【原创】大叔问题定位分享（34）Spring的RestTemplate请求json数据后内容被修改

先看代码

org.springframework.web.client.RestTemplate

    public RestTemplate() {
        this.messageConverters = new ArrayList();
        this.errorHandler = new DefaultResponseErrorHandler();
        this.headersExtractor = new RestTemplate.HeadersExtractor();
        this.messageConverters.add(new ByteArrayHttpMessageConverter());
        this.messageConverters.add(new StringHttpMessageConverter());
        this.messageConverters.add(new ResourceHttpMessageConverter(false));

        try {
            this.messageConverters.add(new SourceHttpMessageConverter());
        } catch (Error var2) {
            ;
        }

        this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
        if(romePresent) {
            this.messageConverters.add(new AtomFeedHttpMessageConverter());
            this.messageConverters.add(new RssChannelHttpMessageConverter());
        }

        if(jackson2XmlPresent) {
            this.messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
        } else if(jaxb2Present) {
            this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
        }

        if(jackson2Present) {
            this.messageConverters.add(new MappingJackson2HttpMessageConverter());
        } else if(gsonPresent) {
            this.messageConverters.add(new GsonHttpMessageConverter());
        } else if(jsonbPresent) {
            this.messageConverters.add(new JsonbHttpMessageConverter());
        }

        if(jackson2SmilePresent) {
            this.messageConverters.add(new MappingJackson2SmileHttpMessageConverter());
        }

        if(jackson2CborPresent) {
            this.messageConverters.add(new MappingJackson2CborHttpMessageConverter());
        }

        this.uriTemplateHandler = initUriTemplateHandler();
    }

构造函数中会根据各种boolean标志添加很多MessageConverter，而这些boolean标志来自

    static {
        ClassLoader classLoader = RestTemplate.class.getClassLoader();
        romePresent = ClassUtils.isPresent("com.rometools.rome.feed.WireFeed", classLoader);
        jaxb2Present = ClassUtils.isPresent("javax.xml.bind.Binder", classLoader);
        jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) && ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);
        jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", classLoader);
        jackson2SmilePresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.smile.SmileFactory", classLoader);
        jackson2CborPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.cbor.CBORFactory", classLoader);
        gsonPresent = ClassUtils.isPresent("com.google.gson.Gson", classLoader);
        jsonbPresent = ClassUtils.isPresent("javax.json.bind.Jsonb", classLoader);
    }

在发请求时

    public <T> ResponseEntity<T> postForEntity(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables) throws RestClientException {
        RequestCallback requestCallback = this.httpEntityCallback(request, responseType);
        ResponseExtractor<ResponseEntity<T>> responseExtractor = this.responseEntityExtractor(responseType);
        return (ResponseEntity)nonNull(this.execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables));
    }

会创建一个ResponseExtractor

    private class ResponseEntityResponseExtractor<T> implements ResponseExtractor<ResponseEntity<T>> {
        @Nullable
        private final HttpMessageConverterExtractor<T> delegate;

        public ResponseEntityResponseExtractor(@Nullable Type responseType) {
            if(responseType != null && Void.class != responseType) {
                this.delegate = new HttpMessageConverterExtractor(responseType, RestTemplate.this.getMessageConverters(), RestTemplate.this.logger);
            } else {
                this.delegate = null;
            }

        }

可见是根据responseType创建了一个代理，然后代理中包含了所有添加过的MessageConverter

而在execute中会调用

    protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
        Assert.notNull(url, "URI is required");
        Assert.notNull(method, "HttpMethod is required");
        ClientHttpResponse response = null;

        Object var14;
        try {
            ClientHttpRequest request = this.createRequest(url, method);
            if(requestCallback != null) {
                requestCallback.doWithRequest(request);
            }

            response = request.execute();
            this.handleResponse(url, method, response);
            var14 = responseExtractor != null?responseExtractor.extractData(response):null;

即responseExecutor.extractData，来看下这个函数

    public T extractData(ClientHttpResponse response) throws IOException {
        MessageBodyClientHttpResponseWrapper responseWrapper = new MessageBodyClientHttpResponseWrapper(response);
        if(responseWrapper.hasMessageBody() && !responseWrapper.hasEmptyMessageBody()) {
            MediaType contentType = this.getContentType(responseWrapper);

            try {
                Iterator var4 = this.messageConverters.iterator();

                while(var4.hasNext()) {
                    HttpMessageConverter<?> messageConverter = (HttpMessageConverter)var4.next();
                    if(messageConverter instanceof GenericHttpMessageConverter) {
                        GenericHttpMessageConverter<?> genericMessageConverter = (GenericHttpMessageConverter)messageConverter;
                        if(genericMessageConverter.canRead(this.responseType, (Class)null, contentType)) {
                            if(this.logger.isDebugEnabled()) {
                                ResolvableType resolvableType = ResolvableType.forType(this.responseType);
                                this.logger.debug("Reading to [" + resolvableType + "]");
                            }

                            return genericMessageConverter.read(this.responseType, (Class)null, responseWrapper);
                        }
                    }

                    if(this.responseClass != null && messageConverter.canRead(this.responseClass, contentType)) {
                        if(this.logger.isDebugEnabled()) {
                            String className = this.responseClass.getName();
                            this.logger.debug("Reading to [" + className + "] as \"" + contentType + "\"");
                        }

                        return messageConverter.read(this.responseClass, responseWrapper);
                    }
                }
            } catch (HttpMessageNotReadableException | IOException var8) {
                throw new RestClientException("Error while extracting response for type [" + this.responseType + "] and content type [" + contentType + "]", var8);
            }

            throw new RestClientException("Could not extract response: no suitable HttpMessageConverter found for response type [" + this.responseType + "] and content type [" + contentType + "]");
        } else {
            return null;
        }
    }

所以当你发现使用RestTemplate发请求后数据被修改的时候，要检查相应的content type，要检查RestTemplate中有哪些MessageConverter（包括各个boolean标志），

如果确定数据不需要被修改时，可以调用RestTemplate.setMessageConverters方法，传入默认的StringHttpMessageConverter即可；