1. 添加依赖
   在build.gradle中添加

configurations {
    mybatisGenerator
}

注意把前面的compile group改成mybatisGenerator

mybatisGenerator 'org.mybatis.generator:mybatis-generator-core:1.3.6'
mybatisGenerator 'mysql:mysql-connector-java:5.1.45'
mybatisGenerator 'tk.mybatis:mapper:3.5.2'

1. 设置数据库信息

在 resources 下，新建 mybatis 文件夹，并新建 config.properties 和 generatorConfig.xml，文件结构如下：

# JDBC 驱动类名
jdbc.driverClassName=com.mysql.jdbc.Driver
# JDBC URL: jdbc:mysql:// + 数据库主机地址 + 端口号 + 数据库名
jdbc.url=jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8
# JDBC 用户名及密码
jdbc.username=root
jdbc.password=123456

# 生成实体类所在的包
package.model=com.yy.boot.domain
# 生成 mapper 类所在的包
package.mapper=com.yy.boot.dao
# 生成 mapper xml 文件所在的包，默认存储在 resources 目录下
package.xml=mybatis/mapper

generator.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
    <!--MyBatis3Simple或者MyBatis3,生成的xml文件略有不同-->
    <context id="Mysql" targetRuntime="MyBatis3Simple" defaultModelType="flat">
        <commentGenerator>
            <property name="suppressAllComments" value="true"></property>
            <property name="suppressDate" value="true"></property>
            <property name="javaFileEncoding" value="utf-8"/>
        </commentGenerator>

        <jdbcConnection driverClass="${driverClass}"
                        connectionURL="${connectionURL}"
                        userId="${userId}"
                        password="${password}">
        </jdbcConnection>

        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>

        <javaModelGenerator targetPackage="${modelPackage}" targetProject="${src_main_java}">
            <property name="enableSubPackages" value="true"></property>
            <property name="trimStrings" value="true"></property>
        </javaModelGenerator>

        <sqlMapGenerator targetPackage="${sqlMapperPackage}" targetProject="${src_main_resources}">
            <property name="enableSubPackages" value="true"></property>
        </sqlMapGenerator>

        <!--
        type=ANNOTATEDMAPPER表示不生成xml文件
        这里我用XMLMAPPER
        -->
        <javaClientGenerator targetPackage="${mapperPackage}" targetProject="${src_main_java}" type="XMLMAPPER">
            <property name="enableSubPackages" value="true"/>
        </javaClientGenerator>

        <!--
         sql占位符，表示所有的表
         这里只用city表
        -->
        <!--<table tableName="%">-->
            <!--<generatedKey column="id" sqlStatement="Mysql" identity="true" />-->
        <!--</table>-->
        <table tableName="city" domainObjectName="City" enableCountByExample="false" enableUpdateByExample="false"
               enableDeleteByExample="false" enableSelectByExample="false" selectByExampleQueryId="false"></table>
    </context>
</generatorConfiguration>

在build.gradle中添加

def getDbProperties = {
    def properties = new Properties()
    file("src/main/resources/mybatis/config.properties").withInputStream { inputStream ->
        properties.load(inputStream)
    }
    properties
}

task mybatisGenerate << {
    def properties = getDbProperties()
    ant.properties['targetProject'] = projectDir.path
    ant.properties['driverClass'] = properties.getProperty("jdbc.driverClassName")
    ant.properties['connectionURL'] = properties.getProperty("jdbc.url")
    ant.properties['userId'] = properties.getProperty("jdbc.username")
    ant.properties['password'] = properties.getProperty("jdbc.password")
    ant.properties['src_main_java'] = sourceSets.main.java.srcDirs[0].path
    ant.properties['src_main_resources'] = sourceSets.main.resources.srcDirs[0].path
    ant.properties['modelPackage'] = properties.getProperty("package.model")
    ant.properties['mapperPackage'] = properties.getProperty("package.mapper")
    ant.properties['sqlMapperPackage'] = properties.getProperty("package.xml")
    ant.taskdef(
            name: 'mbgenerator',
            classname: 'org.mybatis.generator.ant.GeneratorAntTask',
            classpath: configurations.mybatisGenerator.asPath
    )
    ant.mbgenerator(overwrite: true,
            configfile: 'src/main/resources/mybatis/generatorConfig.xml', verbose: true) {
        propertyset {
            propertyref(name: 'targetProject')
            propertyref(name: 'userId')
            propertyref(name: 'driverClass')
            propertyref(name: 'connectionURL')
            propertyref(name: 'password')
            propertyref(name: 'src_main_java')
            propertyref(name: 'src_main_resources')
            propertyref(name: 'modelPackage')
            propertyref(name: 'mapperPackage')
            propertyref(name: 'sqlMapperPackage')
        }
    }
}