在上一篇博客中说到，Mybatis是灵活的SQL语句应用，不想Hibernate一样有其封装好的方法，那么，当我们用Mybatis的时候（Hibernate），我们都需要编写其实体类，和配置文件。本篇博客，就介绍一下Mybatis的逆向生成工具。

一、思路

回想一下，在最早运用EF的时候，我们首先通过可视化界面，连接数据库，然后选择要使用的表单，然后，我们就可以自动生成实体类。在运用Hibernate的时候，我们可以先编写Hibernate的配置文件，连接数据库，然后编写实体类文件，然后通过读取HIbernate的配置文件，正向生成数据库表单。然后我们也可以运用工具，从数据库表，生成HIbernate的实体。那么，到了Mybatis这儿，可以怎么做呢？思路如下：

1，连接数据库，指定表单生成

2，指定代码生成后的存放路径，以及要生成哪些代码

2，读取配置文件，生成代码

二、实现

首先是建立了一个Java project，然后引入了5个jar包，分别是：

log4j-1.2.16.jar；Mybatis-3.2.3.jar；Mybatis-generator-core-1.3.2.jar；mysal-connector-java-5.1.28-bin.jar；ojdbc14.jar

版本可以自行确定！

然后，编写mybatis.xml配置文件，代码内容如下：

<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfigurationPUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN""http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd"><generatorConfiguration><context id="testTables" targetRuntime="MyBatis3"><commentGenerator><!-- 是否去除自动生成的注释 true：是 ： false:否 --><property name="suppressAllComments" value="true" /></commentGenerator><!--数据库连接的信息：驱动类、连接地址、用户名、密码 --><jdbcConnection driverClass="com.mysql.jdbc.Driver"connectionURL="jdbc:mysql://localhost:3306/Test" userId="root"password="Angel0626"></jdbcConnection><!-- 默认false，把JDBC DECIMAL 和 NUMERIC 类型解析为 Integer，为 true时把JDBC DECIMAL 和 NUMERIC 类型解析为java.math.BigDecimal --><javaTypeResolver><property name="forceBigDecimals" value="false" /></javaTypeResolver><!-- targetProject:生成PO类的位置 --><javaModelGenerator targetPackage="pojo"targetProject=".\src"><!-- enableSubPackages:是否让schema作为包的后缀 --><property name="enableSubPackages" value="false" /><!-- 从数据库返回的值被清理前后的空格 --><property name="trimStrings" value="true" /></javaModelGenerator><!-- targetProject:mapper映射文件生成的位置 --><sqlMapGenerator targetPackage="mapper" targetProject=".\src"><!-- enableSubPackages:是否让schema作为包的后缀 --><property name="enableSubPackages" value="false" /></sqlMapGenerator><!-- targetPackage：mapper接口生成的位置 --><javaClientGenerator type="XMLMAPPER"targetPackage="mapper" targetProject=".\src"><!-- enableSubPackages:是否让schema作为包的后缀 --><property name="enableSubPackages" value="false" /></javaClientGenerator><!-- 指定数据库表 --><table schema="" tableName="tb_content"></table><table schema="" tableName="tb_content_category"></table><table schema="" tableName="tb_item"></table><table schema="" tableName="tb_item_cat"></table><table schema="" tableName="tb_item_desc"></table><table schema="" tableName="tb_item_param"></table><table schema="" tableName="tb_item_param_item"></table><table schema="" tableName="tb_order"></table><table schema="" tableName="tb_order_item"></table><table schema="" tableName="tb_order_shipping"></table><table schema="" tableName="tb_user"></table></context>
</generatorConfiguration>
</span>

