Web services are a middleware, like CORBA and RMI. What makes web services unique is that the language being used is XML

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Daniella Holmes
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1 Web Services

2 Web Services Web services are a middleware, like CORBA and RMI. What makes web services unique is that the language being used is XML This is good for several reasons: Debugging is possible using a text editor Platform independence, since XML is just text Development of web services middleware is simple, since XML is easy to parse & generate

3 SOAP The XML language used by web services is called SOAP The Simple Object j Access Protocol Other middleware technologies use different communication languages IIOP is the wire protocol used by CORBA JRMP is the wire protocol used by RMI These languages are binary, however

4 SOAP Simple Object Access Protocol SOAP is the language used (over HTTP) for web services requests and responses This is much like how HTML is used for traditional web responses SOAP is usually hidden from developers, but developers may examine the SOAP code for debugging purposes SOAP is easy to understand since it is XML

5 How SOAP Works The client sends a SOAP message (called a SOAP envelope) using HTTP to the service The service is installed into a web server, which receives the HTTP request and passes the message to the service The service processes the requested operation, and returns another SOAP envelope as the HTTP response The client reads and interprets the response SOAP envelope, and reacts to it somehow

6 How SOAP Works (Contd.) SOAP Request Envelope Client SOAP Response Envelope HTTP Server Web Service

7 How SOAP Works (Contd.) One major advantage that SOAP has is that it uses HTTP, which is a protocol already prevalent on the web It is used for web browser/web server communication Typically, SOAP clients, however, are not users, but other programs SOAP clients are typically similar in nature to CORBA or RMI clients

8 Example: SOAP Request POST /InStock HTTP/1.1 Host: Content-Type: application/soap+xml;charset=utf-8 Content-Length: nnn <?xml version="1.0 0"?> <soap:envelope xmlns:soap=" soap:encodingstyle=" <soap:body xmlns:m=" org/stock"> <m:getstockprice> <m:stockname>ibm</m:stockname> </m:getstockprice> </soap:body> </soap:envelope> p

9 Example: SOAP Response HTTP/ OK Content-Type: application/soap; charset=utf-8 Content-Length: nnn <?xml version="1.0"?> <soap:envelope xmlns:soap=" soap:encodingstyle=" <soap:body xmlns:m=" <m:getstockpriceresponse> <m:price>34.5</m:price> </m:getstockpriceresponse> </soap:body> </soap:envelope>

10 Web Services Many people think that web services will soon become ubiquitous Mostly, these people are betting that Microsoft s support will be enough to convince everyone to switch their middleware Whether or not they become ubiquitous, eventually they will cooperate with CORBA & EJBs This will mean that they can be used in any application Many Java gurus/ developers HATE XML and Web services. too slow, too high an overhead, and back to the future because RPC is used and real objects can not be passed.

11 Web Service Middleware Most web service middleware prevents you from having to know the SOAP language However, it is a good idea to know something about the language if you intend to use SOAP There are several middleware choices if you plan to use web services (and they are roughly compatible):.net Web Services JAX-RPC Apache Axis Each of these technologies are configured differently, but the main idea is the same

12 Web Service Architecture

13 JAX-WS: Overview

14 JAX-WS Annotations ti Annotations play a critical role in JAX-WS Annotations are used in mapping Java to WSDL and schema 2. Annotations are used in runtime to control how the JAX-WS runtime processes and responds to web service invocations Annotations utilized by JAX-WS 2.0 are defined in separate JSRs: JSR 181: Web Services Metadata for the JavaTM Platform JSR 222: JavaTM Architecture for XML Binding (JAXB) 2.0 JSR 224: JavaTM API for XML Web Services (JAX-WS) 2.0 JSR 250: Common Annotations for the JavaTM Platform

15 Web Service Implementation ti 1. Write a POJO implementing the service 2. annotation to it 3. Optionally, inject a WebServiceContext t WebServiceContext makes it possible for a web service endpoint implementation class to access message context and security information relative to a request 4. Deploy the application 5 Point your clients at the WSDL 5. Point your clients at the WSDL e.g.

16 Example: = style = SOAPBinding.Style.DOCUMENT, use = SOAPBinding.Use.LITERAL, parameterstyle = SOAPBinding.ParameterStyle.WRAPPED) public class HelloWebService public String hello(@webparam(name = "name") String name){ return "Welcome " + name + "!!!"; } }

17 Web Service Client wsimport The above command will generate a number of compiled Java classes that allow client applications to access web services: Add.class AddResponse.class Calculator.classclass CalculatorService.class ObjectFactory.class package-info.class Subtract.class SubtractResponse.class

18 We will now develop a simple client to access our web service. import javax.xml.ws.webserviceref; public class CalculatorServiceClient = " + "CalculatorService?wsdl") private static CalculatorService calculatorservice; public void calculate() { Calculator calculator = calculatorservice.getcalculatorport(); System.out.println("1 + 2 = " + calculator.add(1, 2)); System.out.println("1-2 = " + calculator.subtract(1, 2)); } public static void main(string[] args) { new CalculatorServiceClient().calculate(); calculate(); } }

19 Web Service Client annotation injects an instance of the web service into our client application. Its wsdllocation attribute contains the URL of the WSDL corresponding to the web service we are invoking.

20 Web Service Client The web service class is an instance of a class called CalculatorService. This class was created when we invoked the wsimport utility; wsimport always generates a class whose name is the name of the class we implemented plus the "Service" suffix. We use this service class to obtain an instance of the web service class we developed. In our example, we do this by invoking the getcalculatorport() method on the CalculatorService instance. In general, the method to invoke to get an instance of our web service class follows the pattern getnameport(), where Name is the name of the class we wrote to implement the web service. Once we get an instance of our web service class, we can simply invoke its methods as with any regular Java object.

21 Reference The J2EE 1.4 Tutorial: Building Web Services with JAX-RPC, Sun MicroSystems. y p j j

Web Applications. Web Services problems solved. Web services problems solved. Web services - definition. W3C web services standard

Web Applications. Web Services problems solved. Web services problems solved. Web services - definition. W3C web services standard Web Applications 31242/32549 Advanced Internet Programming Advanced Java Programming Presentation-oriented: PAGE based App generates Markup pages (HTML, XHTML etc) Human oriented : user interacts with