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DistributedProgramming in Java

Web Services (3)

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Tracing SOAP Messages

•Enable trace messages by enabling theelectric.logging property or using Log.startLogging

•Run the client with SOAP logging enabled

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Logging

Generated when the source of a Java interfacecannot be found

SOURCE

Generated by any remote SOAP requests orSOAP responses

SOAP

Generated when an exception for oneway msgoccurs

ONEWAY

Generated when a map file is readMAPPING

Generated when a JMS warning occursJMS

Generated by any SOAP-related HTTP trafficHTTP

Generated when a SOAPException constructedEXCEPTION

Generated when internal GLUE exception occursERROR

A general commentCOMMENT

Generated when line in a command file executedCOMMAND

MEANINGCATEGORY

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Tracing using In-code Loggingpublic class ExchangeClient { public static void main(String args[]) throws Exception { // bind to web service from WSDL at the specified URL String url = "http://localhost:8004/soap/exchange.wsdl"; IExchange exchange = (IExchange) Registry.bind(url,IExchange.class);

// Start Logging SOAP messages (using text from table) Log.startLogging("SOAP");

// invoke the web service via its proxy double rate = exchange.getRate("canada", "usa"); System.out.println("canada/usa exchange rate = " + rate); }

}

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Anatomy of a SOAP Request

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HTTP Request

LOG.HTTP: outbound request to tcp://192.168.15.104:8004

POST /soap/exchange HTTP/1.1Host: 192.168.15.104:8004Content-Type: text/xml; charset=UTF-8User-Agent: GLUE/2.1Connection: Keep-AliveSOAPAction: "getRate"Content-Length: 534

< material deleted >

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SOAP Message Model

Header: optional, 1 or more header entriesBody: 0 or more body entries0 or more non-standard elements

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SOAP Request

LOG.SOAP: request to http://192.168.15.104:8004/soap/exchange

<?xml version='1.0' encoding='UTF-8'?> <soap:Envelope xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xsd='http://www.w3.org/2001/XMLSchema'xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'xmlns:soapenc='http://schemas.xmlsoap.org/soap/encoding/'soap:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'> <soap:Body> <n:getRate xmlns:n='http://tempuri.org/exchange.Exchange'> <country1 xsi:type='xsd:string'>canada</country1> <country2 xsi:type='xsd:string'>usa</country2> </n:getRate> </soap:Body> </soap:Envelope>

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Anatomy of a SOAP Response

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HTTP Response

LOG.HTTP:

<?xml version='1.0' encoding='UTF-8'?><soap:Envelope xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xsd='http://www.w3.org/2001/XMLSchema'xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'xmlns:soapenc='http://schemas.xmlsoap.org/soap/encoding/'soap:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'><soap:Body><n:getRateResponsexmlns:n='http://tempuri.org/exchange.Exchange'><Resultxsi:type='xsd:double'>1.0638297872340425</Result></n:getRateResponse></soap:Body></soap:Envelope>

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SOAP Response

LOG.SOAP: response from http://192.168.15.104:8004/soap/exchange

<?xml version='1.0' encoding='UTF-8'?> <soap:Envelope xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xsd='http://www.w3.org/2001/XMLSchema'xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'xmlns:soapenc='http://schemas.xmlsoap.org/soap/encoding/'soap:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'> <soap:Body> <n:getRateResponsexmlns:n='http://tempuri.org/exchange.Exchange'> <Result xsi:type='xsd:double'>1.0638297872340425</Result> </n:getRateResponse> </soap:Body> </soap:Envelope>

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Envelope-Message

http://192.168.15.104:8004/soap/exchange

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WSDL

•Web Service Description Language

•Neutral format for services to advertisethemselves on the network

• In future, can choose between competingproviders of same service (price, etc.)

•GLUE generates WSDL file automatically

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WSDLhttp://localhost:8004/soap/exchange.wsdl

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WSDL Messages

Request

Response

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WSDL Port Type•Defines operations offered by a service

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WSDL Binding

•How messages will be handled

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WSDL Service Definition

•How to access the service (defines port,binding, and service URL)

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Web Service DesignConsiderations

• Transport Protocol• HTTP -- firewall friendly, unreliable. Tends to beused synchronously for request/response.

