Automated Billing and Faxing for the Web - Getting a Transaction Notification continued

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Example 6-3. A PayPal receipt

package com.cascadetg.ch06;

import java.util.*;
import java.net.*;
import java.io.*;

import javax.servlet.http.*;
import javax.mail.*;
import javax.mail.internet.*;

public class PayPalReciept
{
    // Used to store retrived values from the PayPal submission.
    String paymentStatus;
    String txnId;
    String receiverEmail;
    String payerEmail;
    private static final boolean debug = false;

    // System.getProperty line to get the proper new line character[s].
    String newLine = System.getProperty("line.separator", ".");

    // Keep track of sent transactions. Note that this is in-memory
    // storage only - for a "real" system you would want to persist
    // this information, as well as the rest of fields of this object.
    // (mostly likely to a database of some sort).
    private static Hashtable processedTxnId = new Hashtable();

    // This method takes an incoming request and validates it both
    // against the PayPal server and some internal logic.
    public boolean validateRequest(HttpServletRequest request)
    {
        try
        {
            // Read the post from PayPal system.
            Enumeration parameters = request.getParameterNames();
            // We then add a "cmd" attribute to send back to PayPal
            // to indicate that we want to validate the request.
            StringBuffer send =
               new StringBuffer("cmd=_notify-validate");

            // Here, we put all of the parameters passed in from the
            // PayPal notification POST.
            while (parameters.hasMoreElements())
            {
                String paramName = (String)parameters.nextElement();
                String paramValue = request.getParameter(paramName);
                send.append("&");
                send.append(paramName);
                send.append("=");
                send.append(URLEncoder.encode(paramValue));
            }

            if (debug)
                System.out.println(send.toString());

            // This next sequence opens a connection to the PayPal
            // server, sets up the connection, and writes the sent
            // parameters back to the PayPal server.
            URL paypalServer =
                new URL(https://www.paypal.com/cgi-bin/webscr);
            URLConnection paypalConnection =
                paypalServer.openConnection();
            paypalConnection.setDoOutput(true);
         paypalConnection.setRequestProperty(
                "Content-Type", 
                "application/x-www-form-urlencoded");
            PrintWriter paypalServerWriter =
                new PrintWriter(paypalConnection.getOutputStream());
            paypalServerWriter.println(send);
            paypalServerWriter.close();

            if (debug)
                System.out.println("Sent to PayPal server.");

            // We then need to read the response from the PayPal
            // server.
            BufferedReader in =
               new BufferedReader(
                   new InputStreamReader(
             paypalConnection.getInputStream()));
            String paypalResponse = in.readLine();
            in.close();

            if (debug)
                System.out.println(
                    "Read PayPal server response = " + paypalResponse);

            // Set the values of this object from the values sent
            // by the initial request. If these values are verified,
            // we'll want them for later. If the values aren't
            // verified, or something else is wrong, we'll want
            // to track them for logging purposes.
            setValues(request);

            // If everything is ok, the response back should be
            // VERIFIED. Otherwise, something went wrong.
            if (paypalResponse.equals("VERIFIED"))
            {
                // If it isn't completed, it's a status message of
                // some sort. We're only interested in Completed
                // payments.
                if (!paymentStatus.equals("Completed"))
                    return false;

                // Make sure that we are the actual recipients of
                // the money.
                if (receiverEmail
                   .compareToIgnoreCase(PayPalTokens.paypalEmail)
                   != 0)
                   return false;

                // Check the in-memory cache to verify that we
                // haven't already handled this transaction.
                if (processedTxnId.get(this.getTxnId()) != null)
                   return false;

                // Everything looks good, so let's add this to the
                // transaction cache.
                processedTxnId.put(this.getTxnId(), this.getTxnId());
                   return true;
                } else
                {
                   System.out.println("Invalid PayPal transaction!");
                   System.out.println(this.toString());
                   return false;
                }
            } catch (Exception e)
            {
                System.out.println("Unable to connect to PayPal server.");
                e.printStackTrace();
                return false;
            }
        }
        // "Flatten" the object to a String.
        public String toString()
        {
            StringBuffer output = new StringBuffer();
            Enumeration outEnum = this.getAttributes().keys();

            while (outEnum.hasMoreElements())
            {
                String outputStr = (String)outEnum.nextElement();
                output.append(outputStr);
                output.append(" : ");
                output.append(paypalAttributes.get(outputStr).toString());
                output.append(newLine);
            }

            return output.toString();
        }

        public String toHTMLString()
        {
            StringBuffer htmlString = new StringBuffer();
            htmlString.append("<HTML><BODY>");
            htmlString.append("<TABLE HEIGHT='100%' WIDTH='100%'>");
            htmlString.append("<TR><TD>");

            Enumeration myValues = this.getAttributes().keys();
            while (myValues.hasMoreElements())
            {
                String next = (String)myValues.nextElement();
                htmlString.append(next);
                htmlString.append(" : ");
                htmlString.append(this.getAttribute(next).toString());
                htmlString.append("<BR>");
                htmlString.append(newLine);
            } 
            htmlString.append("</TD></TR></TABLE>