CS603Communication Mechanisms:SOAP25 January 2002

SOAP:Simple Object Access ProtocolOverviewGoal: RPC protocol that works over wide area networksInteroperableLanguage independentProblem: FirewallsSolution: HTTP/XMLHistoryWork started in 1998 produced XML-RPCVendor-led, big Microsoft influence1999: SOAP 1 type system from XML SchemasMore vendors2001: Picked up by W3C XML Protocol working groupNow called XP (XML Protocol)Microsoft using it for their .NET replacement for DCOM

SOAPAdvantagesGoes anywherehttp is universal protocolOpen standardBased on XML, defined by W3C working groupDisadvantagesType semantics must be definedExtra work for usersPure text protocolHigh cost to translate at endpointsEats bandwidth

SOAPComponentsClient side: Ability to generate http calls and listen for responseSounds like a browser!Server:Listen for HTTPBind to procedureRespond with HTTPFirst and last are Web Server!

SOAP call

IBM

SOAP response

34.5

SOAP Template

User-created definitions, e.g. language of messageCall and arguments, or results for a responseErrors (response only)

Key SOAP AttributesHeaderActor: URI of intended recipientencodingStyle: URI of definition of types usedmustUnderstand: True if receiver MUST process elementFault: VersionMismatch, MustUnderstand, Client, Server: Error as a string: Who caused it: Additional information

Building a client:Apache SOAPOpen source web server driven by IBMSOAP available as integral partJava packages to interface between java programs and SOAPAlso supports javascript SOAP clients/servers

SOAPSample Clientimport java.net.URL; import java.util.Vector; import org.apache.soap.SOAPException; import org.apache.soap.Constants;import org.apache.soap.Fault; import org.apache.soap.rpc.Call; import org.apache.soap.rpc.Parameter; import org.apache.soap.rpc.Response;public class Client {public static void main(String[] args) throws Exception {URL url = new URL("http://localhost:8080/apache-soap/servlet/rpcrouter"); Call call = new Call();call.setTargetObjectURI("urn:Hello");call.setMethodName(HelloWorld");call.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC); Vector params = new Vector();params.addElement(new Parameter("name", String.class, Argument, null)); call.setParams(params);

SOAPSample ClientResponse resp = null; try { resp = call.invoke(url, ""); }catch( SOAPException e ) {System.err.println("Caught SOAPException (" + e.getFaultCode() + "): " +e.getMessage());System.exit(-1);} // Check the response.if( !resp.generatedFault() ) {Parameter ret = resp.getReturnValue();Object value = ret.getValue(); System.out.println(value);} else {Fault fault = resp.getFault(); System.err.println("Generated fault: ");System.out.println (" Fault Code = " + fault.getFaultCode()); System.out.println (" Fault String = " + fault.getFaultString());}}

SOAPServer codepublic class HelloServer{ public String HelloWorld(String name) {System.out.println(name);return "Hello World!; } }

Activating the serverorg.apache.soap.server.ServiceManagerClient http://localhost:8080/apache-soap/servlet/rpcrouter deploy DeploymentDescriptor.xmlDeploymentDescripter.xml:

Client-generated call

Arguments

Server-generated response

Hello World!

DCE vs. Java RMI vs. SOAPPhilosophyDCE RPC: generic interfaceDefine clean sheet systemPort to variety of protocols/systems/languagesJava RMI: proprietary interfaceCoupled to single language/run time systemPort entire system to multiple platformsSOAP: single standard interfaceDefine interface on single protocolPick protocol that is universal

Which do I use?All-JAVA world? RMINeed security / fault tolerance? RPCNeed to get through firewalls? SOAPPerformance?Objects as arguments?