Mybatis步步进阶（六）——Mybatis Mapper代理和逆向工程

一、原始的开发方式

以dao层为例，业务处理过程如下：

1、Dao实现类

public class UserDaoImpl implements UserDao {

// 需要向dao实现类中注入SqlSessionFactory
// 这里通过构造方法注入
private SqlSessionFactory sqlSessionFactory;

public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
this.sqlSessionFactory = sqlSessionFactory;
}
@Override
public User findUserById(int id) throws Exception {
SqlSession sqlSession = sqlSessionFactory.openSession();
User user = sqlSession.selectOne("test.findUserById", id);
// 释放资源
sqlSession.close();
return user;
}

@Override
public void insertUser(User user) throws Exception {
SqlSession sqlSession = sqlSessionFactory.openSession();
//执行插入操作
sqlSession.insert("test.insertUser", user);
// 提交事务
sqlSession.commit();
// 释放资源
sqlSession.close();
}

2、测试类 

public class UserMapperTest {
private SqlSessionFactory sqlSessionFactory;
// 此方法是在执行testFindUserById之前执行
@Before
public void setUp() throws Exception {
// 创建sqlSessionFactory
// mybatis配置文件
String resource = "SqlMapConfig.xml";
// 得到配置文件流
InputStream inputStream = Resources.getResourceAsStream(resource);
// 创建会话工厂，传入mybatis的配置文件信息
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
public void testFindUserById() throws Exception {
SqlSession sqlSession = sqlSessionFactory.openSession();
//创建UserMapper对象，mybatis自动生成mapper代理对象
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//调用userMapper的方法
User user = userMapper.findUserById(1);
System.out.println(user);

}

3、原始方式的弊端

1）每个方法中重复出现opensession、closesession方法调用

2）selectone、insert方法的参数采用泛型传入，即便传入参数类型错误，也会先执行select，执行过程中再类型错误，无法提前对参数类型进行检查

二、Mybatis Mapper代理类 

Mybatis提供了使用Mapper接口自动生成实现类的代理对象，只需要在配置Mapper.xml遵循Mybatis提供的开发规范：

1、在mapper.xml中namespace等于mapper接口地址

2、mapper.java接口中的方法名和mapper.xml中statement的id一致

3、mapper.java接口中的方法输入参数类型和mapper.xml中statement的parameterType指定的类型一致。

4、mapper.java接口中的方法返回值类型和mapper.xml中statement的resultType指定的类型一致。

mapper配置：

<!-- namespace命名空间，作用就是对sql进行分类化管理，理解sql隔离
注意：使用mapper代理方法开发，namespace有特殊重要的作用，namespace等于mapper接口地址
-->
<mapper namespace="cn.itcast.ssm.mapper.UserMapper">
<select id="findUserById" parameterType="int" resultType="user">
SELECT * FROM USER WHERE id=#{value}
</select>
</mapper>

接口编写：

package cn.itcast.ssm.mapper;
public interface UserMapper {
//根据id查询用户信息
public User findUserById(int id) throws Exception;
}

测试类：

public class UserMapperTest {
private SqlSessionFactory sqlSessionFactory;
// 此方法是在执行testFindUserById之前执行
@Before
public void setUp() throws Exception {
// 创建sqlSessionFactory
// mybatis配置文件
String resource = "SqlMapConfig.xml";
// 得到配置文件流
InputStream inputStream = Resources.getResourceAsStream(resource);
// 创建会话工厂，传入mybatis的配置文件信息
sqlSessionFactory = new SqlSessionFactoryBuilder()
.build(inputStream);
}
@Test
public void testFindUserById() throws Exception {
SqlSession sqlSession = sqlSessionFactory.openSession();

//创建UserMapper对象，mybatis自动生成mapper代理对象
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//调用userMapper的方法
User user = userMapper.findUserById(1);
}
}

注：代理对象的内部调用，通过getMapper()中传入调用类（UserMapper.class 接口），直接调用接口的find方法，通过返回值是单个pojo还是List来判断调用selectone或是selectList方法。
三、Mybatis 逆向工程

