【Mybatis】MyBatis之Generator自动生成代码（九）

MyBatis Generator 简介

　　MyBatis Generator 连接数据库表并生成MyBatis或iBatis文件。这有助于最大限度地减少使用MyBatis时为数据库文件创建简单CRUD操作所需的工作量。

　　参考文档：http://www.mybatis.org/generator/

　　下载地址：https://github.com/mybatis/generator/releases

MyBatis Generator 使用

　　本例环境已安装java环境，且数据库是mysql，表结构如下：

CREATE DATABASE test_mybatis;
USE test_mybatis;

-- ----------------------------
-- Table structure for employee
-- ----------------------------
DROP TABLE IF EXISTS `employee`;
CREATE TABLE `employee` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `last_name` varchar(255) DEFAULT NULL,
  `gender` char(1) DEFAULT NULL,
  `email` varchar(255) DEFAULT NULL,
  `dept_id` int(11) DEFAULT NULL COMMENT '部门ID',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=36 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of employee
-- ----------------------------
BEGIN;
INSERT INTO `employee` VALUES (1, '大白', '1', 'dabai@163.com', 1);
INSERT INTO `employee` VALUES (2, '小明', '1', 'xiaoming@163.com', 1);
INSERT INTO `employee` VALUES (3, '小红', '1', 'xiaohong@163.com', 1);
COMMIT;

　　1、使用命令行的方式使用

　　　　a、下载mybatis-generator，如下：

　　　　　　、

　　　　b、新建配置文件mbg.xml，参考文档：http://www.mybatis.org/generator/

<?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>

    <classPathEntry
        location="/Users/h__d/.m2/repository/mysql/mysql-connector-java/8.0.13/mysql-connector-java-8.0.13.jar" />
     
    <!-- 
        context:生成一组对象的环境 
        id:必选，上下文id，用于在生成错误时提示
        defaultModelType:指定生成对象的样式
            1，conditional：类似hierarchical；
            2，flat：所有内容（主键，blob）等全部生成在一个对象中；
            3，hierarchical：主键生成一个XXKey对象(key class)，Blob等单独生成一个对象，其他简单属性在一个对象中(record class)
        targetRuntime:
            1，MyBatis3：默认的值，生成基于MyBatis3.x以上版本的内容，包括XXXBySample；
            2，MyBatis3Simple：类似MyBatis3，只是不生成XXXBySample；
        introspectedColumnImpl：类全限定名，用于扩展MBG
    -->
    <context id="DB2Tables" targetRuntime="MyBatis3">
    
        
 
        <!-- 自动识别数据库关键字，默认false，如果设置为true，根据SqlReservedWords中定义的关键字列表；
            一般保留默认值，遇到数据库关键字（Java关键字），使用columnOverride覆盖
         -->
        <property name="autoDelimitKeywords" value="false"/>
        <!-- 生成的Java文件的编码 -->
        <property name="javaFileEncoding" value="UTF-8"/>
        <!-- 格式化java代码 -->
        <property name="javaFormatter" value="org.mybatis.generator.api.dom.DefaultJavaFormatter"/>
        <!-- 格式化XML代码 -->
        <property name="xmlFormatter" value="org.mybatis.generator.api.dom.DefaultXmlFormatter"/>
     
        <!-- beginningDelimiter和endingDelimiter：指明数据库的用于标记数据库对象名的符号，比如ORACLE就是双引号，MYSQL默认是`反引号； -->
        <property name="beginningDelimiter" value="`"/>
        <property name="endingDelimiter" value="`"/>
        
        <!-- 配置pojo的序列化 -->
        <plugin type="org.mybatis.generator.plugins.SerializablePlugin" />
       
        <commentGenerator>
            <!-- 是否去除自动生成的文档注释 true：是 ： false:否（默认） -->  
            <property name="suppressAllComments" value="true"/> 
            <!-- 是否添加数据库注释备注 true：是  false:否（默认） -->
            <property name="addRemarkComments" value="true" />
            <!-- 是否去除自动生成的时间 true：是 ： false:否（默认） -->  
              <property name="suppressDate" value="false" />
              <!-- 注释时间格式 -->  
              <property name="dateFormat" value="yyyy-MM-dd HH:mm:ss" />
        </commentGenerator>
        
        <!-- JDBC 连接 -->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
            connectionURL="jdbc:mysql://mysql.naughty7878.top:3306/test_mybatis?allowPublicKeyRetrieval=true"
            userId="hd" password="hd123456">
        </jdbcConnection>


