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Laundering your money |
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Currency conversion using SOAP with Java and WAP |
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Carl Whalley, 30-Nov-2001 |
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| Web services |
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Pick up any computing journal today and you'd be forgiven for thinking the internet is nothing but a huge collection
of web services waiting to happen. Web services? Yup - the cornerstone of the big boys (Microsoft .NET and Sun ONE)
future net strategy is the provision of many small, targeted services which are easily accessible and communicate
using the now universal platform of XML. Think of web sites you've seen which have news tickers, stock prices, the
temperature in Alaska and so on tucked away in small boxes. The data which made up such content was traditionally
sourced from a whole range of bizarre places: scraped from other websites (!), fed with proprietary protocols (eg RSS)
or manually entered by the web administrators. The idea behind web services, and specifically SOAP, is to wrap the whole
idea of providing this kind of content into one unified interface.
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The predominant protocol for the provision of web services is SOAP, the Simple Object Access Protocol. SOAP is a
particular convention that clients and servers can use when passing XML documents between themselves, in fact the only
way they can communicate is via XML. What's great is that it is also done over HTTP. This means that if your web browser can
see it, so can your SOAP client. Suddenly a whole raft of routing and communication problems are eliminated such as
proxy and firewall setups. Typically, a session may go as follows: a SOAP client is asked to get some piece of information
from a SOAP server in order to process it. Say a user had surfed to a site with stock quotes - the SOAP client would be on
the server he visited and the SOAP server would be remote to them both. The SOAP client creates the SOAP XML message in the
correct format, basically a few mandatory elements plus the required service (data), and posts it to the url of the SOAP server.
This then is analyzed and an XML message returned. To get at the data the SOAP client is interested in means understanding the
XML document returned, which in our parlance means an XML parser is needed. Once the client has the required data it can be
treated just like any other local item, and in our scenario displayed on the web page.
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| Why Java? |
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SOAP and Java fit very well together for 2 reasons. The first is XML, which as we've seen Java has huge support for. The second
is the implementation of the clients and servers themselves. Java is terrific on the server because it has the ability to process
the http streams directly with the use of servlets. These are small, targeted processes which run on the server and are triggered
by specific events such as a url pattern match in an incoming request. Because they can control every byte which is sent
back down as a http response they are perfectly suited for implementing SOAP servers. In fact, the Apache SOAP SDK
(http://xml.apache.org) is made up in exactly this way.
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WAP: well, it's had its fair share of critics recently but the idea of instant information being available anywhere is certainly
not to be sniffed at. Smartphones are getting more and more powerful. With the advent of 3G this idea of providing information/services
in such a convenient format will become as important as putting it on your web page.
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| In action |
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So, let's look at bringing all this together. To demonstrate, I'll show you how you can implement a SOAP client in java to supply
live currency rate exchanges to WAP devices. The service itself comes from the excellent xmethods site at http://www.xmethods.com.
Here you will see a list of various services offered and the WSDL specification needed to use them. WSDL is the Web Service
Description Language, implemented as (surprise, surprise) an XML document. The WSDL names the various services available and their
associated parameters. It also specifies the names of the return values - remember this is a two way process and many web services
and return values can be offered at the same time.
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To access a web service from Java we need the appropriate code for establishing the connections and making the calls.
Fortunately, this is made very easy when using the Apache SOAP toolkit from http://xml.apache.org (version 2.2 at time of writing).
This contains Java packages to support both SOAP clients as in our example and SOAP servers.
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The target platform is WAP, so in this design we use a JSP (Java Server Pages) frontend to render the WML user interface.
The JSP will get the users input and call a servlet which issues the SOAP call. The servlet will then process the returned data and
return to the JSP page which updates the WML with the new data. To keep things simple, I have restricted the list to 7 currencies
and just allowed users to choose one and an amount before selecting the target and selecting "convert". This means all I need are 2
listboxes (source and target currencies) and an edit box for the amount. With WAP UI work we always have to consider the limited
capabilities of most currently available devices.
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Once the Apache SOAP toolkit is installed (or at least soap.jar is in the applications classpath) the server code can be deployed.
That's server from the point of view of the connecting WAP clients. You'll need a live internet facing server with a web container
which can handle J2EE web apps. I use the excellent Resin (http://www.caucho.com), but any compliant ones will work. Update its config
files to add the web app exchange, deploy the app and connect with a WAP phone. If you just want to visit the one I made earlier
wapalong to http://wapinfoserv.com/exchange (targetted for the Ericsson R380).
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| Server JSP |
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The JSP is pretty standard stuff - note the first line tells the web container to treat the output stream as WML, otherwise your WAP phone would see a valid WML page as type HTML - not good!
