Streaming Http Proxy Servlet

You know when you just need a streaming http proxy servlet and you just can't find one? Well try this:

HttpProxyServlet.java

package org.adrianwalker.servlet.proxy;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Map;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.methods.GetMethod;
import org.apache.commons.httpclient.methods.PostMethod;

public final class HttpProxyServlet extends HttpServlet {

  private URL url;
  private HttpClient proxy;

  @Override
  public void init(final ServletConfig config) throws ServletException {

    super.init(config);

    try {
      url = new URL(config.getInitParameter("url"));
    } catch (MalformedURLException me) {
      throw new ServletException("Proxy URL is invalid", me);
    }
    proxy = new HttpClient();
    proxy.getHostConfiguration().setHost(url.getHost());
  }

  @Override
  protected void doGet(final HttpServletRequest request, final HttpServletResponse response)
          throws ServletException, IOException {

    Map<String, String[]> requestParameters = request.getParameterMap();

    StringBuilder query = new StringBuilder();
    for (String name : requestParameters.keySet()) {
      for (String value : requestParameters.get(name)) {

        if (query.length() == 0) {
          query.append("?");
        } else {
          query.append("&");
        }

        name = URLEncoder.encode(name, "UTF-8");
        value = URLEncoder.encode(value, "UTF-8");

        query.append(String.format("&%s=%s", name, value));
      }
    }

    String uri = String.format("%s%s", url.toString(), query.toString());
    GetMethod proxyMethod = new GetMethod(uri);
    
    proxy.executeMethod(proxyMethod);
    write(proxyMethod.getResponseBodyAsStream(), response.getOutputStream());
  }

  @Override
  protected void doPost(final HttpServletRequest request, final HttpServletResponse response)
          throws ServletException, IOException {

    Map<String, String[]> requestParameters = request.getParameterMap();

    String uri = url.toString();
    PostMethod proxyMethod = new PostMethod(uri);
    for (String name : requestParameters.keySet()) {
      for (String value : requestParameters.get(name)) {
        proxyMethod.addParameter(name, value);
      }
    }

    proxy.executeMethod(proxyMethod);
    write(proxyMethod.getResponseBodyAsStream(), response.getOutputStream());
  }

  private void write(final InputStream inputStream, final OutputStream outputStream) throws IOException {
    int b;
    while ((b = inputStream.read()) != -1) {
      outputStream.write(b);
    }

    outputStream.flush();
  }

  @Override
  public String getServletInfo() {
    return "Http Proxy Servlet";
  }
}

This class makes use of the Jakarta Commons HttpClient to forward requests to a configurable url and streams back the response.

A sample project using this servlet is available for download below. The servlet acts as a proxy for a google search, returning the search results page. The proxied url is configurable in the web applications web.xml file. The project builds a war and uses the jetty plugin so you can test the code.

Run the project with 'mvn clean install jetty:run-war' and point your brower at http://localhost:8080/http-proxy-servlet

Source Code

• Java Maven Project - HttpProxyServlet.zip