Use custom Typehandler in MyBatis to work with JSON type fields in PostgreSQL

Business extension fields are often stored in the PostgreSQL database using JSON-formatted data, whereas MyBatis defaults to Typehandler that do not implement JSON-type fields, so we typically need to customize the Typehandler of MyBatis.

The following is a simple implementation of the Typehandler for the JSON type field in MyBatis:

 
 
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedTypes;
import org.postgresql.util.PGobject;

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


@MappedTypes({Object.class})
public class JsonTypeHandler extends BaseTypeHandler<Object> {

    private static final PGobject jsonObject = new PGobject();

    @Override
    public void setNonNullParameter(PreparedStatement preparedStatement, int i, Object o, JdbcType jdbcType) throws
            SQLException {
        jsonObject.setType("json");
        jsonObject.setValue(JsonUtil.toJsonString(o));
        preparedStatement.setObject(i, jsonObject);

    }

    @Override
    public Object getNullableResult(ResultSet resultSet, String s) throws SQLException {
        return JsonUtil.fromJson(resultSet.getString(s), Object.class);
    }

    @Override
    public Object getNullableResult(ResultSet resultSet, int i) throws SQLException {
        return JsonUtil.fromJson(resultSet.getString(i), Object.class);
    }

    @Override
    public Object getNullableResult(CallableStatement callableStatement, int i) throws SQLException {
        return JsonUtil.fromJson(callableStatement.getString(i), Object.class);
    }
}
}

In addition to writing Typehandler, the following configuration is required in the XML mapping file:

 <resultMap id="BaseResultMap" type="com.test.entity.EventLog">
        <id column="uuid" jdbcType="VARCHAR" property="uuid"/>
        <result column="payload" jdbcType="OTHER" property="payload" typeHandler="com.test.dao.typehandler.JsonTypeHandler"/>
    </resultMap>
    <insert id="insert" parameterType="com.test.entity.EventLog">
        insert into "test".event_log (uuid,payload)
        values (#{uuid,jdbcType=VARCHAR},#{payload,jdbcType=OTHER,typeHandler=com.test.dao.typehandler.JsonTypeHandler})
    </insert>

When used, the object can be converted to a JSON string and then to the corresponding object, as follows:

        EventLogPayload eventLogPayload = JsonUtil.parser(JsonUtil.toJson(eventLog.getPayload()), EventLogPayload.class);

Use custom Typehandler in MyBatis to work with JSON type fields in PostgreSQL

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