        <!-- java类型处理器 
                用于处理DB中的类型到Java中的类型，默认使用JavaTypeResolverDefaultImpl；
                注意一点，默认会先尝试使用Integer，Long，Short等来对应DECIMAL和 NUMERIC数据类型； 
         -->
        <javaTypeResolver>
            <!-- 
                true：使用BigDecimal对应DECIMAL和 NUMERIC数据类型
                false：默认,
                    scale>0;length>18：使用BigDecimal;
                    scale=0;length[10,18]：使用Long；
                    scale=0;length[5,9]：使用Integer；
                    scale=0;length<5：使用Short；
             -->
            <property name="forceBigDecimals" value="false" />
        </javaTypeResolver>

        <!-- java模型创建器，是必须要的元素
                负责：1，key类（见context的defaultModelType）；2，java类；3，查询类
                targetPackage：生成的类要放的包，真实的包受enableSubPackages属性控制；
                targetProject：目标项目，指定一个存在的目录下，生成的内容会放到指定目录中，如果目录不存在，MBG不会自动建目录
        -->
        <javaModelGenerator targetPackage="com.test.mybatis.pojo"
            targetProject="src/main/java">
            
            <!-- 在targetPackage的基础上，根据数据库的schema再生成一层package，最终生成的类放在这个package下，默认为false -->
            <property name="enableSubPackages" value="true" />
            <!-- 设置是否在getter方法中，对String类型字段调用trim()方法 -->
            <property name="trimStrings" value="false" />
        </javaModelGenerator>

        <!-- 生成SQL map的XML文件生成器，
             注意，在Mybatis3之后，我们可以使用mapper.xml文件+Mapper接口（或者不用mapper接口），
             或者只使用Mapper接口+Annotation，所以，如果 javaClientGenerator配置中配置了需要生成XML的话，这个元素就必须配置
             targetPackage/targetProject:同javaModelGenerator
        -->
        <sqlMapGenerator targetPackage="mapper"
            targetProject="src/main/resources">
            <!-- 在targetPackage的基础上，根据数据库的schema再生成一层package，最终生成的类放在这个package下，默认为false -->
            <property name="enableSubPackages" value="true" />
        </sqlMapGenerator>

        <!-- 对于mybatis来说，即生成Mapper接口，注意，如果没有配置该元素，那么默认不会生成Mapper接口 
            targetPackage/targetProject:同javaModelGenerator
            type：选择怎么生成mapper接口（在MyBatis3/MyBatis3Simple下）：
                1，ANNOTATEDMAPPER：会生成使用Mapper接口+Annotation的方式创建（SQL生成在annotation中），不会生成对应的XML；
                2，MIXEDMAPPER：使用混合配置，会生成Mapper接口，并适当添加合适的Annotation，但是XML会生成在XML中；
                3，XMLMAPPER：会生成Mapper接口，接口完全依赖XML；
            注意，如果context是MyBatis3Simple：只支持ANNOTATEDMAPPER和XMLMAPPER
        -->
        <javaClientGenerator type="XMLMAPPER"
            targetPackage="com.test.mybatis.dao" targetProject="src/main/java">
            <property name="enableSubPackages" value="true" />
        </javaClientGenerator>