其次，编写实现方法，代码如下：

<span style="font-family:KaiTi_GB2312;font-size:18px;">package test;import java.io.File;
import java.util.ArrayList;
import java.util.List;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 GeneratorSqlmap {public void generator() throws Exception{List<String> warnings=new ArrayList<String>();boolean overwrite=true;File configFile=new File("mybatis.xml");ConfigurationParser cp=new ConfigurationParser(warnings);Configuration config=cp.parseConfiguration(configFile);DefaultShellCallback callback=new DefaultShellCallback(overwrite);MyBatisGenerator myBatisGenerator=new MyBatisGenerator(config,callback,warnings);myBatisGenerator.generate(null);}public static void main(String[] args) throws Exception{try{GeneratorSqlmap generatorSqlmap=new GeneratorSqlmap();generatorSqlmap.generator();}catch(Exception e){e.printStackTrace();}}}
</span>

运行其main方法，即可生成相应代码。

代码示例：以TbUser表为例：

实体类：

<span style="font-family:KaiTi_GB2312;font-size:18px;">public class TbUser {private Long id;private String username;private String password;private String phone;private String email;private Date created;private Date updated;public Long getId() {return id;}public void setId(Long id) {this.id = id;}</span>

mapper接口：

<span style="font-family:KaiTi_GB2312;font-size:18px;">package mapper;import java.util.List;
import org.apache.ibatis.annotations.Param;
import pojo.TbUser;
import pojo.TbUserExample;public interface TbUserMapper {int countByExample(TbUserExample example);int deleteByExample(TbUserExample example);int deleteByPrimaryKey(Long id);int insert(TbUser record);int insertSelective(TbUser record);List<TbUser> selectByExample(TbUserExample example);TbUser selectByPrimaryKey(Long id);int updateByExampleSelective(@Param("record") TbUser record, @Param("example") TbUserExample example);int updateByExample(@Param("record") TbUser record, @Param("example") TbUserExample example);int updateByPrimaryKeySelective(TbUser record);int updateByPrimaryKey(TbUser record);
}</span>

