存储或读取时转换JSON数据

一、 数据库类型

二、使用Hutool工具

存储时将数据转换为JSON数据

获取时将JSON数据转换为对象

发现问题：

原本数据对象是Address 和 Firend但是转换完成后数据变成了JSONArray和JSONObject

三、自定义TypeHandler继承Mybatis的BaseTypeHandler处理器

package com.jiusi.config;import cn.hutool.json.JSONUtil;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;public class jsonTypeHandler01<T> extends BaseTypeHandler {@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {//将数据转换为json字符串ps.setString(i, JSONUtil.toJsonStr(parameter));}@Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {//将json字符串转换为任意类型if(rs.getString(columnName).charAt(0)=='{'){return (T) JSONUtil.parseObj(rs.getString(columnName));}return (T)JSONUtil.parseArray(rs.getString(columnName));}@Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return null;}@Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return null;}
}

在xml中使用

添加数据时在需要改变的字段后添加TypeHandler属性，使用自定义的JsonTypeHandler

    <insert id="insert">insert into msg (name, age, height, address, friend)values (#{name}, #{age}, #{height}, #{address,typeHandler=com.jiusi.config.jsonTypeHandler},#{friend,typeHandler=com.jiusi.config.jsonTypeHandler})</insert>

获取数据时在ResultMap里Result上添加typeHandler属性，同样使用自定义的JackonTypeHandler

    <resultMap type="com.jiusi.model.Msg" id="Jackon"><result property="id" column="id"></result><result property="name" column="name"></result><result property="age" column="age"></result><result property="height" column="height"></result><result property="address" column="address" typeHandler="com.jiusi.config.JackonTypeHandler">				</result><result property="friend" column="friend" typeHandler="com.jiusi.config.JackonTypeHandler"></result></resultMap>

但是查询出来的同样是JSONArray和HJSONObject

为什么使用BaseTypeHandler 而不是 TypeHandler

BaseTypeHandler<T>是一个实现了TypeHandler接口的抽象基类，提供了对TypeHandler接口的一些基础实现和默认行为，简化了自定义类型处理器的开发。通过继承BaseTypeHandler，开发者只需要关注具体的转换逻辑，而无需重复实现所有接口方法。

四、结合Redis进行转换

往数据库存储数据的同时将全类名也存入进去

        <dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency>

package com.jiusi.config;import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.springframework.data.redis.serializer.Jackson2JsonRedisSerializer;import java.nio.charset.StandardCharsets;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;public class jsonTypeHandler02<T> extends BaseTypeHandler<T> {Jackson2JsonRedisSerializer<Object> serializer;// 解决序列化乱码问题public jsonTypeHandler02() {       // 指定序列化输入的类型, 即输入到redis的类型serializer = new Jackson2JsonRedisSerializer<>(Object.class);// 指定序列化输出的类型ObjectMapper objectMapper = new ObjectMapper();//JsonAutoDetect.Visibility.ANY 代表所有属性或字段都可以序列化objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);//新版用法//以数组的方式存放到Redis，Class Type 全类名作为为第一个元素，Json字符串为第二个元素。objectMapper.activateDefaultTyping(objectMapper.getPolymorphicTypeValidator(), ObjectMapper.DefaultTyping.NON_FINAL);}@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {//将参数序列化为byts数组然后转成字符串ps.setString(i,new String( serializer.serialize(parameter)));}@Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {//  将字符串反序列化为对象return (T) serializer.deserialize(rs.getString(columnName).getBytes(StandardCharsets.UTF_8));}@Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return null;}@Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return null;}}

将xml中的typeHandler 修改成当前处理器

五、自定义序列化方式

与Redis一样将全类名同时存入数据库

package com.jiusi.config;import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.TypeFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;/*** 自定义序列化方式* @param <T>*/
public class MybatisToJsonConfig<T> {static {DEFAULT_CHARSET = StandardCharsets.UTF_8;}public static final Charset DEFAULT_CHARSET;private final JavaType javaType;private ObjectMapper objectMapper = new ObjectMapper();public MybatisToJsonConfig(Class<T> type) {this.javaType = this.getJavaType(type);}public MybatisToJsonConfig(JavaType javaType) {this.javaType = javaType;}public T deserialize(@Nullable byte[] bytes) throws Exception {try {return this.objectMapper.readValue(bytes, 0, bytes.length, this.javaType);} catch (Exception ex) {throw new Exception("无法读取JSON: " + ex.getMessage(), ex);}}public byte[] serialize(@Nullable Object t) throws Exception {try {return this.objectMapper.writeValueAsBytes(t);} catch (Exception ex) {throw new Exception("无法写入JSON: " + ex.getMessage(), ex);}}public void setObjectMapper(ObjectMapper objectMapper) {Assert.notNull(objectMapper, "'objectMapper' 不能为空");this.objectMapper = objectMapper;}private JavaType getJavaType(Class<?> clazz) {return TypeFactory.defaultInstance().constructType(clazz);}}

package com.jiusi.config;import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.springframework.data.redis.serializer.Jackson2JsonRedisSerializer;import java.nio.charset.StandardCharsets;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;/*** 同样继承BaseTypeHandler但是序列化方式是使用自定义序列化方式* @param <T>*/
public class JsonTypeHandler03<T> extends BaseTypeHandler<T> {private static MybatisToJsonConfig<Object> serializer;static {serializer = new MybatisToJsonConfig<>(Object.class);ObjectMapper objectMapper = new ObjectMapper();//JsonAutoDetect.Visibility.ANY 代表所有属性或字段都可以序列化objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);//以数组的方式存放到Redis，Class Type 全类名作为为第一个元素，Json字符串为第二个元素。objectMapper.activateDefaultTyping(objectMapper.getPolymorphicTypeValidator(), ObjectMapper.DefaultTyping.NON_FINAL);serializer.setObjectMapper(objectMapper);}@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {//使用Redis的序列化将参数序列化为byts数组然后转成字符串try {ps.setString(i,new String( serializer.serialize(parameter)));} catch (Exception e) {e.printStackTrace();}}@Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {//  是使用自定义的Redis反序列化将字符串反序列化为对象try {return (T) serializer.deserialize(rs.getString(columnName).getBytes(StandardCharsets.UTF_8));} catch (Exception e) {e.printStackTrace();}return null;}@Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return null;}@Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return null;}}

将xml中的typeHandler 修改成当前处理器

六、Mybatis-Plus

使用Mybatis-Plus同样可以只需要只需要加两个注解在类上添加@TableName（Value = “表名” , autoResultMap = true）,并且在需要转换的字段上添加@TableField( typeHandler = 处理器)

处理器可以使用上面我们自定义的处理器