Avoid Jackson serialization on non fetched lazy objects

Question

I have a simple controller that return a User object, this user have a attribute coordinates that have the hibernate property FetchType.LAZY.

When I try to get this user, I always have to load all the coordinates to get the user object, otherwise when Jackson try to serialize the User throws the exception:

com.fasterxml.jackson.databind.JsonMappingException: could not initialize proxy - no Session

This is due to Jackson is trying to fetch this unfetched object. Here are the objects:

public class User{

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "user")
    @JsonManagedReference("user-coordinate")
    private List<Coordinate> coordinates;
}

public class Coordinate {

    @ManyToOne
    @JoinColumn(name = "user_id", nullable = false)
    @JsonBackReference("user-coordinate")
    private User user;
}

And the controller:

@RequestMapping(value = "/user/{username}", method=RequestMethod.GET)
public @ResponseBody User getUser(@PathVariable String username) {

    User user = userService.getUser(username);

    return user;

}

There is a way to tell Jackson to not serialize the unfetched objects? I've been looking other answers posted 3 years ago implementing jackson-hibernate-module. But probably it could be achieved with a new jackson feature.

My versions are:

• Spring 3.2.5
• Hibernate 4.1.7
• Jackson 2.2

Thanks in advance.

Solution 1

I finally found the solution! thanks to indybee for giving me a clue.

The tutorial Spring 3.1, Hibernate 4 and Jackson-Module-Hibernate have a good solution for Spring 3.1 and earlier versions. But since version 3.1.2 Spring have his own MappingJackson2HttpMessageConverter with almost the same functionality as the one in the tutorial, so we don't need to create this custom HTTPMessageConverter.

With javaconfig we don't need to create a HibernateAwareObjectMapper too, we just need to add the Hibernate4Module to the default MappingJackson2HttpMessageConverter that Spring already have and add it to the HttpMessageConverters of the application, so we need to:

1. Extend our spring config class from WebMvcConfigurerAdapter and override the method configureMessageConverters.

2. On that method add the MappingJackson2HttpMessageConverter with the Hibernate4Module registered in a previus method.

Our config class should look like this:

@Configuration
@EnableWebMvc
public class MyConfigClass extends WebMvcConfigurerAdapter{

    //More configuration....

    /* Here we register the Hibernate4Module into an ObjectMapper, then set this custom-configured ObjectMapper
     * to the MessageConverter and return it to be added to the HttpMessageConverters of our application*/
    public MappingJackson2HttpMessageConverter jacksonMessageConverter(){
        MappingJackson2HttpMessageConverter messageConverter = new MappingJackson2HttpMessageConverter();

        ObjectMapper mapper = new ObjectMapper();
        //Registering Hibernate4Module to support lazy objects
        mapper.registerModule(new Hibernate4Module());

        messageConverter.setObjectMapper(mapper);
        return messageConverter;

    }

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        //Here we add our custom-configured HttpMessageConverter
        converters.add(jacksonMessageConverter());
        super.configureMessageConverters(converters);
    }

    //More configuration....
}

If you have an xml configuration, you don't need to create your own MappingJackson2HttpMessageConverter either, but you do need to create the personalized mapper that appears in the tutorial (HibernateAwareObjectMapper), so your xml config should look like this:

<mvc:message-converters>
    <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
        <property name="objectMapper">
            <bean class="com.pastelstudios.json.HibernateAwareObjectMapper" />
        </property>
    </bean>
</mvc:message-converters>

Hope this answer be understandable and helps someone find the solution for this problem, any questions feel free to ask!

Solution 2

As of Spring 4.2 and using Spring Boot and javaconfig, registering the Hibernate4Module is now as simple as adding this to your configuration:

@Bean
public Module datatypeHibernateModule() {
  return new Hibernate4Module();
}

ref: https://spring.io/blog/2014/12/02/latest-jackson-integration-improvements-in-spring

Solution 3

This is similar to accepted solution by @rick.

If you don't want to touch existing message converters configuration you can just declare a Jackson2ObjectMapperBuilder bean like:

@Bean
public Jackson2ObjectMapperBuilder configureObjectMapper() {
    return new Jackson2ObjectMapperBuilder()
        .modulesToInstall(Hibernate4Module.class);
}

Do not forget to add the following dependency to your Gradle file (or Maven):

compile 'com.fasterxml.jackson.datatype:jackson-datatype-hibernate4:2.4.4'

Useful if you have a spring-boot application and you want to keep the ability to modify Jackson features from application.properties file.

Solution 4

In the case of Spring Data Rest then, while the solution posted by @r1ckr works, all that is required is to add one of the following dependencies depending on your Hibernate version:

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-hibernate4</artifactId>
    <version>${jackson.version}</version>
</dependency>

or

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-hibernate5</artifactId>
    <version>${jackson.version}</version>
</dependency>

Within Spring Data Rest there is a class:

org.springframework.data.rest.webmvc.json.Jackson2DatatypeHelper

which will auto-detect and register the Module on application start-up.

There is however an issue:

Issue Serializing Lazy @ManyToOne

Solution 5

I've spent whole day trying to solve the same problem. You can do it without changing existing message converters configuration.

In my opinion the easiest way to solve this problem only with 2 steps with help of jackson-datatype-hibernate:

kotlin example (same as java):

1. Add In build.gradle.kts:

implementation("com.fasterxml.jackson.datatype:jackson-datatype-hibernate5:$jacksonHibernate")

2. Create @Bean

   @Bean
   fun hibernate5Module(): Module = Hibernate5Module()

---

• Notice that Module is com.fasterxml.jackson.databind.Module, not java.util.Module

• Also good practice is to add @JsonBackReference & @JsonManagedReference to @OneToMany & @ManyToOne relationships. @JsonBackReference could be only 1 in class.

