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Web Service

Web Service. Jianguo Lu. Motivation. Build a web site about Windsor Include a weather report from cnn.com; Include daily stocks report for companies in Windsor; Include maps from google map; Include currency exchange from xe.com …

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Web Service

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  1. Web Service Jianguo Lu

  2. Motivation • Build a web site about Windsor • Include a weather report from cnn.com; • Include daily stocks report for companies in Windsor; • Include maps from google map; • Include currency exchange from xe.com • … • In the old days, we extract information from various sites using screen/html scraping • It is unreliable • Difficult to extract the data and maintain the web site • The solution: web service • Each web site provide a programmable interface

  3. What is web service • Web Service • A vague term that refers to distributed or virtual applications or processes that use the Internet to link activities or software components. • Another example application (vertical integration) • A travel Web site that takes a reservation from a customer, and then sends a message to a hotel application, accessed via the Web, to determine if a room is available, books it, and tells the customer he or she has a reservation is an example of a Web Services application. • Challenges • Find the services • Publish the services • Invoke the services • Describe the services • …..

  4. Discovery agency Provider Requester Service Oriented Architecture publish find interact

  5. A concrete SOA UDDI Registry Points to description WSDL publish Finds Service Describes Service Service Consumer Web Service Provider SOAP Communicates with XML Messages

  6. Web service definitions • A web service is an application accessible to other applications over the internet • “Self-contained, modular business applications that have open, internet-oriented, standard based interfaces”—UDDI Consortium • “a software application identified by a URI, whose interfaces and bindings are capable of being defined, described, and discovered as XML artifacts. A web service supports direct interactions with other software agents using XML-based messages exchanged via Internet-based protocols.” --W3C • “a standardized way of integrating Web-based applications using the XML, SOAP, WSDL, and UDDI open standards over an Internet protocol backbone. XML is used to tag the data, SOAP is used to transfer the data, WSDL is used for describing the service available, and UDDI is used for listing what services are available”--Webopedia More concrete

  7. Web Service definition • “encapsulated, loosely coupled, contracted software objects offered via standard protocols” --ZapThink Research • Encapsulated • Web Service implementation is invisible to entities outside the service • Exposes an interface but hides details • Loosely Coupled • Service and consumer software can be redesigned independently • Messages are decoupled from the data transport, and are easy to integrate with other platforms and open standards technology. • Changing the implementation of one component does not require changing the rest of the services, which makes configuration and deployment easier to manage. • Self-Describing and Adapting. • Distributed and Location-Independent. • Open Standards-Based.

  8. Why Web Service • “Just as the web revolutionized how users talk to applications, XML transforms way applications talk to each other”—Bill Gates • “Web services will be bigger than Java or XML”. – Rod Smith, VP of Emerging Technology, IBM • “Web services are expected to revolutionize our life in much the same way as the internet has during the past decade or so.”—Gartner • “By 2004, 40% of the financial services transactions and 35% of online government services will be web service-based.” –Gartner • There are web services for Google, Amazon, Fedex, EBay … … • It is a buzzword. Is it another hype?

  9. Three Laws of Computing • Moore's Law • Computing power doubles every 18 months • Gilder's Law • Network bandwidth capacity doubles every 12 months • Metcalfe's Law (Net Effect) • Value of network is proportional to the square of the number of users of the system (n2). • Web services greatly increase network value

  10. HTTP form <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <title>Simple Form</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head> <body> <form action="http://localhost:1234/" method="post" enctype="multipart/form-data" name="simpleForm" > <p>Text Field <input type="text" name="textfield"></p> <p>File to upload <input type="file" name="file"></p> <p> <input type="submit" name="Submit" value="Submit"> </p> </form> </body> </html>

  11. http request POST / HTTP/1.1 Host: cascadetg.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.5) Gecko/20031007 Firebird/0.7 Accept: text/xml,application/xml,application/xhtml+xml,text/ html;q=0.9,text/plain;q=0.8,video/x-mng,image/png,image/ jpeg,image/gif;q=0.2,*/*;q=0.1 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Cookie: CP=null* Content-Type: multipart/form-data; boundary=---------------------------41184676334 Content-Length: 438 -----------------------------41184676334 Content-Disposition: form-data; name="textfield" Test -----------------------------41184676334 Content-Disposition: form-data; name="file"; filename="tiny.txt" Content-Type: text/plain A small text file. Nothing to see here. Move along. -----------------------------41184676334 Content-Disposition: form-data; name="Submit" Submit -----------------------------41184676334--

  12. From HTTP to RPC • Remote procedure calls, or RPC, have been around for a long time. The concept is simple: let's say you have a function: bankAccount.adjust(Money amount); • The method is easy to understand and work with as part of a program compiled and running on a single machine. • A RPC makes a method call on another machine. // Local code Money adjustment = new Money(1.50); // Remote code myBankAccount.adjust(adjustment);

  13. Web service distributed computing

  14. History of Interface Definition Languages (IDLs) • IDL has a long history in distributed computing • DCE (Distributed Computing Environment) • CORBA IDL, OMG (Object Management Group) • COM IDL, Microsoft • WSDL • Traditional IDLs • Specifying what to call: the operation names, their signatures, exceptions. This is the job of IDL. • Agreeing on how to make an invocation: the mechanism of naming, activation, data encoding. This is what distributed standards such as CORBA or COM do. • WSDL needs to specify the both: the operation provided by the service, and the mechanism to access the service.

