How to traverse a Json tree and how to find and extract nested elements in Json?

Micro services communicate with each other using RESTful APIs. The response often is a nested Json. If we want to represent the nested json as a pure object then we need a model of the json which will result in a nested object structure. Often the nested object structure is not required; we just need to find and extract a part of an inner element in the json tree. In this post I will show you how we can traverse a Json tree structure and how we can find and extract an element from the tree.

Let's assume the json tree look like this

{
  "ParentElement1": [{
  "Name": "",
  "Description": "",
  "Id": "",
  },
  "BaseEmement1": [],
  "BaseEmement2": [],
  "BaseEmement3": [[{
  "ChildEmement1": "InvalidCell"
  }
  ]],
  "BaseEmement4": [],
  "BaseEmement5": 0,
  "BaseEmement6": false,
  "Messages": [{
  "Type": 1,
  "Text": "my search text"
  }
  ]
  }],
  "ParentElement2": {
  "Timestamp": "2020-10-27 19:13:04.8800000",
  }
 }
 

We will use Json ObjectMapper to read and traverse this json.

The code for this is shown below

import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
 jsonString = "<string format of the above json>";
 ObjectMapper parser =new ObjectMapper();
 try {
 JsonNode jsonNode = parser.readTree(jsonString);
 if(!JsonNode.has("ParentElement1")) {
 return false;
  }
  JsonNode grids = jsonNode.get("ParentElement1");
  for( JsonNode node: grids) {
  if(node.has("Messages")) {
  JsonNode messages = node.get("Messages");
  String text = messages.get(0).get("Text").textValue();
  if(text.contains("my search text")) {
  return true;
  }
  }
  }
  return false;
 } catch(Exception e) {
  logger.error("Could not parse {}", e.getMessage());
 }