How to Implement Field-Level Data Desensitization with Jackson in Java

Previously a MyBatis plugin was used for data desensitization, but it limited post‑query processing; moving the desensitization step to JSON serialization solves this problem.

Desensitization in Jackson Serialization

The transformation simply postpones desensitization to the JSON serialization phase using the Jackson library.

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Sensitive {
    SensitiveStrategy strategy();
}

Desensitization strategies are defined as follows:

import java.util.function.Function;
/**
 * Desensitization strategies.
 */
public enum SensitiveStrategy {
    /** Username sensitive strategy. */
    USERNAME(s -> s.replaceAll("(\\S)\\S(\\S*)", "$1*$2")),
    /** ID card sensitive type. */
    ID_CARD(s -> s.replaceAll("(\\d{4})\\d{10}(\\w{4})", "$1****$2")),
    /** Phone sensitive type. */
    PHONE(s -> s.replaceAll("(\\d{3})\\d{4}(\\d{4})", "$1****$2")),
    /** Address sensitive type. */
    ADDRESS(s -> s.replaceAll("(\\S{3})\\S{2}(\\S*)\\S{2}", "$1****$2****"));

    private final Function<String, String> desensitizer;
    SensitiveStrategy(Function<String, String> desensitizer) {
        this.desensitizer = desensitizer;
    }
    public Function<String, String> desensitizer() {
        return desensitizer;
    }
}

Custom Desensitization Serializer

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.BeanProperty;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.ContextualSerializer;
import java.io.IOException;
import java.util.Objects;
/**
 * @author felord.cn
 * @since 1.0.8.RELEASE
 */
public class SensitiveJsonSerializer extends JsonSerializer<String> implements ContextualSerializer {
    private SensitiveStrategy strategy;
    @Override
    public void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        gen.writeString(strategy.desensitizer().apply(value));
    }
    @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);
    }
}

The createContextual method obtains the @Sensitive annotation on a field and initializes the appropriate JsonSerializer; the serialize method applies the desensitization logic during JSON output.

Modified Sensitive Annotation

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@JacksonAnnotationsInside
@JsonSerialize(using = SensitiveJsonSerializer.class)
public @interface Sensitive {
    SensitiveStrategy strategy();
}

Usage Example

@Data
public class User {
    @Sensitive(strategy = SensitiveStrategy.USERNAME)
    private String realName;
    @Sensitive(strategy = SensitiveStrategy.ADDRESS)
    private String address;
    @Sensitive(strategy = SensitiveStrategy.PHONE)
    private String phoneNumber;
    @Sensitive(strategy = SensitiveStrategy.ID_CARD)
    private String idCard;
}

User user = new User();
user.setRealName("张三丰");
user.setPhoneNumber("13333333333");
user.setAddress("湖北省十堰市丹江口市武当山");
user.setIdCard("4333333333334334333");
ObjectMapper objectMapper = new ObjectMapper();
String json = objectMapper.writeValueAsString(user);
System.out.println(json);

{
    "realName":"张*丰",
    "address":"湖北省****市丹江口市武****",
    "phoneNumber":"133****3333",
    "idCard":"4333****34333"
}

The result shows successful field‑level masking; a switch could be added later to enable or disable desensitization based on context.