View more solutions

Comments

[Robin]

Thanks for sharing the solution. However after a few tries, I found that the latest jackson at the moment (2.4.2) does NOT work with spring 4.0.6. I still have the "no session" error. Only when I down graded jackson version back to 2.3.4 (or 2.4.2), did it start working.

[LanceP]

Thanks for pointing MappingJackson2HttpMessageConverter out! I was looking for a class like this for a while.

[Isthar]

Thank you very much! I have just tested it and its working with Spring 4.2.4, Jackson 2.7.1-1 and JacksonDatatype 2.7.1 :)

[hemu]

How can we achieve this (Configuring Jackson to avoid lazy loaded object) using application.properties file?

[Alessandro C]

This doesn't resolve the problem in Spring Data REST.

[Zeemee]

For Hibernate 5 (as in the current version of Spring Boot), it is Hibernate5Module. It additionally needs a dependency to <groupId>com.fasterxml.jackson.datatype</groupId><artifactId‌​>jackson-datatype-hi‌​bernate5</artifactId‌​>

[Ryan D]

This works perfectly for me except that I call hibernate5Module.enable(Feature.FORCE_LAZY_LOADING); That was required to not return "null"

[Krish]

@rgdayo It is working for json. then what about xml ?

[SalutonMondo]

don't forget to add Maven dependency. <!-- mvnrepository.com/artifact/com.fasterxml.jackson.datatype/… --> <dependency> <groupId>com.fasterxml.jackson.datatype</groupId> <artifactId>jackson-datatype-hibernate5</artifactId> <version>2.7.9</version> </dependency>

[kapad]

That's not what is being said here. @Luis Belloch's solution suggests that you create the Jackson2ObjectMapperBuilder so that you don't override spring boots default message converter and continue to use the application.properties values to control jackson properties.

[Eric Huang]

How do you configure this with spring boot when you are not using Spring Data Rest?

[Eric Huang]

sorry... I am new where would you implement this method? With spring boot It uses Spring 5 which WebMvcConfigurerAdapter is deprecated

[ranjith Gampa]

How to solve the same issue, if Springboot is used in place of Spring?. I have tried registering the Hibernate4 module(which is the version I have currently), but that did not solve my issue.

[Daniel Henao]

Do you have an update about this topic? I'm having the issue currently. Ofcourse whenI add the hibernate5Module (because im using hibernate 5), jackson ignores the proxy of non initialized objects, but it seems that the " well-known modules" are not being registered despite I useyour approach. I do know this, because some parts of my application are broken, and when I remove the Module, they work again.

[Markus Pscheidt]

@DanielHenao Have you studied spring.io/blog/2014/12/02/…? I switched to Hibernate5, using the DelegatingWebMvcConfiguration class (instead of WebMvcConfigurerAdapter) as suggested by the Jackson-Antpath-Filter: @Override public void configureMessageConverters(List<HttpMessageConverter<?>> messageConverters) { messageConverters.add(jacksonMessageConverter()); addDefaultHttpMessageConverters(messageConverters); }

[Kevin Orriss]

Been trying to fix this for two days and this answer finally fixed it! For those stuck, at the time of writing this, the only other thing I did was ensure I was using the latest spring / hibernate etc

[Van Dame]

Worked for me as well on Spring Boot 2.1. Was beginning to drive me crazy.

[aardbol]

It's not clear how to implement this. I get an incompatible types error.

[GarouDan]

Awesome! Worked for me with Spring Boot 2.0.6 and Hibernate 5.

[peterong]

Hi. Thanks for your answer. FYI, your XML configuration need to be put inside <mvc:annotation-driven></mvc:annotation-driven> in order to work. This also assume you have properly declared the schema location.

[gburgalum01]

This was very helpful. It should be pointed out that registering the Hibernate5Module class instance as a bean isn't enough. If you wish to apply it to a single ObjectMapper instance, you can autowire the module into your Spring-managed class and then register it with the ObjectMapper instance. @Autowire Module jacksonHibernateModule; ObjectMapper mapper = new ObjectMapper(); mapper.registerModule(this.jacksonHibernateModule).

[Dmitry Kaltovich]

This wouldn't help

[Dmitry Kaltovich]

1. Hibernate4Module is legacy . 2 SerializationFeature.WRITE_DATES_AS_TIMESTAMPS - not about the question

[Dmitry Kaltovich]

Not about the question

[Dmitry Kaltovich]

The solution could be much more easier: kotlin @Bean fun hibernate5Module(): Module = Hibernate5Module()

[Dmitry Kaltovich]

xml config is legacy

[Dmitry Kaltovich]

Not enough. You also need @Bean hibernate5Module()

[Dmitry Kaltovich]

Hibernate4Module is legacy

[Markus Pscheidt]

@DmitryKaltovich ad 1) it wasn't legacy at the time of writing; ad 2) ok, removed.

[Dmitry Kaltovich]

Not good solution, because: 1. Hibernate4Module is legacy. 2 Too much lines of code. 3. You are changing existing preconfigured Message Converter

[bluelurker]

@EarthMind It may be too late, but for someone reading this now, Module is of type com.fasterxml.jackson.databind.Module and not java.lang.Module.

[Johannes]

thanks @chrismarx, I'd give you 1337 upvotes for this answer if SO let me.