  15. Web Service Description Language • WSDL defines • What the service is: the operations the service provides, including the signature of the operation –- what • Access specification: details of the data format and protocol necessary to access the service’s operation–- how • Location of the service: details of the network address, such as a URL –- where

  16. Legend: • What • how • where WSDL functionality view Interface Supports Port Type Operation How to invoke Formats & Protocols Input & Output Binding Message How to encode Implements Provides Port Service Endpoints In WSDL 2.0, portType is changed to interface.

  17. WSDL specification abstract part types messages operations port types concrete part bindings services and ports WSDL document structure view

  18. <?xml version="1.0"?> <definitions name="Procurement" targetNamespace="http://example.com/procurement/definitions" xmlns:tns="http://example.com/procurement/definitions" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns="http://schemas.xmlsoap.org/wsdl/" > <message name="OrderMsg"> <part name="productName" type="xs:string"/> <part name="quantity" type="xs:integer"/> </message> <portType name="procurementPortType"> <operation name="orderGoods"> <input message = "OrderMsg"/> </operation> </portType> <binding name="ProcurementSoapBinding" type="tns:procurementPortType"> <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/> <operation name="orderGoods"> <soap:operation soapAction="http://example.com/orderGoods"/> <input> <soap:body use="literal"/> </input> <output> <soap:body use="literal"/> </output> </operation> </binding> <service name="ProcurementService"> <port name="ProcurementPort" binding="tns:ProcurementSoapBinding"> <soap:address location="http://example.com/procurement"/> </port> </service> </definitions> abstract part messages operation and port type concrete part binding port and service

  19. <definitions … name="BNQuoteService"> <message name="getPriceRequest"><part name="isbn" type="xsd:string"/></message> <message name="getPriceResponse"> <part name="return" type="xsd:float"/></message> <portType name="BNQuotePortType"> <operation name="getPrice"> <input name="getPrice" message="tns:getPriceRequest"/> <output name="getPriceResponse" message="tns:getPriceResponse"/> </operation> </portType> <binding name="BNQuoteBinding" type="tns:BNQuotePortType"> <soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/> <operation name="getPrice"><soap:operation/> <input> <soap:body use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:xmethods-BNPriceCheck"/> </input> <output> <soap:body use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" namespace="urn:xmethods-BNPriceCheck"/> </output> </operation> </binding> <service name="BNQuoteService"> <documentation>Returns price of a book at BN.com given an ISBN number</documentation> <port name="BNQuotePort" binding="tns:BNQuoteBinding"> <soap:address location="http://services.xmethods.net:80/soap/servlet/rpcrouter"/> </port> </service> </definitions>

  20. Visual representation

  21. WSDL structure—interconnection view WSDL document Types (type information for the document, e.g., XML Schema) Message 1 Message 2 Message 3 Message 4 Message 5 Abstract description of the service Operation 1 Operation 2 Operation 3 Interface (abstract service) binding 1 binding 2 binding 3 binding 4 endpoint 1 endpoint 2 endpoint 3 endpoint 4 Concrete description of the service Service (the interface in all its available implementations) By Gustavo Alonso and Cesare Pautasso

  22. A WSDL example <?xml version="1.0"?> <definitions name="PriceCheck" targetNamespace="http://www.skatestown.com/services/PriceCheck" xmlns:pc="http://www.skatestown.com/services/PriceCheck" xmlns:avail="http://www.skatestown.com/ns/availability" xmlns:wsi="http://ws-i.org/schemas/conformanceClaim/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns="http://schemas.xmlsoap.org/wsdl/"> <types> …</types> <message> …</message> <message> … </message> <portType> … </portType> <binding> … </binding> <service> … </service> </definitions> This example is from Steve Graham et al: Building Web Services with Java

  23. PortType <portType name="PriceCheckPortType"> <operation name="checkPrice"> <input message="pc:PriceCheckRequest"/> <output message="pc:PriceCheckResponse"/> </operation> </portType> • <portType> defines the interface of web service. Just as Java Interface declaration; • Will change the name to <interface> in WSDL 2.0. • It consists of a sequence of operation declarations. • WSDL can have zero or more <portType>s. Typically just one. • It has a name attribute, must be unique. • The binding will refer the portType by its name