<%@ page contentType='text/vnd.wap.wml' %>
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">
<wml>
<head>
<meta http-equiv="Cache-Control" content="max-age=0"
forua="true"/>
</head>
<card title="Wapinfoserv currency converter" id="init"
newcontext="true">
<p align="left">
<img src="images/currencyex.wbmp" width="122" height="31"
alt="Loading..."/>
<%
if (request.getParameter("req") != null) {
String outStr = request.getParameter("req")+" "
+request.getParameter("c1")+" = ";
outStr += request.getParameter("amt")+" "
+request.getParameter("c2");
out.println("</p>");
out.println("<p>");
out.println(outStr);
}
if (request.getParameter("val") != null) {
String outStr = request.getParameter("c1")
+"/"+request.getParameter("c2")
+": "+request.getParameter("val");
out.println("</p><p>( "+outStr+" )");
out.println("</p>");
out.println("<p>");
}
%>
Src
<select name="c1" multiple="false">
<option value="uk">GBP UK Pounds</option>
<option value="euro">EUR Euro</option>
<option value="france">FRF Francs</option>
<option value="sweden">SEK Kronor</option>
<option value="germany">DEM Deutsche Marks</option>
<option value="usa">USD Dollar</option>
<option value="japan">JPY Yen</option>
</select>
Amt [<input type="text" title="Amount:" name="amt"/>]
</p>
<p>
Target
<select name="c2" multiple="false">
<option value="uk">GBP UK Pounds</option>
<option value="euro">EUR Euro</option>
<option value="france">FRF Francs</option>
<option value="sweden">SEK Kronor</option>
<option value="germany">DEM Deutsche Marks</option>
<option value="usa">USD Dollar</option>
<option value="japan">JPY Yen</option>
</select>
</p>
<p>
<do type="accept" label="Home" name="Home">
<go href="http://wap.wapinfoserv.com"/>
</do>
<do type="accept" name="submit" label="Convert">
<go method="post" href="conv">
<postfield name="c1" value="$(c1)"/>
<postfield name="c2" value="$(c2)"/>
<postfield name="amt" value="$(amt)"/>
<postfield name="returnpage" value="index.jsp"/>
</go>
</do>
</p>
</card>
</wml>
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| Server Java |
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I made a small bitmap and converted it to WBMP for extra sparkle, this is currencyex.wbmp. Just remove the appropriate lines if this isn't available or required. The servlet is where all the action happens. The requested currencies and amount is passed in and it makes the SOAP call before returning back to the orginal JSP with its new values:
package com.carmichaeldata.soap;
import java.io.*;
import java.util.*;
import java.net.*;
import javax.servlet.http.*;
import javax.servlet.*;
import org.w3c.dom.*;
import org.xml.sax.*;
import javax.xml.parsers.*;
import org.apache.soap.util.xml.*;
import org.apache.soap.*;
import org.apache.soap.encoding.*;
import org.apache.soap.encoding.soapenc.*;
import org.apache.soap.rpc.*;
import org.apache.soap.transport.http.SOAPHTTPConnection;
public class ConvertCurrency extends HttpServlet
{
SOAPHTTPConnection st = null;
public void doPost
(
HttpServletRequest req,
HttpServletResponse res
) throws ServletException, IOException {
URL url = new URL("http://services.xmethods.com:80/soap");
String redir = req.getParameter("returnpage");
String rate = "";
try {
double amount = 0.00;
try {
rate = ""
+getRate(url, req.getParameter("c1"),
req.getParameter("c2"));
} catch (Exception e) {
e.printStackTrace();
}
redir += "?val="+rate;
redir += "&c1="+req.getParameter("c1");
redir += "&c2="+req.getParameter("c2");
redir += "&req="+req.getParameter("amt");
try {
amount = (Double.valueOf(rate)).doubleValue()
* (Double.valueOf(
req.getParameter("amt")).doubleValue());
} catch (Exception e) {
System.err.println(e.toString());
}
redir += "&amt="+amount;
} catch (Exception e) {
System.err.println(e.toString());
}
res.sendRedirect(redir);
}
public Object getRate (URL serviceUrl,
String currency1, String currency2) {
SOAPHTTPConnection st = new SOAPHTTPConnection();
Call call = new Call();
call.setSOAPTransport(st);
call.setTargetObjectURI("urn:xmethods-CurrencyExchange");
call.setMethodName("getRate");
call.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC);
Vector params = new Vector();
params.addElement
(new Parameter("country1",
String.class, currency1, null));
params.addElement
(new Parameter("country2",
String.class, currency2, null));
call.setParams(params);
Response resp;
try {
resp = call.invoke(serviceUrl, null);
} catch(Exception e) {
System.err.println(e.toString());
return null;
}
Object value = null;
if (!resp.generatedFault()) {
Parameter ret = resp.getReturnValue();
value = ret.getValue();
} else {
Fault fault = resp.getFault();
System.err.println("SOAP call raised fault code:"
+fault.getFaultCode()
+" Text:"+ fault.getFaultString());
}
return value;
}
}
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Never before has it been possible to interact with such a vast market. Your business can extend right to
the place you want it the most : your customers. |
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Automated ebusiness is now very much an everyday reality across the globe. |
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Instant access to realtime data. Make updates from any device and see
it change on all connected systems. All views of your data are supplied from one central |
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source. Use timely, accurate information where you need it the most - all secured by industry-standard
encryption systems as used by the military and governments. |
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No-one knows your business better than you. When extending it to the internet your individuality will be
preserved. Methodologies exist which enable tried and
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tested business systems to be implemented modelling perfectly the business rules and logic you are using today. |
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