如何根据 java arraylist 中存在的嵌套对象中的元素拆分对象？

Question

我有以下对象的列表（例如，仅显示数组中的一个对象）。如何在 JAVA 中将用户列表拆分为具有相同原始对象的不同对象。我已经给出了从 db 获得的结果，以及在 java 中处理后的预期结果。 正如您在附加的 JSON（第二个 JSON）中看到的结果所期望的那样，除了每个对象中的用户数组列表之外，所有对象都保持不变。我们必须在 users 数组中的所有对象中根据 "parent_user_id" 拆分数组，因此具有相同 "parent_user_id" 的公共对象将作为一个整体在一个对象中。

结果来自数据库：

 [
  {
        "_id" : "63a8808652f40e1d48a3d1d7",
        "name" : "A",
        "description" : null,
        "users" : [
            {
                "id" : "63a8808c52f40e1d48a3d1da",
                "owner" : "John Doe",
                "purchase_date" : "2022-12-25",
                "status" : "active",
                "parent_user_id" : "63a8808c52f40e1d48a3d1da"
            },
            {
                "id" : "63a880a552f40e1d48a3d1dc",
                "owner" : "John Doe 1",
                "purchase_date" : "2022-12-25",
                "parent_user_id" : "63a8808c52f40e1d48a3d1da"
            },
            {
                "id" : "63a880f752f40e1d48assddd"
                "owner" : "John Doe 2",
                "purchase_date" : "2022-12-25",
                "parent_user_id" : "63a8808c52f40e1d48a3d1da"
            },
            {
                "id" : "63a880f752f40e1d48a3d207"
                "owner" : "John Doe 11",
                "dt" : "2022-12-25",
                "status" : "inactive",
                "parent_user_id" : "63a880f752f40e1d48a3d207"
            },
            {
                "id" : "63a880f752f40e1d48agfmmb"
                "owner" : "John Doe 112",
                "dt" : "2022-12-25",
                "status" : "active",
                "parent_user_id" : "63a880f752f40e1d48agfmmb"
            }
            {
                "id" : "63a880f752f40e1d48agggg"
                "owner" : "John SS",
                "dt" : "2022-12-25",
                "status" : "inactive",
                "parent_user_id" : "63a880f752f40e1d48agggg"
            }
            {
                "id" : "63a880f752f40e1d487777"
                "owner" : "John SS",
                "dt" : "2022-12-25",
                "parent_user_id" : "63a880f752f40e1d48agggg"
            }
        ]
    }
]

我在java中需要的结果

[
  {
    "_id": "63a8808652f40e1d48a3d1d7",
    "name": "A",
    "description": null,
    "users": [
      {
        "id": "63a8808c52f40e1d48a3d1da",
        "owner": "John Doe",
        "purchase_date": "2022-12-25",
        "status": "active",
        "parent_user_id": "63a8808c52f40e1d48a3d1da"
      },
      {
        "id": "63a880a552f40e1d48a3d1dc",
        "owner": "John Doe 1",
        "purchase_date": "2022-12-25",
        "parent_user_id": "63a8808c52f40e1d48a3d1da"
      },
      {
        "id": "63a880f752f40e1d48assddd",
        "owner": "John Doe 2",
        "purchase_date": "2022-12-25",
        "parent_user_id": "63a8808c52f40e1d48a3d1da"
      }
    ]
  },
  {
    "_id": "63a8808652f40e1d48a3d1d7",
    "name": "A",
    "description": null,
    "users": [
      {
        "id": "63a880f752f40e1d48a3d207",
        "owner": "John Doe 11",
        "dt": "2022-12-25",
        "status": "inactive",
        "parent_user_id": "63a880f752f40e1d48a3d207"
      }
    ]
  },
  {
    "_id": "63a8808652f40e1d48a3d1d7",
    "name": "A",
    "description": null,
    "users": [
      {
        "id": "63a880f752f40e1d48agfmmb",
        "owner": "John Doe 112",
        "dt": "2022-12-25",
        "status": "active",
        "parent_user_id": "63a880f752f40e1d48agfmmb"
      }
    ]
  },
  {
    "_id": "63a8808652f40e1d48a3d1d7",
    "name": "A",
    "description": null,
    "users": [
      {
        "id": "63a880f752f40e1d48agggg",
        "owner": "John SS",
        "dt": "2022-12-25",
        "status": "inactive",
        "parent_user_id": "63a880f752f40e1d48agggg"
      },
      {
        "id": "63a880f752f40e1d487777",
        "owner": "John SS",
        "dt": "2022-12-25",
        "parent_user_id": "63a880f752f40e1d48agggg"
      }
    ]
  }
]

