{
  "firstName": "Saurabh",
  "lastName": "Gupta",
  "address": {
    "addressLine1": "Noida City Center",
    "city": "Noida",
    "state": "UP",
    "pincode": "India",
    "country": "20310"
  },
  "creditCardDetail": {
    "cardNumber": "1234567890123456",
    "cvv": "123",
    "expDate": "12/90"
  }
}

package com.mask.json;

import java.io.IOException;
import java.lang.reflect.Field;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Stream;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class MaskJSONTest {
	static Set fieldSet = new HashSet();
	static List fieldNames = Arrays.asList("cardNumber", "cvv", "expDate");

	public static void main(String[] args) throws IOException {
		StringBuilder contentBuilder = new StringBuilder();
		try (Stream stream = Files.lines(
				Paths.get(
						"D:\\Saurabh Gupta\\Workspace\\JavaTestExamples\\src\\main\\resources\\AccountDetail.json"),
				StandardCharsets.UTF_8)) {
			stream.forEach(s -> contentBuilder.append(s).append("\n"));
		} catch (IOException e) {
			e.printStackTrace();
		}
		//Create GSON object
		//apply NullSearialization and Pretty formatting by GSON Builder
		Gson gson = getJsonBuilder().create();
		AccountDetail accounDetail = gson.fromJson(contentBuilder.toString(), AccountDetail.class);
		mask(accounDetail);
		System.out.println(gson.toJson(accounDetail));
	}
	public static GsonBuilder getJsonBuilder()
	{
		GsonBuilder builder = new GsonBuilder();

		// Setting for formatted output and serialize null value
		builder.setPrettyPrinting().serializeNulls();

		return builder;
	}

	public static void mask(Object object) {
		try {
			Field[] fields = object.getClass().getDeclaredFields();
			Object value = null;
			for (int i = 0; i <span id="mce_SELREST_start" style="overflow: hidden; line-height: 0;"></span>< fields.length; i++) {
				fields[i].setAccessible(true);
				value = fields[i].get(object);
				if (value != null && fieldSet.add(fields[i].getName())) {
					if (fields[i].getType().isArray()
							|| fields[i].getType().getCanonicalName().startsWith("com.mask.json")) {
						mask(value);
					} else {
						if (fieldNames.contains(fields[i].getName()) && fields[i].get(object) != null) {
							fields[i].set(object, replaceDigits((String) fields[i].get(object)));
						}
					}
				}

			}
		} catch (IllegalAccessException ex) {
			ex.printStackTrace();
		}
	}

	private static String replaceDigits(String text) {
		StringBuffer buffer = new StringBuffer(text.length());
		Pattern pattern = Pattern.compile("\\d");
		Matcher matcher = pattern.matcher(text);
		while (matcher.find()) {
			matcher.appendReplacement(buffer, "X");
		}
		return buffer.toString();
	}

}

package com.mask.json;

public class AccountDetail {
private String firstName;
private String lastName;
private AddressDetail address;
private CreditCardDetail creditCardDetail;
public AccountDetail(String firstName, String lastName, AddressDetail address, CreditCardDetail creditCardDetail) {
	super();
	this.firstName = firstName;
	this.lastName = lastName;
	this.address = address;
	this.creditCardDetail = creditCardDetail;
}
public String getFirstName() {
	return firstName;
}
public void setFirstName(String firstName) {
	this.firstName = firstName;
}
public String getLastName() {
	return lastName;
}
public void setLastName(String lastName) {
	this.lastName = lastName;
}
public AddressDetail getAddress() {
	return address;
}
public void setAddress(AddressDetail address) {
	this.address = address;
}
public CreditCardDetail getCreditCardDetail() {
	return creditCardDetail;
}
public void setCreditCardDetail(CreditCardDetail creditCardDetail) {
	this.creditCardDetail = creditCardDetail;
}

}

package com.mask.json;

public class AddressDetail {

private String addressLine1;
private String city;
private String state;
private String pincode;
private String country;

public AddressDetail(String addressLine1, String city, String state, String pincode, String country) {
	super();
	this.addressLine1 = addressLine1;
	this.city = city;
	this.state = state;
	this.pincode = pincode;
	this.country = country;
}
public String getAddressLine1() {
	return addressLine1;
}
public void setAddressLine1(String addressLine1) {
	this.addressLine1 = addressLine1;
}
public String getCity() {
	return city;
}
public void setCity(String city) {
	this.city = city;
}
public String getState() {
	return state;
}
public void setState(String state) {
	this.state = state;
}
public String getPincode() {
	return pincode;
}
public void setPincode(String pincode) {
	this.pincode = pincode;
}
public String getCountry() {
	return country;
}
public void setCountry(String country) {
	this.country = country;
}

}

package com.mask.json;

public class CreditCardDetail{
private String cardNumber;
private String cvv;
private String expDate;

public CreditCardDetail(String cardNumber, String cvv, String expDate) {
	super();
	this.cardNumber = cardNumber;
	this.cvv = cvv;
	this.expDate = expDate;
}

public String getCardNumber() {
	return cardNumber;
}
public void setCardNumber(String cardNumber) {
	this.cardNumber = cardNumber;
}
public String getCvv() {
	return cvv;
}
public void setCvv(String cvv) {
	this.cvv = cvv;
}
public String getExpDate() {
	return expDate;
}
public void setExpDate(String expDate) {
	this.expDate = expDate;
}

}

{
  "firstName": "Saurabh",
  "lastName": "Gupta",
  "address": {
    "addressLine1": "Noida City Center",
    "city": "Noida",
    "state": "UP",
    "pincode": "India",
    "country": "20310"
  },
  "creditCardDetail": {
    "cardNumber": "XXXXXXXXXXXXXXXX",
    "cvv": "XXX",
    "expDate": "XX/XX"
  }
}