Java Stream API：高效实现数据分组与嵌套JSON列表转换

public interface Response {
    Long getId();
    String getSData();
    String getSName();
}

// Response接口的实现类，用于模拟数据
public class ResponseImpl implements Response {
    private Long id;
    private String sData;
    private String sName;

    public ResponseImpl(Long id, String sData, String sName) {
        this.id = id;
        this.sData = sData;
        this.sName = sName;
    }

    @Override
    public Long getId() { return id; }
    @Override
    public String getSData() { return sData; }
    @Override
    public String getSName() { return sName; }

    @Override
    public String toString() {
        return "ResponseImpl{" +
               "id=" + id +
               ", sData='" + sData + '\'' +
               ", sName='" + sName + '\'' +
               '}';
    }
}

public class SubData {
    private String sData;
    private String sName;

    public SubData(String sData, String sName) {
        this.sData = sData;
        this.sName = sName;
    }

    public String getSData() { return sData; }
    public String getSName() { return sName; }

    @Override
    public String toString() {
        return "SubData{" +
               "sData='" + sData + '\'' +
               ", sName='" + sName + '\'' +
               '}';
    }
}

import java.util.List;

public class NewResponse {
    private Long id;
    private List<SubData> subDataList;

    public NewResponse(Long id, List<SubData> subDataList) {
        this.id = id;
        this.subDataList = subDataList;
    }

    public Long getId() { return id; }
    public List<SubData> getSubDataList() { return subDataList; }

    @Override
    public String toString() {
        return "NewResponse{" +
               "id=" + id +
               ", subDataList=" + subDataList +
               '}';
    }
}

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class DataAggregator {

    public static void main(String[] args) {
        // 模拟原始数据列表
        List<Response> responses = Arrays.asList(
            new ResponseImpl(1L, "UK,FR", "X"),
            new ResponseImpl(2L, "UK,FR", "Y"),
            new ResponseImpl(4L, "EU", "X"),
            new ResponseImpl(4L, "Others", "O")
        );

        // 步骤一：使用groupingBy和mapping进行分组和映射
        Map<Long, List<SubData>> groupedDataMap = responses.stream()
            .collect(Collectors.groupingBy(
                Response::getId, // 分组键：根据Response对象的ID
                Collectors.mapping(
                    r -> new SubData(r.getSData(), r.getSName()), // 下游收集器：将每个Response映射为SubData
                    Collectors.toList() // 将映射后的SubData对象收集成一个列表
                )
            ));

        System.out.println("--- 步骤一：分组后的Map ---");
        groupedDataMap.forEach((id, subDataList) ->
            System.out.println("ID: " + id + ", SubData List: " + subDataList)
        );
        // 预期输出示例:
        // ID: 1, SubData List: [SubData{sData='UK,FR', sName='X'}]
        // ID: 2, SubData List: [SubData{sData='UK,FR', sName='Y'}]
        // ID: 4, SubData List: [SubData{sData='EU', sName='X'}, SubData{sData='Others', sName='O'}]
    }
}

// ... (接续上面的DataAggregator类)

        // 步骤二