mysql从5.7.版本开始支持json列。它本质上仍然是一个字符串，比起直接用varchar来说，它有专门对于json的的检索，修改方法。更加的灵活。
在jdbc规范中，还没json类型的定义。所以对象一般都是用String属性，映射数据库的json列。在存储和读取的时候，需要自己完成json的序列化和反序列化。
在使用MyBatis的框架，可以通过定义TypeHandler来自动完成Json属性的序列化和反序列化。
演示一个Demo这里使用Gson的JsonElement作为对象的Json属性对象。我觉得它比较灵活，可以在JsonObject和JsonArray中随意转换。
整合MyBatis… 略
表结构 & 模型对象 表结构CREATE TABLE `website` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'id',
`name` varchar(255) NOT NULL COMMENT '网站名称',
`properties` json DEFAULT NULL COMMENT '网站属性，这是一个Json列',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
import com.google.gson.JsonElement;
public class WebSite {
// 网站id
private Integer id;
// 网站名称
private String name;
// 网站属性，json
private JsonElement properties;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public JsonElement getProperties() {
return properties;
}
public void setProperties(JsonElement properties) {
this.properties = properties;
}
@Override
public String toString() {
return "WebSite [id=" + id + ", name=" + name + ", properties=" + properties + "]";
}
}
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.apache.ibatis.type.baseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import com.google.gson.JsonElement;
import com.google.gson.JsonParser;
public class JsonElementTypeHandler extends baseTypeHandler {
@Override
public void setNonNullParameter(PreparedStatement ps, int i, JsonElement parameter, JdbcType jdbcType) throws SQLException {
String value = parameter.toString();
if (jdbcType == null) {
ps.setObject(i, value);
} else {
ps.setObject(i, value, jdbcType.TYPE_CODE);
}
}
@Override
public JsonElement getNullableResult(ResultSet rs, String columnName) throws SQLException {
String result = rs.getString(columnName);
return result == null ? null : JsonParser.parseString(result);
}
@Override
public JsonElement getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
String result = rs.getString(columnIndex);
return result == null ? null : JsonParser.parseString(result);
}
@Override
public JsonElement getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
String result = cs.getString(columnIndex);
return result == null ? null : JsonParser.parseString(result);
}
}
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Options;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import io.springboot.jpa.entity.WebSite;
@Mapper
public interface WebSiteMapper {
@Insert("INSERT INTO `website`(`id`, `name`, `properties`) VALUES(#{id}, #{name}, #{properties});")
@Options(useGeneratedKeys = true, keyColumn = "id", keyProperty = "id")
int save(WebSite webSite);
@Select("SELECT * FROM `website` WHERe `id` = #{id};")
WebSite findById(@Param("id") Integer id);
}
private static final Logger LOGGER = LoggerFactory.getLogger(JpaApplicationTest.class);
@Autowired
private WebSiteMapper webSiteMapper;
@Test
@Transactional
@Rollback(false)
public void test () {
WebSite webSite = new WebSite();
webSite.setName("SpringBoot中文社区");
// 初始化properties属性
JsonObject jsonObject = new JsonObject();
jsonObject.addProperty("url", "https://springboot.io");
jsonObject.addProperty("initializr", "https://start.springboot.io");
jsonObject.addProperty("Github", "https://github.com/springboot-community");
webSite.setProperties(jsonObject);
// 存储
this.webSiteMapper.save(webSite);
// 根据id检索
webSite = this.webSiteMapper.findById(webSite.getId());
LOGGER.info("resut={}", new Gson().toJson(webSite));
}
org.mybatis.spring.SqlSessionUtils: Creating a new SqlSession
org.mybatis.spring.SqlSessionUtils: Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@34be7efb]
o.m.s.t.SpringManagedTransaction : JDBC Connection [HikariProxyConnection@885723920 wrapping com.mysql.cj.jdbc.ConnectionImpl@625487a6] will be managed by Spring
i.s.jpa.mapper.WebSiteMapper.save : ==> Preparing: INSERT INTO `website`(`id`, `name`, `properties`) VALUES(?, ?, ?);
i.s.jpa.mapper.WebSiteMapper.save : ==> Parameters: null, SpringBoot中文社区(String), {"url":"https://springboot.io","initializr":"https://start.springboot.io","Github":"https://github.com/springboot-community"}(String)
i.s.jpa.mapper.WebSiteMapper.save : <== Updates: 1
org.mybatis.spring.SqlSessionUtils: Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@34be7efb]
org.mybatis.spring.SqlSessionUtils: Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@34be7efb] from current transaction
i.s.jpa.mapper.WebSiteMapper.findById : ==> Preparing: SELECt * FROM `website` WHERe `id` = ?;
i.s.jpa.mapper.WebSiteMapper.findById : ==> Parameters: 4(Integer)
i.s.jpa.mapper.WebSiteMapper.findById : <== Total: 1
org.mybatis.spring.SqlSessionUtils: Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@34be7efb]
i.s.jpa.test.JpaApplicationTest : resut={"id":4,"name":"SpringBoot中文社区","properties":{"url":"https://springboot.io","Github":"https://github.com/springboot-community","initializr":"https://start.springboot.io"}}
不论是写入还是读取，都无误的对JsonElement完成了编码和解码。
核心只要明白了 TypeHandler的几个方法，不管是Gson, Fastjson, Jackson 甚至是自定义对象，都可以很简单的完成自动映射。
原文：https://springboot.io/t/topic/2455
