How to get nested JSON content by key?

Question

I have the following code which I use to download a JSON file from a URL:

static void getPost() throws Exception {
        String webPage = "https://www.reddit.com/r/arabfunny/top.json?limit=100";

        URL url = new URL(webPage);
        URLConnection request = url.openConnection();
        request.setRequestProperty("Content-Type", "application/json; utf-8");
        request.setRequestProperty("User-Agent", "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.4; en-US; rv:1.9.2.2) Gecko/20100316 Firefox/3.6.2");

        JsonParser jp = new JsonParser();
        JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent()));
        JsonObject rootobj = root.getAsJsonObject();
        String imageURL = rootobj.get("data").toString();
        System.out.println(imageURL);
    }

This correctly gets the code but I'm having trouble getting data past the first level, I can use .get("data") and that works as expected but I cannot do .get("data").get("children").

The JSON file can be found here.

Here is the JSON prettyfied.

I want to get a random children where I don't know the number of children. Something like rootobj.get("data").get("children").get(RANDOM).toString();

EDIT:

I really just need a simple solution to get a few parameters from a random children.

I need to get JSON -> data -> children[random item] -> data -> subreddrit (or other final field)

Can anyone show me a basic working example that would give me any final value which I can then modify?

Answer 1

Use Jackson from maven

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.11.2</version>
</dependency>

ObjectMapper objectMapper = new ObjectMapper();
JsonNode node = objectMapper.readValue(<OUTPUT_JSON>,JsonNode.class);
rootobj.get("data").get("children")[INDEX].get(RANDOM).asText();

Answer 2

For me it is easier to define your return object using Pojo and use Gson to deserialize it.

Maven dependency

<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.3</version>
</dependency>

Then define your Result Pojo

public class MyResult{

   public Data data;

   //getter

}

//Data POJO

public class Data{

      public String modhash;
      public Integer dist;
      public List<Children> children; //define your object
      public String after;
      public String before;

      //getters
      
   }

Children POJO

public class Children{
     private String kind;
     private String data; //You can define another Data Object if you want to

     //getters
     
     //toString() method.
}

NOTE: Make sure that JSON field names are exactly the same as POJO field names.

To convert Json string to object:

//get Json String from request : START
InputStream inputStream = request.getInputStream();
       
InputStreamReader isReader = new InputStreamReader(inputStream);
//Creating a BufferedReader object
BufferedReader reader = new BufferedReader(isReader);
StringBuffer sb = new StringBuffer();
String str;
while((str = reader.readLine())!= null){
   sb.append(str);
}
       
String jsonString = sb.toString();
//get Json String from request : END
        
MyResult result = new Gson().fromJson(jsonString,MyResult.class)
result.getData().getChildren()
    .get(0) //get index 0 from list
    .toString();

If you do not want to create too many layer of Pojos, create your own JsonAdapter.

I haven't tested this so there might be some syntax error.

Also you can look at JsonPath library for parsing json file using dot notation.