java - 在android中保存/读取文件

Question

我想保存到 android 中的一个文件，我的一些 arrayList 之后将被删除。我已经有两种从 android 文件写入/读取的方法 here但问题是我希望这两种方法可以做到这一点:

• 第一个方法必须保存 arraylist 的元素，然后如果我再次调用它，它不会将新元素写入同一行，而是写入另一行

  • 第二个必须读取一行(例如，我向方法提供哪一行，它返回该行包含的内容)

文件看起来像这样:

firstelem
secondelem
thridelem

anotherelem
another ..

这可以在 android java 中实现吗？ PS:我不需要数据库。

更新 这是我的方法:

 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;
    }

Answer 1

使用您链接到的保存方法，您可以创建要使用StringBuilder保存的文本:

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();
}

解析同一文件中的内容(再次假设相同长度的列表和字符串输入):

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;
}