HttpMessageConverters not prepended with HAL Message Converter

[SirMaster]

Hi,

On the startup of our application Spring instantiates certain processors like HttpEntityMethodProcessor and RequestResponseBodyMethodProcessor. These will be created with a reference to a list of HttpMessageConverters.

The list instance is set in the abstract class AbstractMessageConverterMethodArgumentResolver#messageConverters. But because some of the processors get created before HypermediaSupportBeanDefinitionRegistrar#registerBeanDefinitions is called it occurs that the replacing of the HttpMessageConverters will not have the proper effect.

I.e. HypermediaSupportBeanDefinitionRegistrar#registerBeanDefinitions does :

public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
    ....
    if (JACKSON2_PRESENT) {
        ...
        BeanDefinitionBuilder builder = rootBeanDefinition(Jackson2ModuleRegisteringBeanPostProcessor.class);
        ....
    }
    ....
}

Jackson2ModuleRegisteringBeanPostProcessor#postProcessAfterInitialization does

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    ....
    if (bean instanceof RequestMappingHandlerAdapter) {
        RequestMappingHandlerAdapter adapter = (RequestMappingHandlerAdapter) bean;
        adapter.setMessageConverters(potentiallyRegisterModule(adapter.getMessageConverters()));
    }
    ....
}

Jackson2ModuleRegisteringBeanPostProcessor#potentiallyRegisterModule does

private List<HttpMessageConverter<?>> potentiallyRegisterModule(List<HttpMessageConverter<?>> converters) {
    ....
    List<HttpMessageConverter<?>> result = new ArrayList<HttpMessageConverter<?>>(converters.size());
    result.add(halConverter);
    result.addAll(converters);
    return result;
}

The problem seems to be here in potentiallyRegisterModule, it returns a new List of HttpMessageConverts while there are still objects looking at the original list.

I tested this with :
Spring 3.2.5
Spring Hateoas 0.9.0.BUILD-SNAPSHOT

Many thx in advance for any input on this.

M.

[steventhomson]

I am experiencing this issue on Spring 4.0.1 as well. Spring Hateoas 0.9.0 RELEASE

[SirMaster]

Ok great thx!

[jiwhiz]

Any workaround for Spring Hateoas 0.9.0.RELEASE?

[SirMaster]

In short yes. What we did is the following (let me know if you need specific code details)

We have already were extending the MappingJackson2HttpMessageConverter in a class called MappingJsonJackson2HttpMessageConverter. In a @PostContruct method of that class we call the method MappingJackson2HttpMessageConverter#setObjectMapper.

We pass it a custom HalJacksonObjectMapper which looks like :

public class HalJacksonObjectMapper extends JacksonObjectMapper implements BeanFactoryAware
{
    private static final long serialVersionUID = -1120363614492817224L;

    private CurieProvider curieProvider;

    public HalJacksonObjectMapper()
    {
        registerModule(new Jackson2HalModule());
        setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(new AnnotationRelProvider(), curieProvider));
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException
    {
        this.curieProvider = getCurieProvider(beanFactory);
    }

    private static CurieProvider getCurieProvider(BeanFactory factory)
    {
        try
        {
            return factory.getBean(CurieProvider.class);
        }
        catch (NoSuchBeanDefinitionException e)
        {
            return null;
        }
    }

Hope that helps.

[jiwhiz]

Thank you @SirMaster . So do I just use the MappingJsonJackson2HttpMessageConverter inside Jackson2ModuleRegisteringBeanPostProcessor#potentiallyRegisterModule? What else do I need to change?

private List<HttpMessageConverter<?>> potentiallyRegisterModule(List<HttpMessageConverter<?>> converters) {
    ...
    MappingJackson2HttpMessageConverter halConverter = new   MappingJsonJackson2HttpMessageConverter();
    ...

Could you post the complete MappingJsonJackson2HttpMessageConverter code?

Thanks.

[jiwhiz]

I just directly updated Jackson2ModuleRegisteringBeanPostProcessor#potentiallyRegisterModule, and it can return HAL now. Not sure if it is the right fix:

        private List<HttpMessageConverter<?>> potentiallyRegisterModule(List<HttpMessageConverter<?>> converters) {

            for (HttpMessageConverter<?> converter : converters) {
                if (converter instanceof MappingJackson2HttpMessageConverter) {
                    MappingJackson2HttpMessageConverter halConverterCandidate = (MappingJackson2HttpMessageConverter) converter;
                    ObjectMapper objectMapper = halConverterCandidate.getObjectMapper();
                    if (!Jackson2HalModule.isAlreadyRegisteredIn(objectMapper)) {
                        registerHalModule(halConverterCandidate);
                    }
                    return converters;
                }
            }

            MappingJackson2HttpMessageConverter halConverter = new MappingJackson2HttpMessageConverter();
            registerHalModule(halConverter);

            List<HttpMessageConverter<?>> result = new ArrayList<HttpMessageConverter<?>>(converters.size());
            result.add(halConverter);
            result.addAll(converters);
            return result;
        }

        private void registerHalModule(MappingJackson2HttpMessageConverter halConverter) {
            halObjectMapper.registerModule(new Jackson2HalModule());
            halObjectMapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(relProvider, curieProvider));
            halConverter.setSupportedMediaTypes(Arrays.asList(HAL_JSON));
            halConverter.setObjectMapper(halObjectMapper);
        }

