【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

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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;
}
}