Lecture 21

1. CS441 CURRENT TOPICS IN PROGRAMMING LANGUAGES Lecture 21 George Koutsogiannakis Summer 2011

2. Topics • Web Services. • XML • SOAP • WSDL • UDDI

3. Web Services • Two competing architectures. • .NET (Microsoft). • Sun’s Java Web Services. • We will discuss Sun’s Web Services.

4. Web Services • Deployment is independent of the two technologies. • Interoperability between different languages. • Interoperability between different platforms. • Interoperability between transport protocols (messages can ride on top of existing protocols by adding an extra layer).

5. Java Web Services • Java Web Services Developer Pack is used for web services and clients. • Java Web Services Developer Pack includes the following: • Java API for XML Messaging (JAXM) • Java API for XML Processing (JAXP) • Java API for XML Registries (JAXR) • Java API for XML based RPC (JAX-RPC) • Java API for XML Web Services (JAX-WS) • SOAP with Attachments API for Java (SAAJ) • Java Server Pages Standard Tag Library (JSTL) • Java Server Faces • Java WSDP Registry Server • Web Applications Deployment Tool • Ant Build Tool • Apache Tomcat servlet container • All of the above are part of EE5 and up .

6. Java Web Services Convert XML to Java Service Client Convert Java Type to XML Java Types Communicatiosn XML messages communications

7. Web Services • Web Services is a technology geared for Internet Based Distributed Computing. • Requires adding to the Internet infrastructure another layer that is responsible for managing the resources needed for Web Services. • Designers can design a Web Service without a concern as to the type or the number of nodes that are going to use the service. • It is based on request/response messages.

8. Web Services • Web Services use Internet protocols to publish their existence, discover each other and invoke each other. • Publishing and discovery is done via: • UDDI Universal Description, Discovery and Integration specification. • It is used to list the available services. • WSDL Web Services Description Language • Describes the available services.

9. Web Services • Other Protocols involved: • XML • Custom made tags are used to structure the message. • SOAP (Simple Object Access protocol) • Transfers the messages.

10. Web Services • Web Services are based on the concept of Service-Oriented Architecture (SOA). • SOAP is based on building components that can communicate with each other. • The components as in previous architectures that we studied (RMI, EJBs) must have well defined interfaces.

11. Web Services • Any service architecture contains 3 roles: • A service provider • Deployment of the service. • Publishing (registering) the service. • A service requestor • Finds a service description published in one or more registries. • Invokes the desired service. • A service registry • Advertizes web services descriptions published. It is the match maker between requestor and provider.

12. Web Services-XML • XML mark up language’ specification identifies element as: • A pairing of start and end tags in a XML document. • Elements have one of the following: • element-only content • Nested elements • mixed content • Nested elements and text mixed. • empty content.

13. Web Services -XML • Elements can have attributes • A name value pair • Value is enclosed in quotation marks. • For instance we can have an element called purchase order (<po>) <po id=“43871” submitted=“2009-04-21” customerID=“1234”> </po>

14. Web Services -XML • Alternatively instead of attributes we can define nested elements: <po> <id>43871</id> <submitted>2009-04-21</submitted> <customerID>1234</customerID> </po>

15. Web Services-XML- • XML schemas • Document Type Definitions (DTD) document describes rules regarding the elements used. • Schemas are used to validate the contents of XML documents as they are parsed by the XML parser. • Schemas enable the following: • Identification of the elements that are in a XML document. • Identification of the order and relationship between elements in the XML document.

16. Web Services-XML • Identification of the attributes of an element. • Identification of the data type of the value of an attribute. • Thus in summary, we have: • An XML document that defines the messages (data) in terms of XML elements. • A DTD document that describes the elements. • A need for a parser (can be written in Java) that checks the XML document against the DTD. • If the XML document adheres to DTD it is called “well formed” otherwise errors are generated.