[SirMaster]

@jiwhiz, I think that could work yes. We did it a little different, but from what I am seeing of your code I think in essence it's the same, see :

MappingJsonJackson2HttpMessageConverter.java

@Component
public class MappingJsonJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter
{
    ....
    @PostConstruct
    private void postConstruct()
    {
        setObjectMapper(new HalJacksonObjectMapper());
    }
    ....
}

And in our config class we tell it to add it to the HttpMessageConverters, see ApplicationConfig.java

@Configuration
@EnableWebMvc
@EnableHypermediaSupport(type = HAL)
@ComponentScan(basePackageClasses = {
        MappingJsonJackson2HttpMessageConverter.class
 })
public class ApplicationConfig extends WebMvcConfigurerAdapter
{
    @Autowired
    private MappingJsonJackson2HttpMessageConverter mappingJackson2HttpMessageConverter;

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters)
    {
        converters.add(mappingJackson2HttpMessageConverter);
    }
}

[jiwhiz]

I missed the configuration change, no wonder couldn't get your workaround work. Since I don't need a customized MappingJackson2HttpMessageConverter, my hack will be fine to me. Thanks a lot!

[SirMaster]

Sorry about that, I should have just posted the whole thing and save you some time.

[jiwhiz]

No problem at all. I was so frustrated when I couldn't get HAL message returned, until saw your issue report. You pointed out where the problem is, and that saved me lots of time.

[jiwhiz]

Another issue I found is to add HAL_JSON to supportedMediaTypes, not to set it as the supportedMediaTypes. Otherwise I got "415 (Unsupported Media Type)".

The updated code is

        private void registerHalModule(MappingJackson2HttpMessageConverter halConverter) {
            halObjectMapper.registerModule(new Jackson2HalModule());
            halObjectMapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(relProvider, curieProvider));
            List<MediaType> supportedMediaTypes = new ArrayList<MediaType>(halConverter.getSupportedMediaTypes());
            supportedMediaTypes.add(HAL_JSON);
            halConverter.setSupportedMediaTypes(supportedMediaTypes);
            halConverter.setObjectMapper(halObjectMapper);
        }

[odrotbohm]

Is anyone able to come up with a test case that shows, this issue really exists? I don't necessarily doubt it, but I've seen the current code working flawlessly in standard Spring MVC applications. We also use it heavily in the Spring Data REST test code. So I am interested in finding out what is actually causing the erroneous behavior.

I can't see anything obviously wrong here, as we're simply re-setting the messageConverters property of RequestMappingHandlerAdapter. Maybe @rstoyanchev can share his view as well?

[jiwhiz]

Hi Oliver, I created a very simple application to demonstrate the issue, see my CIExample project in GitHub https://github.com/jiwhiz/CIExample. This example was built and deployed by CloudBee and you can access it at http://ciexample.jiwhiz.cloudbees.net/

The backend will expose a simple RESTful API "http://ciexample.jiwhiz.cloudbees.net/api/user", if you use any rest client, like Advanced Rest Client from Chrome shop, you can see the return json object is like:

{"name":"Yuan","email":"yuan@jiwhiz.com","links":[{"rel":"self","href":"http://ciexample.jiwhiz.cloudbees.net/api/user"}]}

Definitely it is not HAL. If I change the code as my previous comments, it works, the output json is:

{"name":"Yuan","email":"yuan@jiwhiz.com","_links":{"self":{"href":"http://localhost:8080/example/api/user"}}}

Please see the config file and let me know what the problem is:

package com.jiwhiz.example.config;

import java.util.Properties;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.hateoas.MediaTypes;
import org.springframework.hateoas.config.EnableHypermediaSupport;
import org.springframework.hateoas.config.EnableHypermediaSupport.HypermediaType;
import org.springframework.web.servlet.config.annotation.ContentNegotiationConfigurer;
import org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
import org.springframework.web.servlet.handler.SimpleMappingExceptionResolver;

@Configuration
@EnableWebMvc
@EnableHypermediaSupport(type = { HypermediaType.HAL })
@ComponentScan(basePackages = {
        "com.jiwhiz.example.rest"
})
public class WebConfig extends WebMvcConfigurerAdapter {
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/resources/**").addResourceLocations("/resources/");
    }

    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
    }

    @Bean
    public SimpleMappingExceptionResolver exceptionResolver() {
        SimpleMappingExceptionResolver exceptionResolver = new SimpleMappingExceptionResolver();

        Properties exceptionMappings = new Properties();

        exceptionMappings.put("java.lang.Exception", "error/error");
        exceptionMappings.put("java.lang.RuntimeException", "error/error");

        exceptionResolver.setExceptionMappings(exceptionMappings);

        Properties statusCodes = new Properties();

        statusCodes.put("error/404", "404");
        statusCodes.put("error/error", "500");

        exceptionResolver.setStatusCodes(statusCodes);

        return exceptionResolver;
    }

    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer c) {
        c.defaultContentType(MediaTypes.HAL_JSON);
    }

}

Thanks a lot!

Yuan