        <!-- 选择一个table来生成相关文件，可以有一个或多个table，必须要有table元素
            选择的table会生成一下文件：
            1，SQL map文件
            2，生成一个主键类；
            3，除了BLOB和主键的其他字段的类；
            4，包含BLOB的类；
            5，一个用户生成动态查询的条件类（selectByExample, deleteByExample），可选；
            6，Mapper接口（可选）
            tableName（必要）：要生成对象的表名；
            注意：大小写敏感问题。正常情况下，MBG会自动的去识别数据库标识符的大小写敏感度，在一般情况下，MBG会
                根据设置的schema，catalog或tablename去查询数据表，按照下面的流程：
                1，如果schema，catalog或tablename中有空格，那么设置的是什么格式，就精确的使用指定的大小写格式去查询；
                2，否则，如果数据库的标识符使用大写的，那么MBG自动把表名变成大写再查找；
                3，否则，如果数据库的标识符使用小写的，那么MBG自动把表名变成小写再查找；
                4，否则，使用指定的大小写格式查询；
            另外的，如果在创建表的时候，使用的""把数据库对象规定大小写，就算数据库标识符是使用的大写，在这种情况下也会使用给定的大小写来创建表名；
            这个时候，请设置delimitIdentifiers="true"即可保留大小写格式；
            可选：
            1，schema：数据库的schema；
            2，catalog：数据库的catalog；
            3，alias：为数据表设置的别名，如果设置了alias，那么生成的所有的SELECT SQL语句中，列名会变成：alias_actualColumnName
            4，domainObjectName：生成的domain类的名字，如果不设置，直接使用表名作为domain类的名字；可以设置为somepck.domainName，那么会自动把domainName类再放到somepck包里面；
            5，enableInsert（默认true）：指定是否生成insert语句；
            6，enableSelectByPrimaryKey（默认true）：指定是否生成按照主键查询对象的语句（就是getById或get）；
            7，enableSelectByExample（默认true）：MyBatis3Simple为false，指定是否生成动态查询语句；
            8，enableUpdateByPrimaryKey（默认true）：指定是否生成按照主键修改对象的语句（即update)；
            9，enableDeleteByPrimaryKey（默认true）：指定是否生成按照主键删除对象的语句（即delete）；
            10，enableDeleteByExample（默认true）：MyBatis3Simple为false，指定是否生成动态删除语句；
            11，enableCountByExample（默认true）：MyBatis3Simple为false，指定是否生成动态查询总条数语句（用于分页的总条数查询）；
            12，enableUpdateByExample（默认true）：MyBatis3Simple为false，指定是否生成动态修改语句（只修改对象中不为空的属性）；
            13，modelType：参考context元素的defaultModelType，相当于覆盖；
            14，delimitIdentifiers：参考tableName的解释，注意，默认的delimitIdentifiers是双引号，如果类似MYSQL这样的数据库，使用的是`（反引号，那么还需要设置context的beginningDelimiter和endingDelimiter属性）
            15，delimitAllColumns：设置是否所有生成的SQL中的列名都使用标识符引起来。默认为false，delimitIdentifiers参考context的属性
            注意，table里面很多参数都是对javaModelGenerator，context等元素的默认属性的一个复写；
         -->
        <table schema="test_mybatis" tableName="employee"
            domainObjectName="Employee" >
            <!-- 如果设置为true，生成的model类会直接使用column本身的名字，而不会再使用驼峰命名方法，比如BORN_DATE，生成的属性名字就是BORN_DATE,而不会是bornDate -->
            <property name="useActualColumnNames" value="false" />
            <!-- generatedKey用于生成生成主键的方法，
                如果设置了该元素，MBG会在生成的<insert>元素中生成一条正确的<selectKey>元素，该元素可选
                column:主键的列名；
                sqlStatement：要生成的selectKey语句，有以下可选项：
                    Cloudscape:相当于selectKey的SQL为： VALUES IDENTITY_VAL_LOCAL()
                    DB2       :相当于selectKey的SQL为： VALUES IDENTITY_VAL_LOCAL()
                    DB2_MF    :相当于selectKey的SQL为：SELECT IDENTITY_VAL_LOCAL() FROM SYSIBM.SYSDUMMY1
                    Derby      :相当于selectKey的SQL为：VALUES IDENTITY_VAL_LOCAL()
                    HSQLDB      :相当于selectKey的SQL为：CALL IDENTITY()
                    Informix  :相当于selectKey的SQL为：select dbinfo('sqlca.sqlerrd1') from systables where tabid=1
                    MySql      :相当于selectKey的SQL为：SELECT LAST_INSERT_ID()
                    SqlServer :相当于selectKey的SQL为：SELECT SCOPE_IDENTITY()
                    SYBASE      :相当于selectKey的SQL为：SELECT @@IDENTITY
                    JDBC      :相当于在生成的insert元素上添加useGeneratedKeys="true"和keyProperty属性
            -->
            <generatedKey column="ID" sqlStatement="MySql"
                identity="true" />
            <!-- 用来修改表中某个列的属性，MBG会使用修改后的列来生成domain的属性；
                 column:要重新设置的列名；
                 注意，一个table元素中可以有多个columnOverride元素哈~
            -->
            <columnOverride column="DATE_FIELD"
                property="startDate" />
            <!-- ignoreColumn设置一个MGB忽略的列，如果设置了改列，那么在生成的domain中，生成的SQL中，都不会有该列出现 
                 column:指定要忽略的列的名字；
                 delimitedColumnName：参考table元素的delimitAllColumns配置，默认为false
                 注意，一个table元素中可以有多个ignoreColumn元素    
            -->
            <ignoreColumn column="dept_id" />
            <columnOverride column="gender" jdbcType="VARCHAR" />
            
