.     /**
  12.      * This property corresponds to db column <tt>id</tt>
  13.      */
  14.     private Long id;
  16.     /**
  17.      * This property corresponds to db column <tt>name</tt>
  18.      */
  19.     private String name;
  21.     /**
  22.      * This property corresponds to db column <tt>age</tt>
  23.      */
  24.     private Byte age;
  26.     /**
  27.      * Getter method for property <tt>id</tt>
  28.      *
  29.      * @return property value of id
  30.      */
  31.     public Long getId() {
  32.         return id;
  33.     }
  35.     /**
  36.      * Setter method for property <tt>id</tt>
  37.      *
  38.      * @param id value to be assigned to property id
  39.      */
  40.     public void setId(Long id) {
  41.         this.id = id;
  42.     }
  44.     /**
  45.      * Getter method for property <tt>name</tt>
  46.      *
  47.      * @return property value of name
  48.      */
  49.     public String getName() {
  50.         return name;
  51.     }
  53.     /**
  54.      * Setter method for property <tt>name</tt>
  55.      *
  56.      * @param name value to be assigned to property name
  57.      */
  58.     public void setName(String name) {
  59.         this.name = name == null ? null : name.trim();
  60.     }
  62.     /**
  63.      * Getter method for property <tt>age</tt>
  64.      *
  65.      * @return property value of age
  66.      */
  67.     public Byte getAge() {
  68.         return age;
  69.     }
  71.     /**
  72.      * Setter method for property <tt>age</tt>
  73.      *
  74.      * @param age value to be assigned to property age
  75.      */
  76.     public void setAge(Byte age) {
  77.         this.age = age;
  78.     }
  80.     /**
  81.      * This method was generated by MyBatis Generator.
  82.      * This method corresponds to the database table spring_user
  83.      */
  84.     @Override
  85.     public String toString() {
  86.         StringBuilder sb = new StringBuilder();
  87.         sb.append(getClass().getSimpleName());
  88.         sb.append(" [");
  89.         sb.append("Hash = ").append(hashCode());
  90.         sb.append(", id=").append(id);
  91.         sb.append(", name=").append(name);
  92.         sb.append(", age=").append(age);
  93.         sb.append("]");
  94.         return sb.toString();
  95.     }
  96. }

SqlMap

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  3. <mapper namespace="com.example.start.springdemo.mybatis.generator.SpringUserDao">
  4.   <resultMap id="BaseResultMap" type="com.example.start.springdemo.mybatis.generator.SpringUserDO">
  5.     <id column="id" property="id" />
  6.     <result column="name" property="name" />
  7.     <result column="age" property="age" />
  8.   </resultMap>
  9.   <sql id="Base_Column_List">
  10.     id, `name`, age
  11.   </sql>
  12.   <select id="selectByPrimaryKey" resultMap="BaseResultMap">
  13.     select 
  14.     <include refid="Base_Column_List" />
  15.     from spring_user
  16.     where id = #{id}
  17.   </select>
  18.   <delete id="deleteByPrimaryKey">
  19.     delete from spring_user
  20.     where id = #{id}
  21.   </delete>
  22.   <insert id="insert">
  23.     insert into spring_user (id, `name`, age)
  24.     values (#{id}, #{name}, #{age})
  25.   </insert>
  26.   <insert id="insertSelective">
  27.     insert into spring_user
  28.     <trim prefix="(" suffix=")" suffixOverrides=",">
  29.       <if test="id != null">
  30.         id,
  31.       </if>
  32.       <if test="name != null">
  33.         `name`,
  34.       </if>
  35.       <if test="age != null">
  36.         age,
  37.       </if>
  38.     </trim>
  39.     <trim prefix="values (" suffix=")" suffixOverrides=",">
  40.       <if test="id != null">
  41.         #{id},
  42.       </if>
  43.       <if test="name != null">
  44.         #{name},
  45.       </if>
  46.       <if test="age != null">
  47.         #{age},
  48.       </if>
  49.     </trim>
  50.   </insert>
  51.   <update id="updateByPrimaryKeySelective">
  52.     update spring_user
  53.     <set>
  54.       <if test="name != null">
  55.         `name` = #{name},
  56.       </if>
  57.       <if test="age != null">
  58.         age = #{age},
  59.       </if>
  60.     </set>
  61.     where id = #{id}
  62.   </update>
  63.   <update id="updateByPrimaryKey">
  64.     update spring_user
  65.     set `name` = #{name},
  66.       age = #{age}
  67.     where id = #{id}
  68.   </update>
  69. </mapper>