Forward HttpServletRequest to a different server

Question

I got a HttpServletRequest request in my Spring Servlet which I would like to forward AS-IS (i.e. GET or POST content) to a different server.

What would be

Answer 1

Discussions of whether you should do forwarding this way aside, here's how I did it:

package com.example.servlets;

import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Enumeration;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.example.servlets.GlobalConstants;

@SuppressWarnings("serial")
public class ForwardServlet extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        forwardRequest("GET", req, resp);
    }

    @Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp) {
        forwardRequest("POST", req, resp);
    }

    private void forwardRequest(String method, HttpServletRequest req, HttpServletResponse resp) {
        final boolean hasoutbody = (method.equals("POST"));

        try {
            final URL url = new URL(GlobalConstants.CLIENT_BACKEND_HTTPS  // no trailing slash
                    + req.getRequestURI()
                    + (req.getQueryString() != null ? "?" + req.getQueryString() : ""));
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod(method);

            final Enumeration headers = req.getHeaderNames();
            while (headers.hasMoreElements()) {
                final String header = headers.nextElement();
                final Enumeration values = req.getHeaders(header);
                while (values.hasMoreElements()) {
                    final String value = values.nextElement();
                    conn.addRequestProperty(header, value);
                }
            }

          //conn.setFollowRedirects(false);  // throws AccessDenied exception
            conn.setUseCaches(false);
            conn.setDoInput(true);
            conn.setDoOutput(hasoutbody);
            conn.connect();

            final byte[] buffer = new byte[16384];
            while (hasoutbody) {
                final int read = req.getInputStream().read(buffer);
                if (read <= 0) break;
                conn.getOutputStream().write(buffer, 0, read);
            }

            resp.setStatus(conn.getResponseCode());
            for (int i = 0; ; ++i) {
                final String header = conn.getHeaderFieldKey(i);
                if (header == null) break;
                final String value = conn.getHeaderField(i);
                resp.setHeader(header, value);
            }

            while (true) {
                final int read = conn.getInputStream().read(buffer);
                if (read <= 0) break;
                resp.getOutputStream().write(buffer, 0, read);
            }
        } catch (Exception e) {
            e.printStackTrace();
            // pass
        }
    }
}

Obviously this could use a bit of work with regard to error handling and the like but it was functional. I stopped using it, however, because it was easier in my case to make calls directly to the CLIENT_BACKEND than to deal with cookies, auth, etc. across two distinct domains.