如何有效地获取json响应的特定位？

Question

Im requesting data from instagram api when I search for any tag. In return I get a massive chunk of json data corresponding to like 20 pictures. The response below is the chunk I used to generate my pojos online

{
  "pagination":  {
    "next_max_tag_id": "1193052000552992097",
    "deprecation_warning": "next_max_id and min_id are deprecated for this endpoint; use min_tag_id and max_tag_id instead",
    "next_max_id": "1193052000552992097",
    "next_min_id": "1193052554319844057",
    "min_tag_id": "1193052554319844057",
    "next_url": "https://api.instagram.com/v1/tags/cats/media/recent?access_token=631477962.1fb234f.f7c5cda97c7f4df983b1c764f066ed37&max_tag_id=1193052000552992097"
  },
  "meta":  {
    "code": 200
  },
  "data":  [
     {
      "attribution": null,
      "tags":  [
        "cats",
        "caseworker",
        "homestuck"
      ],
      "type": "image",
      "location": null,
      "comments":  {
        "count": 0,
        "data":  []
      },
      "filter": "Normal",
      "created_time": "1456442969",
      "link": "https://www.instagram.com/p/BCOkvoim1LZ/",
      "likes":  {
        "count": 0,
        "data":  []
      },
      "images":  {
        "low_resolution":  {
          "url": "https://scontent.cdninstagram.com/t51.2885-15/s320x320/e35/12729405_224148847934280_1450226662_n.jpg?ig_cache_key=MTE5MzA1MjU1NDMxOTg0NDA1Nw%3D%3D.2",
          "width": 320,
          "height": 320
        },
        "thumbnail":  {
          "url": "https://scontent.cdninstagram.com/t51.2885-15/s150x150/e35/12729405_224148847934280_1450226662_n.jpg?ig_cache_key=MTE5MzA1MjU1NDMxOTg0NDA1Nw%3D%3D.2",
          "width": 150,
          "height": 150
        },
        "standard_resolution":  {
          "url": "https://scontent.cdninstagram.com/t51.2885-15/s640x640/sh0.08/e35/12729405_224148847934280_1450226662_n.jpg?ig_cache_key=MTE5MzA1MjU1NDMxOTg0NDA1Nw%3D%3D.2",
          "width": 640,
          "height": 640
        }
      },
      "users_in_photo":  [],
      "caption":  {
        "created_time": "1456442969",
        "text": "Bitch! I'm fabulous! That's my case worker..she is obsessed with cats\n\n#cats #caseworker #homestuck",
        "from":  {
          "username": "strider_inc",
          "profile_picture": "https://scontent.cdninstagram.com/t51.2885-19/s150x150/12558836_953196128050469_1739102_a.jpg",
          "id": "2322171747",
          "full_name": "WE All 4EVER KAWAII TRASH GODS"
        },
        "id": "1193052563471815092"
      },
      "user_has_liked": false,
      "id": "1193052554319844057_2322171747",
      "user":  {
        "username": "strider_inc",
        "profile_picture": "https://scontent.cdninstagram.com/t51.2885-19/s150x150/12558836_953196128050469_1739102_a.jpg",
        "id": "2322171747",
        "full_name": "WE All 4EVER KAWAII TRASH GODS"
      }
    }

So when I do that I get like 10-12 different pojo classes into which I should map this data. Now firstly...Im just trying that out and Im 100% Ill have some problem mapping them I mean gson will do it for me but i dont know if there are any more that I would need etc.

but most importantly my app only needs the low standard url pictures all the other information is useless for me.

Ofcourse, I know one way to do it which is to convert the whole thing into a string and parse the whole string through multiple times looking for key words etc and making images etc. I dont want to do that because its ugly. It works but I want a concise way of doing that at the same time without mapping completely.

Answer 1

Using Gson's JsonParser class, you can parse your JSON into a tree of JsonElements , and then extract just the data that you need.

For example, in order to print out all the low resolution URLs, you could use the following code:

String json = "...";

JsonParser parser = new JsonParser();
JsonObject object = parser.parse(json).getAsJsonObject();
JsonArray data = object.getAsJsonArray("data");

for (JsonElement element : data) {
    JsonObject images = element.getAsJsonObject().getAsJsonObject("images");
    JsonObject lowResolution = images.getAsJsonObject("low_resolution");
    String url = lowResolution.getAsJsonPrimitive("url").getAsString();
    System.out.println(url);
}

Using your example JSON, this would print:

https://scontent.cdninstagram.com/t51.2885-15/s320x320/e35/12729405_224148847934280_1450226662_n.jpg?ig_cache_key=MTE5MzA1MjU1NDMxOTg0NDA1Nw%3D%3D.2