How to Update JSON value using Java

Question

I have below json, i want to update each and every value of that json but sometimes only one value

{ 
"msgType": "NEW",
"code": "205",
"plid": "PLB52145",
}

I've already tried to update using below code

FileReader reader = new FileReader(filePath);

JSONParser jsonParser = new JSONParser();
JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);

System.out.println(jsonObject);


long id =Long.valueOf((String) idNewObj.get("plid"));
System.out.println(plid);


idNewObj.put("plid",PL809809809);

System.out.println(jsonObject);

value weren't changed , so below solution is given to write the values. it works :) Thanks @papaya — Dhananjay_Khade
– Dhananjay_Khade, Commented Oct 20, 2020 at 10:29

Ayush28 · Accepted Answer · 2020-10-19 17:11:11Z

1

You need to write the updated JSON into the file from where JSON was read. Also, I did not understand your variable assignment so I have updated that as well. Use below code:

FileReader reader = new FileReader(filePath);

JSONParser jsonParser = new JSONParser();
JSONObject jsonObject = (JSONObject) jsonParser.parse(reader);

System.out.println(jsonObject);


long id =Long.valueOf((String) idNewObj.get("plid"));
System.out.println(id);


jsonObject.put("plid",PL809809809);

System.out.println(jsonObject);
FileWriter writer = new FileWriter(filePath, false); //overwrites the content of file
writer.write(jsonObject.toString());
writer.close();

edited Oct 19, 2020 at 17:11

answered Oct 19, 2020 at 7:12

Ayush28

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4 Comments

Ayush28 Over a year ago

Can anyone let me know why my answer got a downvote?

Dhananjay_Khade Over a year ago

first of all don't know who downvoted your anwser....... tried above code, but at writer.write(jsonObject); i'm getting error write(int) in the type OutPutStreamWriter is not applicable for the arguments (JSONObject)

Ayush28 Over a year ago

@Dhananjay_Khade I have edited my answer, this will work! FileWriter.write(...) accepts String argument, hence, changed it to writer.write(jsonObject.toString());

Dhananjay_Khade Over a year ago

Thanks for the answer... i have already done this but it's printing in string format and it's changing the format of json like sequence of json objects...is it fine if sequence is changed ?

AnatolyG · Accepted Answer · 2020-12-10 14:58:56Z

To make transformation/filtering of JSON files, I'd suggest to use stream/event-oriented parsing and generating rather than any object mapping. Just an example, which uses simple and lightweight JSON parser https://github.com/anatolygudkov/green-jelly :

import org.green.jelly.AppendableWriter;
import org.green.jelly.JsonEventPump;
import org.green.jelly.JsonParser;

import java.io.StringWriter;
import java.io.Writer;

public class UpdateMyJson {
    private static final String jsonToUpdate = "{\n" +
            "\"msgType\": \"NEW\",\n" +
            "\"code\": \"205\",\n" +
            "\"plid\": \"PLB52145\",\n" +
            "}";

    public static void main(String[] args) {
        final StringWriter result = new StringWriter();

        final JsonParser parser = new JsonParser();
        parser.setListener(new MyJsonUpdater(result));
        parser.parse(jsonToUpdate); // if you read a file with a buffer,
        // call parse() several times part by part in a loop until EOF
        parser.eoj(); // and then call .eoj()

        System.out.println(result);
    }

    static class MyJsonUpdater extends JsonEventPump {
        private boolean isPlid;

        MyJsonUpdater(final Writer output) {
            super(new AppendableWriter<>(output));
        }

        @Override
        public boolean onObjectMember(final CharSequence name) {
            isPlid = "plid".contentEquals(name);
            return super.onObjectMember(name);
        }

        @Override
        public boolean onStringValue(final CharSequence data) {
            if (isPlid) {
                if ("PLB52145".contentEquals(data)) {
                    return super.onStringValue("PL809809809");
                }
            }
            return super.onStringValue(data);
        }
    }
}

Props:

the file/data doesn't require to be loaded entirely into memory, you can process megs/gigs with no problems
it works much more faster, especially for large files
it's easy to implement any custom type/rule of transformation with this pattern

Both of standard Gson and Jackson libs also provide tokenizers to work with JSON in streaming manner.

UPDATED: JsonEventPump used

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