MyBatis 入门(五)--typeHandlers

一、作用及默认的处理

类型处理器的作用就是

• 查询时把数据库存储的值转换成java类型
• 修改是把java类型转换成数据库类型存储，处理
• 下面这个表格描述了默认的类型处理器。

二、自定义类型

   例如我们在数据库经常把时间存储为一个14位的VARCHAR（YYYYmmddssss）。而前台java层为java.util.Date,在这里我们就简单做一个类型处理。

• 定义类型处理

package com.elements.typehandler;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

public class DataTimeTypeHandler extends BaseTypeHandler<Date> {

    /**
     *
     * 这里应该是在保存数据的时候，把前台的日期类型转换成数据的varchar 我们使用了SimpleDateFormat来转换data类型
     * */
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i,
            Date parameter, JdbcType jdbcType) throws SQLException {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmss");
        ps.setString(i, sdf.format(parameter));
    }

    /**
     * 下面三个函数应该都是返回到java层时调用，我们把varchar转换成Date类型
     */
    @Override
    public Date getNullableResult(ResultSet rs, String columnName)
            throws SQLException {
        String varchartime = rs.getString(columnName);
        if (varchartime!=null)
        return new Date(Long.parseLong(varchartime));
        else return null;
    }

    @Override
    public Date getNullableResult(ResultSet rs, int columnIndex)
            throws SQLException {
        String varchartime = rs.getString(columnIndex);
        if (varchartime!=null)
            return new Date(Long.parseLong(varchartime));
            else return null;
    }

    @Override
    public Date getNullableResult(CallableStatement cs, int columnIndex)
            throws SQLException {
        String varchartime = cs.getString(columnIndex);
        if (varchartime!=null)
            return new Date(Long.parseLong(varchartime));
            else return null;
    }

}

• mybatis-config.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>

    <properties resource="jdbc.properties" />

  <typeHandlers>
     <typeHandler handler="com.elements.typehandler.DataTimeTypeHandler" javaType="java.util.Date" jdbcType="VARCHAR"/>
      <package name="com.elements.user"/>
  </typeHandlers>

    <environments default="dev">
        <environment id="dev">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${driver}" />
                <property name="url" value="${url}" />
                <property name="username" value="${username}" />
                <property name="password" value="${password}" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper class="com.elements.user.dao.UserMapper" />

    </mappers>

</configuration>

• Ｕｓｅｒ类

package com.elements.user.model;

import java.util.Date;

public class User {
    private Integer userid;
    private String username;
    private String useremail;
    private Date createtime;
    private Date updatetime;

    public Integer getUserid() {
        return userid;
    }
    public void setUserid(Integer userid) {
        this.userid = userid;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username == null ? null : username.trim();
    }
    public String getUseremail() {
        return useremail;
    }
    public void setUseremail(String useremail) {
        this.useremail = useremail == null ? null : useremail.trim();
    }
    public Date getCreatetime() {
        return createtime;
    }
    public void setCreatetime(Date createtime) {
        this.createtime = createtime ;
    }
    public Date getUpdatetime() {
        return updatetime;
    }
    public void setUpdatetime(Date updatetime) {
        this.updatetime = updatetime;
    }
    @Override
    public String toString() {
        return "User [userid=" + userid + ", username=" + username
                + ", useremail=" + useremail + ", createtime=" + createtime
                + ", updatetime=" + updatetime + "]";
    }

}

• UserMapper配置文件

<?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.elements.user.dao.UserMapper" >

  <resultMap id="BaseResultMap" type="com.elements.user.model.User" >

    <id column="userId" property="userid" jdbcType="INTEGER" />
    <result column="UserName" property="username" jdbcType="VARCHAR" />
    <result column="UserEmail" property="useremail" jdbcType="VARCHAR" />
    <result column="createTime" property="createtime" jdbcType="VARCHAR" />
    <result column="updateTime" property="updatetime" jdbcType="VARCHAR" />
  </resultMap>
  <sql id="Base_Column_List" >

    userId, UserName, UserEmail, createTime, updateTime
  </sql>

  <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >

    select
    <include refid="Base_Column_List" />
    from user
    where userId = #{userid,jdbcType=INTEGER}
  </select>

  <insert id="insert" parameterType="com.elements.user.model.User" >

    insert into user (userId, UserName, UserEmail,
      createTime, updateTime)
    values (#{userid,jdbcType=INTEGER}, #{username,jdbcType=VARCHAR}, #{useremail,jdbcType=VARCHAR},
      #{createtime,jdbcType=VARCHAR}, #{updatetime,jdbcType=VARCHAR})
  </insert>

</mapper>

注意：我们没有在mapper文件内显示的做类型转换 ，他已经默认把这两种类型（javaType=”java.util.Date” jdbcType=”VARCHAR” ）的互转都调用我们的类型处理了

代码下载地址：http://pan.baidu.com/s/1eRDzY6m