Mybatis中有一些系统内置的TypeHandler,比如说BooleanTypeHandler、IntegerTypeHandler、StringTypeHandler等等,其完成javaType和jdbcType之间的相互转换。在大部分场景下都能满足需求,但在某些场景下可以使用自定义的TypeHandler,以此来实现特殊的转换规则。
接下来实现一个将数据库中的性别属性sex进行相互转换的例子,sex属性在MySQL中是tinyint类型,在Java中是String类型(1代表男,0代表女)。相应的SexEnumTypeHandler的代码如下所示:
package com.hys.person.typehandler;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedJdbcTypes;
import org.apache.ibatis.type.MappedTypes;
import org.apache.ibatis.type.TypeHandler;
import com.hys.person.model.SexEnum;
@MappedTypes(String.class)
@MappedJdbcTypes(JdbcType.INTEGER)
public class SexEnumTypeHandler implements TypeHandler<String> {
@Override
public void setParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {
ps.setInt(i, SexEnum.getIdByName(parameter));
}
@Override
public String getResult(ResultSet rs, String columnName) throws SQLException {
int id = rs.getInt(columnName);
return SexEnum.getNameById(id);
}
@Override
public String getResult(ResultSet rs, int columnIndex) throws SQLException {
int id = rs.getInt(columnIndex);
return SexEnum.getNameById(id);
}
@Override
public String getResult(CallableStatement cs, int columnIndex) throws SQLException {
int id = cs.getInt(columnIndex);
return SexEnum.getNameById(id);
}
}
以上的转换过程需要使用一个性别的枚举SexEnum来实现,其代码如下所示:
package com.hys.person.model;
public enum SexEnum {
MALE(1, "男"), FEMALE(0, "女");
private int id;
private String name;
private SexEnum(int id, String name) {
this.id = id;
this.name = 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;
}
public static int getIdByName(String name) {
for (SexEnum sex : SexEnum.values()) {
if (sex.getName().equals(name)) {
return sex.getId();
}
}
throw new RuntimeException("类型不匹配!");
}
public static String getNameById(int id) {
for (SexEnum sex : SexEnum.values()) {
if (id == sex.getId()) {
return sex.getName();
}
}
throw new RuntimeException("类型不匹配!");
}
}
完成了上面的准备工作之后,在Mapper的xml中使用如下所示:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD//EN Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hys.person.dao.IPersonDao">
<sql id="allColumns">
id,
name,
sex,
address
</sql>
<resultMap id="personMapper"
type="com.hys.person.model.Person">
<result property="id" column="id" />
<result property="name" column="name" />
<result property="sex" column="sex"
typeHandler="com.hys.person.typehandler.SexEnumTypeHandler" />
<result property="address" column="address" />
</resultMap>
<select id="getAllPerson" resultMap="personMapper">
SELECT
<include refid="allColumns" />
FROM person
</select>
<insert id="insertPerson"
parameterType="com.hys.person.model.Person">
INSERT INTO person (
<include refid="allColumns" />
)
VALUES
(
#{person.id}, #{person.name},
#{person.sex,typeHandler=com.hys.person.typehandler.SexEnumTypeHandler},
#{person.address})
</insert>
</mapper>
由上面可以看到,在查询和插入语句中声明相应的typeHandler即可,在调用时即可完成自动的转换工作,不再需要在service层进行显示地转换。