     Mybatis的逆向工程就是运用了mapper代理的方式，通过配置db的表字段，根据数据库生成对单个表操作的service接口、mapper配置、pojo实体。generatorConfig.xml配置文件如下：

<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/mybatis" userId="root"
password="mysql">
</jdbcConnection>
<!-- <jdbcConnection driverClass="oracle.jdbc.OracleDriver"
connectionURL="jdbc:oracle:thin:@127.0.0.1:1521:yycg"
userId="yycg"
password="yycg">
</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="cn.itcast.ssm.po"
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="cn.itcast.ssm.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="cn.itcast.ssm.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 tableName="items"></table>
<table tableName="orders"></table>
<table tableName="orderdetail"></table>
<table tableName="user"></table>
<!-- <table schema="" tableName="sys_user"></table>
<table schema="" tableName="sys_role"></table>
<table schema="" tableName="sys_permission"></table>
<table schema="" tableName="sys_user_role"></table>
<table schema="" tableName="sys_role_permission"></table> -->

<!-- 有些表的字段需要指定java类型
<table schema="" tableName="">
<columnOverride column="" javaType="" />
</table> -->
</context>
</generatorConfiguration>

java类

public class GeneratorSqlmap {
public void generator() throws Exception{
List<String> warnings = new ArrayList<String>();
boolean overwrite = true;
//指定 逆向工程配置文件
File configFile = new File("generatorConfig.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();
}
}
}

生成的pojo和pojo扩展类

public class Items {
private Integer id;
private String name;
private Float price;
private String pic;
private Date createtime;
private String detail;
}
//扩展类
public class ItemsExample {
protected String orderByClause;
protected boolean distinct;
protected List<Criteria> oredCriteria;
}

