Write ArrayList of custom objects to File

Question

I have an ArrayList which contains custom Service objects. I want to write the whole ArrayList to a File and be able to read it afterwards.

I tried Gson for that, but it

Answer 1

I would recommend using serialization for such an operation. You can implement Java's Serializable interface and you are then able to deflate your objects into a .ser file and then inflate them back from that very file to call the methods you need from them.

Here is a nice tutorial regarding Serialization - http://www.tutorialspoint.com/java/java_serialization.htm

Answer 2

With little tweaks your json approach works fine. However the solution by Booch would be the ideal recommendation for these kind of requirements.

Since you are appending to a file the below methods will append the objects to file and on reading it will read all previously written list and make it to a single list. Since services is a global variable you should consider initializing it or clearing it before read method to avoid duplicates.

public int saveListToFile() {
    String filename = "service_entries";
    File file = new File(getFilesDir(), filename);
    try {
        BufferedWriter buffWriter = new BufferedWriter(new FileWriter(file, true));
        Gson gson = new Gson();
        Type type = new TypeToken<List<Service>>() {}.getType();
        String json = gson.toJson(services, type);
        buffWriter.append(json);
        buffWriter.newLine();
        buffWriter.close();
    } catch (IOException e) {
        return -1;
    }
    return 0;
}

public int readCurrentList() {
    String filename = "service_entries";
    File file = new File(getFilesDir(), filename);
    try {
        BufferedReader buffReader = new BufferedReader(new FileReader(file));
        String line;
        Gson gson = new Gson();
        Type type = new TypeToken<List<Service>>() {}.getType();
        while ((line = buffReader.readLine()) != null) {
            services.addAll(gson.fromJson(line, type));
        }
        buffReader.close();
    } catch (IOException e) {
        return -1;
    }
    return 0;
}