@Valid when creating objects with jackson without controller

Question

I have a model that I validate with @Valid in my Controllers when requests are send from the front-end:

@NotNull
@Size(min=1, message="Name should be at least 1 character.")
private String name;

@NotNull
@Pattern(regexp = "^https://github.com/.+/.+$", message = "Link to github should match https://github.com/USER/REPOSITORY")
private String github;

but now I am also creating a object with Jackson's ObjectMapper without the controller. Is there a way to register this validation in the ObjectMapper or should I just check the variables in the setters?

Answer 1

You can extend BeanDeserializer and validate object after deserialisation. To register this bean use SimpleModule.

Simple bean deserialiser with validation:

class BeanValidationDeserializer extends BeanDeserializer {

    private final static ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
    private final Validator validator = factory.getValidator();

    public BeanValidationDeserializer(BeanDeserializerBase src) {
        super(src);
    }

    @Override
    public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        Object instance = super.deserialize(p, ctxt);
        validate(instance);

        return instance;
    }

    private void validate(Object instance) {
        Set<ConstraintViolation<Object>> violations = validator.validate(instance);
        if (violations.size() > 0) {
            StringBuilder msg = new StringBuilder();
            msg.append("JSON object is not valid. Reasons (").append(violations.size()).append("): ");
            for (ConstraintViolation<Object> violation : violations) {
                msg.append(violation.getMessage()).append(", ");
            }
            throw new ConstraintViolationException(msg.toString(), violations);
        }
    }
}

We can use it as below:

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.BeanDeserializer;
import com.fasterxml.jackson.databind.deser.BeanDeserializerBase;
import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;
import com.fasterxml.jackson.databind.module.SimpleModule;

import javax.validation.ConstraintViolation;
import javax.validation.ConstraintViolationException;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;
import java.io.File;
import java.io.IOException;
import java.util.Set;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        SimpleModule validationModule = new SimpleModule();
        validationModule.setDeserializerModifier(new BeanDeserializerModifier() {
            @Override
            public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer) {
                if (deserializer instanceof BeanDeserializer) {
                    return new BeanValidationDeserializer((BeanDeserializer) deserializer);
                }

                return deserializer;
            }
        });

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(validationModule);

        System.out.println(mapper.readValue(jsonFile, Pojo.class));
    }
}

class Pojo {

    @NotNull
    @Size(min = 1, message = "Name should be at least 1 character.")
    private String name;

    @NotNull
    @Pattern(regexp = "^https://github.com/.+/.+$", message = "Link to github should match https://github.com/USER/REPOSITORY")
    private String github;

    // getters, setters, toString()
}

For valid JSON payload:

{
  "name": "Jackson",
  "github": "https://github.com/FasterXML/jackson-databind"
}

prints:

Pojo{name='Jackson', github='https://github.com/FasterXML/jackson-databind'}

For invalid JSON payload:

{
  "name": "",
  "github": "https://git-hub.com/FasterXML/jackson-databind"
}

prints:

Exception in thread "main" javax.validation.ConstraintViolationException: JSON object is not valid. Reasons (2): Name should be at least 1 character., Link to github should match https://github.com/USER/REPOSITORY, 
    at BeanValidationDeserializer.validate(JsonApp.java:110)
    at BeanValidationDeserializer.deserialize(JsonApp.java:97)

See also:

• Java Bean Validation Basics
• Deserialize to String or Object using Jackson
• Jackson custom serialization and deserialization