Introduction to Web Services Bina Ramamurthy bina@cse.buffalo.edu This work is partially supported by NSF-DUE-CCLI-A&I Grant 0311473 12/10/2018
Topics for Discussion Webservices and Service Oriented Architectures (SOA) XML (eXtensible Markup Language) SOAP (Simple Object Access Protocol) WS (Web Services) Summary 12/10/2018
Web Services and SOA Web Services is a technology that allows for applications to communicate with each other in a standard format. A Web Service exposes an interface that can be accessed through XML messaging. A Web service uses XML based protocol to describe an operation or the data exchange with another web service. Ex: SOAP A group of web services collaborating accomplish the tasks of an application. The architecture of such an application is called Service-Oriented Architecture (SOA). 12/10/2018
SOA in Real World: Report in InfoWorld, May 2, 2005 Issue 18 http://www.infoworld.com/article/05/05/02/18FEsoabt_1.html?WEB%20SERVICES State of Massachusetts uses SOA to deliver healthcare services. With HTML web application it had no control of look and feel and handling many hospitals. With SOAP based messaging they can easily handle different systems, billing systems, medical records systems etc. Use Microsoft-based systems. Countrywide financial simplifies lending: IBM Websphere based SOA is used to deliver services. Guardian Life Insurance uses SOA: IBM websphere based services. Uses EJB for business logic. British Telecom uses combination of BEA systems and Microsoft’s Connected Services Framework. Billing backend and operational support for the organization are web services. Legacy systems are enabled as web services. Amazon.com provides WS API for developers to implement applications leveraging their architecture and data. 12/10/2018
XML XML is a markup language, developed by W3C (World Wide Web Consortium), mainly to overcome the limitations of HTML. But it took a life of its own and has become a very popular part of distributed systems. We will examine its definition, associated specifications (DTD, XSLT etc.), Java APIs available to process XML, protocols and services based on XML, and the role XML plays in a distributed computing environment. 12/10/2018
First Look at XML It has no predefined tags. It is stricter. Such as in HTML Domains may specify their own set of standard tags It is stricter. Most html document have errors and the browser have to built to take care of these. On the other hand XML has a strict syntax. There is a notion of validity and A notion of well-formed. 12/10/2018
An Example: Memo See the two documents enclosed: one in html and the other in XML formats. Observe the meaningful tags in XML. Compare it to a class definition: it looks like a class with data definitions and accessors (tags). 12/10/2018
Memo.html vs memo.xml <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> <title>memo.html</title> </head> <body> <h3>Hello World</h3> Bina<br> CS 220 Advanced Java Programming Students <br> Wake up everyone<br> BR<br> <br> </body> </html> <?xml version="1.0" ?> <!DOCTYPE memo (View Source for full doctype...)> - <memo> <header>Hello World</header> <from>bina</from> <to>CS220 Advanced Java Programming Students</to> <body>Wake up everyone</body> <sign>br</sign> </memo> 12/10/2018
Memo Class Memo Header From To Body Para[] Link Signature 12/10/2018
XML document Content XML documents are composed of markup and contents Some of markup tags: Element Attributes Entity References Comments Processing instructions CDATA sections 12/10/2018
Elements Elements are the most common form of markup. Delimited by angle brackets, most elements identify the nature of the content they surround. Example: <allen><quote>Goodnight, Gracie.</quote></allen> Some elements may be empty, as seen above, in which case they have no content. If an element is not empty,it begins with a start-tag, <element>, and ends with an end-tag, </element>. Example:<applause/> 12/10/2018
Attributes Attributes are name-value pairs that occur inside start-tags after the element name. For example, <div class="preface"> is a div element with the attribute class having the value preface. In XML, all attribute values must be quoted. 12/10/2018
Entities In XML, entities are used to represent these special characters. Entities are also used to refer to often repeated or varying text and to include the content of external files. Example: & to represent & &US to represent United States XML also has a set of predefined entities: ", & 12/10/2018
Comments Comments begin with <!-- and end with -->. Comments can contain any data except the literal string --. You can place comments between markup anywhere in your document. Example: <!– loosely inspired by the vcard3.0 --> 12/10/2018
Processing Instructions (PI) Processing instructions (PIs) are an escape hatch to provide information to an application. Like comments, they are not textually part of the XML document, but the XML processor is required to pass them to an application. Processing instructions have the form: <?name pidata?> Example: <?xml-stylesheet href=“simple-ie5.xsl” type=“text/xsl”?> 12/10/2018
CDATA In a document, a CDATA section instructs the parser to ignore most markup characters. <?xml version=“1.0”?> <example> <[CDATA[ <?xml verion=“1.0”?> <entry> …. </entry>]]> </example> 12/10/2018
XML Processing Models XML Input Processing Business Logic Handling XML Output Processing WEB EXTRACT Business Logic XML input XML output 12/10/2018
XML input Processing Processing and validating the source document Recognizing/searching for relevant information based on its location or its tagging in the source document Extracting relevant information once it has been located Mapping/binding retrieved information to business objects 12/10/2018
XML Processing Technologies SAX, Simple API for XML DOM, Document Object Model API from W3C XSLT, XML Style Sheets Language Transformations from W3C XPath, the XML Path Language from W3C Other third party APIs. 12/10/2018
Apache Ant Tool Ant tool is an XML based build tool. Ant requires its config files to be specified in XML format. Config file build.xml has general commands for ant tool. Ant tool is used for build, deploy, and run java applications. See these tutorial for more information on ant: Tutorial1: http://www.ii.uni.wroc.pl/~nthx/java/ant.html Tutorial2: http://www.iseran.com/Java/ant/tutorial/ant_tutorial.html Ant Book Chapter: http://www.oreilly.com/catalog/anttdg/chapter/ch01.pdf 12/10/2018
