SpringMvc接口中转设计（策略+模板方法）

一、前言

　　最近带着两个兄弟做支付宝小程序后端相关的开发，小程序首页涉及到很多查询的服务。小程序后端服务在我司属于互联网域，相关的查询服务已经在核心域存在了，查询这块所要做的工作就是做接口中转。参考了微信小程序的代码，发现他们要么新写一个接口调用，要么新写一个接口包裹多个接口调用。这种方式不容易扩展。由于开发周期比较理想，所以决定设计一个接口中转器。

二、接口中转器整体设计

　　

三、接口中转器核心Bean

@Bean
public SimpleUrlHandlerMapping directUrlHandlerMapping(@Autowired RequestMappingHandlerAdapter handlerAdapter
        , ObjectProvider<List<IDirectUrlProcessor>> directUrlProcessorsProvider) {
    List<IDirectUrlProcessor> directUrlProcessors = directUrlProcessorsProvider.getIfAvailable();
    Assert.notEmpty(directUrlProcessors, "接口直达解析器（IDirectUrlProcessor）列表不能为空！！！");
    SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
    Map<String, Controller> urlMappings = Maps.newHashMap();
    urlMappings.put("/alipay-applet/direct/**", new AbstractController() {
        @Override
        protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception {
            for (IDirectUrlProcessor directUrlProcessor : directUrlProcessors) {
                if (directUrlProcessor.support(request)) {
                    String accept = request.getHeader("Accept");
                    request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, Sets.newHashSet(MediaType.APPLICATION_JSON_UTF8));
                    if (StringUtils.isNotBlank(accept) && !accept.contains(MediaType.ALL_VALUE)) {
                        request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, Sets.newHashSet(
                                Arrays.stream(accept.split(","))
                                        .map(value -> MediaType.parseMediaType(value.trim()))
                                        .toArray(size -> new MediaType[size])
                        ));
                    }
                    HandlerMethod handlerMethod = new HandlerMethod(directUrlProcessor, ReflectionUtils.findMethod(IDirectUrlProcessor.class, "handle", HttpServletRequest.class));
                    return handlerAdapter.handle(request, response, handlerMethod);
                }
            }
            throw new RuntimeException("未找到具体的接口直达处理器...");
        }
    });
    mapping.setUrlMap(urlMappings);
    mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
    return mapping;
}

　　关于核心Bean的示意如下。

• 使用SimpleUrlHandlerMapping 来过滤请求路径中包含"/alipay-applet/direct/**"的请求，认为这样的请求需要做接口中转。
• 针对中转的请求使用一个Controller进行处理，即AbstractController的一个实例，并重写其handleRequestInternal。
• 对于不同的中转请求找到对应的中转处理器，然后创建相应的HandlerMethod ，再借助SpringMvc的RequestMappingHandlerAdapter调用具体中转处理器接口以及返回值的处理。

　　为什么要使用RequestMappingHandlerAdapter？因为中转处理器的返回值类型统一为ReponseEntity<String>，想借助RequestMappingHandlerAdapter中的HandlerMethodReturnValueHandler来处理返回结果。

request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, Sets.newHashSet(MediaType.APPLICATION_JSON_UTF8));

　　为什么会有这段代码？这是HandlerMethodReturnValueHandler调用的MessageConverter需要的，代码如下。

　　

　　我手动设置的原因是因为RequestMappingHandlerAdapter是和RequestMappingHandlerMapping配合使用的，RequestMappingHandlerMapping会在request的attribute中设置RequestMappingInfo.producesCondition.getProducibleMediaTypes()这个值。具体参考代码如下。

org.springframework.web.servlet.mvc.method.RequestMappingInfoHandlerMapping#handleMatch
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#createRequestMappingInfo

