spring mvc messageConverters及406等问题

最新推荐文章于 2024-08-03 22:30:28 发布

karott

最新推荐文章于 2024-08-03 22:30:28 发布

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本文介绍了Spring MVC在处理@ResponseBody或response.getWriter().print()时，如何通过内置converters进行自动转换。当配置不当，可能会导致406错误。常见问题出现在RequestMappingHandlerAdapter配置中，它仅包含几种默认转换器。为了解决这个问题，可以不直接配置HandlerAdapter，而是使用`@EnableWebMvc`注解，这会自动注册大部分converters，并允许自定义需要的转换器，同时确保默认转换器不受影响。此外，若需将StringHttpMessageConverter的默认字符集从'ISO-8859-1'更改为'UTF-8'，可通过配置实现。

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提要：spring mvc 在@ResponseBody或者response.getWriter().print()的时候，默认会通过其内置的系列converters进行自动转换，接口如下：

org.springframework.http.converter.HttpMessageConverter<T>

其中，比较常用的有以下几个：

org.springframework.http.converter.StringHttpMessageConverter，实现string类型转换
org.springframework.http.converter.ByteArrayHttpMessageConverter，二进制类型转换
org.springframework.http.converter.MappingJackson2HttpMessageConverter，json类型转换

以上转换器，是通过对request里面的Accept属性进行逐个解析并匹配实现(逗号分隔)，如果相关converter配置出现错误，就会导致异常发生，以及可能导致响应406出现。

一般出现这样的情况多半是直接配置了RequestMappingHandlerAdapter这个类(比如请求为json类型时，就会无法自动转换，返回结果响应406 not accepted)，因为它默认只会注册以下几个转换器：

public RequestMappingHandlerAdapter() {
        StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
        stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316
        this.messageConverters = new ArrayList<HttpMessageConverter<?>>(4);
        this.messageConverters.add(new ByteArrayHttpMessageConverter());
        this.messageConverters.add(stringHttpMessageConverter);
        this.messageConverters.add(new SourceHttpMessageConverter<Source>());
        this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
    }

为了解决这个问题，我们可以将需要的转换器配置到Adapter类上，但是，配置后会覆盖原有的converters，所以，配置的时候需要配置全面。更为简单的做法是不去配置HandlerAdapter这个类，而是直接配置<mvc:annotation-driven />，这个配置会默认配置HandlerAdapter以及HandlerMapping，并且会自动注册大部分的converters：

