programming-examples/java/Using Proxy.java

Using Proxy

import java.net.URL;
import java.net.URLConnection;
import java.net.HttpURLConnection;

import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ProxyDemo
{
	// Set to true if you want to see verbose output.
	private final static boolean bDebug = false;

	/**
	* This function makes an HTTP GET request of the specified URL using a proxy if provided.
	* If successfully, the HTTP response headers are printed out.
	* If the MIME type of the response is text/html, then the number of lines of text
	* is printed as well.
	*
	* @param strURL - A string representing the URL to request, eg, "http://bdn.borland.com/"
	* @param strProxy - A string representing either the IP address or host name of the proxy server.
	* @param iProxyPort - An integer that indicates the proxy port or -1 to indicate the default port for the protocol.
	* @return rc is true if the request succeeded and false otherwise.
	*/
	static boolean doURLRequest(String strURL, String strProxy, int iProxyPort)
	{
		boolean rc = false;

		URL url = null;
		URLConnection c = null;

		try
		{
			System.out.println("\nHTTP Request: " + strURL);

			URL urlOriginal = new URL(strURL);

			if ((null != strProxy) && (0 < strProxy.length()))
			{
				URL urlProxy = new URL(urlOriginal.getProtocol(),
				strProxy,
				iProxyPort,// A value of -1 means use the default port for the specified protocol.
				strURL);// The original URL is passed as "the file on the host".

				System.out.println("Using Proxy: " + strProxy);
				if (-1 != iProxyPort)
				{
					System.out.println("Using Proxy Port: " + iProxyPort);
				}

				url = urlProxy;
			}
			else
			{
				url = urlOriginal;
			}

			c = url.openConnection();

			// In this example, we only consider HTTP connections.
			if (c instanceof HttpURLConnection)// instanceof returns true only if the object is not null.
			{

				HttpURLConnection h = (HttpURLConnection) c;
				h.connect();

				String strStatus = h.getResponseMessage() + " (" + h.getResponseCode() + ")";
				System.out.println("HTTP Status: " + strStatus);

				System.out.println("HTTP Response Headers: ");

				// Evidently, index 0 always returns null, so we start with index 1.
				for (int i = 1; ; i++)
				{
					String strKey = h.getHeaderFieldKey(i);
					if (null == strKey)
					{
						break;
					}
					System.out.println(i + ": " + strKey + ": " + h.getHeaderField(i));
				}

				// Normally at this point, one would download data from the connection.
				// For example, if the MIME type is html, then download the string and display it.
				String strContentType = h.getContentType();
				if ((null != strContentType) && (0 == strContentType.compareTo("text/html")))
				{
					// Set boolean bDebug to true if you want verbose output.
					// For simplicity's sake, we just count the number of lines of text.
					if (bDebug) System.out.println("Received text/html:[");

						int iNumLines = 0;

						try
						{
							InputStream in = h.getInputStream();
							BufferedReader data = new BufferedReader(new InputStreamReader(in));

							String line = null;
							while((line = data.readLine()) != null)
							{
								if (bDebug) System.out.println(line);

								iNumLines++;
							}
						}
						catch(Exception exc2)
						{
							System.out.println("**** IO failure: " + exc2.toString());
						}
						finally
						{
							if (bDebug) System.out.println("]");
							System.out.println("Received text/html has " + iNumLines + " lines");
						}
				}

				h.disconnect();
			}
			else
			{
				System.out.println("**** No download: connection was not HTTP");
			}

			rc = true;
		}
		// Catch all exceptions.
		catch(Exception exc)
		{
			System.out.println("**** Connection failure: " + exc.toString());
			// System.out.println("**** Connection failure: " + exc.getMessage());// Same as above line but without the exception class name.
		}
		finally
		{
			// Do cleanup here.
			// For example, the following, in theory, could make garbage collection more efficient.
			// This might be the place where you choose to put your method call to your connection's "disconnect()";
			// curiously, while every URLConnection has a connect() method, they don't necessarily have a disconnect() method.
			// HttpURLConnection has a disconnect() which is called above.
			c = null;
			url = null;

			return rc;
		}
	}

	public static void main(String[] args)
	{
		// Simple request, not using a proxy server.
		ProxyDemo.doURLRequest("http://www.borland.com/", null, -1);
		ProxyDemo.doURLRequest("http://www.borland.com", null, -1);

		// Request, using a proxy server.
		/**
		* @todo: Note that the proxy indicated below will fail. Change to a valid server.
		* (If you do not have a proxy server available, then search for a web site that
		* lists public HTTP proxy servers.
		* I hesitate to list any here as I'm not sure about the "legitimacy" of all these sites.)
		*/
		// *** If you don't change the proxy setting to something valid in the following,
		// then you will get the following error message:
		// **** Connection failure: java.net.BindException: Cannot assign requested address: connect
		ProxyDemo.doURLRequest("http://www.borland.com/", "0.0.0.0", -1); // **** Change this line to use a valid proxy.
	}
}