MyBatis对SpringAI聊天记忆存取的处理器（聊天对话以Json存储的）

今天在实现自己的ChatMemory时，数据表设计将与AI的对话数据以JSON格式进行存储。在存储过程很顺利，但是在读取数据时出现了问题，经过观察分析，因为SpringAI的存储的对话集合里面的类型都是不一样的。

所以反序列化后读取对应的字段的时候会框框报错。我的解决办法就是定制MyBatis的字段类型处理器了

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java
复制代码
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.core.type.TypeReference;
import lombok.NoArgsConstructor;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedJdbcTypes;
import org.apache.ibatis.type.MappedTypes;
import org.springframework.ai.chat.messages.*;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;


@MappedJdbcTypes(JdbcType.VARCHAR)
@MappedTypes({List.class})
@NoArgsConstructor
public class MessageTypeHandler extends BaseTypeHandler<List<Message>> {
    private static final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, List<Message> parameter, JdbcType jdbcType) throws SQLException {
        try {
            ps.setString(i, objectMapper.writeValueAsString(parameter));
        } catch (JsonProcessingException e) {
            throw new SQLException("Error converting object to JSON", e);
        }
    }

    @Override
    public List<Message> getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String json = rs.getString(columnName);
        return parseJson(json);
    }

    @Override
    public List<Message> getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String json = rs.getString(columnIndex);
        return parseJson(json);
    }

    @Override
    public List<Message> getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String json = cs.getString(columnIndex);
        return parseJson(json);
    }

    private List<Message> parseJson(String json) {
        List<Message> arrayList = new ArrayList<>();
        if (json == null || json.isEmpty() || "[]".equals(json)) {
            return arrayList;
        }
        try {
            List<LinkedHashMap> list = objectMapper.readValue(json, new TypeReference<>() {});
            for (LinkedHashMap map : list) {
                String type = (String) map.get("messageType");
                MessageType messageType = MessageType.fromValue(type.toLowerCase());
                String message = (String) map.get("text");;
                arrayList.add(switch (messageType) {
                    case SYSTEM -> new SystemMessage(message);
                    case USER -> new UserMessage(message);
                    case ASSISTANT -> new AssistantMessage(message);
                    default -> throw new IllegalArgumentException("Unknown message type: " + type);
                });
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
       return arrayList;
    }
}