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 generatorConfiguration
PUBLIC "-//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_user
where id = #{id,jdbcType=BIGINT}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.Long" >
delete from tb_user
where 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_user
set 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_user
set 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！