Answer 1

您可以使用 JSON 库，例如约森做改造。

https://github.com/octomix/josson

反序列化

Josson josson = Josson.fromJsonString(
    "[" +
    "    {" +
    "        "_id": "63a8808652f40e1d48a3d1d7"," +
    "        "name": "A"," +
    "        "description": null," +
    "        "users": [" +
    "            {" +
    "                "id": "63a8808c52f40e1d48a3d1da"," +
    "                "owner": "John Doe"," +
    "                "purchase_date": "2022-12-25"," +
    "                "status": "active"," +
    "                "parent_user_id": "63a8808c52f40e1d48a3d1da"" +
    "            }," +
    "            {" +
    "                "id": "63a880a552f40e1d48a3d1dc"," +
    "                "owner": "John Doe 1"," +
    "                "purchase_date": "2022-12-25"," +
    "                "parent_user_id": "63a8808c52f40e1d48a3d1da"" +
    "            }," +
    "            {" +
    "                "id": "63a880f752f40e1d48assddd"," +
    "                "owner": "John Doe 2"," +
    "                "purchase_date": "2022-12-25"," +
    "                "parent_user_id": "63a8808c52f40e1d48a3d1da"" +
    "            }," +
    "            {" +
    "                "id": "63a880f752f40e1d48a3d207"," +
    "                "owner": "John Doe 11"," +
    "                "dt": "2022-12-25"," +
    "                "status": "inactive"," +
    "                "parent_user_id": "63a880f752f40e1d48a3d207"" +
    "            }," +
    "            {" +
    "                "id": "63a880f752f40e1d48agfmmb"," +
    "                "owner": "John Doe 112"," +
    "                "dt": "2022-12-25"," +
    "                "status": "active"," +
    "                "parent_user_id": "63a880f752f40e1d48agfmmb"" +
    "            }," +
    "            {" +
    "                "id": "63a880f752f40e1d48agggg"," +
    "                "owner": "John SS"," +
    "                "dt": "2022-12-25"," +
    "                "status": "inactive"," +
    "                "parent_user_id": "63a880f752f40e1d48agggg"" +
    "            }," +
    "            {" +
    "                "id": "63a880f752f40e1d487777"," +
    "                "owner": "John SS"," +
    "                "dt": "2022-12-25"," +
    "                "parent_user_id": "63a880f752f40e1d48agggg"" +
    "            }" +
    "        ]" +
    "    }," +
    "    {" +
    "        "_id": "111111111111111111111111"," +
    "        "name": "B"," +
    "        "users": [" +
    "            {" +
    "                "id": "22222222222222222222222"," +
    "                "owner": "John XX"," +
    "                "purchase_date": "2022-12-25"," +
    "                "status": "active"," +
    "                "parent_user_id": "22222222222222222222222"" +
    "            }" +
    "        ]" +
    "    }" +
    "]");
    

转型

JsonNode node = josson.getNode(
    "[]@" + // 1
    ".users" + // 2
    ".group(parent_user_id)" + // 3
    ".map(parent_user_id:, ..._id, ...name, ...description, users:elements)" + // 4
    ".@flatten()"); // 5
System.out.println(node.toPrettyString());

1. 将每个元素转移到单独的分支
2. 前往节点users
3. 分组parent_user_id
4. 删除parent_user_id，退后两步获取_id/name/description，并将elements重命名为users
5. 将所有分支结果合并到一个数组中，然后展平数组

   输出

   [ {
     "_id" : "63a8808652f40e1d48a3d1d7",
     "name" : "A",
     "description" : null,
     "users" : [ {
       "id" : "63a8808c52f40e1d48a3d1da",
       "owner" : "John Doe",
       "purchase_date" : "2022-12-25",
       "status" : "active",
       "parent_user_id" : "63a8808c52f40e1d48a3d1da"
     }, {
       "id" : "63a880a552f40e1d48a3d1dc",
       "owner" : "John Doe 1",
       "purchase_date" : "2022-12-25",
       "parent_user_id" : "63a8808c52f40e1d48a3d1da"
     }, {
       "id" : "63a880f752f40e1d48assddd",
       "owner" : "John Doe 2",
       "purchase_date" : "2022-12-25",
       "parent_user_id" : "63a8808c52f40e1d48a3d1da"
     } ]
   }, {
     "_id" : "63a8808652f40e1d48a3d1d7",
     "name" : "A",
     "description" : null,
     "users" : [ {
       "id" : "63a880f752f40e1d48a3d207",
       "owner" : "John Doe 11",
       "dt" : "2022-12-25",
       "status" : "inactive",
       "parent_user_id" : "63a880f752f40e1d48a3d207"
     } ]
   }, {
     "_id" : "63a8808652f40e1d48a3d1d7",
     "name" : "A",
     "description" : null,
     "users" : [ {
       "id" : "63a880f752f40e1d48agfmmb",
       "owner" : "John Doe 112",
       "dt" : "2022-12-25",
       "status" : "active",
       "parent_user_id" : "63a880f752f40e1d48agfmmb"
     } ]
   }, {
     "_id" : "63a8808652f40e1d48a3d1d7",
     "name" : "A",
     "description" : null,
     "users" : [ {
       "id" : "63a880f752f40e1d48agggg",
       "owner" : "John SS",
       "dt" : "2022-12-25",
       "status" : "inactive",
       "parent_user_id" : "63a880f752f40e1d48agggg"
     }, {
       "id" : "63a880f752f40e1d487777",
       "owner" : "John SS",
       "dt" : "2022-12-25",
       "parent_user_id" : "63a880f752f40e1d48agggg"
     } ]
   }, {
     "_id" : "111111111111111111111111",
     "name" : "B",
     "users" : [ {
       "id" : "22222222222222222222222",
       "owner" : "John XX",
       "purchase_date" : "2022-12-25",
       "status" : "active",
       "parent_user_id" : "22222222222222222222222"
     } ]
   } ]