Can't set ProblemHandler to ObjectMapper in Spring Boot

Question

I tried to add custom problem handler to object mapper with Jackson2ObjectMapperBuilderCustomizer:

@Bean
public Jackson2ObjectMapperBuilderCustomizer customizer() {
    return new Jackson2ObjectMapperBuilderCustomizer() {
        @Override
        public void customize(Jackson2ObjectMapperBuilder builder) {
            ObjectMapper m = builder.build();
            m.addHandler(
                    new DeserializationProblemHandler() {
                        @Override
                        public boolean handleUnknownProperty(DeserializationContext ctxt, JsonParser p, JsonDeserializer<?> deserializer, Object beanOrClass, String propertyName) throws IOException {
                            System.out.println("ahahahaa");
                            return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
                        }
                    }
            );
        }
    };
}

But when i autowired ObjectMapper bean _problemHandlers property is null.

I also tried just customize existed ObjectMapper with:

@Autowired
public customize(ObjectMapper mapper) {
...
}

But result is the same. I don't know who can erasure this property. I don't initialize another builders/factories/etc of object mapper in another place at all. What i'm doing wrong?

Primordial

Answer 1

It's not possible to directly add a DeserializationProblemHandler to the ObjectMapper via a Jackson2ObjectMapperBuilder or Jackson2ObjectMapperBuilderCustomizer. Calling build() on the builder is a no-go, since the resulting ObjectMapper is local to the method: Spring itself will call build() later, creating another ObjectMapper instance.

However, it's possible to do so by registering a Jackson module :

• the builder has a modules() method
• the module has access via setupModule() to a SetupContext instance, which has a addDeserializationProblemHandler() method

This should then work

@Bean
public Jackson2ObjectMapperBuilderCustomizer customizer() {
    return new Jackson2ObjectMapperBuilderCustomizer() {
        @Override
        public void customize(Jackson2ObjectMapperBuilder builder) {
            builder.modules(new MyModule());
        }
    };
}

private static class MyModule extends SimpleModule {
    @Override
    public void setupModule(SetupContext context) {
        // Required, as documented in the Javadoc of SimpleModule
        super.setupModule(context);
        context.addDeserializationProblemHandler(new MyDeserializationProblemHandler());
    } 
}

private static class MyDeserializationProblemHandler extends DeserializationProblemHandler {
    @Override
    public boolean handleUnknownProperty(DeserializationContext ctxt,
                                         JsonParser p,
                                         JsonDeserializer<?> deserializer,
                                         Object beanOrClass,
                                         String propertyName)
            throws IOException {
        System.out.println("ahahahaa");
        return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
    }
}

---

EDIT (2022-06-27)

As mentioned by E-Riz in the comments, with newer Spring Boot versions you can just register the module as a Spring Bean and it will be configured on the ObjectMapper with all the other modules.

// Or declare it as a @Bean in a @Configuration
@Component
public class MyModule extends SimpleModule {
    @Override
    public void setupModule(SetupContext context) {
        // Required, as documented in the Javadoc of SimpleModule
        super.setupModule(context);
        context.addDeserializationProblemHandler(new MyDeserializationProblemHandler());
    } 

    private static class MyDeserializationProblemHandler extends DeserializationProblemHandler {
        @Override
        public boolean handleUnknownProperty(DeserializationContext ctxt,
                                             JsonParser p,
                                             JsonDeserializer<?> deserializer,
                                             Object beanOrClass,
                                             String propertyName)
                throws IOException {
            System.out.println("ahahahaa");
            return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
        }
    }
}

Gobbet

Hi, I used your code. But control is not coming inside handleUnknownProperty when my request has an invalid JSON field. Am I missing something here ? – Freethinker

context.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false) maybe? It depends on what it's doing instead. – Gobbet

This solution most likely has unintended consequences. That's because builder.modules() circumvents the auto-discovery of modules that Spring Boot does, so things like Java Time and other important modules on the classpath won't get registered. Check the JavaDoc of Jackson2ObjectMapperBuilder.modules() for more info. – Seabrooke

With newer versions of Spring you don't need the customizer at all; any @Bean of type Module will automatically be registered with the ObjectMapper builder. That also avoids the nasty side effect I mentioned above; Spring Boot will still include auto-discovered modules it finds. – Seabrooke

Answer 2

I am new to Spring Boot, then, it was difficult to understand how I could use this. But after some research I managed to figure out.

I had to create a class named src.main.java.com.applicationname.config.JacksonUnknownPropertyConfig.java with the contents:

package com.applicationname.config;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.deser.DeserializationProblemHandler;
import com.fasterxml.jackson.databind.module.SimpleModule;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.http.HttpStatus;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.web.server.ResponseStatusException;

import java.io.IOException;

@SpringBootConfiguration
public class JacksonUnknownPropertyConfig {
  private static final Logger logger = LoggerFactory.getLogger(JacksonUnknownPropertyConfig.class);

  @Bean
  public Jackson2ObjectMapperBuilderCustomizer customizer() {
    return new Jackson2ObjectMapperBuilderCustomizer() {
      @Override
      public void customize(Jackson2ObjectMapperBuilder builder) {
        builder.modules(new MyModule());
      }
    };
  }

  private static class MyModule extends SimpleModule {
    @Override
    public void setupModule(SetupContext context) {
      // Required, as documented in the Javadoc of SimpleModule
      super.setupModule(context);
      context.addDeserializationProblemHandler(new MyDeserializationProblemHandler());
    }
  }

  private static class MyDeserializationProblemHandler extends DeserializationProblemHandler {
    @Override
    public boolean handleUnknownProperty(
        DeserializationContext ctxt,
        JsonParser p,
        JsonDeserializer<?> deserializer,
        Object beanOrClass,
        String propertyName)
        throws IOException {

      System.out.println("ahahahaa");

      final String missing = String.format("Unknown request property '%s'", propertyName);
      logger.warn(missing);

      if (ctxt.isEnabled(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)) {
        throw new ResponseStatusException(HttpStatus.BAD_REQUEST, missing);
      }
      return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
    }
  }
}

And I also had to add FAIL_ON_UNKNOWN_PROPERTIES to the file src.main.resources.application.properties

spring.jackson.deserialization.FAIL_ON_UNKNOWN_PROPERTIES=true

After this, looks like Sprint Boot automatically recognizes the new class I created and correctly loads it.

2020-07-20 23:41:22.934  INFO 16684 --- [         task-1] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
2020-07-20 23:41:22.944 TRACE 16684 --- [         task-1] o.h.type.spi.TypeConfiguration$Scope     : Handling #sessionFactoryCreated from [org.hibernate.internal.SessionFactoryImpl@3edd0926] for TypeConfiguration
2020-07-20 23:41:22.946  INFO 16684 --- [         task-1] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2020-07-20 23:41:23.209  INFO 16684 --- [           main] DeferredRepositoryInitializationListener : Spring Data repositories initialized!
2020-07-20 23:41:23.222  INFO 16684 --- [           main] c.a.p.AppointmentPublishingApplication   : Started AppointmentPublishingApplication in 6.445 seconds (JVM running for 7.615)
2020-07-20 23:41:26.229  INFO 16684 --- [nio-8081-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2020-07-20 23:41:26.229  INFO 16684 --- [nio-8081-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2020-07-20 23:41:26.236  INFO 16684 --- [nio-8081-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 7 ms
ahahahaa

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Canthus