Web Services Essentials

Prepared for Developers

Transcript

1. © Mahindra Satyam 2009 V 1.0 Web Services
2. 2 © Mahindra Satyam 2009 Agenda  Introduction – Service Oriented Architecture  .NET Web Service basics – Creating a Web Service – Discovering Web Services – Determining Web Service Functionality – Testing a Web Service Method – Building a client to Use a Web Service  Simple Object Access Protocol (SOAP)  Publishing and consuming Web Services – Defining a web service – Building a web service in Visual Studio – Deploying the Web Service – Creating a client to consume the web service – Consuming the Web service  User-defined types in Web Services
3. 3 © Mahindra Satyam 2009 Introduction A web service is a class that allows its methods to be called by methods on other machines via common data formats and protocols, such as XML and HTTP. A web service promotes software reusability in distributed systems where applications execute across multiple computers on a network. In .NET the over-the-network methods calls are generally implemented through the SOAP (Simple Object Access Protocol) SOAP is an XML-based protocol describing how to mark up requests and responses so that they can be transferred via protocols such as HTTP.
4. 4 © Mahindra Satyam 2009 Service Oriented Architecture  Web Services refers to the technologies that allow for making connections.  Services are what you connect together using Web Services.  A service is the endpoint of a connection.  A combination of services—internal and external to an organization—make up a service-oriented architecture.  Also known as a composite application.  A composite application is created by combining services.  Composite applications are built using a service-oriented architecture.
5. 5 © Mahindra Satyam 2009 Service Oriented Architecture (contd.)
6. 6 © Mahindra Satyam 2009 .NET Web Service Basics A web service is a software component stored on one machine that can be accessed by an application or other software component on another machine over a network. The machine on which the Web Service resides is the remote machine The application that accesses the web service is the client
7. 7 © Mahindra Satyam 2009 Creating a web service  Create a project of type ASP.NET Web Service  Solution contains – Files to contain the Web Service code (which implements the web service) – ASMX file (which provides access to the web service) – DISCO file (which clients use to discover the Web service)  Methods in a web service are invoked through a Remote Procedure Call (RPC)  The methods are marked with the WebMethod attribute – which makes them accessible to other classes through RPCs. This is called as exposing a method
8. 8 © Mahindra Satyam 2009 Discovering Web Services  After a web service is implemented, compiled and deployed on a Web Server, client application can consume the Web Service.  The client uses the .disco file to discover the web service and know its capabilities  Discovery of Web Services (DISCO) is a Microsoft-specific technology used to located web services on a server.  DISCO files consist of XML markup that describes the location of the Web services to the client.  A .disco file is accessed via a Web Service’s ASMX page and contains the markup specifying references to the documents that define various Web Services  Resulting data returned from accessing a .disco file is placed in .discomap file.
9. 9 © Mahindra Satyam 2009 Determining a Web Service’s functionality  For the client to determine the web service’s functionality, Web services contain a service description  This is an XML document that conforms to the Web Service Description Language (WSDL)  WSDL document defines the methods exposed by the web service and how client must use them  Also specifies required formats for requests and responses.  WSDL is generated dynamically when a client requests the web service’s WSDL description – (i) By appending ?WSDL to the ASMX file’s URL – (ii) By clicking the Service Description link in the ASMX file
10. 10 © Mahindra Satyam 2009 Testing a Web Service’s methods  In the ASMX page, clicking on the method name requests a test page that describes the method  Test page allows users to test the method by clicking on the Invoke button  Page displays the sample request and response messages using SOAP and HTTP POST  The protocol that transmits request and response messages in Web Services is called wire format or wire protocol  SOAP is commonly used wire format as it can be sent using several transport protocols. HTTP POST requires HTTP protocol
11. 11 © Mahindra Satyam 2009 Building a client to use the Web Service  Client can be Console App, WinForm App or Web App  Enable client to consume Web Service by adding a reference to the client  Visual Studio accesses the WSDL information and copies into a WSDL file stored in the client’s Web References folder.  WSDL information is used to create a proxy class which handles the method call (i.e. networking details and formation of the SOAP messages)  When client app calls the Web method, the application actually calls a corresponding method in the proxy class. This method has the same name and parameters as the Web method but formats the call to be sent as a request in a SOAP message  Web service receives the request as a SOAP message, executes the method call and returns the result as another SOAP message.  When the client application receives the SOAP message, the proxy class deserializes it and returns the results as the return value of the web method that was called.