        </table>

    </context>
</generatorConfiguration>

　　　　c、使用命令：java -jar mybatis-generator-core-1.3.7.jar -configfile mbg.xml -overwrite

　　　　d、查看生成目录文件：

package com.test.mybatis.pojo;

public class Employee {
    private Integer id;

    private String lastName;

    private String gender;

    private String email;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

package com.test.mybatis.pojo;

import java.util.ArrayList;
import java.util.List;

public class EmployeeExample {
    protected String orderByClause;

    protected boolean distinct;

    protected List<Criteria> oredCriteria;

    public EmployeeExample() {
        oredCriteria = new ArrayList<Criteria>();
    }

    public void setOrderByClause(String orderByClause) {
        this.orderByClause = orderByClause;
    }

    public String getOrderByClause() {
        return orderByClause;
    }

    public void setDistinct(boolean distinct) {
        this.distinct = distinct;
    }

    public boolean isDistinct() {
        return distinct;
    }

    public List<Criteria> getOredCriteria() {
        return oredCriteria;
    }

    public void or(Criteria criteria) {
        oredCriteria.add(criteria);
    }

    public Criteria or() {
        Criteria criteria = createCriteriaInternal();
        oredCriteria.add(criteria);
        return criteria;
    }

    public Criteria createCriteria() {
        Criteria criteria = createCriteriaInternal();
        if (oredCriteria.size() == 0) {
            oredCriteria.add(criteria);
        }
        return criteria;
    }

    protected Criteria createCriteriaInternal() {
        Criteria criteria = new Criteria();
        return criteria;
    }

    public void clear() {
        oredCriteria.clear();
        orderByClause = null;
        distinct = false;
    }

    protected abstract static class GeneratedCriteria {
        protected List<Criterion> criteria;

        protected GeneratedCriteria() {
            super();
            criteria = new ArrayList<Criterion>();
        }

        public boolean isValid() {
            return criteria.size() > 0;
        }

        public List<Criterion> getAllCriteria() {
            return criteria;
        }

        public List<Criterion> getCriteria() {
            return criteria;
        }

        protected void addCriterion(String condition) {
            if (condition == null) {
                throw new RuntimeException("Value for condition cannot be null");
            }
            criteria.add(new Criterion(condition));
        }

        protected void addCriterion(String condition, Object value, String property) {
            if (value == null) {
                throw new RuntimeException("Value for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value));
        }

        protected void addCriterion(String condition, Object value1, Object value2, String property) {
            if (value1 == null || value2 == null) {
                throw new RuntimeException("Between values for " + property + " cannot be null");
            }
            criteria.add(new Criterion(condition, value1, value2));
        }

        public Criteria andIdIsNull() {
            addCriterion("id is null");
            return (Criteria) this;
        }

        public Criteria andIdIsNotNull() {
            addCriterion("id is not null");
            return (Criteria) this;
        }

        public Criteria andIdEqualTo(Integer value) {
            addCriterion("id =", value, "id");
            return (Criteria) this;
        }

        public Criteria andIdNotEqualTo(Integer value) {
            addCriterion("id <>", value, "id");
            return (Criteria) this;
        }

        public Criteria andIdGreaterThan(Integer value) {
            addCriterion("id >", value, "id");
            return (Criteria) this;
        }

        public Criteria andIdGreaterThanOrEqualTo(Integer value) {
            addCriterion("id >=", value, "id");
            return (Criteria) this;
        }

        public Criteria andIdLessThan(Integer value) {
            addCriterion("id <", value, "id");
            return (Criteria) this;
        }

        public Criteria andIdLessThanOrEqualTo(Integer value) {
            addCriterion("id <=", value, "id");
            return (Criteria) this;
        }

        public Criteria andIdIn(List<Integer> values) {
            addCriterion("id in", values, "id");
            return (Criteria) this;
        }

        public Criteria andIdNotIn(List<Integer> values) {
            addCriterion("id not in", values, "id");
            return (Criteria) this;
        }

        public Criteria andIdBetween(Integer value1, Integer value2) {
            addCriterion("id between", value1, value2, "id");
            return (Criteria) this;
        }