17. Web Services-XML • The XML document then is made of 3 pieces: Called entities: • Elements • Attributes • Data

18. Web Services-SOAP • SOAP is a specification that describes how data should be structured in order to be transported over the Internet as part of distributed services. • SOAP is intended for B2B (Business to Business) or A2A (Application to Application) or EAI (Enterprise Application Integration). • It is not intended for Business to Customer.

19. Web Services -SOAP • SOAP is usually embedded in HTTP packets as part of request / response • The riding of one protocol on top of another is called “tunneling”. • SOAP handles data in terms of a textual form (RMI, CORBA and other distributed services protocols handle data in binary form).

20. Web Services-SOAP • SOAP message • An instance of the XML document • SOAP nodes • Peers of the distributed network that uses SOAP. • SOAP receiver • A SOAP node that receives the SOAP message and processes it. • SOAP intermediary • A SOAP node that acts as receiver and sender.

21. Web Services-SOAP intermediary Ultimate receiver Client requests service intermediay Web Service resides in this node SOAP Message Path

22. Web Services-SOAP • Intermediaries: • Can both accept and forward a message. • They can do some message processing. • Security domains are defined for the message.

23. Web Services-SOAP • Message Exchange Patterns (MEP) • One way communication that specifies • How many messages are interchanged in a given transaction. • Originator of the message. • Ultimate receiver of the message. • Two types of MEP • Request-Response MEP, similar to POST in http. • Response MEP , similar to GET in http.

24. Web Services-SOAP • A SOAP message consists of: • Envelope (mandatory) • It is the root element of the XML document • Header (Optional) • Passes application specific information. • It is used for transaction processing, authentication, login in. • Body (mandatory) • Actual application data to be transported. • Fault • Used to report errors back to sender

25. Web Services-SOAP • <soap: envelope> <soap: header> <……………> </soap:header> <soap:body> <………………> <soap:fault> <…………….> </soap:fault> </soap:body> </soap:envelope>

26. Web Services-SOAP • The header uses special elements like: <wsa (web services addressing) i.e. <wsa:ReplyTo><wsa:Address>http://MyBusiness/Client/ </wsa:Address></wsa:ReplyTo> <wsa:To>http://YourBusiness/purchasing</wsa:To> <wsa:Action>http://YourBusiness/SubmitPO</wsa:Action> • Message Exchange Pattern (MEP) type can be specified in the header.

27. Web Services-SOAP • The body can be something like: <soap:Body wsu: ID=“Body”> <po:purchaseOrder xmlsn: po=http://YourBusiness/PO> <po:customer>………….</po:customer> <po:creditCardType>……..</po:creditCardType> <po:creditCardNumber>…….</po:creditCardNumber> </po:purchaseOrder> </soap:Body>

28. Web Services-SOAP • SOAP data model follows a hierarchical tree of nodes in the structure of the elements. • Therefore we can have a Java program that creates the elements for the message , based on some tree structure.

29. Web Services-SOAP Bill Eva 1000 streetNumber name name address address Person Address Person gender gender city state Female Male IL Chicago

30. Web Services-SOAP • The java program can be: class Address { String city; String state; int streetNumber; public Address(int stNum, String c, String st) { this.streetNumber=stNum; this.city=c; this.state=st; } }

31. Web Services-SOAP Class Person { String name; String gender; Address address; public Person(String n, String g, Address ad) { this.name=n; this.gender=g; this.Address=address; } }

32. Web Services-SOAP • How Java is used in Web Services: • We can create XML documents in XML • We can use a Java parser to parse the XML document’ s elements. • The Java parser can use our DTD document a steh grammar file. • We can use a Java program based on JAXP API to read the XML elements and the data in the XML document.

33. Web Services-JAXP API • JAXP (java API for XML Processing) has parsers for XML documents. • It provides a default parser. • Or it can be configured to use other parsers. • Can create a DTD programmatically. • Can create the XML document

34. JAX-WS API • AX-WS stands for Java API for XML Web Services. • JAX-WS is a technology for building web services using XML. • It allows developers to write message-oriented as well as RPC-oriented web services. • In JAX-WS, a web service operation invocation is represented by an XML-based protocol such as SOAP

35. JAX-WS API • JAX-WS API hides the SOAP complexity from the application developer. • On the server side, the developer specifies the web service operations by defining methods in an interface written in the Java programming language. • The developer also codes one or more classes that implement those methods.

