什么是Feign？

電子商務(wù)平臺源碼請加企鵝求求：一零三八七七四六二六。Feign 的英文表意為“假裝，偽裝，變形”， 是一個http請求調(diào)用的輕量級框架，可以以Java接口注解的方式調(diào)用Http請求，而不用像Java中通過封裝HTTP請求報文的方式直接調(diào)用。Feign通過處理注解，將請求模板化，當(dāng)實(shí)際調(diào)用的時候，傳入?yún)?shù)，根據(jù)參數(shù)再應(yīng)用到請求上，進(jìn)而轉(zhuǎn)化成真正的請求，這種請求相對而言比較直觀。

Feign被廣泛應(yīng)用在Spring Cloud 的解決方案中，是學(xué)習(xí)基于Spring Cloud 微服務(wù)架構(gòu)不可或缺的重要組件。

1、如何啟用

啟動配置上檢查是否有@EnableFeignClients注解，如果有該注解，則開啟包掃描，掃描被@FeignClient注解接口。掃描出該注解后，通過beanDefinition注入到IOC容器中，方便后續(xù)被調(diào)用使用。

在FeignClientsRegistrar中，registerFeignClients()完成了注冊feign的操作。

public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {ClassPathScanningCandidateComponentProvider scanner = this.getScanner();scanner.setResourceLoader(this.resourceLoader);Map<String, Object> attrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName());......//遍歷該項目所需調(diào)用的服務(wù) Iterator var17 = ((Set)basePackages).iterator();while(var17.hasNext()) {String basePackage = (String)var17.next();Set<BeanDefinition> candidateComponents = scanner.findCandidateComponents(basePackage);Iterator var21 = candidateComponents.iterator();while(var21.hasNext()) {BeanDefinition candidateComponent = (BeanDefinition)var21.next();if (candidateComponent instanceof AnnotatedBeanDefinition) {AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition)candidateComponent;//獲取feign中的詳細(xì)信息AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();Map<String, Object> attributes = annotationMetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName());String name = this.getClientName(attributes);//注冊配置信息this.registerClientConfiguration(registry, name, attributes.get("configuration"));//注冊feign客戶端this.registerFeignClient(registry, annotationMetadata, attributes);}}}} 復(fù)制代碼

注冊feign客戶端，包括使用注解時配置的所有信息。

private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {String className = annotationMetadata.getClassName();BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);this.validate(attributes);definition.addPropertyValue("url", this.getUrl(attributes));definition.addPropertyValue("path", this.getPath(attributes));String name = this.getName(attributes);definition.addPropertyValue("name", name);definition.addPropertyValue("type", className);definition.addPropertyValue("decode404", attributes.get("decode404"));definition.addPropertyValue("fallback", attributes.get("fallback"));definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));definition.setAutowireMode(2);String alias = name + "FeignClient";AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();boolean primary = ((Boolean)attributes.get("primary")).booleanValue();beanDefinition.setPrimary(primary);String qualifier = this.getQualifier(attributes);if (StringUtils.hasText(qualifier)) {alias = qualifier;}BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, new String[]{alias});BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);} 復(fù)制代碼

2、如何發(fā)起請求

ReflectiveFeign內(nèi)部使用了jdk的動態(tài)代理為目標(biāo)接口生成了一個動態(tài)代理類，這里會生成一個InvocationHandler(jdk動態(tài)代理原理)統(tǒng)一的方法攔截器，同時為接口的每個方法生成一個SynchronousMethodHandler攔截器，并解析方法上的 元數(shù)據(jù)，生成一個http請求模板。

在SynchronousMethodHandler類中生成RequestTemplate發(fā)起請求。

public Object invoke(Object[] argv) throws Throwable {RequestTemplate template = buildTemplateFromArgs.create(argv);Retryer retryer = this.retryer.clone();while (true) {try {return executeAndDecode(template);} catch (RetryableException e) {retryer.continueOrPropagate(e);if (logLevel != Logger.Level.NONE) {logger.logRetry(metadata.configKey(), logLevel);}continue;}}} 復(fù)制代碼 Object executeAndDecode(RequestTemplate template) throws Throwable {Request request = targetRequest(template);Response response;long start = System.nanoTime();try {response = client.execute(request, options);// ensure the request is set. TODO: remove in Feign 10response.toBuilder().request(request).build();} catch (IOException e) {if (logLevel != Logger.Level.NONE) {logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));}throw errorExecuting(request, e);}} 復(fù)制代碼

發(fā)送http請求

@Overridepublic Response execute(Request request, Options options) throws IOException {HttpURLConnection connection = convertAndSend(request, options);return convertResponse(connection).toBuilder().request(request).build();}HttpURLConnection convertAndSend(Request request, Options options) throws IOException {final HttpURLConnectionconnection =(HttpURLConnection) new URL(request.url()).openConnection();if (connection instanceof HttpsURLConnection) {HttpsURLConnection sslCon = (HttpsURLConnection) connection;if (sslContextFactory != null) {sslCon.setSSLSocketFactory(sslContextFactory);}if (hostnameVerifier != null) {sslCon.setHostnameVerifier(hostnameVerifier);}}connection.setConnectTimeout(options.connectTimeoutMillis());connection.setReadTimeout(options.readTimeoutMillis());connection.setAllowUserInteraction(false);connection.setInstanceFollowRedirects(true);connection.setRequestMethod(request.method());Collection<String> contentEncodingValues = request.headers().get(CONTENT_ENCODING);booleangzipEncodedRequest =contentEncodingValues != null && contentEncodingValues.contains(ENCODING_GZIP);booleandeflateEncodedRequest =contentEncodingValues != null && contentEncodingValues.contains(ENCODING_DEFLATE);boolean hasAcceptHeader = false;Integer contentLength = null;for (String field : request.headers().keySet()) {if (field.equalsIgnoreCase("Accept")) {hasAcceptHeader = true;}for (String value : request.headers().get(field)) {if (field.equals(CONTENT_LENGTH)) {if (!gzipEncodedRequest && !deflateEncodedRequest) {contentLength = Integer.valueOf(value);connection.addRequestProperty(field, value);}} else {connection.addRequestProperty(field, value);}}}// Some servers choke on the default accept string.if (!hasAcceptHeader) {connection.addRequestProperty("Accept", "*/*");}if (request.body() != null) {if (contentLength != null) {connection.setFixedLengthStreamingMode(contentLength);} else {connection.setChunkedStreamingMode(8196);}connection.setDoOutput(true);OutputStream out = connection.getOutputStream();if (gzipEncodedRequest) {out = new GZIPOutputStream(out);} else if (deflateEncodedRequest) {out = new DeflaterOutputStream(out);}try {out.write(request.body());} finally {try {out.close();} catch (IOException suppressed) { // NOPMD}}}return connection;} 復(fù)制代碼

java B2B2C Springboot電子商務(wù)平臺源碼

轉(zhuǎn)載于:https://juejin.im/post/5cb921146fb9a068a84fe3d2

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