append data to existing JSON file

Question

I'm using this code:

JSONObject jO = new JSONObject();

try {
    jO.put("item1", true);
    jO.put("item2", value2);
    jO.put("item3", value3);
} catch (JSONException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
}

String json = null;
try {
    json = jO.toString(4);
} catch (JSONException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
}

File jsonFile = new File(nContext.getDir("json", 0), "dashboard.json");
//simple utility method to write the json file
Utils.writeToFile(jsonFile, json);

to have this result:

{
    "item3": "12345",
    "item2": "abcde",
    "item1": true
}

What I want to achieve, on the next run of the same piece of code, is to end with something like:

{
    "pass1": {
        "item3": "12345",
        "item2": "abcde",
        "item1": true
    },
    "pass2": {
        "item3": "67890",
        "item2": "zxcvb",
        "item1": true
    }
}

Or maybe is it better to have this?

{
    "pass1": [
        {
            "item3": "12345",
            "item2": "abcde",
            "item1": true
        }
    ],
    "pass2": [
        {
            "item3": "67890",
            "item2": "zxcvb",
            "item1": true
        }
    ]
}

I know this implies a change in the code to include a "nested" object/array. Which one is better, considering that I'll have to parse the JSON to build a ListView? Any ideas?

first time when your code execute, there will be no "pass1" like tag in json output right? But can't it be added when there is only one child in that object. — Chintan Rathod
– Chintan Rathod, Commented Jun 6, 2013 at 9:46
Yes, I want to add "pass1" on 1st pass also. And then continue with later passes. — dentex
– dentex, Commented Jun 6, 2013 at 9:49
so i think will be your first output something like this -> { "pass1": { "item3": "12345", "item2": "abcde", "item1": true } } — Chintan Rathod
– Chintan Rathod, Commented Jun 6, 2013 at 9:52

dentex · Accepted Answer · 2014-05-26 07:46:52Z

2

I found the solution, thanks to the comments by other users and to a "retired" answer, not present here anymore. Maybe it was my fault not being clear.

public void addEntryToJsonFile(Context ctx, String id, String name, String size) {

    // parse existing/init new JSON 
    File jsonFile = new File(ctx.getDir("my_data_dir", 0), "my_json_file.json");
    String previousJson = null;
    if (jsonFile.exists()) {
        try {
            previousJson = Utils.readFromFile(jsonFile);
        } catch (IOException e) {
            e.printStackTrace();
        }
    } else {
        previousJson = "{}";
    }

    // create new "complex" object
    JSONObject mO = null;
    JSONObject jO = new JSONObject();

    try {
        mO = new JSONObject(previousJson);
        jO.put("completed", true);
        jO.put("name", name);
        jO.put("size", size);
        mO.put(id, jO); //thanks "retired" answer
    } catch (JSONException e) {
        e.printStackTrace();
    }

    // generate string from the object
    String jsonString = null;
    try {
        jsonString = mO.toString(4);
    } catch (JSONException e) {
        e.printStackTrace();
    }

    // write back JSON file
    Utils.writeToFile(jsonFile, jsonString);

}

edited May 26, 2014 at 7:46

answered Jun 6, 2013 at 17:09

dentex

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3 Comments

nawlrus Over a year ago

can you please explain what the line: mO.put(String.valueOf(id), jO); means? What is the id variable and what is this line doing?

dentex Over a year ago

Hi. Answer edited. [the two methods from Utils read and write a file from a string.]

dentex Over a year ago

Anyway, the line mO.put(id, jO) adds the "nested" object jO to the base object mO. You can see a reference for this scheme into the question above.

njzk2 · Accepted Answer · 2013-06-06 10:17:30Z

1

Edited after dentex comment

Read your file
Parse the root Json object
If the root object not is already a complex object
1. Create a new root object
2. put your root object in it
put your second object in the root object
Write bnack your file

in pseudo code:

oldJson = ParseJsonFromFile()
newJson = {"item1": true, "item2": "abcde" ...}
JSONObject root;
if (oldJson.hasKey("pass1") {
    root = oldJson
} else {
    root = new JSONObject()
    root.add("pass1", oldJson)
}
root.add("pass" + root.getSize() + 2, newJson)
WriteJsonToFile(root)

edited Jun 6, 2013 at 10:17

answered Jun 6, 2013 at 10:00

njzk2

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3 Comments

dentex Over a year ago

Yes, this is what I meant. The only difference is that on every pass I have to append ONE new object to an existing json file. Ending with two objects, before, was just an example. ;)

njzk2 Over a year ago

the difficulty, then, is that on your first pass you have a simple object, and after the second pass, you have a complex object.

dentex Over a year ago

thanks @njzk2 for your efforts. Maybe I was not clear enough. My sequence should be 1. parse json file (1st time ever it will be empty); 2. put one "complex" object from every pass; 3. write back the Json file every time. ;)

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