在微服务中，rest服务互相调用是很普遍的，我们该如何优雅地调用，其实在Spring框架使用RestTemplate类可以优雅地进行rest服务互相调用，它简化了与http服务的通信方式，统一了RESTful的标准，封装了http链接，操作使用简便，还可以自定义RestTemplate所需的模式。其中：
1.RestTemplate默认使用HttpMessageConverter实例将HTTP消息转换成POJO或者从POJO转换成HTTP消息。默认情况下会注册主mime类型的转换器，但也可以通过setMessageConverters注册自定义转换器。
2.RestTemplate使用了默认的DefaultResponseErrorHandler，对40X Bad Request或50X internal异常error等错误信息捕捉。
3.RestTemplate还可以使用拦截器interceptor，进行对请求链接跟踪，以及统一head的设置。
其中，RestTemplate还定义了很多的REST资源交互的方法，其中的大多数都对应于HTTP的方法，如下：
- RestTemplate源码
1.1 默认调用链路
restTemplate进行API调用时，默认调用链：
###########1.使用createRequest创建请求########
resttemplate->execute()->doExecute()
HttpAccessor->createRequest()
//获取拦截器Interceptor，InterceptingClientHttpRequestFactory，SimpleClientHttpRequestFactory
InterceptingHttpAccessor->getRequestFactory()
//获取默认的SimpleBufferingClientHttpRequest
SimpleClientHttpRequestFactory->createRequest()
#######2.获取响应response进行处理###########
AbstractClientHttpRequest->execute()->executeInternal()
AbstractBufferingClientHttpRequest->executeInternal()
###########3.异常处理#####################
resttemplate->handleResponse()
##########4.响应消息体封装为java对象#######
HttpMessageConverterExtractor->extractData()1.2 restTemplate->doExecute()
在默认调用链中，restTemplate 进行API调用都会调用 doExecute 方法，此方法主要可以进行如下步骤：
1）使用createRequest创建请求，获取响应
2）判断响应是否异常，处理异常
3）将响应消息体封装为java对象
[@Nullable](https://my.oschina.net/u/2896689)
protected <T> T doExecute(URI url, [@Nullable](https://my.oschina.net/u/2896689) HttpMethod method, [@Nullable](https://my.oschina.net/u/2896689) RequestCallback requestCallback,
[@Nullable](https://my.oschina.net/u/2896689) ResponseExtractor<T> responseExtractor) throws RestClientException {
Assert.notNull(url, "URI is required");
Assert.notNull(method, "HttpMethod is required");
ClientHttpResponse response = null;
try {
//使用createRequest创建请求
ClientHttpRequest request = createRequest(url, method);
if (requestCallback != null) {
requestCallback.doWithRequest(request);
}
//获取响应response进行处理
response = request.execute();
//异常处理
handleResponse(url, method, response);
//响应消息体封装为java对象
return (responseExtractor != null ? responseExtractor.extractData(response) : 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();
}
}
}1.3 InterceptingHttpAccessor->getRequestFactory()
在默认调用链中，InterceptingHttpAccessor的getRequestFactory()方法中，如果没有设置interceptor拦截器，就返回默认的SimpleClientHttpRequestFactory，反之，返回InterceptingClientHttpRequestFactory的requestFactory，可以通过resttemplate.setInterceptors设置自定义拦截器interceptor。
//Return the request factory that this accessor uses for obtaining client request handles.
public ClientHttpRequestFactory getRequestFactory() {
//获取拦截器interceptor(自定义的)
List<ClientHttpRequestInterceptor> interceptors = getInterceptors();
if (!CollectionUtils.isEmpty(interceptors)) {
ClientHttpRequestFactory factory = this.interceptingRequestFactory;
if (factory == null) {
factory = new InterceptingClientHttpRequestFactory(super.getRequestFactory(), interceptors);
this.interceptingRequestFactory = factory;
}
return factory;
}
else {
return super.getRequestFactory();
}
}
然后再调用SimpleClientHttpRequestFactory的createRequest创建连接：
[@Override](https://my.oschina.net/u/1162528)
public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {
HttpURLConnection connection = openConnection(uri.toURL(), this.proxy);
prepareConnection(connection, httpMethod.name());
if (this.bufferRequestBody) {
return new SimpleBufferingClientHttpRequest(connection, this.outputStreaming);
}
else {
return new SimpleStreamingClientHttpRequest(connection, this.chunkSize, this.outputStreaming);
}