36. JAX-WS API • A client creates a proxy (a local object representing the service) and then simply invokes methods on the proxy. • The developer does not generate or parse SOAP messages. It is the JAX-WS runtime system that converts the API calls and responses to and from SOAP messages.

37. JAX-WS API Just like in EE beans and JPA classes , annotations are used here also.

38. JAX-WS API • package helloservice.endpoint; import javax.jws.WebService; @WebService public class Hello { private String message = new String("Hello, "); public void Hello() {} @WebMethod public String sayHello(String name) { return message + name + "."; } }

39. JAX-WS API • In this example, the implementation class, Hello, is annotated as a web service endpoint using the @WebService annotation. • Hello declares a single method named sayHello, annotated with the @WebMethod annotation. • @WebMethod exposes the annotated method to web service clients. sayHello returns a greeting to the client, using the name passed to sayHello to compose the greeting. The implementation class also must define a default, public, no-argument constructor.

40. JAX-WS API • When invoking the remote methods on the port, the client performs these steps: • Uses the generated helloservice.endpoint.HelloService class which represents the service at the URI of the deployed service’s WSDL file. • HelloService service = new HelloService(); • Retrieves a proxy to the service, also known as a port, by invoking getHelloPort on the service. • Hello port = service.getHelloPort();The port implements the SEI defined by the service. • Invokes the port’s sayHello method, passing to the service a name.

41. JAX-WS API • package simpleclient; import javax.xml.ws.WebServiceRef; import helloservice.endpoint.HelloService; import helloservice.endpoint.Hello; public class HelloClient { public static void main(String[] args) { try { HelloClient client = new HelloClient(); client.doTest(args); } catch(Exception e) { e.printStackTrace(); } }

42. JAX-WS API public void doTest(String[] args) { try { System.out.println("Retrieving the port from the following service: " + service); HelloService service = new HelloService(); Hello port = service.getHelloPort(); System.out.println("Invoking the sayHello operation on the port."); String name; if (args.length > 0) { name = args[0]; } else { name = "No Name"; } String response = port.sayHello(name); System.out.println(response); } catch(Exception e) { e.printStackTrace(); } }

43. Web Services-WSDL • WSDL is used to describe the message syntax associated with the invocation and response of a web service. • It is an XML document that conforms to WSDL schema definition. • WSDL is to the web services what IDL is to RMI over IIOP and Corba.

44. Web Services-WSDL • It describes 3 fundamental properties of a web service: • What a service does- that is the methods of the web service that can be invoked. • How a service is accessed- the data formats and protocols required to access the service. • Where a service is located- such as the URL for the service. • It has special elements to allow description of the above i.e <portType name=“PriceCheckPortType”> <operation name=”checkPrice”> <input message=“pc:PriceCheckRequest”/> <output message=“PriceCheckResponse”> </operation> </portType>

45. Web Services-WSDL • Where message is modeled via the XML document. • It has a collection of elements. • A special element in WSDL called binding tells how to format the message (the XML elements) • The binding element tells how to invoke the operation using SOAP over HTTP (or some other protocol). • WSDL maps to Java via tools that automate the process. • A tool like that is WSDL2Java provided by Apache Axis. (AXIS = Apache eXtensible Interaction System) .

46. Web Services-UDDI • UDDI facilitates service discovery • At design time (static discovery) • Or, at runtime (dynamic discovery). • UDDI makes reference to a specific WSDL document for the service. • UDDI uses its own elements to provide the description of the service. • You can use Java to do the registration or the discovery of the service. • A UDDI can be looked at as another web service. • It could be accomplished by using JAX (Java for XML ) API.

47. UDDI Registry Links to WSDL Documents Publish Search Service Consumers Service Provider SOAP messages

48. Study Guide • Chapter 16 of EE5 Tutorial • Or Chapters 11,12,13 of EE6 Tutorial