如何使用 Gson 将作为字符串存储在文件中的 Point 的 ArrayList 转换为 Arraylist 对象？

Question

I have Arraylist of Points object stored in file as a string. I converted it into string using gson library.

for (final VisionDetRet ret : results) {
    ArrayList<Point> landmarks = ret.getFaceLandmarks();
    Gson gson = new Gson();
    FileWriter writer = new FileWriter(Environment.getExternalStorageDirectory()+"fileName.txt", true);
    gson.toJson(landmarks, writer);
    writer.close();
}

This store list of points in file like

[{"X":90, "Y":120},{"X":50, "Y":121},...][{"X":90, "Y":120},
{"X":50, "Y":121},...][{"X":90, "Y":120},{"X":50, "Y":121},...]

I want to read string from that file and want to convert back into ArrayList.

Answer 1

You just need to create a TypeToken for the ArrayList with the specific generic type defined.

FileReader reader = new FileReader(Environment.getExternalStorageDirectory()+"fileName.txt");

Type listType = new TypeToken<ArrayList<Point>>() { }.getType();

ArrayList<Point> landmarks = new Gson().fromJson(reader, listType);