在我们的rest服务中，需要暴露一个中间件的接口给用户，但是需要经过rest服务的认证，这是典型的网关使用场景。可以引入网关组件来搞定，但是引入zuul等中间件会增加系统复杂性，这里实现一个超轻量级的网关，只实现请求转发，认证等由rest服务的spring security来搞定。

如何进行请求转发呢？ 熟悉网络请求的同学应该很清楚，请求无非就是请求方式、HTTP header，以及请求body，我们将这些信息取出来，透传给转发的url即可。

举例：

/graphdb/** 转发到 Graph_Server/**

获取转发目的地址：

private String createRedictUrl(HttpServletRequest request, String routeUrl, String prefix) { String queryString = request.getQueryString(); return routeUrl + request.getRequestURI().replace(prefix, "") + (queryString != null ? "?" + queryString : ""); }

解析请求头和内容

然后从request中提取出header、body等内容，构造一个RequestEntity，后续可以用RestTemplate来请求。

private RequestEntity createRequestEntity(HttpServletRequest request, String url) throws URISyntaxException, IOException { String method = request.getMethod(); HttpMethod httpMethod = HttpMethod.resolve(method); MultiValueMap<String, String> headers = parseRequestHeader(request); byte[] body = parseRequestBody(request); return new RequestEntity<>(body, headers, httpMethod, new URI(url)); } private byte[] parseRequestBody(HttpServletRequest request) throws IOException { InputStream inputStream = request.getInputStream(); return StreamUtils.copyToByteArray(inputStream); } private MultiValueMap<String, String> parseRequestHeader(HttpServletRequest request) { HttpHeaders headers = new HttpHeaders(); List<String> headerNames = Collections.list(request.getHeaderNames()); for (String headerName : headerNames) { List<String> headerValues = Collections.list(request.getHeaders(headerName)); for (String headerValue : headerValues) { headers.add(headerName, headerValue); } } return headers; }

透明转发

最后用RestTemplate来实现请求：

private ResponseEntity<String> route(RequestEntity requestEntity) { RestTemplate restTemplate = new RestTemplate(); return restTemplate.exchange(requestEntity, String.class); }

全部代码

以下是轻量级转发全部代码：

import org.springframework.http.*;import org.springframework.stereotype.Service;import org.springframework.util.MultiValueMap;import org.springframework.util.StreamUtils;import org.springframework.web.client.RestTemplate;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.InputStream;import java.net.URI;import java.net.URISyntaxException;import java.util.Collections;import java.util.List;@Servicepublic class RoutingDelegate { public ResponseEntity<String> redirect(HttpServletRequest request, HttpServletResponse response,String routeUrl, String prefix) { try { // build up the redirect URL String redirectUrl = createRedictUrl(request,routeUrl, prefix); RequestEntity requestEntity = createRequestEntity(request, redirectUrl); return route(requestEntity); } catch (Exception e) { return new ResponseEntity("REDIRECT ERROR", HttpStatus.INTERNAL_SERVER_ERROR); } } private String createRedictUrl(HttpServletRequest request, String routeUrl, String prefix) { String queryString = request.getQueryString(); return routeUrl + request.getRequestURI().replace(prefix, "") + (queryString != null ? "?" + queryString : ""); } private RequestEntity createRequestEntity(HttpServletRequest request, String url) throws URISyntaxException, IOException { String method = request.getMethod(); HttpMethod httpMethod = HttpMethod.resolve(method); MultiValueMap<String, String> headers = parseRequestHeader(request); byte[] body = parseRequestBody(request); return new RequestEntity<>(body, headers, httpMethod, new URI(url)); } private ResponseEntity<String> route(RequestEntity requestEntity) { RestTemplate restTemplate = new RestTemplate(); return restTemplate.exchange(requestEntity, String.class); } private byte[] parseRequestBody(HttpServletRequest request) throws IOException { InputStream inputStream = request.getInputStream(); return StreamUtils.copyToByteArray(inputStream); } private MultiValueMap<String, String> parseRequestHeader(HttpServletRequest request) { HttpHeaders headers = new HttpHeaders(); List<String> headerNames = Collections.list(request.getHeaderNames()); for (String headerName : headerNames) { List<String> headerValues = Collections.list(request.getHeaders(headerName)); for (String headerValue : headerValues) { headers.add(headerName, headerValue); } } return headers; }}

Spring 集成

Spring Controller,RequestMapping里把GET \ POST\PUT\DELETE 支持的请求带上，就能实现转发了。

@RestController@RequestMapping(GraphDBController.DELEGATE_PREFIX)@Api(value = "GraphDB", tags = { "graphdb-Api"})public class GraphDBController { @Autowired GraphProperties graphProperties; public final static String DELEGATE_PREFIX = "/graphdb"; @Autowired private RoutingDelegate routingDelegate; @RequestMapping(value = "/**", method = {RequestMethod.GET, RequestMethod.POST, RequestMethod.PUT, RequestMethod.DELETE}, produces = MediaType.TEXT_PLAIN_VALUE) public ResponseEntity catchAll(HttpServletRequest request, HttpServletResponse response) { return routingDelegate.redirect(request, response, graphProperties.getGraphServer(), DELEGATE_PREFIX); }}

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