mapper.xml实现：

<span style="font-family:KaiTi_GB2312;font-size:18px;"><?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="mapper.TbUserMapper" ><resultMap id="BaseResultMap" type="pojo.TbUser" ><id column="id" property="id" jdbcType="BIGINT" /><result column="username" property="username" jdbcType="VARCHAR" /><result column="password" property="password" jdbcType="VARCHAR" /><result column="phone" property="phone" jdbcType="VARCHAR" /><result column="email" property="email" jdbcType="VARCHAR" /><result column="created" property="created" jdbcType="TIMESTAMP" /><result column="updated" property="updated" jdbcType="TIMESTAMP" /></resultMap><sql id="Example_Where_Clause" ><where ><foreach collection="oredCriteria" item="criteria" separator="or" ><if test="criteria.valid" ><trim prefix="(" suffix=")" prefixOverrides="and" ><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 collection="criterion.value" item="listItem" open="(" close=")" 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="(" suffix=")" prefixOverrides="and" ><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 collection="criterion.value" item="listItem" open="(" close=")" separator="," >#{listItem}</foreach></when></choose></foreach></trim></if></foreach></where></sql><sql id="Base_Column_List" >id, username, password, phone, email, created, updated</sql><select id="selectByExample" resultMap="BaseResultMap" parameterType="pojo.TbUserExample" >select<if test="distinct" >distinct</if><include refid="Base_Column_List" />from tb_user<if test="_parameter != null" ><include refid="Example_Where_Clause" /></if><if test="orderByClause != null" >order by ${orderByClause}</if></select><select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Long" >select <include refid="Base_Column_List" />from tb_userwhere id = #{id,jdbcType=BIGINT}</select><delete id="deleteByPrimaryKey" parameterType="java.lang.Long" >delete from tb_userwhere id = #{id,jdbcType=BIGINT}</delete><delete id="deleteByExample" parameterType="pojo.TbUserExample" >delete from tb_user<if test="_parameter != null" ><include refid="Example_Where_Clause" /></if></delete><insert id="insert" parameterType="pojo.TbUser" >insert into tb_user (id, username, password, phone, email, created, updated)values (#{id,jdbcType=BIGINT}, #{username,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}, #{phone,jdbcType=VARCHAR}, #{email,jdbcType=VARCHAR}, #{created,jdbcType=TIMESTAMP}, #{updated,jdbcType=TIMESTAMP})</insert><insert id="insertSelective" parameterType="pojo.TbUser" >insert into tb_user<trim prefix="(" suffix=")" suffixOverrides="," ><if test="id != null" >id,</if><if test="username != null" >username,</if><if test="password != null" >password,</if><if test="phone != null" >phone,</if><if test="email != null" >email,</if><if test="created != null" >created,</if><if test="updated != null" >updated,</if></trim><trim prefix="values (" suffix=")" suffixOverrides="," ><if test="id != null" >#{id,jdbcType=BIGINT},</if><if test="username != null" >#{username,jdbcType=VARCHAR},</if><if test="password != null" >#{password,jdbcType=VARCHAR},</if><if test="phone != null" >#{phone,jdbcType=VARCHAR},</if><if test="email != null" >#{email,jdbcType=VARCHAR},</if><if test="created != null" >#{created,jdbcType=TIMESTAMP},</if><if test="updated != null" >#{updated,jdbcType=TIMESTAMP},</if></trim></insert><select id="countByExample" parameterType="pojo.TbUserExample" resultType="java.lang.Integer" >select count(*) from tb_user<if test="_parameter != null" ><include refid="Example_Where_Clause" /></if></select><update id="updateByExampleSelective" parameterType="map" >update tb_user<set ><if test="record.id != null" >id = #{record.id,jdbcType=BIGINT},</if><if test="record.username != null" >username = #{record.username,jdbcType=VARCHAR},</if><if test="record.password != null" >password = #{record.password,jdbcType=VARCHAR},</if><if test="record.phone != null" >phone = #{record.phone,jdbcType=VARCHAR},</if><if test="record.email != null" >email = #{record.email,jdbcType=VARCHAR},</if><if test="record.created != null" >created = #{record.created,jdbcType=TIMESTAMP},</if><if test="record.updated != null" >updated = #{record.updated,jdbcType=TIMESTAMP},</if></set><if test="_parameter != null" ><include refid="Update_By_Example_Where_Clause" /></if></update><update id="updateByExample" parameterType="map" >update tb_userset id = #{record.id,jdbcType=BIGINT},username = #{record.username,jdbcType=VARCHAR},password = #{record.password,jdbcType=VARCHAR},phone = #{record.phone,jdbcType=VARCHAR},email = #{record.email,jdbcType=VARCHAR},created = #{record.created,jdbcType=TIMESTAMP},updated = #{record.updated,jdbcType=TIMESTAMP}<if test="_parameter != null" ><include refid="Update_By_Example_Where_Clause" /></if></update><update id="updateByPrimaryKeySelective" parameterType="pojo.TbUser" >update tb_user<set ><if test="username != null" >username = #{username,jdbcType=VARCHAR},</if><if test="password != null" >password = #{password,jdbcType=VARCHAR},</if><if test="phone != null" >phone = #{phone,jdbcType=VARCHAR},</if><if test="email != null" >email = #{email,jdbcType=VARCHAR},</if><if test="created != null" >created = #{created,jdbcType=TIMESTAMP},</if><if test="updated != null" >updated = #{updated,jdbcType=TIMESTAMP},</if></set>where id = #{id,jdbcType=BIGINT}</update><update id="updateByPrimaryKey" parameterType="pojo.TbUser" >update tb_userset username = #{username,jdbcType=VARCHAR},password = #{password,jdbcType=VARCHAR},phone = #{phone,jdbcType=VARCHAR},email = #{email,jdbcType=VARCHAR},created = #{created,jdbcType=TIMESTAMP},updated = #{updated,jdbcType=TIMESTAMP}where id = #{id,jdbcType=BIGINT}</update>
</mapper></span>

三、总结

从生成的代码可以看出，生成的代码，基本上解决了对于一个实体操作的增删改查，但是，每个实体的代码都是这样的丰富，还能不能继续往上抽象一层呢？下一篇博客介绍Mybatis的底层封装思路！