Using Spring Boot ObjectMapper with hibernate-types

Posted at — Nov 18, 2021

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The hibernate-types library has extra types that are not found in Hibernate by default.

One of the most interesting aspects of the library is the support for JSON types. Unfortunately, by default, the library will not pick up any Jackson configuration or custom serializers defined in your Spring Boot project.

This blog post will show how to configure things so the JSON related configuration of Spring Boot is used.

The blog of Vlad Mihalcea has an entry on How to customize the Jackson ObjectMapper used by Hibernate-Types, but it is not very straight forward to apply this on a Spring Boot project.

The central class that Jackson (the default library used by Spring Boot for JSON serialization) is ObjectMapper. The hibernate-types library needs such an instance, and it should be supplied by an Supplier<ObjectMapper> class.

We will use a bit of a hack, by saving a reference to the ObjectMapper in a static field. It is the only way I have found to make it work. If you know anything else, don’t hesitate to contact me on Twitter, or via GitHub discussions.

First, create a HibernateObjectMapper class:

import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.util.function.Supplier;

@Component("hibernateObjectMapper") (1)
public class HibernateObjectMapper implements Supplier<ObjectMapper> { (2)

    private static ObjectMapper objectMapper; (3)

    @Autowired (4)
    public void setObjectMapper(ObjectMapper objectMapper) {
        HibernateObjectMapper.objectMapper = objectMapper;
    }

    @Override
    public ObjectMapper get() { (5)
        return objectMapper;
    }
}

1	Use `@Component` so Spring Boot will automatically create an instance of this class. We give it an explicit name because we will need to reference it by name later.
2	Implement the `Supplier` interface as `hibernate-types` needs this.
3	`static` field to store the `ObjectMapper` reference.
4	`@Autowired` method so Spring Boot will inject the `ObjectMapper` and we can store the reference statically.
5	`get()` method from the `Supplier` interface.

Next step is instructing hibernate-types to use our custom supplier. We can add the following property to application.properties:

hibernate.types.jackson.object.mapper=com.company.app.infrastructure.jpa.HibernateObjectMapper

Adjust the full qualified name for the package structure that you are using.

The final step is adding the proper dependencies so that our HibernateObjectMapper is first injected by Spring before hibernate-types needs to do any work.

We can do this via a BeanFactoryPostProcessor:

import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;

@Component
public class HibernateBeanDependencyProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory factory) {
        BeanDefinition beanDefinition = factory.getBeanDefinition("entityManagerFactory");
        String[] dependsOn = beanDefinition.getDependsOn();
        dependsOn = dependsOn == null ? new String[]{} : dependsOn;
        String[] newDependsOn = new String[dependsOn.length + 1];
        System.arraycopy(dependsOn, 0, newDependsOn, 1, dependsOn.length);
        newDependsOn[0] = "hibernateObjectMapper";
        beanDefinition.setDependsOn(newDependsOn);
    }
}

With this in place, the Spring Boot provided ObjectMapper is used by hibernate-types.

If you have any questions or remarks, feel free to post a comment at GitHub discussions.

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Wim Deblauwe

Wim Deblauwe

Using Spring Boot ObjectMapper with hibernate-types