JSON File - Java: editing/updating fields values

Question

I have some JSONObject(s) in my workflow, and the same JSONObjects are stored by writting them into a json file.

I would like an efficient way to update the json file, only fields where is needed, with the content of newer JSONObjects instances.

Eg:

On file I have

ObjectOnFile = {key1:val1, key2:val2,...}

In memory I have

ObjectInMemory = {key1:val1_newer, key2:val2_newer,...}

The update will be like:

 if (!(ObjectInMemory.get(key1).equals(ObjectOnFile.get(key1)))
       // update file field value <--- how to?

In general I would like to update the value of every key where its content is newer (different).

Actually my code is:

import org.json.JSONObject;
import com.fasterxml.jackson.databind.ObjectMapper;

ObjectMapper mapper = new ObjectMapper();
Sting key = "key1"; //whatever
JSONObject jo = new JSONObject("{key1:\"val1\", key2:\"val2\"}");
JSONObject root = mapper.readValue(new File(json_file), JSONObject.class);
JSONObject val_newer = jo.getJSONObject(key);
JSONObject val_older = root.getJSObject(key);
if(!val_newer.equals(val_older)){
   root.put(key,val_newer);
/*write back root to the json file...how? */
}

PVR · Accepted Answer · 2016-06-26 19:18:42Z

7

Simply you can do like this:

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

import org.json.JSONException;
import org.json.JSONObject;

import com.fasterxml.jackson.databind.ObjectMapper;


public class Test {

    public static void main(String[] args) throws JSONException, IOException 
    {
        ObjectMapper mapper = new ObjectMapper();
        String key = "key1"; //whatever

        JSONObject jo = new JSONObject("{key1:\"val1\", key2:\"val2\"}");
        //Read from file
        JSONObject root = mapper.readValue(new File("json_file"), JSONObject.class);

        String val_newer = jo.getString(key);
        String val_older = root.getString(key);

        //Compare values
        if(!val_newer.equals(val_older))
        {
          //Update value in object
           root.put(key,val_newer);

           //Write into the file
            try (FileWriter file = new FileWriter("json_file")) 
            {
                file.write(root.toString());
                System.out.println("Successfully updated json object to file...!!");
            }
        }
    }
}

answered Jun 26, 2016 at 19:18

PVR

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3 Comments

GrayFox Over a year ago

Hi PVR, thanks for answer. In this way the write function will rewrite the entire file or just the portion updated?

PVR Over a year ago

Rewrite your whole json in file

Somnath Singh Over a year ago

In this code only one key being checked for newer values what if we want to update all of the keys in updated Object, which can maybe not have some keys

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