I am trying to PARSE Json and pull values based on input key. JSON structure is not same every time below is sample JSON structure and JSON starts and ends with [] and some time {}

[
    {
        "id": "0001",
        "type": "donut",
        "name": "Cake",
        "ppu": 0.55,
        "days": {
            "weekdays": "Friday",
            "weekends": "Sunday",
        },
        "batters": {
            "batter": [
                {
                    "id": "1001",
                    "type": "Regular"
                },
                {
                    "id": "1002",
                    "type": "Chocolate"
                },
            ]
        },
        "topping": [
            {
                "id": "5001",
                "type": "None"
            },
            {
                "id": "5002",
                "type": "Glazed"
            },
        ]
    }
]

{
        "id": "0001",
        "type": "donut",
        "name": "Cake",
        "ppu": 0.55,
        "days": {
            "weekdays": "Friday",
            "weekends": "Sunday",
        },
        "batters": {
            "batter": [
                {
                    "id": "1001",
                    "type": "Regular"
                },
                {
                    "id": "1002",
                    "type": "Chocolate"
                },
            ]
        },
        "topping": [
            {
                "id": "5001",
                "type": "None"
            },
            {
                "id": "5002",
                "type": "Glazed"
            },
        ]
    }

i tried below code

import org.json.simple.*;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

    public static void main(String[] args) throws IOException, Exception {

        File InputFolder = new File(System.getProperty("user.dir")   "//Files//new.json");

        JsonElementFromFile(InputFolder,"name");        
    }

public static void JsonElementFromFile(File FilePath, String key) throws IOException, Exception {
  
   JSONParser parser = new JSONParser();
   FileReader reader = new FileReader(FilePath);
   JSONArray obj = (JSONArray) parser.parse(reader);  
   for (Object o : obj) { 
      JSONObject json = (JSONObject) o; 
      String jsonKeyValue = (String)json.get(key).toString(); 
      System.out.println(key   " : "   jsonKeyValue); }
  
  }

1. above code works when JSON data start with "[" but not working if it start with "{" , irrespective of any structure I should be able to get value
2. i am able to pull only value from first object keys "id","type","name","ppu" but when i pass key as "days.weekdays" it is not pulling. even if i have more arrays and objectsi should be able to pull just by passing path of key, ex: "batters.batter[0].id" or "batters.batter[1].type"**
3. basically i am looking for reusable code to pull values based on keys passed, dont want to hardcode any values from JSON.

thank you

CodePudding user response：

If you don't want to hardcode for different JSON structure, the solution is to use JSON query library.

https://github.com/octomix/josson

Deserialize Array

Josson array = Josson.fromJsonString(
    "["  
    "    {"  
    "        \"id\": \"0001\","  
    "        \"type\": \"donut\","  
    "        \"name\": \"Cake\","  
    "        \"ppu\": 0.55,"  
    "        \"days\": {"  
    "            \"weekdays\": \"Friday\","  
    "            \"weekends\": \"Sunday\""  
    "        },"  
    "        \"batters\": {"  
    "            \"batter\": ["  
    "                {"  
    "                    \"id\": \"1001\","  
    "                    \"type\": \"Regular\""  
    "                },"  
    "                {"  
    "                    \"id\": \"1002\","  
    "                    \"type\": \"Chocolate\""  
    "                }"  
    "            ]"  
    "        },"  
    "        \"topping\": ["  
    "            {"  
    "                \"id\": \"5001\","  
    "                \"type\": \"None\""  
    "            },"  
    "            {"  
    "                \"id\": \"5002\","  
    "                \"type\": \"Glazed\""  
    "            }"  
    "        ]"  
    "    },"  
    "    {"  
    "        \"batters\": {"  
    "            \"batter\": ["  
    "                {"  
    "                    \"id\": \"1003\","  
    "                    \"type\": \"Special\""  
    "                },"  
    "                {"  
    "                    \"id\": \"1004\","  
    "                    \"type\": \"DarkChocolate\""  
    "                }"  
    "            ]"  
    "        }"  
    "    }"  
    "]");

Deserialize Object

Josson object = Josson.fromJsonString(
    "{"  
    "    \"id\": \"0001\","  
    "    \"type\": \"donut\","  
    "    \"name\": \"Cake\","  
    "    \"ppu\": 0.55,"  
    "    \"days\": {"  
    "        \"weekdays\": \"Friday\","  
    "        \"weekends\": \"Sunday\""  
    "    },"  
    "    \"batters\": {"  
    "        \"batter\": ["  
    "            {"  
    "                \"id\": \"1001\","  
    "                \"type\": \"Regular\""  
    "            },"  
    "            {"  
    "                \"id\": \"1002\","  
    "                \"type\": \"Chocolate\""  
    "            }"  
    "        ]"  
    "    },"  
    "    \"topping\": ["  
    "        {"  
    "            \"id\": \"5001\","  
    "            \"type\": \"None\""  
    "        },"  
    "        {"  
    "            \"id\": \"5002\","  
    "            \"type\": \"Glazed\""  
    "        }"  
    "    ]"  
    "}");

Query

System.out.println(array.getString("batters.batter[0].id"));       // 1001
System.out.println(object.getString("batters.batter[0].id"));      // 1001
System.out.println(array.getString("batters.batter[1].type"));     // Chocolate
System.out.println(object.getString("batters.batter[1].type"));    // Chocolate
System.out.println(array.getString("[0].batters.batter[1].id"));   // 1002
System.out.println(array.getString("[1].batters.batter[1].type")); // DarkChocolate
System.out.println(array.getString("batters.batter[3].type"));     // DarkChocolate

CodePudding user response：

i found easy way for this question. using com.fasterxml.jackson , we can pull any any value from JSON ,

enter code here
 filepath= place where file stored
 nodepath= path of node 
    File File = new File(filePath);
    ObjectMapper objectMapper = new ObjectMapper();
    JsonNode jsonTree = objectMapper.readTree(File);
    String value = jsonTree.at(nodepath).asText();
    return value;