【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', '', 'dabai@163.com', 1);
 INSERT INTO `employee` VALUES (2, '小明', '', 'xiaoming@163.com', 1);
 INSERT INTO `employee` VALUES (3, '小红', '', '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;
     }
 }

Employee.java

 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);
         }
     }
 }

EmployeeExample.java

 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);
 }

EmployeeMapper.java

 <?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>

EmployeeMapper.xml

　　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