Java 8 : Group Object array to Map to return as JSON

Question

我有一个从查询数据库返回的对象二维数组 (Object [][])。我现在想将它映射到分组后可以在 API 调用中返回的对象。

这是我的二维对象数组。

Object [][] dbResult = 
{
  {1, "a", 9, "Content1", "format1", false, true},
  {1, "a", 9, "Content1", "format2", true, false},
  {2, "b", 8, "Content2", "format3", true, false},
  {2, "b", 8, "Content2", "format4", false, false},
  {3, "c", 7, "Content3", "format5", true, true},
  {4, "d", 8, "Content2", "format6", false, true},
  {4, "d", 6, "Content3", "format7", true, true},
  {4, "d", 5, "Content4", "format8", false, false},
  {5, "e", 4, "Content5", "format9", false, true},
  {6, "f", 3, "Content6", "format10", true, false}
};

Here is the legend/key for the index.
[ID, Name, AnotherID, AnotherName, Format, Boolean, Boolean]

我要回去

List<IdName> idsNames;

每个类都应该像这样映射。

class IdName {
    String id;
    String name;
    List<Another> anotherNameList;
}

class Another {
    String anotherId;
    String anotherName;
    List<Format> formatList;
}

class Format {
    String format;
    Boolean isEnabled;
    Boolean isManaged;
}

我尝试使用 Java 8 的 groupingBy 但我无法达到我想要的状态。

示例预期结果:

[
      {
      "id": 1,
      "name": "a",
      "another": [
        {
          "anotherId": 9,
          "anotherName": "Content1",
          "format": [
            {
              "format": "format1",
              "isEnabled": true,
              "isManaged": false
            },
            {
              "format": "format2",
              "isEnabled": true,
              "isManaged": false
            }
          ]
        }
      ]
    }
]

Answer 1

看起来你应该使用 Collectors.collectingAndThen。

首先创建提取器(假设您的类有构造函数和 getter):

// The cast types are just an example. You can Cast/convert the array values to any type you want

IdName extractIdName(Object[] row) {
    return new IdName((String) row[0], (String) row[1], null);
}

Another extractAnother(Object[] row) {
    return new Another((String) row[2], (String) row[3], null);
}

Format extractFormat(Object[] row) {
    return new Format((String) row[4], (boolean) row[5], (boolean) row[6]);
}

然后您将需要合并功能:

List<Another> setFormats(Map<Another, List<Format>> map) {
    return map.entrySet()
              .stream()
              .map(e -> {
                  e.getKey().setFormatList(e.getValue());
                  return e.getKey();
              })
              .collect(toList());
}

List<IdName> setAnothers(Map<IdName, List<Another>> map) {
    return map.entrySet()
              .stream()
              .map(entry -> {
                  entry.getKey().setAnotherNameList(entry.getValue());
                  return entry.getKey();
              })
              .collect(toList());
}

最后这会成功:

// Converting Object[][] to List<IdName>
List<IdName> list = 
      Arrays.stream(dbResult)
            .collect(
                collectingAndThen(
                    groupingBy(this::extractIdName,
                        collectingAndThen(
                            groupingBy(this::extractAnother,
                                mapping(this::extractFormat, toList())),
                            this::setFormats
                        )),                                                             
                    this::setAnothers));