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

秒速五厘米 2022-10-01 11:52 118阅读 0赞

什么是Feign？

电子商务平台源码请加企鹅求求：一零三八七七四六二六。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);
                    }
                }
            }
          }
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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);
        }
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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;
          }
        }
      }
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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);
        }
      }
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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;
        }
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[java B2B2C Springboot电子商务平台源码][java B2B2C Springboot]

转载于:https://juejin.im/post/5cb921146fb9a068a84fe3d2

[java B2B2C Springboot]: https://link.juejin.im?target=https%3A%2F%2F2147775633.iteye.com%2Fblog%2F2434341