        public Criteria andIdNotBetween(Integer value1, Integer value2) {
            addCriterion("id not between", value1, value2, "id");
            return (Criteria) this;
        }

        public Criteria andLastNameIsNull() {
            addCriterion("last_name is null");
            return (Criteria) this;
        }

        public Criteria andLastNameIsNotNull() {
            addCriterion("last_name is not null");
            return (Criteria) this;
        }

        public Criteria andLastNameEqualTo(String value) {
            addCriterion("last_name =", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameNotEqualTo(String value) {
            addCriterion("last_name <>", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameGreaterThan(String value) {
            addCriterion("last_name >", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameGreaterThanOrEqualTo(String value) {
            addCriterion("last_name >=", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameLessThan(String value) {
            addCriterion("last_name <", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameLessThanOrEqualTo(String value) {
            addCriterion("last_name <=", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameLike(String value) {
            addCriterion("last_name like", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameNotLike(String value) {
            addCriterion("last_name not like", value, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameIn(List<String> values) {
            addCriterion("last_name in", values, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameNotIn(List<String> values) {
            addCriterion("last_name not in", values, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameBetween(String value1, String value2) {
            addCriterion("last_name between", value1, value2, "lastName");
            return (Criteria) this;
        }

        public Criteria andLastNameNotBetween(String value1, String value2) {
            addCriterion("last_name not between", value1, value2, "lastName");
            return (Criteria) this;
        }

        public Criteria andGenderIsNull() {
            addCriterion("gender is null");
            return (Criteria) this;
        }

        public Criteria andGenderIsNotNull() {
            addCriterion("gender is not null");
            return (Criteria) this;
        }

        public Criteria andGenderEqualTo(String value) {
            addCriterion("gender =", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderNotEqualTo(String value) {
            addCriterion("gender <>", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderGreaterThan(String value) {
            addCriterion("gender >", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderGreaterThanOrEqualTo(String value) {
            addCriterion("gender >=", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderLessThan(String value) {
            addCriterion("gender <", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderLessThanOrEqualTo(String value) {
            addCriterion("gender <=", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderLike(String value) {
            addCriterion("gender like", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderNotLike(String value) {
            addCriterion("gender not like", value, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderIn(List<String> values) {
            addCriterion("gender in", values, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderNotIn(List<String> values) {
            addCriterion("gender not in", values, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderBetween(String value1, String value2) {
            addCriterion("gender between", value1, value2, "gender");
            return (Criteria) this;
        }

        public Criteria andGenderNotBetween(String value1, String value2) {
            addCriterion("gender not between", value1, value2, "gender");
            return (Criteria) this;
        }

        public Criteria andEmailIsNull() {
            addCriterion("email is null");
            return (Criteria) this;
        }

        public Criteria andEmailIsNotNull() {
            addCriterion("email is not null");
            return (Criteria) this;
        }

        public Criteria andEmailEqualTo(String value) {
            addCriterion("email =", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailNotEqualTo(String value) {
            addCriterion("email <>", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailGreaterThan(String value) {
            addCriterion("email >", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailGreaterThanOrEqualTo(String value) {
            addCriterion("email >=", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailLessThan(String value) {
            addCriterion("email <", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailLessThanOrEqualTo(String value) {
            addCriterion("email <=", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailLike(String value) {
            addCriterion("email like", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailNotLike(String value) {
            addCriterion("email not like", value, "email");
            return (Criteria) this;
        }

        public Criteria andEmailIn(List<String> values) {
            addCriterion("email in", values, "email");
            return (Criteria) this;
        }

        public Criteria andEmailNotIn(List<String> values) {
            addCriterion("email not in", values, "email");
            return (Criteria) this;
        }

        public Criteria andEmailBetween(String value1, String value2) {
            addCriterion("email between", value1, value2, "email");
            return (Criteria) this;
        }

        public Criteria andEmailNotBetween(String value1, String value2) {
            addCriterion("email not between", value1, value2, "email");
            return (Criteria) this;
        }
    }

    public static class Criteria extends GeneratedCriteria {

        protected Criteria() {
            super();
        }
    }

    public static class Criterion {
        private String condition;

        private Object value;

        private Object secondValue;

        private boolean noValue;

        private boolean singleValue;

        private boolean betweenValue;

        private boolean listValue;

        private String typeHandler;

