spring boot实现超轻量级网关（反向代理、转发）

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;

@Service
public 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);
    }
}

来源：https://www.tuicool.com/articles/3MNB7zj