AnnotationDrivenBeanDefinitionParser类下的parse方法：
@Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        Object source = parserContext.extractSource(element);
        CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
        parserContext.pushContainingComponent(compDefinition);
        RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, parserContext);
        RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
        handlerMappingDef.setSource(source);
        handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        handlerMappingDef.getPropertyValues().add("order", 0);
        handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
        String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(handlerMappingDef);
        if (element.hasAttribute("enable-matrix-variables")) {
            Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enable-matrix-variables"));
            handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
        }
        else if (element.hasAttribute("enableMatrixVariables")) {
            Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enableMatrixVariables"));
            handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
        }
        configurePathMatchingProperties(handlerMappingDef, element, parserContext);
        RuntimeBeanReference conversionService = getConversionService(element, source, parserContext);
        RuntimeBeanReference validator = getValidator(element, source, parserContext);
        RuntimeBeanReference messageCodesResolver = getMessageCodesResolver(element);
        RootBeanDefinition bindingDef = new RootBeanDefinition(ConfigurableWebBindingInitializer.class);
        bindingDef.setSource(source);
        bindingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        bindingDef.getPropertyValues().add("conversionService", conversionService);
        bindingDef.getPropertyValues().add("validator", validator);
        bindingDef.getPropertyValues().add("messageCodesResolver", messageCodesResolver);
        ManagedList<?> messageConverters = getMessageConverters(element, source, parserContext);
        ManagedList<?> argumentResolvers = getArgumentResolvers(element, parserContext);
        ManagedList<?> returnValueHandlers = getReturnValueHandlers(element, parserContext);
        String asyncTimeout = getAsyncTimeout(element);
        RuntimeBeanReference asyncExecutor = getAsyncExecutor(element);
        ManagedList<?> callableInterceptors = getCallableInterceptors(element, source, parserContext);
        ManagedList<?> deferredResultInterceptors = getDeferredResultInterceptors(element, source, parserContext);
        RootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
        handlerAdapterDef.setSource(source);
        handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        handlerAdapterDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
        handlerAdapterDef.getPropertyValues().add("webBindingInitializer", bindingDef);
        handlerAdapterDef.getPropertyValues().add("messageConverters", messageConverters);
        addResponseBodyAdvice(handlerAdapterDef);
        if (element.hasAttribute("ignore-default-model-on-redirect")) {
            Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignore-default-model-on-redirect"));
            handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
        }
        else if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {
            // "ignoreDefaultModelOnRedirect" spelling is deprecated
            Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignoreDefaultModelOnRedirect"));
            handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
        }
        if (argumentResolvers != null) {
            handlerAdapterDef.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
        }
        if (returnValueHandlers != null) {
            handlerAdapterDef.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
        }
        if (asyncTimeout != null) {
            handlerAdapterDef.getPropertyValues().add("asyncRequestTimeout", asyncTimeout);
        }
        if (asyncExecutor != null) {
            handlerAdapterDef.getPropertyValues().add("taskExecutor", asyncExecutor);
        }
        handlerAdapterDef.getPropertyValues().add("callableInterceptors", callableInterceptors);
        handlerAdapterDef.getPropertyValues().add("deferredResultInterceptors", deferredResultInterceptors);
        String handlerAdapterName = parserContext.getReaderContext().registerWithGeneratedName(handlerAdapterDef);
        String uriCompContribName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;
        RootBeanDefinition uriCompContribDef = new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);
        uriCompContribDef.setSource(source);
        uriCompContribDef.getPropertyValues().addPropertyValue("handlerAdapter", handlerAdapterDef);
        uriCompContribDef.getPropertyValues().addPropertyValue("conversionService", conversionService);
        parserContext.getReaderContext().getRegistry().registerBeanDefinition(uriCompContribName, uriCompContribDef);
        RootBeanDefinition csInterceptorDef = new RootBeanDefinition(ConversionServiceExposingInterceptor.class);
        csInterceptorDef.setSource(source);
        csInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, conversionService);
        RootBeanDefinition mappedCsInterceptorDef = new RootBeanDefinition(MappedInterceptor.class);
        mappedCsInterceptorDef.setSource(source);
        mappedCsInterceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, (Object) null);
        mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(1, csInterceptorDef);
        String mappedInterceptorName = parserContext.getReaderContext().registerWithGeneratedName(mappedCsInterceptorDef);
        RootBeanDefinition exceptionHandlerExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);
        exceptionHandlerExceptionResolver.setSource(source);
        exceptionHandlerExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        exceptionHandlerExceptionResolver.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
        exceptionHandlerExceptionResolver.getPropertyValues().add("messageConverters", messageConverters);
        exceptionHandlerExceptionResolver.getPropertyValues().add("order", 0);
        addResponseBodyAdvice(exceptionHandlerExceptionResolver);
        String methodExceptionResolverName =
                parserContext.getReaderContext().registerWithGeneratedName(exceptionHandlerExceptionResolver);
        RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);
        responseStatusExceptionResolver.setSource(source);
        responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        responseStatusExceptionResolver.getPropertyValues().add("order", 1);
        String responseStatusExceptionResolverName =
                parserContext.getReaderContext().registerWithGeneratedName(responseStatusExceptionResolver);
        RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);
        defaultExceptionResolver.setSource(source);
        defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        defaultExceptionResolver.getPropertyValues().add("order", 2);
        String defaultExceptionResolverName =
                parserContext.getReaderContext().registerWithGeneratedName(defaultExceptionResolver);
        parserContext.registerComponent(new BeanComponentDefinition(handlerMappingDef, methodMappingName));
        parserContext.registerComponent(new BeanComponentDefinition(handlerAdapterDef, handlerAdapterName));
        parserContext.registerComponent(new BeanComponentDefinition(uriCompContribDef, uriCompContribName));
        parserContext.registerComponent(new BeanComponentDefinition(exceptionHandlerExceptionResolver, methodExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(responseStatusExceptionResolver, responseStatusExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(defaultExceptionResolver, defaultExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(mappedCsInterceptorDef, mappedInterceptorName));
        // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
        MvcNamespaceUtils.registerDefaultComponents(parserContext, source);
        parserContext.popAndRegisterContainingComponent();
        return null;
    }

