java B2B2C Springboot电子商务平台源码-Feign设计原理

什么是Feign？

Feign 的英文表意为“假装，伪装，变形”， 是一个http请求调用的轻量级框架，可以以Java接口注解的方式调用Http请求，而不用像Java中通过封装HTTP请求报文的方式直接调用。Feign通过处理注解，将请求模板化，当实际调用的时候，传入参数，根据参数再应用到请求上，进而转化成真正的请求，这种请求相对而言比较直观。

Feign被广泛应用在Spring Cloud 的解决方案中，是学习基于Spring Cloud 微服务架构不可或缺的重要组件。

1、如何启用

启动配置上检查是否有@EnableFeignClients注解，如果有该注解，则开启包扫描，扫描被@FeignClient注解接口。扫描出该注解后，通过beanDefinition注入到IOC容器中，方便后续被调用使用。

在FeignClientsRegistrar中，registerFeignClients()完成了注册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()); ...... //遍历该项目所需调用的服务 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; //获取feign中的详细信息 AnnotationMetadata annotationMetadata = beanDefinition.getMetadata(); Map<String, Object> attributes = annotationMetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName()); String name = this.getClientName(attributes); //注册配置信息 this.registerClientConfiguration(registry, name, attributes.get("configuration")); //注册feign客户端 this.registerFeignClient(registry, annotationMetadata, attributes); } } } }

注册feign客户端，包括使用注解时配置的所有信息。

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); }

2、如何发起请求

ReflectiveFeign内部使用了jdk的动态代理为目标接口生成了一个动态代理类，这里会生成一个InvocationHandler(jdk动态代理原理)统一的方法拦截器，同时为接口的每个方法生成一个SynchronousMethodHandler拦截器，并解析方法上的 元数据，生成一个http请求模板。

在SynchronousMethodHandler类中生成RequestTemplate发起请求。

 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; } } }

 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 10 response.toBuilder().request(request).build(); } catch (IOException e) { if (logLevel != Logger.Level.NONE) { logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start)); } throw errorExecuting(request, e); } }

发送http请求

 @Override public 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 HttpURLConnection connection = (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); boolean gzipEncodedRequest = contentEncodingValues != null && contentEncodingValues.contains(ENCODING_GZIP); boolean deflateEncodedRequest = 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; }

java B2B2C Springboot电子商务平台源码