四、请求转发RestTempate配置

@Bean
public RestTemplate directRestTemplate() throws Exception {
    try {
        RestTemplate restTemplate = new RestTemplate(clientHttpRequestFactory());
        restTemplate.setErrorHandler(new DefaultResponseErrorHandler() {
            @Override
            public void handleError(ClientHttpResponse response) throws IOException {
                throw new RestClientResponseException(response.getStatusCode().value() + " " + response.getStatusText(),
                        response.getStatusCode().value()
                        , response.getStatusText()
                        , response.getHeaders()
                        , getResponseBody(response)
                        , getCharset(response));
            }

            protected byte[] getResponseBody(ClientHttpResponse response) {
                try {
                    InputStream responseBody = response.getBody();
                    if (responseBody != null) {
                        return FileCopyUtils.copyToByteArray(responseBody);
                    }
                } catch (IOException ex) {
                    // ignore
                }
                return new byte[0];
            }

            protected Charset getCharset(ClientHttpResponse response) {
                HttpHeaders headers = response.getHeaders();
                MediaType contentType = headers.getContentType();
                return contentType != null ? contentType.getCharset() : null;
            }
        });
        // 修改StringHttpMessageConverter内容转换器
        restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(StandardCharsets.UTF_8));
        return restTemplate;
    } catch (Exception e) {
        throw new Exception("网络异常或请求错误.", e);
    }
}

/**
 * 接受未信任的请求
 *
 * @return
 * @throws KeyStoreException
 * @throws NoSuchAlgorithmException
 * @throws KeyManagementException
 */
@Bean
public ClientHttpRequestFactory clientHttpRequestFactory()
        throws KeyStoreException, NoSuchAlgorithmException, KeyManagementException {
    HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
    SSLContext sslContext = new SSLContextBuilder().loadTrustMaterial(null, (arg0, arg1) -> true).build();

    httpClientBuilder.setSSLContext(sslContext)
            .setMaxConnTotal(MAX_CONNECTION_TOTAL)
            .setMaxConnPerRoute(ROUTE_MAX_COUNT)
            .evictIdleConnections(CONNECTION_IDLE_TIME_OUT, TimeUnit.MILLISECONDS);

    httpClientBuilder.setRetryHandler(new DefaultHttpRequestRetryHandler(RETRY_COUNT, true));
    httpClientBuilder.setKeepAliveStrategy(new DefaultConnectionKeepAliveStrategy());
    CloseableHttpClient client = httpClientBuilder.build();

    HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(client);
    clientHttpRequestFactory.setConnectTimeout(CONNECTION_TIME_OUT);
    clientHttpRequestFactory.setReadTimeout(READ_TIME_OUT);
    clientHttpRequestFactory.setConnectionRequestTimeout(CONNECTION_REQUEST_TIME_OUT);
    clientHttpRequestFactory.setBufferRequestBody(false);
    return clientHttpRequestFactory;
}

　　关于RestTemplte配置的示意如下。

• 设置RestTemplte统一异常处理器，统一返回RestClientResponseException。
• 设置RestTemplte HttpRequestFactory连接池工厂（HttpClientBuilder的build方法会创建PoolingHttpClientConnectionManager）。
• 设置RestTemplte StringHttpMessageConverter的编码格式为UTF-8。
• 设置最大连接数、路由并发数、重试次数、连接超时、数据超时、连接等待、连接空闲超时等参数。

五、接口中转处理器设计

 　　考虑到针对不同类型的接口直达请求会对应不同的接口中转处理器，设计原则一定要明确（open-close）。平时也阅读spingmvc源码，很喜欢其中消息转换器和参数解析器的设计模式（策略+模板方法）。仔细想想，接口中转处理器的设计也可以借鉴一下。

　　接口中转处理器接口类

public interface IDirectUrlProcessor {
    /**
     * 接口直达策略方法
     * 处理接口直达请求
     * */
    ResponseEntity<String> handle(HttpServletRequest request) throws Exception;

    /**
     * 处理器是否支持当前直达请求
     * */
    boolean support(HttpServletRequest request);
}

　　接口定义了子类需要根据不同的策略实现的两个方法。

　　接口中转处理器抽象类

public abstract class AbstractIDirectUrlProcessor implements IDirectUrlProcessor {
    private static Logger LOGGER = LoggerFactory.getLogger(AbstractIDirectUrlProcessor.class);

    @Autowired
    private RestTemplate directRestTemplate;

