Implementing Data Desensitization with Custom Jackson Annotations in Java

In many API responses, sensitive data like ID numbers, phone numbers, and addresses must be masked; a common technique is to replace part of the value with asterisks.

The article presents two main ways to achieve data masking in Java, focusing on the Jackson‑based solution.

1. Define a custom Jackson annotation

Create a @Sensitive annotation that references a desensitization strategy.

/**
 * 自定义jackson注解，标注在属性上
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@JacksonAnnotationsInside
@JsonSerialize(using = SensitiveJsonSerializer.class)
public @interface Sensitive {
    //脱敏策略
    SensitiveStrategy strategy();
}

2. Define desensitization strategies

An enum SensitiveStrategy supplies lambda expressions for different masking rules (username, ID card, phone, address).

/**
 * 脱敏策略，枚举类，针对不同的数据定制特定的策略
 */
public enum SensitiveStrategy {
    /**
     * 用户名
     */
    USERNAME(s -> s.replaceAll("(\\S)\\S(\\S*)", "$1*$2")),
    /**
     * 身份证
     */
    ID_CARD(s -> s.replaceAll("(\\d{4})\\d{10}(\\w{4})", "$1****$2")),
    /**
     * 手机号
     */
    PHONE(s -> s.replaceAll("(\\d{3})\\d{4}(\\d{4})", "$1****$2")),
    /**
     * 地址
     */
    ADDRESS(s -> s.replaceAll("(\\S{3})\\S{2}(\\S*)\\S{2}", "$1****$2****"));

    private final Function
desensitizer;

    SensitiveStrategy(Function
desensitizer) {
        this.desensitizer = desensitizer;
    }

    public Function
desensitizer() {
        return desensitizer;
    }
}

3. Implement JSON serializer

Implement SensitiveJsonSerializer extending JsonSerializer and ContextualSerializer to apply the selected strategy during serialization.

/**
 * 序列化注解自定义实现
 * JsonSerializer
：指定String 类型，serialize()方法用于将修改后的数据载入
 */
public class SensitiveJsonSerializer extends JsonSerializer
implements ContextualSerializer {
    private SensitiveStrategy strategy;

    @Override
    public void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        gen.writeString(strategy.desensitizer().apply(value));
    }

    /**
     * 获取属性上的注解属性
     */
    @Override
    public JsonSerializer
createContextual(SerializerProvider prov, BeanProperty property) throws JsonMappingException {
        Sensitive annotation = property.getAnnotation(Sensitive.class);
        if (Objects.nonNull(annotation) && Objects.equals(String.class, property.getType().getRawClass())) {
            this.strategy = annotation.strategy();
            return this;
        }
        return prov.findValueSerializer(property.getType(), property);
    }
}

4. Apply annotation to a model class

Annotate fields of the Person class with @Sensitive(strategy = …) to specify how each field should be masked.

@Data
public class Person {
    /**
     * 真实姓名
     */
    @Sensitive(strategy = SensitiveStrategy.USERNAME)
    private String realName;
    /**
     * 地址
     */
    @Sensitive(strategy = SensitiveStrategy.ADDRESS)
    private String address;
    /**
     * 电话号码
     */
    @Sensitive(strategy = SensitiveStrategy.PHONE)
    private String phoneNumber;
    /**
     * 身份证号码
     */
    @Sensitive(strategy = SensitiveStrategy.ID_CARD)
    private String idCard;
}

5. Test via a REST controller

A simple Spring @RestController returns a Person instance; the response shows masked values such as "197****8206".

@RestController
public class TestController {
    @GetMapping("/test")
    public Person test() {
        Person user = new Person();
        user.setRealName("不才陈某");
        user.setPhoneNumber("19796328206");
        user.setAddress("浙江省杭州市....");
        user.setIdCard("4333333333334334333");
        return user;
    }
}

Calling the endpoint returns JSON with masked fields, for example:

{
    "realName": "不*陈某",
    "address": "浙江省****市..****",
    "phoneNumber": "197****8206",
    "idCard": "4333****34333"
}

The article concludes that many masking techniques exist, and the optimal choice depends on project requirements and the desired elegance of the implementation.