JSON Parsing Tutorial

In this tutorial, we will learn how to parse different types of JSON and concepts regarding JSON such as JSONObject, JSONArray e.t.c.

{
"schema": "http://json.org/example",
"title": "Product",
"description": "A product from catalog",
"type": "object",
"properties": {
"id": {
"description": "The unique identifier for a product",
"type": "integer"
},
"name": {
"description": "Name of the product",
"type": "string"
}
},
"required": ["id", "name"]
}

First of all we will learn how to verify that whether the node is a JSONObject or a JSONArray

JSONArray:

[ – represents that it is a json array node.

JSONObject:

{ – represents that it is a json object node.

Here is the method to parse json and get values inside above json:

//suppose we have above JSON in jsonString
public void parseJson(String jsonString) throws JSONException{
    	
    	//getting whole object in obj1 from jsonString
    	
    	//{
    	//"schema":...
    	//		   ....
    	//		   ....
    	//....,"name"]
    	//}

    	JSONObject obj1=new JSONObject(jsonString);
    	
    	//Getting String values  inside JSONObject obj1 :
    	
    	//String value with key - schema
     	String schema=obj1.getString("schema");
    	//String value with key - title
    	String title=obj1.getString("title");
    	//String value with key - description
    	String description=obj1.getString("description");
    	//String value with key - type
    	String type=obj1.getString("type");
    	
    	System.out.println("Schema : "+schema+" Title : "+title+" Description : "+description+" Type : "+type);
    	
    	// JSONObject values inside obj1 with key - properties
    	JSONObject obj2=obj1.getJSONObject("properties");
    	
    	// JSONObject values inside obj2 with key - id
    	JSONObject obj3=obj2.getJSONObject("id");
    	//String value inside obj3 with key - description
    	String description2=obj3.getString("description");
    	//String value inside obj3 with key - type
    	String type2=obj3.getString("type");
    	
    	System.out.println("Description of JSONObject with key- id : "+description2+" Type of JSONObject with key- id : "+type2);
    	
    	// JSONObject values inside obj2 with key - name
    	JSONObject obj4=obj2.getJSONObject("name");
    	//String value inside obj4 with key - description
    	String description3=obj4.getString("description");
    	//String value inside obj4 with key - type
    	String type3=obj4.getString("type");
    	
    	System.out.println("Description of JSONObject with key- name : "+description3+" Type of JSONObject with key- name : "+type3);
    	
    	
    	//JSONArray value inside obj1 with key - required
    	JSONArray array=obj1.getJSONArray("required");
    	//String values inside JSONArray array
    	for(int i=0;i<array.length();i++){
    		System.out.println(array.getString(i));
    	}
    }

Let’s take another example:

{
    	"name": "Cake",
    	"batters":
    		{
    			"batter":
    				[
    					{ "id": "1001", "type": "Regular" },
    					{ "id": "1002", "type": "Chocolate" },
    					{ "id": "1003", "type": "Blueberry" },
    					{ "id": "1004", "type": "Devil's Food" }
    				]
    		},
    	"topping":
    		[
    			{ "id": 5001, "type": "None" },
    			{ "id": 5002, "type": "Glazed" },
    			{ "id": 5005, "type": "Sugar" },
    			{ "id": 5007, "type": "Powdered Sugar" },
    			{ "id": 5006, "type": "Chocolate with Sprinkles" },
    			{ "id": 5003, "type": "Chocolate" },
    			{ "id": 5004, "type": "Maple" }
    		]
    }
    

Below is the method to parse above JSON:

public void parseJson2(String jsonString2) throws JSONException{
    	JSONObject obj=new JSONObject(jsonString2);
    	String name=obj.getString("name");
    	
    	System.out.println("Name is: "+name);
    	
    	JSONObject obj2=obj.getJSONObject("batters");
    	
    	//Here we get json array inside obj2 with key- batter
    	JSONArray array=obj2.getJSONArray("batter");
    	
    	//Getting json objects inside array
    	for(int i=0;i<array.length();i++){
    		JSONObject obj3=array.getJSONObject(i);
    		//Getting id and type of json objects inside array
    		System.out.println("Id of obj3 : "+obj3.getString("id")+" Type of obj3 : "+obj3.getString("type"));
    	}
    	
    	//Here we get json array inside obj1 with key- topping
    	JSONArray array2=obj.getJSONArray("topping");
    	
    	//Getting json objects inside array
    	for(int i=0;i<array2.length();i++){
    		JSONObject obj4=array2.getJSONObject(i);
    		//Getting id and type of json objects inside array2
    		System.out.println("Id of obj4 at index "+i+" is : "+obj4.getInt("id")+" Type of obj4 at index "+i+" is : "+obj4.getString("type"));
    	}
    	
    }

Moving to another example where we have 100 json objects with same attributes. Here we would not want to get attributes inside every json object by writing same code again and again, so to do that, we will follow a simpler and efficient way:

Note* : This way can also be used when we do not know the key name whose attributes we want to retrieve.

{
        "batchcomplete": "abc",
        "query": {
            "pages": {
                "1": {
                    "pageid": 280636,
                    "title": "Gary Moore"
                },
                "2": {
                    "pageid": 280645,
                    "title": "Tim"
                },
                "3": {
                    "pageid": 280624,
                    "title": "John"
                },
                "4": {
                    "pageid": 280607,
                    "title": "Mary"
                },
                "5": {
                    "pageid": 280626,
                    "title": "Sam"
                },
                .
                .
                .
                "100": {
                    "pageid": 280658,
                    "title": "Mitchell"
                }
            }
        }
    }

Below is the method to get values from above json:

 public void parseJson3(String jsonString3) throws JSONException{
    	JSONObject obj=new JSONObject(jsonString3);
    	String batchcomplete=obj.getString("batchcomplete");
    	
    	System.out.println("Batchcomplete : "+batchcomplete);
    	
    	JSONObject obj2=obj.getJSONObject("query");
    	JSONObject obj3=obj2.getJSONObject("pages");
    	JSONObject obj4=null;
    	//Getting all the keys inside json object with key- pages
    	   Iterator<String> keys= obj3.keys();
    	   while (keys.hasNext()) 
    	  {
    	        String keyValue = (String)keys.next();
    	        obj4 = obj3.getJSONObject(keyValue);
    	        //getting string values with keys- pageid and title
    	        String pageid = obj4.getString("pageid");
    	        String title = obj4.getString("title");
    	        System.out.println("Page id : "+pageid+" Title : "+title);
    	  }

    }
    

Note*: To avoid exceptions you should use below function if you want to check whether a JSONObject or JSONArray exists in the json whose key you are specifying in your code.

jsonobject.has("KEY_NAME");//returns true or false

In case of any queries, please feel free to comment.

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