}1.4 resttemplate->handleResponse()
在默认调用链中，resttemplate的handleResponse，响应处理，包括异常处理，而且异常处理可以通过调用setErrorHandler方法设置自定义的ErrorHandler，实现对请求响应异常的判别和处理。自定义的ErrorHandler需实现ResponseErrorHandler接口，同时Spring boot也提供了默认实现DefaultResponseErrorHandler，因此也可以通过继承该类来实现自己的ErrorHandler。
DefaultResponseErrorHandler默认对40X Bad Request或50X internal异常error等错误信息捕捉。如果想捕捉服务本身抛出的异常信息，需要通过自行实现RestTemplate的ErrorHandler。
ResponseErrorHandler errorHandler = getErrorHandler();
//判断响应是否有异常
boolean hasError = errorHandler.hasError(response);
if (logger.isDebugEnabled()) {
try {
int code = response.getRawStatusCode();
HttpStatus status = HttpStatus.resolve(code);
logger.debug("Response " + (status != null ? status : code));
}catch (IOException ex) {
// ignore
}
}
//有异常进行异常处理
if (hasError) {
errorHandler.handleError(url, method, response);
}
}1.5 HttpMessageConverterExtractor->extractData()
在默认调用链中， HttpMessageConverterExtractor的extractData中进行响应消息体封装为java对象，就需要使用message转换器，可以通过追加的方式增加自定义的messageConverter：先获取现有的messageConverter，再将自定义的messageConverter添加进去。
根据restTemplate的setMessageConverters的源码可得，使用追加的方式可防止原有的messageConverter丢失，源码：
public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
//检验
validateConverters(messageConverters);
// Take getMessageConverters() List as-is when passed in here
if (this.messageConverters != messageConverters) {
//先清除原有的messageConverter
this.messageConverters.clear();
//后加载重新定义的messageConverter
this.messageConverters.addAll(messageConverters);
}
}HttpMessageConverterExtractor的extractData源码：
MessageBodyClientHttpResponseWrapper responseWrapper = new MessageBodyClientHttpResponseWrapper(response);
if (!responseWrapper.hasMessageBody() || responseWrapper.hasEmptyMessageBody()) {
return null;
}
//获取到response的ContentType类型
MediaType contentType = getContentType(responseWrapper);
try {
//依次循环messageConverter进行判断是否符合转换条件，进行转换java对象
for (HttpMessageConverter<?> messageConverter : this.messageConverters) {
//会根据设置的返回类型responseType和contentType参数进行匹配，选择合适的MessageConverter
if (messageConverter instanceof GenericHttpMessageConverter) {
GenericHttpMessageConverter<?> genericMessageConverter =
(GenericHttpMessageConverter<?>) messageConverter;
if (genericMessageConverter.canRead(this.responseType, null, contentType)) {
if (logger.isDebugEnabled()) {
ResolvableType resolvableType = ResolvableType.forType(this.responseType);
logger.debug("Reading to [" + resolvableType + "]");
}
return (T) genericMessageConverter.read(this.responseType, null, responseWrapper);
}
}
if (this.responseClass != null) {
if (messageConverter.canRead(this.responseClass, contentType)) {
if (logger.isDebugEnabled()) {
String className = this.responseClass.getName();
logger.debug("Reading to [" + className + "] as \"" + contentType + "\"");
}
return (T) messageConverter.read((Class) this.responseClass, responseWrapper);
}
}
}
}
.....
}1.6 contentType与messageConverter之间的关系
在HttpMessageConverterExtractor的extractData方法中看出，会根据contentType与responseClass选择messageConverter是否可读、消息转换。关系如下：
- springboot集成RestTemplate
根据上述源码的分析学习，可以轻松，简单地在项目进行对RestTemplate进行优雅地使用，比如增加自定义的异常处理、MessageConverter以及拦截器interceptor。本文使用示例demo，详情请查看接下来的内容。
2.1. 导入依赖：（RestTemplate集成在Web Start中）
<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-web -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>2.2.0.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.10</version>
<scope>provided</scope>
</dependency>2.2. RestTemplat配置：
1.使用ClientHttpRequestFactory属性配置RestTemplat参数，比如ConnectTimeout，ReadTimeout;
2.增加自定义的interceptor拦截器和异常处理;
3.追加message转换器;
4.配置自定义的异常处理.