        public String getCondition() {
            return condition;
        }

        public Object getValue() {
            return value;
        }

        public Object getSecondValue() {
            return secondValue;
        }

        public boolean isNoValue() {
            return noValue;
        }

        public boolean isSingleValue() {
            return singleValue;
        }

        public boolean isBetweenValue() {
            return betweenValue;
        }

        public boolean isListValue() {
            return listValue;
        }

        public String getTypeHandler() {
            return typeHandler;
        }

        protected Criterion(String condition) {
            super();
            this.condition = condition;
            this.typeHandler = null;
            this.noValue = true;
        }

        protected Criterion(String condition, Object value, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.typeHandler = typeHandler;
            if (value instanceof List<?>) {
                this.listValue = true;
            } else {
                this.singleValue = true;
            }
        }

        protected Criterion(String condition, Object value) {
            this(condition, value, null);
        }

        protected Criterion(String condition, Object value, Object secondValue, String typeHandler) {
            super();
            this.condition = condition;
            this.value = value;
            this.secondValue = secondValue;
            this.typeHandler = typeHandler;
            this.betweenValue = true;
        }

        protected Criterion(String condition, Object value, Object secondValue) {
            this(condition, value, secondValue, null);
        }
    }
}

package com.test.mybatis.dao;

import com.test.mybatis.pojo.Employee;
import com.test.mybatis.pojo.EmployeeExample;
import java.util.List;
import org.apache.ibatis.annotations.Param;

public interface EmployeeMapper {
    long countByExample(EmployeeExample example);

    int deleteByExample(EmployeeExample example);

    int deleteByPrimaryKey(Integer id);

    int insert(Employee record);

    int insertSelective(Employee record);

    List<Employee> selectByExample(EmployeeExample example);

    Employee selectByPrimaryKey(Integer id);

    int updateByExampleSelective(@Param("record") Employee record, @Param("example") EmployeeExample example);

    int updateByExample(@Param("record") Employee record, @Param("example") EmployeeExample example);

    int updateByPrimaryKeySelective(Employee record);

