如何配置spring- MappingJackson2HttpMessageConverter注册的hateoas

Question

我喜欢在我的项目中使用spring-hateoas，并用@EnableHypermediaSupport对其进行了配置。现在的问题是，这个神奇的配置注释注册了自己的MappingJackson2HttpMessageConverter，而我自己定制的转换器将被忽略。

背景:我在我的项目中添加了一些杰克逊模块(比如JodaModule)，我想让它们使用objectMapper.findAndRegisterModules();进行注册。这是通过在WebMvcConfigurationSupport或WebMvcConfigurer中覆盖configureMessageConverters(List<HttpMessageConverter<?>> converters)来完成的。

我当前的配置如下所示：

@Configuration
@EnableHypermediaSupport(type = HAL)
public class WebMvcConfiguration extends WebMvcConfigurationSupport {

  @Override
  protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    final MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.getObjectMapper().findAndRegisterModules();

    converters.add(converter);
  }
}

有没有办法定制spring-hateoas使用的MappingJackson2HttpMessageConverter或ObjectMapper？

Answer 1

我为我的问题找到了一个丑陋的解决方案：

我使用了一个BeanPostProcessor和很多反射魔法，用我自己的ConversionService替换了Spring HATEOAS的内部a，它以前已经添加到了Spring上下文中。这样，我可以确保Spring HATEOAS使用与Spring MVC完全相同的ConversionService。

/**
 * This is a HACK to work around a not yet implemented feature. At the moment Spring Hateoas uses a
 * {@link ConversionService}, which is hold in a private static final field and hence cannot be accessed to add more
 * Converters<br/>
 *
 * <ul>
 *   <li><a href="https://github.com/spring-projects/spring-hateoas/issues/118">Spring Hateoas Issue</a></li>
 *   <li><a
 *     href="http://stackoverflow.com/questions/22240155/converter-from-pathvariable-domainobject-to-string-using-controllerlinkbuilde">
 *     Solution on Stackoverflow</a></li>
 * </ul>
 */
public static class HateoasConversionServicePostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(final Object bean, final String beanName) throws BeansException {
        if (bean instanceof ConversionService) {
            try {
                Class<?> clazz = Class.forName(
                        "org.springframework.hateoas.mvc.AnnotatedParametersParameterAccessor$BoundMethodParameter");
                Field field = clazz.getDeclaredField("CONVERSION_SERVICE");
                field.setAccessible(true);

                Field modifiersField = Field.class.getDeclaredField("modifiers");
                modifiersField.setAccessible(true);
                modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);

                field.set(null, bean);

                modifiersField.setInt(field, field.getModifiers() & Modifier.FINAL);
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }
        }

        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
        return bean;
    }
}

Answer 2

我不得不做同样的事情。有了HATEOAS .16，我就能让这款working..but变得非常非常丑陋。

关键在于，在HypermediaSupportBeanDefinitionRegistrar中，寄存器HAL转换器的部分在尝试添加另一个之前检查是否已经存在一个HAL转换器。所以我自己在WebMVCConfig::configureMessageConverters中添加了一个HAL转换器。

类似于：

private static final String DELEGATING_REL_PROVIDER_BEAN_NAME = "_relProvider";
private static final String LINK_DISCOVERER_REGISTRY_BEAN_NAME = "_linkDiscovererRegistry";
private static final String HAL_OBJECT_MAPPER_BEAN_NAME = "_halObjectMapper";

@Autowired
private ListableBeanFactory beanFactory;

private static CurieProvider getCurieProvider(BeanFactory factory) {

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

@Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        List<HttpMessageConverter<?>> baseConverters = new ArrayList<HttpMessageConverter<?>>();
        super.configureMessageConverters(baseConverters);

        //Need to override some behaviour in the HAL Serializer...so let's make our own
        CurieProvider curieProvider = getCurieProvider(beanFactory);
        RelProvider relProvider = beanFactory.getBean(DELEGATING_REL_PROVIDER_BEAN_NAME, RelProvider.class);
        ObjectMapper halObjectMapper = beanFactory.getBean(HAL_OBJECT_MAPPER_BEAN_NAME, ObjectMapper.class);

        halObjectMapper.registerModule(new Jackson2HalModule());
        halObjectMapper.setHandlerInstantiator(new Jackson2HalModule.HalHandlerInstantiator(relProvider, curieProvider));

        MappingJackson2HttpMessageConverter halConverter = new TypeConstrainedMappingJackson2HttpMessageConverter(
            ResourceSupport.class);
        halConverter.setSupportedMediaTypes(Arrays.asList(HAL_JSON));
        halConverter.setObjectMapper(halObjectMapper);

        converters.add(halConverter);
    }

这显然是依赖于实现的，使用了实现细节，并且确实不允许修改@EnableHyperMediaSupport为you....but构建的版本。

Answer 3

我使用以下方法

@Configuration
@EnableHypermediaSupport(type = HypermediaType.HAL)
public class MvcConfig {    

  @Bean
  public MappingJackson2HttpMessageConverter mappingJacksonHttpMessageConverter() {