@Configuration
public class RestTemplateConfig {
@Value("${resttemplate.connection.timeout}")
private int restTemplateConnectionTimeout;
@Value("${resttemplate.read.timeout}")
private int restTemplateReadTimeout;
@Bean
//@LoadBalanced
public RestTemplate restTemplate( ClientHttpRequestFactory simleClientHttpRequestFactory) {
RestTemplate restTemplate = new RestTemplate();
//配置自定义的message转换器
List<HttpMessageConverter<?>> messageConverters = restTemplate.getMessageConverters();
messageConverters.add(new CustomMappingJackson2HttpMessageConverter());
restTemplate.setMessageConverters(messageConverters);
//配置自定义的interceptor拦截器
List<ClientHttpRequestInterceptor> interceptors=new ArrayList<ClientHttpRequestInterceptor>();
interceptors.add(new HeadClientHttpRequestInterceptor());
interceptors.add(new TrackLogClientHttpRequestInterceptor());
restTemplate.setInterceptors(interceptors);
//配置自定义的异常处理
restTemplate.setErrorHandler(new CustomResponseErrorHandler());
restTemplate.setRequestFactory(simleClientHttpRequestFactory);
return restTemplate;
}
@Bean
public ClientHttpRequestFactory simleClientHttpRequestFactory(){
SimpleClientHttpRequestFactory reqFactory= new SimpleClientHttpRequestFactory();
reqFactory.setConnectTimeout(restTemplateConnectionTimeout);
reqFactory.setReadTimeout(restTemplateReadTimeout);
return reqFactory;
}
}2.3. 组件(自定义异常处理、interceptor拦截器、message转化器)
自定义interceptor拦截器，实现ClientHttpRequestInterceptor接口
1.自定义TrackLogClientHttpRequestInterceptor，记录resttemplate的request和response信息，可进行追踪分析；
2.自定义HeadClientHttpRequestInterceptor，设置请求头的参数。API发送各种请求，很多请求都需要用到相似或者相同的Http Header。如果在每次请求之前都把Header填入HttpEntity/RequestEntity，这样的代码会显得十分冗余，可以在拦截器统一设置。
TrackLogClientHttpRequestInterceptor：
/**
* @Auther: ccww
* @Date: 2019/10/25 22:48，记录resttemplate访问信息
* @Description: 记录resttemplate访问信息
*/
@Slf4j
public class TrackLogClientHttpRequestInterceptor implements ClientHttpRequestInterceptor {
public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
trackRequest(request,body);
ClientHttpResponse httpResponse = execution.execute(request, body);
trackResponse(httpResponse);
return httpResponse;
}
private void trackResponse(ClientHttpResponse httpResponse)throws IOException {
log.info("============================response begin==========================================");
log.info("Status code : {}", httpResponse.getStatusCode());
log.info("Status text : {}", httpResponse.getStatusText());
log.info("Headers : {}", httpResponse.getHeaders());
log.info("=======================response end=================================================");
}
private void trackRequest(HttpRequest request, byte[] body)throws UnsupportedEncodingException {
log.info("======= request begin ========");
log.info("uri : {}", request.getURI());
log.info("method : {}", request.getMethod());
log.info("headers : {}", request.getHeaders());
log.info("request body : {}", new String(body, "UTF-8"));
log.info("======= request end ========");
}
}HeadClientHttpRequestInterceptor：
@Slf4j
public class HeadClientHttpRequestInterceptor implements ClientHttpRequestInterceptor {
public ClientHttpResponse intercept(HttpRequest httpRequest, byte[] bytes, ClientHttpRequestExecution clientHttpRequestExecution) throws IOException {
log.info("#####head handle########");
HttpHeaders headers = httpRequest.getHeaders();
headers.add("Accept", "application/json");
headers.add("Accept-Encoding", "gzip");
headers.add("Content-Encoding", "UTF-8");
headers.add("Content-Type", "application/json; charset=UTF-8");
ClientHttpResponse response = clientHttpRequestExecution.execute(httpRequest, bytes);
HttpHeaders headersResponse = response.getHeaders();
headersResponse.add("Accept", "application/json");
return response;
}
}自定义异常处理，可继承DefaultResponseErrorHandler或者实现ResponseErrorHandler接口：
1.实现自定义ErrorHandler的思路是根据响应消息体进行相应的异常处理策略，对于其他异常情况由父类DefaultResponseErrorHandler来进行处理。
2.自定义CustomResponseErrorHandler进行30x异常处理
CustomResponseErrorHandler:
/**
* @Auther: Ccww
* @Date: 2019/10/28 17:00
* @Description: 30X的异常处理
*/
@Slf4j
public class CustomResponseErrorHandler extends DefaultResponseErrorHandler {
@Override
public boolean hasError(ClientHttpResponse response) throws IOException {
HttpStatus statusCode = response.getStatusCode();
if(statusCode.is3xxRedirection()){
return true;
}
return super.hasError(response);
}
@Override
public void handleError(ClientHttpResponse response) throws IOException {
HttpStatus statusCode = response.getStatusCode();
if(statusCode.is3xxRedirection()){
log.info("########30X错误，需要重定向！##########");
return;
}
super.handleError(response);
}
}自定义message转化器
/**
* @Auther: Ccww
* @Date: 2019/10/29 21:15
* @Description: 将Content-Type:"text/html"转换为Map类型格式
*/
public class CustomMappingJackson2HttpMessageConverter extends MappingJackson2HttpMessageConverter {
public CustomMappingJackson2HttpMessageConverter() {
List<MediaType> mediaTypes = new ArrayList<MediaType>();
mediaTypes.add(MediaType.TEXT_PLAIN);
mediaTypes.add(MediaType.TEXT_HTML); //加入text/html类型的支持
setSupportedMediaTypes(mediaTypes);// tag6
}
}