mybatis学习之枚举typehandler

在绝大数的情况下，typeHandler因为枚举类而使用，MyBatis已经定义了两个类作为枚举类的支持，这两个类是

• EnumOrdinalTypeHandler
• EnumTypeHandler
  前者是按mybatis根据枚举数组下标索引的方式进行匹配的，它要求数据库返回一个整数作为其下标，它会根据下标找到对应的枚举类型，后者是EnumTypeHandler会把使用的名称转化为对应的枚举，具体的在实例在进行解释
  首先先来建立一个性别的枚举类-SexEnum

package com.learn.ssm.chapter4.enumeration;

public enum SexEnum {
    MALE(1,"男"),
    FEMALE(0,"女");

    
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    //构造方法
    SexEnum(int id,String name){
        this.id=id;
        this.name=name;
    }
    public static SexEnum getSexById(int id){
        for(SexEnum sex:SexEnum.values()){
            if(sex.getId()==id){
                return sex;
//  返回male或者fmale，是为了后面的自定义的typehandler
            }
        }
        return null;
    }
//  public static void main(String[] args) {
//      SexEnum[] season1 = SexEnum.values();
//      System.out.println();
//      System.out.println(season1[0].getSexById(season1[0].getId()).getName());
//    // 枚举类的使用方法，values是枚举型数据的声明值，比如MALE,返回的是一个数组、
//  }
}

为了使用这个关于性别的枚举类，先创建一个pojo类

package com.learn.ssm.chapter3.pojo;

import com.learn.ssm.chapter4.enumeration.SexEnum;

public class User {
    private Long id;
    private String userName;
    private String password;
    private SexEnum sex;
//  枚举类的sex
    private String mobile;
    private String tel;
    private String email;
    private String note;

    /** setter and getter **/
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public SexEnum getSex() {
        return sex;
    }

    public void setSex(SexEnum sex) {
        this.sex = sex;
    }

    public String getMobile() {
        return mobile;
    }

    public void setMobile(String mobile) {
        this.mobile = mobile;
    }

    public String getTel() {
        return tel;
    }

    public void setTel(String tel) {
        this.tel = tel;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }

}

数据库设计如下：

数据.png
设计表.png

EnumOrdinalTypeHandler

为了测试，可以创建一个UserMapper.xml

<?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.learn.ssm.chapter3.mapper.UserMapper">
    <resultMap id="userMapper" type="user">
        <result property="id" column="id" />
        <result property="userName" column="user_name" />
        <result property="password" column="password" />
        <result property="sex" column="sex" 
        typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler"/>
           <!--  typeHandler="com.learn.ssm.chapter4.typehandler.SexEnumTypeHandler"/> -->
        <!--  
        <result property="sex" column="sex" 
            typeHandler="org.apache.ibatis.type.EnumTypeHandler"/> 
        -->
        <!-- 
        <result property="sex" column="sex"  
            typeHandler="com.learn.ssm.chapter4.typehandler.SexEnumTypeHandler"/>
        -->
        <result property="mobile" column="mobile" />
        <result property="tel" column="tel" />
        <result property="email" column="email" />
        <result property="note" column="note" />
    </resultMap>
    <select id="getUser" resultMap="userMapper" parameterType="long">
      select id, user_name, password, sex, mobile, tel, email, note from t_user 
      where id = #{id}
    </select>
</mapper>

因为枚举类声明的顺序是：MALE(1,"男"),FEMALE(0,"女");
所以sex字段在数据库设计为1的时候，返回的结果是女性。mybatis自动把sex字段的值转为int类型，因为在执行EnumOrdinalTypeHandler是根据mybatis返回的数组索引进行匹配的，所以要求数据库返回的是一个整数，如果不是整数，会报错误

