RestTemplate 设置可解析的响应类型
今天在做项目的环境迁移工作，恶心的就是环境配置和程序中的可配置参数的更新，这是一件及需要细心与耐心的工作，很无聊。但是，在迁移部署好简单测试时，还是遇到一个未曾出现过的问题，即使用的已经很熟悉的restTemplate。
问题原因
先来看一下问题产生的原因，如下：
org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [class com.ctspcl.sms.gateway.manager.sms.dahansantong.base.DaHanSanTongResult] and content type [application/octet-stream]
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:110)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:655)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:613)
at org.springframework.web.client.RestTemplate.postForObject(RestTemplate.java:380)
问题追踪
上述异常什么意思：即服务器返回的响应是 application/octet-stream 格式的，而我的restTemplate没有解析这种响应的能力。一般在后台开发时，一般会以application/json 作为响应和请求的格式，而restTemplate若没有指定响应解析类型，则默认也为application/json 格式。
已RestTemplate为开始，追踪一下源码：
// postEntity调用execute函数向服务器发起请求
@Override
public <T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Object... uriVariables)
throws RestClientException {
RequestCallback requestCallback = httpEntityCallback(request, responseType);
ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
}
// 执行execute
@Override
public <T> T execute(String url, HttpMethod method, RequestCallback requestCallback,
ResponseExtractor<T> responseExtractor, Object... uriVariables) throws RestClientException {
URI expanded = getUriTemplateHandler().expand(url, uriVariables);
return doExecute(expanded, method, requestCallback, responseExtractor);
}
protected <T> T doExecute(URI url, HttpMethod method, RequestCallback requestCallback,
ResponseExtractor<T> responseExtractor) throws RestClientException {
Assert.notNull(url, "'url' must not be null");
Assert.notNull(method, "'method' must not be null");
ClientHttpResponse response = null;
try {
ClientHttpRequest request = createRequest(url, method);
if (requestCallback != null) {
requestCallback.doWithRequest(request);
}
response = request.execute();
handleResponse(url, method, response);
if (responseExtractor != null) {
// 对结果进行解析处理
return responseExtractor.extractData(response);
}
else {
return null;
}
}
catch (IOException ex) {
String resource = url.toString();
String query = url.getRawQuery();
resource = (query != null ? resource.substring(0, resource.indexOf('?')) : resource);
throw new ResourceAccessException("I/O error on " + method.name() +
" request for \"" + resource + "\": " + ex.getMessage(), ex);
}
finally {
if (response != null) {
response.close();
}
}
}
接着跟踪到HttpMessageConverterExtractor 类：
public T extractData(ClientHttpResponse response) throws IOException {
MessageBodyClientHttpResponseWrapper responseWrapper = new MessageBodyClientHttpResponseWrapper(response);
if (!responseWrapper.hasMessageBody() || responseWrapper.hasEmptyMessageBody()) {
return null;
}
// 获取response的媒体格式
MediaType contentType = getContentType(responseWrapper);
for (HttpMessageConverter<?> messageConverter : this.messageConverters) {
if (messageConverter instanceof GenericHttpMessageConverter) {
GenericHttpMessageConverter<?> genericMessageConverter =
(GenericHttpMessageConverter<?>) messageConverter;
if (genericMessageConverter.canRead(this.responseType, null, contentType)) {
if (logger.isDebugEnabled()) {
logger.debug("Reading [" + this.responseType + "] as \"" +
contentType + "\" using [" + messageConverter + "]");
}
return (T) genericMessageConverter.read(this.responseType, null, responseWrapper);
}
}
if (this.responseClass != null) {
if (messageConverter.canRead(this.responseClass, contentType)) {
if (logger.isDebugEnabled()) {
logger.debug("Reading [" + this.responseClass.getName() + "] as \"" +
contentType + "\" using [" + messageConverter + "]");
}
return (T) messageConverter.read((Class) this.responseClass, responseWrapper);
}
}
}
throw new RestClientException("Could not extract response: no suitable HttpMessageConverter found " +
"for response type [" + this.responseType + "] and content type [" + contentType + "]");
}
// 获取响应格式，若contentType为空，默认为MediaType.APPLICATION_OCTET_STREAM;
private MediaType getContentType(ClientHttpResponse response) {
MediaType contentType = response.getHeaders().getContentType();
if (contentType == null) {
if (logger.isTraceEnabled()) {
logger.trace("No Content-Type header found, defaulting to application/octet-stream");
}
contentType = MediaType.APPLICATION_OCTET_STREAM;
}
return contentType;
}
从上面可以看出，如果从response中获取的contentType为空，则默认设置为MediaType.APPLICATION_OCTET_STREAM 类型。
那我们再来看看，若作为服务端的自己，如果不设置响应类型，返回客户端的将是什么类型呢？
以 HttpServletResponse 追踪到 ResponseIncludeWrapper， 其getContentType() 如下：
@Override
public String getContentType() {
if (contentType == null) {
String url = request.getRequestURI();
String mime = context.getMimeType(url);
if (mime != null) {
setContentType(mime);
} else {
// return a safe value
setContentType("application/x-octet-stream");
}
}
return contentType;
}
解决问题
既然是不支持的响应类型，这里添加相应的解析器即可，解决方法：
// 关掉cookie自动管理，设置服务最大连接数 和 每个接口最大连接数
CloseableHttpClient httpClient
= HttpClients.custom().disableCookieManagement()
.setSSLHostnameVerifier(new NoopHostnameVerifier())
.setMaxConnTotal(8192)
.setMaxConnPerRoute(256)
.build();
HttpComponentsClientHttpRequestFactory requestFactory
= new HttpComponentsClientHttpRequestFactory();
requestFactory.setHttpClient(httpClient);
// 设置请求超时时长
requestFactory.setConnectionRequestTimeout(30000);
requestFactory.setConnectTimeout(30000);
requestFactory.setReadTimeout(30000);
// 设置restTemplate拦截器
RestTemplate restTemplate = new RestTemplate(requestFactory);
List<ClientHttpRequestInterceptor> interceptorList = new ArrayList<>();
interceptorList.add(new RestTemplateHeaderInterceptor());
restTemplate.setInterceptors(interceptorList);
// 设置可解析的响应类型-json和cotet-stream；编码格式utf-8
MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter = new MappingJackson2HttpMessageConverter(); mappingJackson2HttpMessageConverter.setSupportedMediaTypes(Arrays.asList(MediaType.APPLICATION_JSON, MediaType.APPLICATION_OCTET_STREAM));
restTemplate.getMessageConverters().add(mappingJackson2HttpMessageConverter);
restTemplate.getMessageConverters().add(new StringHttpMessageConverter(StandardCharsets.UTF_8));
return restTemplate;
参考博客
- RestTemplate对于响应的处理解析：https://anguslean.github.io/2018/07/06/Java/Framework/spring/RestTemplate%E5%AF%B9%E4%BA%8E%E5%93%8D%E5%BA%94%E7%9A%84%E5%A4%84%E7%90%86%E8%A7%A3%E6%9E%90/
- Could not extract response: no suitable HttpMessageConverter found for response type：http://www.technicalkeeda.com/spring-tutorials/could-not-extract-response-no-suitable-httpmessageconverter-found-for-response-type
