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Java Server Programming Lecture 1 focuses on: Introduction to web services Web Services using Axis The bigger Picture: Introduction to J2EE Java Servlets Java Server Pages (JSP) Servlets/JSP 1 What is a web service? A web Service is a server side application component accessible via web protocols (HTTP over TCP) It provides services and data to remote clients and other applications It provides a generic and standardized support for client-server paradigm accessible via the web The idea behind web services came about to allow big corps like Microsoft to provide a web service registry, and then you'd pay (on a per-use basis) for every web service you wanted to use (as opposed to having individual applications installed on your computer 2 How do web services work? Clients communicate with the web service via XML messages based on a protocol called SOAP (encoding and decoding messages in XML is supported by Apache Axis) web service registry (UDDI) Find the Web service (WSDL) Client Publish the web service (WSDL) (SOAP) Messages Web service Provider 3 More on Web Services loosely coupled, reusable components encapsulate discrete functionality distributed programmatically accessible over standard internet protocols add new level of functionality on top of the current web Web services are self-contained and selfdescribing Web services can be discovered using UDDI 4 Standard Protocols used by Web Services UDDI -- The "Universal Description, Discovery and Integration" protocol. A protocol for publishing web service descriptions WSDL – “Web Service Description Language” is a description language: using XML that describes exactly what your web service does SOAP – “Simple Object Access Protocol” A transport protocol that sends XML messages using HTTP (which runs on top of TCP, usually on port 80) 5 What is SOAP? The basic Web services platform is XML plus HTTP. SOAP SOAP SOAP SOAP SOAP SOAP SOAP SOAP SOAP SOAP stands for Simple Object Access Protocol is a communication protocol is for communication between applications is a format for sending messages is designed to communicate via Internet is platform independent is language independent is based on XML is simple and extensible allows you to get around firewalls 6 The Promise of Web Services web-based SOA as new system design paradigm 7 Apache eXtensible Interaction System (Axis) Axis supports the interaction between the client and the server (the web service) Axis is an implementation of the SOAP protocol. It shields the developer from the details of dealing with SOAP and WSDL You use Axis on the server side to write your web service (and deploy it as a Tomcat webapp) At the client side, Axis sends SOAP messages to invoke the methods of the server (using remote procedure calls) Axis lets the client make the method calls on the web service object as if it were a local object (AXIS generates a WSDL for the web service) 8 import java.util.*; Example: A simple Web Service. Lets the user gives the name of one of the teams in the U.S. National Hockey League, and the service returns the team's current position. public class NHLService { HashMap standings = new HashMap(); public NHLService() { // NHL - part of the standings as per 04/07/2002 standings.put("atlantic/philadelphia", "1"); standings.put("atlantic/ny islanders", "2"); standings.put("atlantic/new jersey", "3"); standings.put("central/detroit", "1"); standings.put("central/chicago", "2"); standings.put("central/st.louis", "3"); } public String getCurrentPosition(String division, String team) { String p = (String)standings.get(division + '/' + team); return (p == null) ? "Team not found" : p; } } 9 How to delpoy and use a web service The steps needed to create and use the "getCurrentPosition" web service. First you copy the NHLService.java file into the Axis directory on your web server Then you rename the file to NHLService.jws (JWS stands for Java Web Service). The web service is now deployed 10 package hansen.playground; The client import org.apache.axis.client.Call; needs to specify import org.apache.axis.client.Service; import javax.xml.rpc.namespace.QName; is the URL of import java.net.*; the jws-file public class NHLServiceClient { public static void main(String [] args) throws Exception { and the name Service service = new Service(); of the method Call call = (Call)service.createCall(); to invoke, String endpoint = "http://localhost:8080/axis/NHLService.jws"; call.setTargetEndpointAddress(new URL(endpoint)); Prepare the QName("getCurrentPosition")); Arguments of the call.setOperationName(new String division = args[0]; Method and String team = args[1]; String position = Invoke it (String)call.invoke(new Object [] {new String(division), new String(team)}); System.out.println("Got result : " + position);}} 11 The Bigger Picture: Java 2 Enterprise Edition J2EE J2EE Architecture 12 J2EE Container Architecture 13 Container Service APIs Example: create audio component, publish its name in a naming service (JNDI) available to your application. This provides a simple method to access the service APIs 14 Java Servlets Servlets are small server-side programs 15 Accessing Servlets The Java Servlet API provides a simple framework for building applications on web servers 16 The Servlet Life Cycle 17 Example of a servlet 18 Servlet code cont. 19 Example: HelloServelet 20 The HelloServer servlet output 21 Using Form Data Example: An HTML Form With Three Parameters <FORM ACTION="/servlet/coreservlets.ThreeParams"> First Parameter: <INPUT TYPE="TEXT" NAME="param1"><BR> Second Parameter: <INPUT TYPE="TEXT" NAME="param2"><BR> Third Parameter: <INPUT TYPE="TEXT" NAME="param3"><BR> <CENTER><INPUT TYPE="SUBMIT"></CENTER> </FORM> 22 Example: The ThreeParams Servlet 23 The Result 24 Java Server Pages JSP , an extension of the servlet technology, is a text based document (name.jsp) that contains two parts HTML or XML for static content JSP tags and scriplets in Java that generates the dynamic content The web container converts the JSP page into a servlet class and compiles it Example of scriplets: <%! private int someField = 5; %> <%! private void someMethod(...) {...} %> 25 JSP • JavaServer Pages (JSP) lets you separate the dynamic part of your pages from the static HTML. • Simply write the regular HTML in the normal manner, using whatever Web-page-building tools you normally use • then enclose the code for the dynamic parts in special tags, most of which start with "<%" and end with "%>". •For example, here is a section of a JSP page that results in something like "Thanks for ordering Core Web Programming" for a URL of http://host/OrderConfirmation.jsp?title=Core+Web+Program ming: Thanks for ordering <I><%= request.getParameter("title") %></I>26 The ThreeParams example in JSP <HTML> <TITLE>INPUT FORM</TITLE> <BODY> First Parameter-: <%=request.getParameter("param1")%> <BR> Second Parameter-:<%=request.getParameter("param2")%> <BR> Third Parameter-: <%=request.getParameter("param3")%> <BR> </BODY> </HTML> 27 Servlets/JSP 28 Servlets/JSP 29 Servlets/JSP Example 30