类型错误.png

测试类：

    private static void testTypeHandler() {
        Logger log = Logger.getLogger(chapter4Main.class);
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionFactoryUtils.openSqlSession();
            UserMapper userMapper  = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.getUser(1L);
//          自带的EnumordinalTypeHandler和EnumTypehandler前置存储的是枚举的顺序号，后者是枚举实例名，但是有时候我们想用枚举的id来确定。这需要自定义枚举类typeHandler
            
            System.out.println("user的sex在这里"+user);
            System.out.println("user的sex在这里"+user.getSex());
            System.out.println(user.getSex().getName());
            System.out.println("userName这里"+user.getUserName());
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

执行的日志

日志

EnumTypeHandler

EnumTypeHandler是根据数据库返回的字符串如“MALE”或者"FEMALE"，进行Enum.valueOf(SexEnum.class,"MALE")转换，多以为了测试EnumTypeHandler的转换，我们把数据库的字段的sex字段修改为字符型（varchar(10)）并把数据修改为FEMALE
注意修改UserMapper.xml中的tyopehandler为EnumTypeHandler

<?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.learn.ssm.chapter3.mapper.UserMapper">
    <resultMap id="userMapper" type="user">
        <result property="id" column="id" />
        <result property="userName" column="user_name" />
        <result property="password" column="password" />
        <result property="sex" column="sex" 
        typeHandler="org.apache.ibatis.type.EnumTypeHandler"/>
           <!--  typeHandler="com.learn.ssm.chapter4.typehandler.SexEnumTypeHandler"/> -->
        <!--  
        <result property="sex" column="sex" 
            typeHandler="org.apache.ibatis.type.EnumTypeHandler"/> 
        -->
        <!-- 
        <result property="sex" column="sex"  
            typeHandler="com.learn.ssm.chapter4.typehandler.SexEnumTypeHandler"/>
        -->
        <result property="mobile" column="mobile" />
        <result property="tel" column="tel" />
        <result property="email" column="email" />
        <result property="note" column="note" />
    </resultMap>
    <select id="getUser" resultMap="userMapper" parameterType="long">
      select id, user_name, password, sex, mobile, tel, email, note from t_user 
      where id = #{id}
    </select>
</mapper>

自定义枚举typeHandler

我们已经讨论了Mybatis内部提供的两种转换的typeHandler,但是他们有很大的局限性，更多的时候我们希望使用自定义的typeHandler，修改数据库为以下：

image.png

其中sex的数据类型改为int(10)
此时，按SexEnum的定义，sex=1为男性，sex=0为女性。为了满足这个规则，让我们自定义一个SexEnumTypeHandler

package com.learn.ssm.chapter4.typehandler;

import java.sql.CallableStatement;
import java.sql.JDBCType;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

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

import com.learn.ssm.chapter4.enumeration.SexEnum;

public class SexEnumTypeHandler implements TypeHandler<SexEnum> {

    @Override
    public void setParameter(PreparedStatement ps, int i, SexEnum parameter,
            JdbcType jdbcType) throws SQLException {
        ps.setInt(i, parameter.getId());
//      是使用typeHandler通过preparedStatment对象进行设置SQL参数的时候使用的具体方法，i是SQL的下标，parameter是参数，jdbcType是数据库类型
//  执行预编译sql
    }

    @Override
    public SexEnum getResult(ResultSet rs, String columnName)
            throws SQLException {
        int id = rs.getInt(columnName);
        return SexEnum.getSexById(id);
    }

    @Override
   public SexEnum getResult(ResultSet rs, int columnIndex) throws SQLException {
        int id = rs.getInt(columnIndex);
        return SexEnum.getSexById(id);
    }

    @Override
    public SexEnum getResult(CallableStatement cs, int columnIndex)
            throws SQLException {
        int id = cs.getInt(columnIndex);
        return SexEnum.getSexById(id);
    }

}

然后修改UserMapper.xml中的

    <result property="sex" column="sex" 
        typeHandler="com.learn.ssm.chapter4.typehandler.SexEnumTypeHandler"/>```