Save/Read File in android

Question

I want to save to a file in android , Some of my arrayList that will be deleted after that.I already have two methods to write/read from android file here but the problem is I want the two methods do that:

the first method must save the element of arraylist then if I call it again it will not write the new element in the same line but write it in another line
- The second must read a line (for example I give to the method which line and it returns what the lines contains)

The file looks like that :

firstelem
secondelem
thridelem

anotherelem
another ..

is this possible to do in android java? PS: I don't need database.

Update This is My methods :

 private void writeToFile(String data) {
        try {
            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput("config.txt", Context.MODE_PRIVATE));
            outputStreamWriter.write(data);
            outputStreamWriter.close();
        }
        catch (IOException e) {
            Log.e("Exception", "File write failed: " + e.toString());
        }
    }



    private String readFromFile() {

        String ret = "";

        try {
            InputStream inputStream = openFileInput("config.txt");

            if ( inputStream != null ) {
                InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
                BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
                String receiveString = "";
                StringBuilder stringBuilder = new StringBuilder();

                while ( (receiveString = bufferedReader.readLine()) != null ) {
                    stringBuilder.append(receiveString);
                    // stringBuilder.append("\\n");
                }

                inputStream.close();
                ret = stringBuilder.toString();
            }
        }
        catch (FileNotFoundException e) {
            Log.e("login activity", "File not found: " + e.toString());
        } catch (IOException e) {
            Log.e("login activity", "Can not read file: " + e.toString());
        }

        return ret;
    }

Please show us the code you have so far. It's difficult to make out the exact use cases from your description of the problem and the code should help clear that up. — indivisible, May 29 '14 at 17:19

indivisible · Accepted Answer · 2014-05-29T17:53:53.983

Using the save method you linked to you can create the text to save with a StringBuilder:

public String makeArrayListFlatfileString(List<List<String>> listOfLists)
{
    StringBuilder sb = new StringBuilder();
    if (!listOfLists.isEmpty()) {
        // this assumes all lists are the same length
        int listLengths = listOfLists.get(0).size();
        for (int i=0; i<listLengths; i++)
        {
            for (List<String> list : listOfLists)
            {
                sb.append(list.get(i)).append("\n");
            }
            sb.append("\n");  // blank line after column grouping
        }
    }
    return sb.toString();
}

To parse the contents from that same file (again assuming equal length lists and a String input):

public List<List<String>> getListOfListsFromFlatfile(String data)
{
    // split into lines
    String[] lines = data.split("\\n");
    // first find out how many Lists we'll need
    int numberOfLists = 0;
    for (String line : lines){
        if (line.trim().equals(""))
        {
            // blank line means new column grouping so stop counting
            break;
        }
        else
        {
            numberOfLists++;
        }
    }
    // make enough empty lists to hold the info:
    List<List<String>> listOfLists = new ArrayList<List<String>>();
    for (int i=0; i<numberOfLists; i++)
    {
        listOfLists.add(new ArrayList<String>());
    }
    // keep track of which list we should be adding to, and populate the lists
    int listTracker = 0;
    for (String line : lines)
    {
        if (line.trim().equals(""))
        {
            // new block so add next item to the first list again
            listTracker = 0;
            continue;
        }
        else
        {
            listOfLists.get(listTracker).add(line);
            listTracker++;
        }
    }
    return listOfLists;
}

it's not a homework , but a small project to do this is just a part of my project (and I don't have enough time because of that I asked for help). Thank you for the answer ! — AndroLife, May 29 '14 at 17:34
Ok, in that case, I'll throw in a quick solution for reading too. — indivisible, May 29 '14 at 17:42
Keep in mind that this will not work if the lists are of differing lengths and is not a great solution for large data sets. — indivisible, May 29 '14 at 17:49

Albert Sadowski · Answer 2 · 2014-05-29T17:35:32.007

For writing, just as Illegal Argument states - append '\n':

void writeToFileWithNewLine(String data) {
    try {
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput("config.txt", Context.MODE_PRIVATE));
        outputStreamWriter.write(data + "\n");
        outputStreamWriter.close();
    }
    catch (IOException e) { /* handle exception */ } 
}

For reading (just the idea, in practice you should read the file only once):

String readLine(final int lineNo) {
  InputStream in = new FileInputStream("file.txt");
  ArrayList<String> lines = new ArrayList<String>();
  try {
    InputStreamReader inReader = new InputStreamReader(in);
    BufferedReader reader = new BufferedReader(inReader);

    String line;
    do {
      line = reader.readLine();
      lines.add(line);
    } while(line != null);
  } catch (Exception e) { /* handle exceptions */ }
  finally {
    in.close();
  }

  if(lineNo < lines.size() && lineNo >= 0) {
    return lines.get(lineNo);
  } else {
    throw new IndexOutOfBoundsException();
  }
}

The second method dosen't work but I get the idea thank you ! :) — AndroLife, May 29 '14 at 17:34

Save/Read File in android

2 Answers2