• Asynchronous/Synchronous Messaging• Synchronous: connection remains open untilresponse sent. Servers have to maintain multipleconcurrent messages -- complex. Server has todo error handling•WS-ReliableMessaging designed to addressreliable delivery and message processing

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Web Service DesignConsiderations

• Encoding style:• Encoded: primitive (standard) mapping of objectsand parameters to XML.• Literal: external specification provided for “wire”representation.• Style is mostly “encoded”

• Binding style:• RPC: Receiver must interpret message as aprocedure call (rules are SOAP-specified)• Document: XML document is delivered

• Summary: most Web Services uses SOAP encodingwith synchronous, RPC binding; i.e., looks just likeRMI, CORBA requests.

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Apache Axis

•Open source web service framework

•Client programming model of Axis providescomponents for client to invoke a serviceendpoint and receive the response message

•Server programming model based on a listenerfor each transport protocol, a set of messagehandlers, and service handlers

•Let us have a closer look at its architecture

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Axis Engine Architecture

HTTP, JMS, etc. SOAP, XML-RPC

java:RPC

http://ws.apache.org/axis/java/architecture-guide.htmlhttp://www.enterpriseintegrationpatterns.com/ComposedMessagingWS.html

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Axis Architecture

• Framework made up of handlers:• Invoked in order depending on configuration•Whether client or server accessing framework

• Handlers grouped in chains: request and response

• 3 chains:• Transport• Global• Service

• Reference http://xml.apache.org/axis

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Service Activator

Activator handles all messaging details and invokes the service like any client. Service can be POJO.

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Techniques for Deploying WebServices in Axis

•Automatic Deployment

•Using a Web Services DeploymentDescriptor (WSDD)

•Generate proxies from an existing WSDLdocument

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Automatic Deployment

•Write business logic as Java Web Service file(*.jws)• Deploy SOURCE file into webapps directory of Axis

server• File name forms part of endpoint that axis server

exposes as a Web Service:

•WSDL is automatically generated, as is the location• Can also generate client stub classes (like GLUE)• Cannot set deployment parameters though

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Creating a Service

• Implement the service in a web serviceagnostic manner (as a regular class)

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Deploying the Service

• In Axis you use a Web Service DeploymentDescriptor (WSDD) to tell Axis how to routerequests to the correct target class

•SmallCompanyImpl.wsdd

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Starting the Axis Server

•Two options for running Axis:•as a servlet from within a servlet engine (eg

Tomcat): code in webapps/axis•as a standalone server (for testing and simple

applications only)

• Invoking the standalone server

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Deploying the Service

•Make the service available to clients bydeploying it using the AdminClient

• If deploying to the standalone Axis server,also supply the port number

•Now we are ready to invoke the service

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Create the Client

•Again two options:•Dynamic web service client: create a Call

object for each method at runtime•Static web service client: generate a proxy

from a WSDL description

•First we will use the dynamic option•Most interesting from the perspective of

understanding low level operation

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Client

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Appendix

•This appendix collects information you mayfind useful setting up Apache Axis

•Apache Axis “requires” Tomcat (or otherservlet container)

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Tomcat

•http://tomcat.apache.org•Servlet container, provides reference

implementation for Java Servlet andJavaServer pages technologies.

•Good release is 5.5.25

•Download and install

•Create start_tomcat, stop_tomcat shellscripts ==>

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Tomcat Scripts

•Startup script:

•Shutdown script:

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Configuring Tomcat Port

•Edit server.xml in $CATALINA_HOME/conf

•Change 8080 to required value

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Axis Installation

•Download Apache Axis from website•http://ws.apache.org/axis/•Latest stable v1 release is axis-1_4.zip•Also have axis 2, supports SOAP 2, REST, …• Install in a directory and put the jar files in the

axis/lib directory into your classpath•Can also install in Eclipse by adding all jar files to

the Eclipse project•Should also set default output directory to putcompiled classes into webapps/axis

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Setting up Axis in Tomcat

•Axis as a servlet• Install axis subdir.

from dist’n intotomcat webappsdirectory•Set up classpath as

shown in appendix•Services classes in

WEB-INF/classes

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Axis is Running!• After configuration, type http://localhost:8080/axis

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Setting up the Classpath

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Axis User Guide

http://ws.apache.org/axis/java/user-guide.html