    int updateByPrimaryKey(Employee record);
}

<?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.test.mybatis.dao.EmployeeMapper">
  <resultMap id="BaseResultMap" type="com.test.mybatis.pojo.Employee">
    <id column="id" jdbcType="INTEGER" property="id" />
    <result column="last_name" jdbcType="VARCHAR" property="lastName" />
    <result column="gender" jdbcType="VARCHAR" property="gender" />
    <result column="email" jdbcType="VARCHAR" property="email" />
  </resultMap>
  <sql id="Example_Where_Clause">
    <where>
      <foreach collection="oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Update_By_Example_Where_Clause">
    <where>
      <foreach collection="example.oredCriteria" item="criteria" separator="or">
        <if test="criteria.valid">
          <trim prefix="(" prefixOverrides="and" suffix=")">
            <foreach collection="criteria.criteria" item="criterion">
              <choose>
                <when test="criterion.noValue">
                  and ${criterion.condition}
                </when>
                <when test="criterion.singleValue">
                  and ${criterion.condition} #{criterion.value}
                </when>
                <when test="criterion.betweenValue">
                  and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                </when>
                <when test="criterion.listValue">
                  and ${criterion.condition}
                  <foreach close=")" collection="criterion.value" item="listItem" open="(" separator=",">
                    #{listItem}
                  </foreach>
                </when>
              </choose>
            </foreach>
          </trim>
        </if>
      </foreach>
    </where>
  </sql>
  <sql id="Base_Column_List">
    id, last_name, gender, email
  </sql>
  <select id="selectByExample" parameterType="com.test.mybatis.pojo.EmployeeExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from employee
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
  </select>
  <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from employee
    where id = #{id,jdbcType=INTEGER}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer">
    delete from employee
    where id = #{id,jdbcType=INTEGER}
  </delete>
  <delete id="deleteByExample" parameterType="com.test.mybatis.pojo.EmployeeExample">
    delete from employee
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </delete>
  <insert id="insert" parameterType="com.test.mybatis.pojo.Employee">
    <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
      SELECT LAST_INSERT_ID()
    </selectKey>
    insert into employee (last_name, gender, email
      )
    values (#{lastName,jdbcType=VARCHAR}, #{gender,jdbcType=VARCHAR}, #{email,jdbcType=VARCHAR}
      )
  </insert>
  <insert id="insertSelective" parameterType="com.test.mybatis.pojo.Employee">
    <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
      SELECT LAST_INSERT_ID()
    </selectKey>
    insert into employee
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="lastName != null">
        last_name,
      </if>
      <if test="gender != null">
        gender,
      </if>
      <if test="email != null">
        email,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="lastName != null">
        #{lastName,jdbcType=VARCHAR},
      </if>
      <if test="gender != null">
        #{gender,jdbcType=VARCHAR},
      </if>
      <if test="email != null">
        #{email,jdbcType=VARCHAR},
      </if>
    </trim>
  </insert>
  <select id="countByExample" parameterType="com.test.mybatis.pojo.EmployeeExample" resultType="java.lang.Long">
    select count(*) from employee
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
  </select>
  <update id="updateByExampleSelective" parameterType="map">
    update employee
    <set>
      <if test="record.id != null">
        id = #{record.id,jdbcType=INTEGER},
      </if>
      <if test="record.lastName != null">
        last_name = #{record.lastName,jdbcType=VARCHAR},
      </if>
      <if test="record.gender != null">
        gender = #{record.gender,jdbcType=VARCHAR},
      </if>
      <if test="record.email != null">
        email = #{record.email,jdbcType=VARCHAR},
      </if>
    </set>
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByExample" parameterType="map">
    update employee
    set id = #{record.id,jdbcType=INTEGER},
      last_name = #{record.lastName,jdbcType=VARCHAR},
      gender = #{record.gender,jdbcType=VARCHAR},
      email = #{record.email,jdbcType=VARCHAR}
    <if test="_parameter != null">
      <include refid="Update_By_Example_Where_Clause" />
    </if>
  </update>
  <update id="updateByPrimaryKeySelective" parameterType="com.test.mybatis.pojo.Employee">
    update employee
    <set>
      <if test="lastName != null">
        last_name = #{lastName,jdbcType=VARCHAR},
      </if>
      <if test="gender != null">
        gender = #{gender,jdbcType=VARCHAR},
      </if>
      <if test="email != null">
        email = #{email,jdbcType=VARCHAR},
      </if>
    </set>
    where id = #{id,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.test.mybatis.pojo.Employee">
    update employee
    set last_name = #{lastName,jdbcType=VARCHAR},
      gender = #{gender,jdbcType=VARCHAR},
      email = #{email,jdbcType=VARCHAR}
    where id = #{id,jdbcType=INTEGER}
  </update>
</mapper>

　　2、使用java代码方式

　　　　a、pom中引入mybatis-generator-core依赖

<dependency>
    <groupId>org.mybatis.generator</groupId>
    <artifactId>mybatis-generator-core</artifactId>
    <version>1.3.7</version>
</dependency>

　　　　b、代码

package com.test.mybatis.generator;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.mybatis.generator.api.MyBatisGenerator;
import org.mybatis.generator.config.Configuration;
import org.mybatis.generator.config.xml.ConfigurationParser;
import org.mybatis.generator.internal.DefaultShellCallback;

public class TestMBG {

    public static void main(String[] args) throws Exception {
        List<String> warnings = new ArrayList<String>();
        boolean overwrite = true;
        // File configFile = new File("mbg.xml");
        InputStream inputStream = Resources.getResourceAsStream("mbg.xml");

        ConfigurationParser cp = new ConfigurationParser(warnings);
        Configuration config = cp.parseConfiguration(inputStream);
        DefaultShellCallback callback = new DefaultShellCallback(overwrite);
        MyBatisGenerator myBatisGenerator = new MyBatisGenerator(config, callback, warnings);
        myBatisGenerator.generate(null);
    }
}

 　　3、使用maven插件mybatis-generator-plus

　　　　a、pom文件

<build>
    <plugins>
        <plugin>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-maven-plugin</artifactId>
            <version>1.3.7</version>
            <dependencies>
                <dependency>
                    <groupId>mysql</groupId>
                    <artifactId>mysql-connector-java</artifactId>
                    <version>8.0.13</version>
                </dependency>
            </dependencies>
            <configuration>
                <!-- mybatis用于生成代码的配置文件 -->
                <configurationFile>src/main/resources/mbg.xml</configurationFile>
                <verbose>true</verbose>
                <overwrite>true</overwrite>
            </configuration>
        </plugin>
    </plugins>
</build>

　　　　b、mvn命令：mybatis-generator:generate