Simple Java Proxy Servlet Using HttpURLConnection

Aim
The aim of this is to create a simple Java Proxy Servlet using HttpURLConnection. About 75 lines of code only. How simple is that!? The java servlet is deployed to the 'root' context of any java container such as Glassfish or Tomcat. You have to configure your web browser proxy settings to point to the host and port where the servlet is deployed. The java source code is available through a link below. Please leave any question or comments at the end and I will endeavour to answer them.

Assumptions
This article assumes that you have Glassfish or Tomcat or an equivalent java container installed and configured. This is a basic proxy and does not cover some features such as https etc.

Versions used in this example

Sofware/Component	Image
Windows XP SP2	N/A
Glassfish	N/A
Java JDK 1.5.0	N/A

Links to these files can be found here

For the purposes of this tutorial the files are stored in the structure below. The ServletProxy directory is the working directory. You can ignore the buil.xml and passwords.txt file as these are not required to compile the example. However, if you have glassfish and ant installed you can use the build.xml file.

ServletProxy
_|_web_bin
_|__|_WEB-INF
_|__|__|_web.xml
_|__|__|_classes
_|_web_src
_|__|_myproxy
_|__|__|_MyProxy.java
_|_build.xml
_|_passwords.txt

You can download the zipped example here.

Create and deploy the Service

1. Write and save the code below as myproxy/MyProxy.java in the web_src directory. This is the MyProxy servlet class. It recreates the url and uses HttpURLConnection to fetch the data from the requested host. As you can see the servlet request headers are copied to the outgoing HttpURLConnection headers, and incomming HttpURLConnection headers are copied back to the servlet response. This way we don't have to mess around with any headers.
   

   1. package myproxy; 2. 3. import java.io.*; 4. import java.util.Enumeration; 5. import java.util.Iterator; 6. import java.util.Map; 7. import java.util.List; 8. import java.util.logging.*; 9. 10. import javax.servlet.*; 11. import javax.servlet.http.*; 12. 13. import java.net.URL; 14. import java.net.HttpURLConnection; 15. 16. public class MyProxy extends HttpServlet { 17. 18. private ServletContext servletContext; 19. private Logger log; 20. 21. public void init(ServletConfig servletConfig) throws ServletException { 22. servletContext = servletConfig.getServletContext(); 23. log = Logger.getLogger(MyProxy.class.getName()); 24. } 25. 26. public void doGet(HttpServletRequest request, HttpServletResponse response){ 27. doPost(request, response); 28. } 29. 30. public void doPost(HttpServletRequest request, HttpServletResponse response){ 31. 32. BufferedInputStream webToProxyBuf = null; 33. BufferedOutputStream proxyToClientBuf = null; 34. HttpURLConnection con; 35. 36. try{ 37. int statusCode; 38. int oneByte; 39. String methodName; 40. String headerText; 41. 42. String urlString = request.getRequestURL().toString(); 43. String queryString = request.getQueryString(); 44. 45. urlString += queryString==null?"":"?"+queryString; 46. URL url = new URL(urlString); 47. 48. log.info("Fetching >"+url.toString()); 49. 50. con =(HttpURLConnection) url.openConnection(); 51. 52. methodName = request.getMethod(); 53. con.setRequestMethod(methodName); 54. con.setDoOutput(true); 55. con.setDoInput(true); 56. con.setFollowRedirects(false); 57. con.setUseCaches(true); 58. 59. for( Enumeration e = request.getHeaderNames() ; e.hasMoreElements();){ 60. String headerName = e.nextElement().toString(); 61. con.setRequestProperty(headerName, request.getHeader(headerName)); 62. } 63. 64. con.connect(); 65. 66. if(methodName.equals("POST")){ 67. BufferedInputStream clientToProxyBuf = new BufferedInputStream(request.getInputStream()); 68. BufferedOutputStream proxyToWebBuf = new BufferedOutputStream(con.getOutputStream()); 69. 70. while ((oneByte = clientToProxyBuf.read()) != -1) 71. proxyToWebBuf.write(oneByte); 72. 73. proxyToWebBuf.flush(); 74. proxyToWebBuf.close(); 75. clientToProxyBuf.close(); 76. } 77. 78. statusCode = con.getResponseCode(); 79. response.setStatus(statusCode); 80. 81. for( Iterator i = con.getHeaderFields().entrySet().iterator() ; i.hasNext() ;){ 82. Map.Entry mapEntry = (Map.Entry)i.next(); 83. if(mapEntry.getKey()!=null) 84. response.setHeader(mapEntry.getKey().toString(), ((List)mapEntry.getValue()).get(0).toString()); 85. } 86. 87. webToProxyBuf = new BufferedInputStream(con.getInputStream()); 88. proxyToClientBuf = new BufferedOutputStream(response.getOutputStream()); 89. 90. while ((oneByte = webToProxyBuf.read()) != -1) 91. proxyToClientBuf.write(oneByte); 92. 93. proxyToClientBuf.flush(); 94. proxyToClientBuf.close(); 95. 96. webToProxyBuf.close(); 97. con.disconnect(); 98. 99. }catch(Exception e){ 100. System.out.println(e.getMessage()); 101. e.printStackTrace(); 102. } 103. finally{ 104. } 105. } 106. } Hide line numbers

   
   
2. Now cd into the web_src directory and compile the source. Replace the path to Glassfish's lib directory with your local path. This could be lib in tomcat or any servlet container.
   

   ..ServletProxy\web_src>javac myproxy\MyProxy.java -d ..\web_bin\WEB-INF\classes -extdirs d:\downloads\glassfish\lib

   
   
3. Write the web.xml file and save in under the web_bin/WEB-INF directory.
   

   1. <?xml version="1.0" encoding="ISO-8859-1"?> 2. <web-app> 3. <servlet> 4. <servlet-name>My Proxy</servlet-name> 5. <servlet-class>myproxy.MyProxy</servlet-class> 6. </servlet> 7. 8. <servlet-mapping> 9. <servlet-name>My Proxy</servlet-name> 10. <url-pattern>/</url-pattern> 11. </servlet-mapping> 12. </web-app> Hide line numbers

   
   
4. Now create the war file. Cd into the web_bin directory and jar it all up.
   

   ..ServletProxy\web_bin>jar -cvf proxywala.war *

   
   
5. Finally deploy this war file in the servlet container of your choice. Remember it has to be in the ROOT context! .
   
   For glassfish you can specify the root context in the admin console. The steps for glassfish are.
   1. Login to the glassfish console
   2. Navigate to Applications -> Web Applications.
   3. Select deploy.
   4. Under "location" navigate to the war file we created proxywala.war.
   5. Under "Context Root" type in "/".
   6. Click Ok.
   
   For tomcat the steps are
   1. Copy the contents of the web_bin directory. Make sure it's the contents only such as WEB-INF and web.xml etc. Do not copy the web_bin directory itself.
   2. Now paste the contents into the tomcat webapps/ROOT directory.
   3. Restart Tomcat - if required.
   

Testing the filter

1. First change your proxy settings to point to the proxy. In this example the servlet is deployed on the localhost at port 80.
   Proxy http://localhost
   proxy Port 80
   
   
2. Now navigate to a some sites in your brower. You will be going to the web from your proxy. This proxy needs direct internet access.