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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

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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

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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)

ClientWeb service

Provider

Publish the web service(WSDL)

Find the Web service (WSDL)

(SOAP)Messages

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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 self-describing

Web services can be discovered using UDDI

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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)

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What is SOAP?

The basic Web services platform is XML plus HTTP.

SOAP stands for Simple Object Access Protocol SOAP is a communication protocol SOAP is for communication between applications SOAP is a format for sending messages SOAP is designed to communicate via Internet SOAP is platform independent SOAP is language independent SOAP is based on XML SOAP is simple and extensible SOAP allows you to get around firewalls

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The Promise of Web Servicesweb-based SOA as new system design paradigm

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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)

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import java.util.*;

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;

}

}

Example: A simple WebService. Letsthe 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.

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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

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package hansen.playground;

import org.apache.axis.client.Call;

import org.apache.axis.client.Service;

import javax.xml.rpc.namespace.QName;

import java.net.*;

public class NHLServiceClient {

public static void main(String [] args) throws Exception {

Service service = new Service();

Call call = (Call)service.createCall();

String endpoint = "http://localhost:8080/axis/NHLService.jws";

call.setTargetEndpointAddress(new URL(endpoint));

call.setOperationName(new QName("getCurrentPosition"));

String division = args[0];

String team = args[1];

String position =

(String)call.invoke(new Object [] {new String(division), new String(team)});

System.out.println("Got result : " + position);}}

The clientneeds to specify is the URL of the jws-file and the name of the method to invoke,Prepare the Arguments of theMethod andInvoke it

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The Bigger Picture: Java 2 Enterprise Edition J2EE

J2EE Architecture

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J2EE Container Architecture

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Container Service APIsExample: 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

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Java ServletsServlets are small server-side programs

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Accessing ServletsThe Java Servlet API provides a simple

framework for building applications on web servers

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The Servlet Life Cycle

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Example of a servlet

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Servlet code cont.

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Example: HelloServelet

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The HelloServer servlet output

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Using Form DataExample: 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>

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Example: The ThreeParams Servlet

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The Result

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Java Server PagesJSP , 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 contentThe web container converts the JSP page

into a servlet class and compiles itExample of scriplets:

<%! private int someField = 5; %><%! private void someMethod(...) {...} %>

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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+Programming: Thanks for ordering <I><%= request.getParameter("title") %></I>

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<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>

The ThreeParams example in JSP

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Servlets/JSP

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Servlets/JSP

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Servlets/JSP Example