Read JSON Key Values at run time by passing keys in Java

SKC
December 30, 2022
287 views
0 votes
2 Answers

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); }
  
  }

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
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"**
basically i am looking for reusable code to pull values based on keys passed, dont want to hardcode any values from JSON.

thank you

Answers

Chosen as BEST ANSWER
- SKC
- January 3, 2023 at 4:40 pm
- 0 votes
0
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;
```

(Edit)

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

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