Mask value of selected key in JSON

Question

I have JSON request and response, I want to print the JSONs in the log, but there are some secured fields which I want to avoid to print in the log, I am trying to mask fields keys: example:

before masking:

  {"username":"user1","password":"123456","country":"US","creditCardNumber":"1283-1238-0458-3458"}

after masking

{"username":"user1","password":"XXXXXX","country":"US","creditCardNumber":"XXXXXX"}

I am using java Gson lib, please help me to do that

EDIT

I want to pass the keys dynamically, so in function a I want to mask these fields, but in function b different fields.

Answer 1

I think you should exclude that fields from log. Below is a simple example using Gson and @Expose annotation.

public static void main(String[] args) throws IOException {
    String json = "{\"username\":\"user1\",\"password\":\"123456\",\"country\":\"US\",\"creditCardNumber\":\"1283-1238-0458-3458\"}";

    Gson gson = new Gson();
    User user = gson.fromJson(json, User.class);

    System.out.println(gson.toJson(user));

    Gson gsonExpose = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
    System.out.println(gsonExpose.toJson(user));
}

public class User {
    @Expose
    private String username;
    private String password;
    @Expose
    private String country;
    private String creditCardNumber;
}

Output will be:

{"username":"user1","password":"123456","country":"US","creditCardNumber":"1283-1238-0458-3458"}
{"username":"user1","country":"US"}

Another solution using Reflection:

public static void main(String[] args) throws IOException {
    String json = "{\"username\":\"user1\",\"password\":\"123456\",\"country\":\"US\",\"creditCardNumber\":\"1283-1238-0458-3458\"}";

    Gson gson = new Gson();
    User user = gson.fromJson(json, User.class);

    List<String> fieldNames = Arrays.asList("password", "creditCardNumber");
    System.out.println(mask(user, fieldNames, "XXXXXXX"));
}

public static String mask(Object object, List<String> fieldNames, String mask) {
    Field[] fields = object.getClass().getDeclaredFields();
    for (int i = 0; i < fields.length; i++) {
        if (fieldNames.contains(fields[i].getName())) {
            try {
                fields[i].setAccessible(true);
                if (fields[i].get(object) != null) {
                    fields[i].set(object, mask);
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
    Gson gson = new Gson();

    return gson.toJson(object);
}