  24. Operation • Operation defines a method signature; • Name, input, output, and fault • Input and output elements are associated with messages; • Different combinations of input/output define different operations types. <operation name="checkPrice"> <input message="pc:PriceCheckRequest"/> <output message="pc:PriceCheckResponse"/> </operation>

  25. Operation Types • The request-response type is the most common operation type, but WSDL defines four types: • Request-response: The operation can receive a request and will return a response <operation name="checkPrice"> <input message="pc:PriceCheckRequest"/> <output message="pc:PriceCheckResponse"/> </operation> • One-way: The operation can receive a message but will not return a response. <operation name=“cancellation”> <input message=“tns:orderCancellation”/> </operation> • Notification:The operation can send a message but will not wait for a response <operation name=“notification”> <output message=“tns:promotionNotification”/> </operation> • Solicit-response:The operation can send a request and will wait for a response <operation name=“cancellation”> <output message=“tns:pushThis”/> <input message=“tns:reponseToPush”/> </operation> • Different types are defined by decided by the order/occurrences of input and output.

  26. Messages <message name="PriceCheckRequest"> <part name="sku" element="avail:sku"/> </message> <message name="PriceCheckResponse"> <part name="result" element="avail:StockAvailability"/> </message> • Describe the abstract form of input, output, or fault. • A WSDL file can have zero or more messages. • Each message has a name, which is unique within the document. • Each message has a collection of <part> elements.

  27. Part <part name="sku" element="avail:sku"/> <part name="result" element="avail:StockAvailability"/> • A <part> element can be compared to a parameter in a method. • A part element has two properties: one is name, the other is its kind. • Kind can be a type or an element • Element refers to an element defined in XML Schema • Type refers to a simpleType or a complexType in XSD • In corresponding sku definition is: <xsd:element name="sku" type="xsd:string" />

  28. Types in WSDL <types> <xsd:schema targetNamespace="http://www.skatestown.com/ns/availability" > <xsd:element name="sku" type="xsd:string" /> <xsd:complexType name="availabilityType"> <xsd:sequence> <xsd:element ref="avail:sku"/> <xsd:element name="price" type="xsd:double"/> <xsd:element name="quantityAvailable" type="xsd:integer"/> </xsd:sequence> </xsd:complexType> <xsd:element name="StockAvailability" type="avail:availabilityType" /> </xsd:schema> </types> • The default type system is XML Schema; • Theoretically you can use any type system, such as Java types. • To be used in<part> element; • We can also import XML Schemas

  29. SOAP request message <soapenv:Envelope xmlns:soapenv=“http://schema.xmlsoap.org/soap/evelope/” xmlns:xsd=“http://www.w3.org/2001/XMLSchema” xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance”> <soapenv:Body> <sku xmlns=“http://www.skatestown.com/ns/availability”>123</sku> </soapenv:Body> </soapenv:Envelope> • Relevant part of the WSDL file: <xsd:element name="sku" type="xsd:string" /> <message name="PriceCheckRequest"> <part name="sku" element="avail:sku"/> </message> <operation name="checkPrice"> <input message="pc:PriceCheckRequest"/> <output message="pc:PriceCheckResponse"/> </operation> Envelope Header #0 Header #1 Body Message Payload

  30. <soapenv:Envelope xmlns:soapenv= … xmlns:xsd=… xmlns:xsi=… > <soapenv:Body> <StockAvailability xmlns= … > <sku> 123 </sku> <price xmlns=“”>100.00</price> <quantityAvailable xmlns=“”> 12 </quantityAvailable> </StockAvailability> </soapenv:Body> </soapenv:Envelope> Relevant part of the WSDL file: <xsd:complexType name="availabilityType"> <xsd:sequence> <xsd:element ref="avail:sku"/> <xsd:element name="price" type="xsd:double"/> <xsd:element name="quantityAvailable" type="xsd:integer"/> </xsd:sequence> </xsd:complexType> <message name="PriceCheckResponse"> <part name="result" element="avail:StockAvailability"/> </message> <operation name="checkPrice"> <input message="pc:PriceCheckRequest"/> <output message="pc:PriceCheckResponse"/> </operation> SOAP response message

  31. Binding <binding name="PriceCheckSOAPBinding" type="pc:PriceCheckPortType"> <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http" /> <operation name="checkPrice"> <soap:operation soapAction = "http://www.skatestown.com/services/PriceCheck/checkPrice" /> <input> <soap:body use="literal" /> </input> <output> <soap:body use="literal" /> </output> </operation> </binding> • Name of the binding should be unique; • Link to the portType is achieved by the portType name • This explains why portType name should be unique. • Typically, there is only one <binding> element; • Defines: • Invocation style • SOAPAction • Input message appearance • Output message appearance

