Java - Get list of id's from JSON with a variable depth

I have a JSON file with a fluctuating depth and each node (different depth). So it's built like a General tree :

And here is a sample json (not the real one but a mock file but the structure remains the same) :

{
  "arbre" : {
    "children" : [
      {
        "id" : 1,
        "children" : [
          {
            "id" : 3,
            "children" : [
              {
                "id" : 6,
                "children" : []
              }
            ]
          },
          {
            "id" : 4,
            "children": []
          },
          {
            "id" : 5,
            "children": []
          }
        ]
      },
      {
        "id" : 2,
        "children" : [
          {
            "id" : 7,
            "children" : 
            [
              {
                "id" : 8,
                "children" : [
                  {
                    "id" : 9,
                    "children" : []
                  }
                ]
              },
              {
                "id" : 10,
                "children" : [
                  {
                    "id" : 11,
                    "children" : []
                  }
                ]
              }
            ]
          }
        ]
      }
    ]
  }
}

I'm trying to build multiple list of id for each subtrees, so for exemple I need :

• 1, 3, 6
• 1, 4
• 1, 5
• 2, 7, 8, 9
• 2, 7, 10, 11

I previously developped a routine that traverse the entire tree (recursive) using jackson and don't know if I can adapt it to this use case.

Here it is :

/**
     * getJSONNode: not return value, recursive function that will browse (uses functionalities and objects of the com.fasterxml.jackson library)
     * 
     * 
     * {talendTypes} String, JsonNode
     * 
     * {Category} User Defined
     * 
     * {param} JsonNode(jNode) input: the function will check if the node is an array of object and will process and keep iterate until it reaches the bottom of the tree
     * {param} string(filepath) input: The string is a path to a directory where the temp files will be stored
     * 
     * {example} getJSONNode(jNode, "/test/") # Files will be generated in the directory /test/
     */
    public static void getJSONNode(JsonNode jNode, String filepath) throws IOException {
    	//System.out.println("Get Node");
    	JsonNode tempNoded = jNode.get("children");
    	if(tempNoded.isArray()) {
    		for(int i = 0; i < tempNoded.size(); i++) {
    			System.out.println("Name : " + tempNoded.get(i).get("name"));
    			System.out.println("Title : " + tempNoded.get(i).get("title"));
    			System.out.println("Title : " + tempNoded.get(i).get("id"));
    			System.out.println("================== Writing file ===================");
    			String id = tempNoded.get(i).get("id").toString();
    			String name = tempNoded.get(i).get("name").toString();
    			String title = tempNoded.get(i).get("title").toString();
    			String color = tempNoded.get(i).get("color").toString();
    			String order = tempNoded.get(i).get("order").toString();
    			String parentId = tempNoded.get(i).get("parentId").toString();
    			String persons = tempNoded.get(i).get("persons").toString();
    			String profils = tempNoded.get(i).get("profils").toString();
    			String paramNoeud = tempNoded.get(i).get("paramNoeud").toString();
    			String description = tempNoded.get(i).get("description").toString();
    			// disable not present in all dimensions so not usable
    			//String disabled = tempNoded.get(i).get("disabled").toString();
    			String oldId = tempNoded.get(i).get("oldId").toString();
    			
    			String str = id + ";" + name + ";" + title + ";" + color + ";" + order + ";" + parentId + ";" + persons + ";" + profils + ";" + paramNoeud + ";" + description + ";" + oldId;
    			byte[] strToBytes = str.getBytes();
    			
    			String filename = (name + "_" + order + ".csv").replaceAll("\"", "");
    			
    			File file = new File(filepath + filename);
    			file.getParentFile().mkdirs();
    			file.createNewFile();    			
    			FileOutputStream outputStream = new FileOutputStream(filepath + filename);
    			
    			outputStream.write(strToBytes);
    			outputStream.close();
    			
    			getJSONNode(tempNoded.get(i), filepath);
    		}
    		
    	}
    }

So is there a method to build those lists and modify my routine to do it or something else (another routine, ...)

Thanks

I would suggest a recursive solution that keeps track of current subtree:

publi List<List<String>> getSubtrees(JsonNode childrenNode, List<String> currentSubtree) {
    ArrayList<List<String>> subtrees = new ArrayList<>();

    if (childrenNode.isEmpty()) {
        subtrees.add(currentSubtree);
    } else {
        for (JsonNode node : childrenNode) {
            String id = node.get("id").asText();
            JsonNode children = node.get("children");
            List<String> childSubtree = new ArrayList<>(currentSubtree);
            childSubtree.add(id);

            subtrees.addAll(getSubtrees(children, childSubtree));
        }
    }

    return subtrees;
}

call it as

List<List<String>> subtrees = getSubtrees(children, List.of());

where children is an array node of top level children, in your case it's a arbre -> children json node. That's an example, pay attention to type/null checks.

With the solution in the (accpeted) answer (https://stackoverflow.com/a/76456855/14707253)

I made a few modifications but the solution in itself worked so here is the final code : Function

public List<List<String>> getSubtrees(JsonNode childrenNode, List<String> currentSubtree) {
ArrayList<List<String>> subtrees = new ArrayList<>();
if (childrenNode.size() == 0) {
subtrees.add(currentSubtree);
} else {
for (int i = 0; i < childrenNode.size(); i++) {
//System.out.println(childrenNode.get(i).toString());
String id = childrenNode.get(i).get("id").toString();
//System.out.println(id);
JsonNode children = childrenNode.get(i).get("children");
List<String> childSubtree = new ArrayList<>(currentSubtree);
childSubtree.add(id);
//System.out.println(childSubtree.toString());
subtrees.addAll(getSubtrees(children, childSubtree));
}
}
//System.out.println(subtrees.size());
return subtrees;
} 

And the call of the function :

public List<List<String>> preProcessGetSubtrees(String tree) throws JsonProcessingException, IOException {
if(!isNullorEmpty(tree)) {
List<String> currentSubtree = new ArrayList<>();
ObjectMapper objMapper = new ObjectMapper();
System.out.println("=========================== PLANETE TREE PROCESSING ========================");
//List<List<String>> subtrees = 
List<List<String>> subtrees = getSubtrees(objMapper.readTree(tree).get("arbre").get("children"), currentSubtree);
System.out.println("=========================== PLANETE TREE PROCESSED ========================");
return subtrees;
} else {
System.out.println("============================================================================");
System.out.println("==================== WARNING THE TREE IS NOT VALID =========================");
System.out.println("============================================================================");
return null;
}