12. 12 © Mahindra Satyam 2009 Simple Object Access Protocol (SOAP)  SOAP is a platform-independent protocol that uses XML to make remote procedure calls over HTTP  Each request and response is packaged in a SOAP message  SOAP messages are platform independent and human-readable  SOAP types include primitive types (e.g. Integer) as well as DateTime, XmlNode, etc  SOAP can also transmit arrays, DataSets and user defined types  The client invoking the Web method sends the request and related information packaged in a SOAP message.  Web Service processes the contents contained inside a SOAP envelope and interprets the SOAP message’s contents (parsing)  After the web service sends the response to the client in another SOAP message, the client parses the response to retrieve the result of the method call.
13. 13 © Mahindra Satyam 2009 SOAP Request POST /InStock HTTP/1.1 Host: www.example.org Content-Type: application/soap+xml; charset=utf-8 Content-Length: nnn <?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:Body xmlns:m="http://www.example.org/stock"> <m:GetStockPrice> <m:StockName>IBM</m:StockName> </m:GetStockPrice> </soap:Body> </soap:Envelope>
14. 14 © Mahindra Satyam 2009 SOAP Response HTTP/1.1 200 OK Content-Type: application/soap+xml; charset=utf-8 Content-Length: nnn <?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:Body xmlns:m="http://www.example.org/stock"> <m:GetStockPriceResponse> <m:Price>34.5</m:Price> </m:GetStockPriceResponse> </soap:Body> </soap:Envelope>
15. 15 © Mahindra Satyam 2009 Defining the Web Service  The WebService attribute attached to a Web Service class declaration allows to specify a namespace(preferably company URL for uniqueness) and description (appears in the ASMX file)  Web Service must conform to Basic Profile 1.1 (BP 1.1) developed by the Web Services Interoperability Organisation (WS-I) dedicated to promoting interoperability among web services developed on different platforms with different programming languages.  Setting the WebServiceBinding attribute’s ConformsTo property to WsiProfiles.BasicProfile1_1 generates WSDL and ASMX files in conformance with the guidelines specified in BP 1.1  Web Service class inherits from System.Web.Services.WebService  The methods that are to be exposed must have the WebMethod atribute.
16. 16 © Mahindra Satyam 2009 Web Method Attributes  BufferResponse: When set to True, the response from the XML Web Service is held in memory and sent as a complete package. If False (default) the response is sent to client as it is constructed on the server  CacheDuration: Specifies the number of seconds that the response should be held in the system’s cache. Default=0  Description: Allows ASMX page to display information about the method.  EnableSession: True enables session state for the method. Default=False  MessageName: Applies a unique name to the WebMethod; required if methods are overloaded  TransactionOption: Specifies transactional support for the WebMethod. Default=Disabled
17. 17 © Mahindra Satyam 2009 The ASMX file The .asmx file contains a @WebService Page directive which has four possible attributes:  Class: Required! Specifies the class used to define the methods and data types visible to the XML Web Service Clients  CodeBehind: Required only when you are working with an XML web service using the code-behind model. Takes a string value that represents the physical location of the class file containing the web service logic. It is normally stored in the App_Code folder  Debug: Optional! Either True (compiled with debug symbols in place) or False.  Language: Required! Specifies the language used for the web service.
18. 18 © Mahindra Satyam 2009 Creating the Web Service Steps:  Create ASP.NET Web Service Project  Modify the code-behind file. Rename the class, method and file name if necessary  Modify the ASMX file and rename file name (Demo)
19. 19 © Mahindra Satyam 2009 Deploying the Web Service  Build Web Site  Test  Deploy (Demo)
20. 20 © Mahindra Satyam 2009 Creating a client to consume the Web Service  In client application, add web reference of the Web Service by entering the URL  Proxy class is created automatically  In code, create an instance of the proxy class and call its method  New web services can be located using these technologies: – UDDI (Universal Description, Discovery and Integration) and – DISCO (Discovery of Web Services)
21. 21 © Mahindra Satyam 2009 Consuming the Web Service  In the client, instantiate a proxy object to access the web service methods. (Demo)
22. 22 © Mahindra Satyam 2009 Transport Protocols for Web Services Three wire formats are available to web services:  HTTP-GET  HTTP-POST  SOAP (default format)
23. 23 © Mahindra Satyam 2009 Using HTTP-GET Enables to send the request along with any required parameters as a Query String. E.g., http://www.mysite.com?methodArgs=value To enable HTTP-GET, create <protocols> section in the web.config file to add the protocol. <system.web> <webServices> <protocols> <add name = “HttpGet” />
24. 24 © Mahindra Satyam 2009 Using HTTP-POST  Similar to HTTP-GET in that a name/value pair is sent to the server for processing.  HTTP-POST places the name/value pair within a request header which is not visible unlike HTTP-GET <html> <head> </head> <body> <form method = “post” action = http://www.mysite.com/method > <p><input type=“submit” value = “call service” > </p>
25. 25 © Mahindra Satyam 2009 Session Tracking  Setting WebMethod property EnableSession to True indicates that session information should be maintained and should be accessible to this method.
26. 26 © Mahindra Satyam 2009 User defined types Serialization:  Custom types that are sent to or from a Web Service are serialized, enabling them to be passed in XML format. This process is called XML serialization Requirements: Classes that are used to specify return types and parameter types for Web Methods must meet following requirements:  Public default constructor must be present  Properties and instance variables that should be serialized in XML format must be declared public  Properties that should be serialized must provide both get and set accessors even if empty bodied. Read-only properties are not serialized.