里面有个getMessageConverters():

private ManagedList<?> getMessageConverters(Element element, Object source, ParserContext parserContext) {
        Element convertersElement = DomUtils.getChildElementByTagName(element, "message-converters");
        ManagedList<? super Object> messageConverters = new ManagedList<Object>();
        if (convertersElement != null) {
            messageConverters.setSource(source);
            for (Element beanElement : DomUtils.getChildElementsByTagName(convertersElement, "bean", "ref")) {
                Object object = parserContext.getDelegate().parsePropertySubElement(beanElement, null);
                messageConverters.add(object);
            }
        }
        if (convertersElement == null || Boolean.valueOf(convertersElement.getAttribute("register-defaults"))) {
            messageConverters.setSource(source);
            messageConverters.add(createConverterDefinition(ByteArrayHttpMessageConverter.class, source));
            RootBeanDefinition stringConverterDef = createConverterDefinition(StringHttpMessageConverter.class, source);
            stringConverterDef.getPropertyValues().add("writeAcceptCharset", false);
            messageConverters.add(stringConverterDef);
            messageConverters.add(createConverterDefinition(ResourceHttpMessageConverter.class, source));
            messageConverters.add(createConverterDefinition(SourceHttpMessageConverter.class, source));
            messageConverters.add(createConverterDefinition(AllEncompassingFormHttpMessageConverter.class, source));
            if (romePresent) {
                messageConverters.add(createConverterDefinition(AtomFeedHttpMessageConverter.class, source));
                messageConverters.add(createConverterDefinition(RssChannelHttpMessageConverter.class, source));
            }
            if (jackson2XmlPresent) {
                RootBeanDefinition jacksonConverterDef = createConverterDefinition(MappingJackson2XmlHttpMessageConverter.class, source);
                GenericBeanDefinition jacksonFactoryDef = createObjectMapperFactoryDefinition(source);
                jacksonFactoryDef.getPropertyValues().add("createXmlMapper", true);
                jacksonConverterDef.getConstructorArgumentValues().addIndexedArgumentValue(0, jacksonFactoryDef);
                messageConverters.add(jacksonConverterDef);
            }
            else if (jaxb2Present) {
                messageConverters.add(createConverterDefinition(Jaxb2RootElementHttpMessageConverter.class, source));
            }
            if (jackson2Present) {
                RootBeanDefinition jacksonConverterDef = createConverterDefinition(MappingJackson2HttpMessageConverter.class, source);
                GenericBeanDefinition jacksonFactoryDef = createObjectMapperFactoryDefinition(source);
                jacksonConverterDef.getConstructorArgumentValues().addIndexedArgumentValue(0, jacksonFactoryDef);
                messageConverters.add(jacksonConverterDef);
            }
            else if (gsonPresent) {
                messageConverters.add(createConverterDefinition(GsonHttpMessageConverter.class, source));
            }
        }
        return messageConverters;
    }

我们可以通过配置定制需要的转换器，并配置register-defaults=true保证原有转换器不被覆盖.
另外，StringHttpMessageConverter默认字符集为”ISO-8859-1”，需要转换为”UTF-8”时，可以配置覆盖

public class StringHttpMessageConverter extends AbstractHttpMessageConverter<String> {
    public static final Charset DEFAULT_CHARSET = Charset.forName("ISO-8859-1");