逆向工程生成的Itemmapper.xml配置

<?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="cn.itcast.ssm.mapper.ItemsMapper" >
<resultMap id="BaseResultMap" type="cn.itcast.ssm.po.Items" >
<id column="id" property="id" jdbcType="INTEGER" />
<result column="name" property="name" jdbcType="VARCHAR" />
<result column="price" property="price" jdbcType="REAL" />
<result column="pic" property="pic" jdbcType="VARCHAR" />
<result column="createtime" property="createtime" jdbcType="TIMESTAMP" />
</resultMap>
<resultMap id="ResultMapWithBLOBs" type="cn.itcast.ssm.po.Items" extends="BaseResultMap" >
<result column="detail" property="detail" jdbcType="LONGVARCHAR" />
</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, name, price, pic, createtime
</sql>
<sql id="Blob_Column_List" >
detail
</sql>
<select id="selectByExampleWithBLOBs" resultMap="ResultMapWithBLOBs" parameterType="cn.itcast.ssm.po.ItemsExample" >
select
<if test="distinct" >
distinct
</if>
<include refid="Base_Column_List" />
,
<include refid="Blob_Column_List" />
from items
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
<if test="orderByClause != null" >
order by ${orderByClause}
</if>
</select>
<select id="selectByExample" resultMap="BaseResultMap" parameterType="cn.itcast.ssm.po.ItemsExample" >
select
<if test="distinct" >
distinct
</if>
<include refid="Base_Column_List" />
from items
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
<if test="orderByClause != null" >
order by ${orderByClause}
</if>
</select>
<select id="selectByPrimaryKey" resultMap="ResultMapWithBLOBs" parameterType="java.lang.Integer" >
select
<include refid="Base_Column_List" />
,
<include refid="Blob_Column_List" />
from items
where id = #{id,jdbcType=INTEGER}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
delete from items
where id = #{id,jdbcType=INTEGER}
</delete>
<delete id="deleteByExample" parameterType="cn.itcast.ssm.po.ItemsExample" >
delete from items
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
</delete>
<insert id="insert" parameterType="cn.itcast.ssm.po.Items" >
insert into items (id, name, price,
pic, createtime, detail
)
values (#{id,jdbcType=INTEGER}, #{name,jdbcType=VARCHAR}, #{price,jdbcType=REAL},
#{pic,jdbcType=VARCHAR}, #{createtime,jdbcType=TIMESTAMP}, #{detail,jdbcType=LONGVARCHAR}
)
</insert>
<insert id="insertSelective" parameterType="cn.itcast.ssm.po.Items" >
insert into items
<trim prefix="(" suffix=")" suffixOverrides="," >
<if test="id != null" >
id,
</if>
<if test="name != null" >
name,
</if>
<if test="price != null" >
price,
</if>
<if test="pic != null" >
pic,
</if>
<if test="createtime != null" >
createtime,
</if>
<if test="detail != null" >
detail,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides="," >
<if test="id != null" >
#{id,jdbcType=INTEGER},
</if>
<if test="name != null" >
#{name,jdbcType=VARCHAR},
</if>
<if test="price != null" >
#{price,jdbcType=REAL},
</if>
<if test="pic != null" >
#{pic,jdbcType=VARCHAR},
</if>
<if test="createtime != null" >
#{createtime,jdbcType=TIMESTAMP},
</if>
<if test="detail != null" >
#{detail,jdbcType=LONGVARCHAR},
</if>
</trim>
</insert>
<select id="countByExample" parameterType="cn.itcast.ssm.po.ItemsExample" resultType="java.lang.Integer" >
select count(*) from items
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
</select>
<update id="updateByExampleSelective" parameterType="map" >
update items
<set >
<if test="record.id != null" >
id = #{record.id,jdbcType=INTEGER},
</if>
<if test="record.name != null" >
name = #{record.name,jdbcType=VARCHAR},
</if>
<if test="record.price != null" >
price = #{record.price,jdbcType=REAL},
</if>
<if test="record.pic != null" >
pic = #{record.pic,jdbcType=VARCHAR},
</if>
<if test="record.createtime != null" >
createtime = #{record.createtime,jdbcType=TIMESTAMP},
</if>
<if test="record.detail != null" >
detail = #{record.detail,jdbcType=LONGVARCHAR},
</if>
</set>
<if test="_parameter != null" >
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByExampleWithBLOBs" parameterType="map" >
update items
set id = #{record.id,jdbcType=INTEGER},
name = #{record.name,jdbcType=VARCHAR},
price = #{record.price,jdbcType=REAL},
pic = #{record.pic,jdbcType=VARCHAR},
createtime = #{record.createtime,jdbcType=TIMESTAMP},
detail = #{record.detail,jdbcType=LONGVARCHAR}
<if test="_parameter != null" >
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByExample" parameterType="map" >
update items
set id = #{record.id,jdbcType=INTEGER},
name = #{record.name,jdbcType=VARCHAR},
price = #{record.price,jdbcType=REAL},
pic = #{record.pic,jdbcType=VARCHAR},
createtime = #{record.createtime,jdbcType=TIMESTAMP}
<if test="_parameter != null" >
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByPrimaryKeySelective" parameterType="cn.itcast.ssm.po.Items" >
update items
<set >
<if test="name != null" >
name = #{name,jdbcType=VARCHAR},
</if>
<if test="price != null" >
price = #{price,jdbcType=REAL},
</if>
<if test="pic != null" >
pic = #{pic,jdbcType=VARCHAR},
</if>
<if test="createtime != null" >
createtime = #{createtime,jdbcType=TIMESTAMP},
</if>
<if test="detail != null" >
detail = #{detail,jdbcType=LONGVARCHAR},
</if>
</set>
where id = #{id,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKeyWithBLOBs" parameterType="cn.itcast.ssm.po.Items" >
update items
set name = #{name,jdbcType=VARCHAR},
price = #{price,jdbcType=REAL},
pic = #{pic,jdbcType=VARCHAR},
createtime = #{createtime,jdbcType=TIMESTAMP},
detail = #{detail,jdbcType=LONGVARCHAR}
where id = #{id,jdbcType=INTEGER}
</update>
<update id="updateByPrimaryKey" parameterType="cn.itcast.ssm.po.Items" >
update items
set name = #{name,jdbcType=VARCHAR},
price = #{price,jdbcType=REAL},
pic = #{pic,jdbcType=VARCHAR},
createtime = #{createtime,jdbcType=TIMESTAMP}
where id = #{id,jdbcType=INTEGER}
</update>
</mapper>