让spring服务器做为一个反向代理，将一些请求转发给其他的服务来完成响应。实现类似于nginx的功能。

思路：
1、写一个Filter来判断路径来转发符合规则的请求(只转发后端请求且符合特定规则的请求)
2、需要判断后端的服务是否存活
3、转发需要将表单之间的&转为最初的&
HTML中的&用& 来表示,转发过程中需要用
StringEscapeUtils.unescapeHtml3(queryString)来反解，将& 还原为&

代码:

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.List;import org.apache.commons.text.StringEscapeUtils;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.annotation.Order;
import org.springframework.http.ContentDisposition;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.HttpStatusCode;
import org.springframework.http.RequestEntity;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Component;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StreamUtils;
import org.springframework.web.client.RestTemplate;import jakarta.annotation.Resource;
import jakarta.servlet.Filter;
import jakarta.servlet.FilterChain;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletOutputStream;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import lombok.extern.slf4j.Slf4j;@Component
@Order(2)
@Slf4j
public class ForwardFilter implements Filter {@Value("${ha.service.host:}")private String masterServiceHost;@Value("${server.servlet.context-path}")private String apiBasePath;@Resourceprivate HighAvailableService highAvailableService;@Overridepublic void doFilter(ServletRequest servletRequest,ServletResponse servletResponse,FilterChain filterChain)throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;if (request.getRequestURI().startsWith(apiBasePath) &&highAvailableService.isMasterAlive()) {// 转发请求try {final ResponseEntity<byte[]> responseEntity =forward(request, response, masterServiceHost);HttpStatusCode statusCode = responseEntity.getStatusCode();if (statusCode.isError()) {// get from selffilterChain.doFilter(servletRequest, servletResponse);} else {// transfer response informationresponse.setContentType(responseEntity.getHeaders().getContentType().toString());response.setContentLengthLong(responseEntity.getHeaders().getContentLength());response.setCharacterEncoding(StandardCharsets.UTF_8.name());response.setStatus(responseEntity.getStatusCodeValue());final ContentDisposition contentDisposition =responseEntity.getHeaders().getContentDisposition();response.setHeader("Content-Disposition",contentDisposition.toString());ServletOutputStream outputStream = response.getOutputStream();outputStream.write(responseEntity.getBody());outputStream.flush();outputStream.close();}} catch (Exception e) {log.error("{}", e);response.setStatus(400);PrintWriter writer = response.getWriter();writer.write(e.getClass().getName());writer.flush();}} else {filterChain.doFilter(servletRequest, servletResponse);}}public ResponseEntity<byte[]> forward(HttpServletRequest request,HttpServletResponse response,String routeUrl) {try {// build up the forward URLString forwardUrl = createForwardUrl(request, routeUrl);RequestEntity requestEntity =createRequestEntity(request, forwardUrl);return route(requestEntity);} catch (Exception e) {return new ResponseEntity("FORWARD ERROR",HttpStatus.INTERNAL_SERVER_ERROR);}}private String createForwardUrl(HttpServletRequest request,String routeUrl) {String queryString = request.getQueryString();final String decode = StringEscapeUtils.unescapeHtml3(queryString);String requestURI = request.getRequestURI();return routeUrl + requestURI + (decode != null ?"?" + decode : "");}private RequestEntity createRequestEntity(HttpServletRequest request,String url)throws URISyntaxException, IOException {String method = request.getMethod();HttpMethod httpMethod = HttpMethod.valueOf(method);MultiValueMap<String, String> headers = parseRequestHeader(request);byte[] body = parseRequestBody(request);return new RequestEntity<>(body, headers, httpMethod, new URI(url));}private ResponseEntity<byte[]> route(RequestEntity requestEntity) {RestTemplate restTemplate = new RestTemplate();return restTemplate.exchange(requestEntity, byte[].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;}}