XML to SOAP Simple xml can facilitate sending message to receive information. The message could be operations to be performed on objects. Simple Object Access Protocol (SOAP) 12/10/2018
SOAP Request <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <getProductDetails xmlns="http://warehouse.example.com/ws"> <productId>827635</productId> </getProductDetails> </soap:Body> </soap:Envelope> 12/10/2018
SOAP Reply <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <getProductDetailsResponse xmlns="http://warehouse.example.com/ws"> <getProductDetailsResult> <productName>Toptimate 3-Piece Set</productName> <productId>827635</productId> <description>3-Piece luggage set. Black Polyester.</description> <price>96.50</price> <inStock>true</inStock> </getProductDetailsResult> </getProductDetailsResponse> </soap:Body> </soap:Envelope> 12/10/2018
SOAPWeb Services (WS) Literature surveyed: 1. IBM’s alphaworks site: http://www-106.ibm.com/developerworks/webservices/ 2. http://www-3.ibm.com/software/solutions/webservices/pdf/WSCA.pdf 3. O’Reilly book on Web Services: Kim Topley’s Webservices in a Nutshell: http://www.oreilly.com/catalog/javawsian/index.html This link has a sample chapter (SAAJ) and zip of all examples in the book. 4. http://www.w3.org/DesignIssues/WebServices.html 12/10/2018
Web Services Suite of Protocols A suite of protocols define the Web Services Technology. These are used to describe, publish, discover, deliver and interact with services. The information about the protocols is from IBM’s developerworks. 12/10/2018
WS Suite of Protocols Messaging protocol Simple Object Access Protocol (SOAP) encodes messages so that they can be delivered over the transport protocols HTTP, SMTP or IIOP. Web Services Definition Language (WSDL) is used to specify the service details such as name, methods and their parameters, and the location of the service. This facilitates the registering and discovery of the service. For services to locate each other, the Universal Description, Discovery and Integration (UDDI) protocol defines a registry and associated protocols for locating and accessing services. 12/10/2018
WS Suite of Protocols (contd.) The WS-Transaction and WS-Coordination protocols work together to handle distributed transactions. The Business Process Execution Language for Web Services (BPEL4WS) defines workflow operations. WS-Security is a family of protocols that cover authentication, authorization, federated security, secure communications, and delivery. WS-Policy is another group of protocols that define the policy rules behind how and when Web services can interact with each other. WS-Trust defines how trust models work between different services. 12/10/2018
WS Stack Service Flow WSFL Service Discovery UDDI Quality of Service Security Management Quality of Service Service Discovery UDDI Service Publication UDDI Service Description WSDL XML-based Messaging SOAP HTTP, FTP, MQ Email, IIOP Network 12/10/2018
WS Interoperability Infrastructure Service Description WSDL XML Messaging SOAP Network HTTP Do you see any platform or language dependencies here? 12/10/2018
JAX-RPC JAX-RPC: Java API for XML-based Remote Procedure Call (RPC). An API for building Web Services and Web Services clients. Some important concepts in JAX-RPC are: Type-mapping system (WSDL to Java) Service endpoint Exception handling Service endpoint context Message handlers Service clients and service context SOAP with attachments Runtime services JAX-RPC client invocation models 12/10/2018
JAX-RPC (contd.) JAX-RPC is designed to provide a simple way for developers to create Web services server and Web services client. Based on remote procedure calls; so the programming model is familiar to Java developers who have used RMI or CORBA. Major difference between RMI and JAX-RPC is that messages exchanged are encoded in XML based protocol and can be carried over a variety of transport protocols such as HTTP, SMTP etc. You can use JAX-RPC without having to be an expert in XML, SOAP, or HTTP. 12/10/2018
The JAX-RPC Programming Model Services, ports and bindings JAX-RPC web service servers and clients JAX-RPC service creation JAX-RPC client and server programming environments Stubs and ties Client invocation modes Static and dynamic stubs and invocation 12/10/2018
Services, ports and bindings Service endpoint interface or service endpoint that defines one or more operations that the web service offers. Access to an endpoint is provided by binding it to a protocol stack through a port. A port has an address that the client can use to communicate with the service and invoke its operations. An endpoint can be bound to different ports each offering a different suite of protocols for interaction. 12/10/2018
Endpoint, Port and binding Web service endpoint Port1 port2 port3 Web services Client SOAP1.1 Over http SOAP 1.1 over https Other. Ex: ebXML over SMTP https 1.1 transport soap1.1 messages 12/10/2018
WS Development Lifecycle Build: Definition of service interface Definition of service implementation New services Existing application into WS Composing a WS out of other WS and applications Source compiled and Stubs and Ties are generated. Deploy: Publication of the service interface and service implementation to service registry or service requestor. Deployment of executables in an execution environment. 12/10/2018
WS Development Lifecycle (contd.) Run: A WS is available for invocation. Requestor can perform find and bind operation. Manage: on going management and administration for security, availability, performance, QoS, and business processes. 12/10/2018
Service Oriented Architectures Lets look at some success stories. Amazon.com has is data collection available web services developers. See these URLs: Amazon.com E-Commerce Service (ECS) Conceptual Model ECS Usage/Query Scenarios Types of data available through ECS (and not available) Sample applications (some of them are cool) Programming and API for making (SOAP) requests 12/10/2018
Summary We looked at foundational concepts supporting web services: XML, SOAP, WSDL and Web Services standards. We also illustrated the concepts using sample programs. Best way to get started is try out WS tutorials by yourself. 12/10/2018