JSON file Creation and adding nodes to JSON Tree type structure

Question

I write an application which creates a JSON File following the below structure:

{
  identifier:"id",
label:"name",
items:[
  {
     id:"ROOT",
     name:"Parent1",
     type:"ROOT",
     children:[
        {
           _reference:"CHILD1"
        }
     ]
  },
  {
     id:"CHILD1",
     name:"Parent1-Child1",
     type:"Child",
     children:[
        {
           _reference:"CHILD2"
        }
     ]
  },
  {
     id:"CHILD2",
     name:"Child1-Child2",
     type:"Child",
     children:[
        {
           _reference:"Child3"
        },
        {
           _reference:"Child4"
        }
     ]
  },
  {
     id:"Child3",
     name:"Child2-Child3",
     type:"GrandChild"
  },
  {
     id:"Child4",
     name:"Child2-Child4",
     type:"GrandChild"
  },

]
}

So my application actually gets following data for each node of this JSON Tree

PID-- It to which i have to attach the child node CID-- ID of Child Node CNAME-- Child Node Name CTYPE-- Child Type

So currently what i am doing is searching the PID in the json file through iterating ( on file system) and once i find the String which has id=PID,i append a Child Ref to that Node

    {
       _reference:"CHILD-NEXT"
    }

and then after this line adding the whole new child node

{
 id:"CHILD-NEXT",
 name:"Parent1-ChildNext",
 type:"Child",
},

But this is very inefficient solution because of iterating the file every time to search the parent node and appending/inserting the child.

So i am looking for a kind of solution in which i just create this JSON structure in memory and when i am done with adding all the nodes then i can write it to the file. I am doing this in JAVA,so i am looking for some existing JSON Libraries which i can use to fulfil this requirement.

Please comment if you need any other information of the above explanation is not clear.

Answer 1

You can use the org.json library to do this.

You first need to read your json file into a JSONObject which is basically made up of key/value pairs and arrays. You can then loop over the items in the object, look for a pid and add a new child.

Here is some sample code to get you started:

//read file        
BufferedReader in = new BufferedReader(new FileReader("path/json.txt"));
String line;
StringBuilder sb = new StringBuilder();
while((line =in.readLine()) != null){
    sb.append(line);
}
in.close();


//create a json object
JSONObject json = new JSONObject(sb.toString());

//pid to search for
String pid = "XXX";

//loop over the items array and look for pid
JSONArray items = json.getJSONArray("items");
for(int i = 0 ; i < items.length(); i++){
    JSONObject item = items.getJSONObject(i);
    String id = item.getString("id");
    if(pid.equals(id)){

        //get the children
        JSONArray children;
        if(item.has("children")){
            children = item.getJSONArray("children");    
        }
        else{
            children = new JSONArray();
            item.put("children", children);
        }

        //append a new child ref to the children
        JSONObject ref = new JSONObject();
        ref.put("_reference", "CHILD-NEXT");
        children.put(ref);

        //create a new child node
        JSONObject newItem = new JSONObject();
        newItem.put("id", "CHILD-NEXT");
        newItem.put("name", "Parent1-ChildNext");
        newItem.put("type", "Child");
        items.put(newItem);
    }
}

Answer 2

From JSON.org you have JSON in Java that will provide you an in-memory JSON representation that you can manipulate and then write.

This StackOverflow question has a whole list of JSON libraries for Java, including google-gson , JSONlib , FlexJSON , Jackson , json-simple , and yet more on this blog review .

Depending on whether you are focused on full-featured, lightweight, or fast, you may find one or the other more suited to your needs.