retrieving JSONObject from a file

Question

I wanted to store JSONObject in a file. For the purpose I converted the Object to string and then stored it in a file. The code that I used is :

String card_string =  card_object.toString();
//card_object is the JSONObject that I want to store.

f = new File("/sdcard/myfolder/card3.Xcard");
//file 'f' is the file to which I want to store it.

FileWriter  fw = new FileWriter(f);
fw.write(card_string);
fw.close();

The code works as I want it. Now I want to retrieve that object back from the File. How should I do it? I am getting confused on what to use to read the file ? an InputStream or a FileReader or BufferedReader or what. I am new to JAVA / android development.

please help. A detailed explanation in simple words regarding what I/O functions to be used in different scenarios (like this) is welcome. I have had a look at documentation but your suggestions are welcome.

Answer 1

You can use this code to read file.

BufferedReader input = null;
try {
    input = new BufferedReader(new InputStreamReader(
            openFileInput("jsonfile")));
    String line;
    StringBuffer content = new StringBuffer();
    char[] buffer = new char[1024];
    int num;
    while ((num = input.read(buffer)) > 0) {
        content.append(buffer, 0, num);
    }
        JSONObject jsonObject = new JSONObject(content.toString());

}catch (IOException e) {...}

Then you can use your jsonObject:

To get a specific string from JSON Object

String name = jsonObject.getString("name"); 

To get a specific int

int id = jsonObject.getInt("id"); 

To get a specific array

JSONArray jArray = jsonObject.getJSONArray("listMessages"); 

To get the items from the array

JSONObject msg = jArray.getJSONObject(1);
int id_message = msg.getInt("id_message");

Answer 2

Use could use a BufferedReader and FileReader:

File file = new File("/sdcard/myfolder/card3.Xcard");
StringBuilder text = new StringBuilder();
BufferedReader br = null;

try {
    br = new BufferedReader(new FileReader(file));
    String line;

    while ((line = br.readLine()) != null) {
        text.append(line);
        text.append('\n');
    }
} catch (IOException e) {
    // do exception handling
} finally {
    try { br.close(); } catch (Exception e) { }
}

In addition I'd propose that you use Environment.getExternalStorageDirectory(); for building up the path. That's less device specific.

Cheers!