Distributed Programming in Java

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Distributed Programming in Java

• Web Services (3)

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WSDL

• Web Services Description Language interface
  description language for Web services
• Functionality? (operations, types of arguments)
• Access? (data encoding, communication protocols)
• Location?
• Necessary information for writing clients
• Automatic generation of stubs and skeletons

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The Architectural Models
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Definitions

• A message is the basic unit of data sent from one
  Web service agent to another in the context of
  Web services
• A service description is a set of documents that
  describe the interface to and semantics of a
  service
• A policy is a constraint on the behavior of
  agents or people or organizations

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Resoure

• a resource has an identifier
• a resource may have
• zero or more representations
• a resource may have
• zero or more resource descriptions
• a resource is owned by
• a person or organization
• a resource may be governed by
• zero or more policies

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Message Oriented Model
focuses on messages, message structure, message
transport and so on without particular
reference as to the reasons for the messages, nor
to their significance. the agent that sends and
receives messages
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Message Structure
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Service Oriented Model
focuses on aspects of service, action and so on.
While clearly, in any distributed system,
services cannot be adequately realized without
some means of messaging, the converse is not the
case messages do not need to relate to
services A service is realized by an agent and
used by another agent. Services are mediated by
means of the messages exchanged between requester
agents and provider agents.
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Service Structure
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Resource Oriented Model
focuses on resources that exist and have owners
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Policy Model
focuses on constraints on the behavior of agents
and services
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The Architectural Models
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WSDL Specification
types
message
message
message
operation
operation
operation
binding
service
port
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Structure of a WSDL Description
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A Recipe Web Service

• Ad hoc, RPC-style
• Recipes getRecipes()
• Lock lockRecipe(ID)
• void writeRecipe(Lock,Recipe)
• void unlockRecipe(Lock)

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Recipe Server with WSDL and SOAP (1/6)
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Recipe Server with WSDL and SOAP (2/6)
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Recipe Server with WSDL and SOAP (3/6)
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Recipe Server with WSDL and SOAP (4/6)
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Recipe Server with WSDL and SOAP (5/6)
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Recipe Server with WSDL and SOAP (6/6)
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Interface Descriptions

• In-Only one message is received
• Robust In-Only same but a fault may be triggered
• In-Out one message is received followed by one
  message being returned (may be a fault message)
• In-Optional-Out same but response is optional
• Out-Only one message is sent
• Robust Out-Only same but a faulty may be
  triggered
• Out-In one message is sent followed by one
  message being received (may be a fault message)
• Out-Optional-In same but response is optional

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RPC RPC-Style Operations

• Can be used with In-Out, In-Only, Robust In-Only
• Input/output types must describe
• element sequences only
• Wrapper element in request names the operation
• ...

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Binding Descriptions

• Encodings and protocols for an interface
• Predefined
• SOAP binding (often using SOAPs HTTP binding)
• HTTP binding (raw HTTP, no SOAP)

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SOAP Binding
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HTTP Binding
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Service Descriptions
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Summary of WSDL

• Description of interfaces of Web services
• message types
• operations
• encodings and communication protocols
• location

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Example 2- WSDL Types

• lt?xml version"1.0"?gt
• ltdefinitions name"StockQuote" targetNamespace"ht
  tp//example.com/stockquote.wsdl"
  xmlnstns"http//example.com/stockquote.wsdl"
  xmlnsxsd1"http//example.com/stockquote.xsd"
  xmlnssoap"http//schemas.xmlsoap.org/wsdl/soap/"
  xmlns"http//schemas.xmlsoap.org/wsdl/"gt
• lttypesgt
• ltschema targetNamespace"http//example.com/stockq
  uote.xsd" xmlns"http//www.w3.org/2000/10/XMLSche
  ma"gt
• ltelement name"TradePriceRequest"gt
• ltcomplexTypegt ltallgt ltelement name"tickerSymbol"
  type"string"/gt lt/allgt
• lt/complexTypegt
• lt/elementgt
• ltelement name"TradePrice"gt
• ltcomplexTypegt ltallgt ltelement name"price"
  type"float"/gt lt/allgt lt/complexTypegt
• lt/elementgt
• lt/schemagt
• lt/typesgt

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WSDL Operations

• ltmessage name"GetLastTradePriceInput"gt
• ltpart name"body" element"xsd1TradePriceReque
  st"/gt
• lt/messagegt
• ltmessage name"GetLastTradePriceOutput"gt
• ltpart name"body" element"xsd1TradePrice"/gt
• lt/messagegt
• ltportType name"StockQuotePortType"gt
• ltoperation name"GetLastTradePrice"gt
• ltinput message"tnsGetLastTradePriceInput"/gt
• ltoutput message"tnsGetLastTradePric
  eOutput"/gt
• lt/operationgt
• lt/portTypegt

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WSDL Bindings, Services, Ports

• ltbinding name"StockQuoteSoapBinding"
  type"tnsStockQuotePortType"gt
• ltsoapbinding style"document"
  transport"http//schemas.xmlsoap.org/soap/http"/gt
  
• ltoperation name"GetLastTradePrice"gt
  ltsoapoperation soapAction"http//example.com/Get
  LastTradePrice"/gt ltinputgt ltsoapbody
  use"literal"/gt lt/inputgt ltoutputgt ltsoapbody
  use"literal"/gt lt/outputgt
• lt/operationgt
• lt/bindinggt
• ltservice name"StockQuoteService"gt
  ltdocumentationgtMy first servicelt/documentationgt
• ltport name"StockQuotePort" binding"tnsStockQuo
  teBinding"gt ltsoapaddress location"http//example
  .com/stockquote"/gt lt/portgt
• lt/servicegt
• lt/definitionsgt

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WSDL
http//localhost8004/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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Apache Axis

• Open source web service framework
• Client programming model of Axis provides
  components for client to invoke a service
  endpoint and receive the response message
• Server programming model based on a listener for
  each transport protocol, a set of message
  handlers, 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
javaRPC
http//www.enterpriseintegrationpatterns.com/Compo
sedMessagingWS.html
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Creating a Service

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

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Deploying the Service

• In Axis you use a Web Service Deployment
  Descriptor (WSDD) to tell Axis how to route
  requests 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 by
  deploying 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 may find
  useful setting up Apache Axis

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Installation

• Download Apache Axis from website
• http//ws.apache.org/axis/
• Latest stable release is axis-1_4.zip (2006.4)
• 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 put
  compiled classes into webapps/axis

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Setting up Axis in Tomcat

• Axis as a servlet
• Install axis into thewebapps directory
• Set up classpath asshown in appendix
• Services classes inWEB-INF/classes

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Setting up the Classpath
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Axis User Guide
http//ws.apache.org/axis/java/user-guide.html