Mybatis自定义typehandler

Mybatis自定义typehandler

1. 自定义typehandler
   官方的建议是继承BaseTypeHandler,其中Typehandler可以受一个type参数，Mybatis会自动传进来实际的class类型。

   /**
    * 用来处理我们自定义的枚举 
    * @author sut
    * @version $Revision:$
    */
   public class GenericEnumUserType<E extends StringEnumTypeImp> extends BaseTypeHandler<E>{
   
       //mybatis will pass actual class when constructing TypeHandler
       private Class<E> type;
   
       private static final String fromStringCode = "fromStringCode";
   
       public GenericEnumUserType(Class<E> type){
           Preconditions.checkNotNull(type, "Type argument cannot be null");
           this.type = type;
       }
   
       /**
        * 设置非空参数
        * @see org.apache.ibatis.type.BaseTypeHandler#setNonNullParameter(java.sql.PreparedStatement, int, java.lang.Object, org.apache.ibatis.type.JdbcType)
        */
       @Override
       public void setNonNullParameter(PreparedStatement ps, int i, StringEnumTypeImp parameter, JdbcType jdbcType) throws SQLException {
           ps.setString(i, parameter.getStoreValue());
       }
   
       /**
        * 得到非空结果，然后转换成E<br>
        * 利用反射调用静态的方法<br>
        * @see org.apache.ibatis.type.BaseTypeHandler#getNullableResult(java.sql.ResultSet, java.lang.String)
        */
       @Override
       @SuppressWarnings("unchecked")
       public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
           String storeValue =  rs.getString(columnName);
           Preconditions.checkNotNull(type, "Type argument cannot be null");
           try {
               Method fromMethod = type.getMethod(fromStringCode, String.class);
               return (E) fromMethod.invoke(null, storeValue);
           } catch (IllegalAccessException | NoSuchMethodException | SecurityException | IllegalArgumentException | InvocationTargetException e) {
               e.printStackTrace();
           }
           return null;
       }
   
       /**
        * 空的结果返回类型
        * @see org.apache.ibatis.type.BaseTypeHandler#getNullableResult(java.sql.ResultSet, int)
        */
       @Override
       public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
           try {
               return type.newInstance();
           } catch (InstantiationException | IllegalAccessException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           }
           return null;
       }
   
       /**
        * 针对callback的空值结果
        * @see org.apache.ibatis.type.BaseTypeHandler#getNullableResult(java.sql.CallableStatement, int)
        */
       @Override
       public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
           try {
               return type.newInstance();
           } catch (InstantiationException | IllegalAccessException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           }
           return null;
       }
   
   }

2. 注册TypeHandler
   
<!-- 类型处理器 -->
<typeHandlers>
<!-- 是否枚举 -->
<typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
javaType="com.sut.util.meta.WhetherTypeEnum" jdbcType="VARCHAR"/>
<!-- 性别枚举 -->
<typeHandler handler="com.sut.util.enumerate.mybatis.GenericEnumUserType"
javaType="com.sut.util.meta.SexTypeEnum" jdbcType="VARCHAR" />
</typeHandlers>


3. 这样我们在mapper就可以使用了。

   <?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.sut.persist.dao.UserDao">
   
       <!-- 定义User实体 -->
       <resultMap type="com.sut.persist.entity.User" id="userResult">
           <id property="id" javaType="int" column="id" />
           <result property="username" javaType="String" column="USERNAME" />
           <result property="password" javaType="String" column="PASSWORD" />
           <result property="enable" javaType="com.sut.util.meta.WhetherTypeEnum" column="enabled" 
               typeHandler="com.sut.util.enumerate.mybatis.GenericEnumUserType" />
           <result property="createTime" javaType="java.util.Date" column="CREATE_TIME" />
           <result property="lastLoginTime" javaType="java.util.Date" column="LAST_LOGIN_DATE" />
           <result property="sex" javaType="com.sut.util.meta.SexTypeEnum" column="SEX" 
               typeHandler="com.sut.util.enumerate.mybatis.GenericEnumUserType" />
           <result property="email" javaType="String" column="EMAIL" />
           <result property="mobile" javaType="String" column="MOBILE" />
           <result property="province" javaType="String" column="PROVINCE" />
           <result property="city" javaType="String" column="CITY" />
           <result property="area" javaType="String" column="AREA" />
           <result property="address" javaType="String" column="ADDRESS" />
           <result property="remark" javaType="String" column="REMARK" />
       </resultMap>
   
       <!-- query user by id -->
       <select id="getById" parameterType="int"  resultMap="userResult">
           select 
            *
           from user where id = #{id}
       </select>
   
       <!-- query user by name -->
       <select id="getByName" parameterType="String" resultMap="userResult">
           select * from user where username = #{username}
       </select>
   
       <!-- query all user.这里将所有列写出来了，因为最初会报错。字段好像映射的顺序不一样 --> 
       <select id="getAll" resultMap="userResult">
           select 
               id as id,
               username as username,
               password as password,
               enabled as enable,
               create_time as createTime,
               last_login_date as lastLoginTime,
               email as email,
               mobile as mobile,
               province as province,
               city as city,
               area as area,
               address as address,
               remark as remark
           from user
       </select>
   
       <!-- delete by id -->
       <delete id="deleteById" parameterType="int">
           delete from user where id = #{id}
       </delete>
   
       <!-- insert User -->
       <insert id="insert">
           insert into user(
               username,
               password,
               enabled,
               create_time,
               last_login_date,
               sex,
               email,
               mobile,
               province,
               city,
               area,
               address,
               remark
           )values(
               #{username},
               #{password},
               #{enable, typeHandler=com.sut.util.enumerate.mybatis.GenericEnumUserType, jdbcType=VARCHAR,
                    javaType=com.sut.util.meta.WhetherTypeEnum},
               #{createTime},
               #{lastLoginDate},
               #{sex, typeHandler=com.sut.util.enumerate.mybatis.GenericEnumUserType, jdbcType=VARCHAR, 
                    javaType=com.sut.util.meta.SexTypeEnum},
               #{email},
               #{mobile},
               #{province},
               #{city},
               #{area},
               #{address},
               #{remark}
           )
       </insert>
   </mapper>

4. 测试insert和getAll()方法是可以的。

---

UPDATE:

1. 2017/01/07 有一个问题:
   当使用自定义typeHandler的时候，如果bean的属性名和表字段的名称是一样的话，就会被mybatis分为mappedColumns，获取的typeHandler的rawType就不正确，如果是不一样的话，就会成为unMappedColumns， 获取的就是对的. 在测试过程中，即便设置AutoMappingBehavior=NONE，也还是会执行column分类. 最后解决办法只能是改变bean的property名称。

2. 2017/01/23 来自SO的回答说:
   说是将ResultMapping定义的时候，将education的TypeHandler移除掉，然后指定好javaType，jdbcType就可以了。试了一下，果然可以。但是不明白为什么这样。