  32. Invocation Style <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http" /> • All operations in this portType use SOAP messages; • The style attribute indicates that operations will follow a document-centric approach; • The body of the SOAP message is a straight XML document; • This is in contrast to RPC style;

  33. RPC style and document style • When using Document style, you can structure the contents of the SOAP Body any way you like. • When using RPC style, the contents of the SOAP Body must conform to a structure that indicates the method name and contains a set of parameters. It looks like this: <env:Body> <m:methodName xmlns:m="someURI"> <m:m1>...</m:m1> <m:m2>...</m:m2> ... </m:methodName> </env:Body> • Document style: <env:Body> <m:purchaseOrder xmlns:m="someURI"> ... </m:purchaseOrder> </env:Body> • RPC style: <env:Body> <m:placeOrder xmlns:m="someURI"> <m:purchaseOrder> ... </m:purchaseOrder> </m:placeOrder> </env:Body>

  34. Service <service name="PriceCheck"> <port name="Pricecheck" binding="pc:PriceCheckSOAPBinding"> <documentation> <wsi:Claim conformsTo="http://ws-i.org/profiles/basic/1.0" /> </documentation> <soap:address location = "http://www.skatestown.com/services/PriceCheck"/> </port> </service> • Contains a set of <port> elements; • <port> combines the interface binding with a network address specified by a URI; • A web service can be available in different web addresses;

  35. Implications of WSDL • Interaction mode: • Not only expose the operations to invoke, but also a service behave like a client. Blurring the distinction between a client and server. • Does not presume a particular form of communication, protocol, data encoding. • You can use HTTP, or SMTP, or FTP, … • You can use SOAP, or others

  36. WSDL 1.1 vs WSDL 2.0 WSDL 1.1 • Ports • PortTypes • Supported operation overloading • Messages composed of Parts • 6 Top level elements: Messages, Operations, PortTypes, Bindings, Ports and Services. • 4 Transmission Primitives • (One-way, Request-Response, Solicit-Response, Notification) WSDL 2.0 • Endpoints • Interfaces • Support for Interface inheritance • Removed operation overloading • Messages defined through Types • Operations nested inside Interfaces • Endpoints nested inside Bindings • 9 Message Exchange Patterns • New: Features and Properties

  37. Tools • WSDL parser: WSDL4J • Apache Axis • Invoking SOAP web service; • Translate WSDL to Java, and vice versa; • Mapping Java into XML Schema, and vice versa; • Host web service; • API for manipulating SOAP;

  38. Mapping between Java and WSDL in JAX-RPC • A simple example <message name="fooRequest"> <part name="para1" type="xs:string"/> </message> <message name="fooResponse"> <part name="para2" type="xs:float"/> </message> <portType name="FooBar"> <operation name="foo"> <input message="y:fooRequest"/> <output message="y:fooResponse"/> </operation> </portType> public interface FooBar extends java.rmi.Remote{ public float foo(java.lang.String para1) throws java.rmi.RemoteException; }

  39. Multiple input parameters <message name="fooRequest"> <part name="param1" type="xs:string"/> <part name="param2" type="xs:int"/> <part name="param3" type="xs:boolean"/> </message> <message name="fooResponse"> <part name="para2" type="xs:float"/> </message> <portType name="FooBar"> <operation name="foo"> <input message="y:fooRequest"/> <output message="y:fooResponse"/> </operation> </portType> public interface FooBar extends java.rmi.Remote{ public float foo(String param1, int param2, boolean param3) throws java.rmi.RemoteException; }

  40. Multiple output parameters <message name="fooRequest"> <part name="param1" type="xs:string"/> </message> <message name="fooResponse"> <part name="param2" type="xs:int"/> <part name="param3" type="xs:boolean"/> <part name="param4" type="xs:float"/> </message> <portType name="FooBar"> <operation name="foo"> <input message="y:fooRequest"/> <output message="y:fooResponse"/> </operation> </portType> public interface FooBar extends java.rmi.Remote{ public void foo(String param1, javax.xml.rpc.holders.IntHolder param2, javax.xml.rpc.holders.BooleanHolder param3, javax.xml.rpc.holders.FloatHolder param4, ) throws java.rmi.RemoteException; }

  41. Mapping XML Schema to Java public class Address { private String street; private String city; public String getCity(){return city; } public void setCity(String c){city=c; } … … } <complexType name="Address"> <sequence> <element name="city" nillable="true" type="xsd:string"/> <element name="street" nillable="true" type="xsd:string"/> </sequence> </complexType> • Class has to have correct getters and setters; • In axis, you can use WSDL2Java and Java2WSDL to do the mapping.

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