    /**
     * 接口直达模板方法
     * */
    protected ResponseEntity<String> handleRestfulCore(HttpServletRequest request, URI uri, String userId) throws Exception {
        HttpMethod method = HttpMethod.resolve(request.getMethod());
        Object body;
        if (method == HttpMethod.GET) {
            body = null;
        } else {
            body = new BufferedReader(new InputStreamReader(request.getInputStream()))
                    .lines()
                    .collect(Collectors.joining());
            // post/form
            if (StringUtils.isBlank((String) body)) {
                MultiValueMap<String, String> params = new LinkedMultiValueMap<>();
                if (!CollectionUtils.isEmpty(request.getParameterMap())) {
                    request.getParameterMap()
                            .forEach(
                                    (paramName, paramValues) -> Arrays.stream(paramValues)
                                            .forEach(paramValue -> params.add(paramName, paramValue))
                            );
                    body = params;
                }
            }
        }

        HttpHeaders headers = new HttpHeaders();
        CollectionUtils.toIterator(request.getHeaderNames())
                .forEachRemaining(headerName -> CollectionUtils.toIterator(request.getHeaders(headerName))
                        .forEachRemaining(headerValue -> headers.add(headerName, headerValue)));

        RequestEntity directRequest = new RequestEntity(body, headers, method, uri);
        try {
            LOGGER.info(String.format("接口直达UserId = %s, RequestEntity = %s", userId, directRequest));
            ResponseEntity<String> directResponse = directRestTemplate.exchange(directRequest, String.class);
            LOGGER.info(String.format("接口直达UserId = %s, URL = %s, ResponseEntity = %s", userId, directRequest.getUrl(), directResponse));
            return ResponseEntity.ok(directResponse.getBody());
        } catch (RestClientResponseException e) {
            LOGGER.error("restapi 内部异常", e);
            return ResponseEntity.status(e.getRawStatusCode()).body(e.getResponseBodyAsString());
        } catch (Exception e) {
            LOGGER.error("restapi 内部异常，未知错误...", e);
            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("restapi 内部异常，未知错误...");
        }
    }
}

　　抽象类中带有接口直达模板方法，子类可以直接调用，完成请求的转发。

　　接口中转处理器具体实现类

/**
 * 自助服务直达查询
 */
@Component
public class SelfServiceIDirectUrlProcessor extends AbstractIDirectUrlProcessor {

    private static final String CONDITION_PATH = "/alipay-applet/direct";

    @Reference(group = "wmhcomplexmsgcenter")
    private IAlipayAppletUserInfoSV alipayAppletUserInfoSV;

    private void buildQueryAndPath(UriComponentsBuilder uriComponentsBuilder, AlipayAppletUser userInfo) {
        uriComponentsBuilder.path("/" + userInfo.getTelephone())
                .queryParam("channel", "10008")
                .queryParam("uid", userInfo.getUserId())
                .queryParam("provinceid", userInfo.getProvinceCode());
    }

    public ResponseEntity<String> handle(HttpServletRequest request) throws Exception {
        String userId = JwtUtils.resolveUserId();
        AlipayAppletUser userInfo = alipayAppletUserInfoSV.queryUserInfo(userId);

        UriComponentsBuilder uriComponentsBuilder = UriComponentsBuilder.fromHttpUrl(AppletConstants.ISERVICE_BASEURL
                + request.getServletPath().replace(CONDITION_PATH, StringUtils.EMPTY));

        if (StringUtils.isNotBlank(request.getQueryString())) {
            uriComponentsBuilder.query(request.getQueryString());
        }

        this.buildQueryAndPath(uriComponentsBuilder, userInfo);

        String url = uriComponentsBuilder.build().toUriString();
        URI uri = URI.create(url);
        return handleRestfulCore(request, uri, userId);
    }

    @Override
    public boolean support(HttpServletRequest request) {
        return request.getServletPath().contains(CONDITION_PATH);
    }
}

　　接口中转处理器具体实现类需要根据请求的URL判断是否支持处理当前请求，如果中转请求中带有敏感信息（如手机号）需要特殊处理（UriComponentsBuilder 是一个不错的选择呦）。

六、总结

　　接口中转器扩展方便，只要按照如上方式根据不同类型的request实现具体的接口中转处理器就可以了。另外就是接口文档了，有了接口中转处理器，只需要改一下真实服务的接口文档就可以。比如真实服务的请求地址是http://172.17.20.92:28000/XXX/business/points/手机号信息，只需要改成http://172.17.20.92:28000/YYY/alipay-applet/direct/business/points。【手机号信息是敏感信息，需要后端从会话信息中获取】。还有，不要问我为啥要花时间设计这个东西，第一领导同意了，第二开发周期理想，第三我喜欢！！！