Web Applications Basics

Introduction to Web Web features Clent/Server HTTP HyperText Markup Language URL addresses Web server - a computer program that is responsible for accepting HTTP requests from clients and serving them HTTP responses Web application - a dynamic extension of a web or application server

Web Applications & Components Two types of web applications: Presentation-oriented (HTML, XML pages) Service-oriented (Web services) Web components provide the dynamic extension capabilities for a web server: Java servlets JSP pages Web service endpoints

Web Application Interaction [client] sends an HTTP request to the web server [web server] HTTP request  HTTPServletRequest This object is delivered to a web component, which can interact with JavaBeans or a DB to generate dynamic content [web component] generates an HTTPServletResponse or pass the request to another web component [web server] HTTPServletResponse  HTTP response [web server] returns HTTP response to the client

Web Application Interaction

Web Components Servlets - Java classes that dynamically process requests and construct responses JSP pages - text-based documents that execute as servlets but allow a more natural approach to creating static content Appropriate usage Servlets - service-oriented applications, control functions JSP - generating text-based markup (HTML, SVG, WML, XML)

Java Web Application Technologies Java Servlet technology is the foundation of all the web application technologies

Web Containers Web components are supported by the services of a runtime platform called a web container In J2EE, a web container "implements the web component contract of the J2EE architecture“ Web container services: request dispatching security concurrency life-cycle management naming, transactions, APIs

Web Container Examples Non-commercial Apache Tomcat Jetty Commertial Sun Java System Application Server BEA WebLogic Server Oracle Application Server WebSphere Open source JBoss

Deployment Web components have to be installed or deployed to the web container Aspects of web application behaviour can be configured during application deployment The configuration information is maintained in a XML file called a web application deployment descriptor

Web Application Development A web application consists of: Web components Static resource files (such as images) Helper classes and libraries The process for creating and running a web application is different from that of traditional stand-alone Java classes

Development Cycle 1.Develop the web component code 2.Develop the web application deployment descriptor 3.Compile the web application components and helper classes referenced by the components 4.Optionally package the application into a deployable unit 5.Deploy the application into a web container 6.Access a URL that references the web application

Web Modules According to Java EE architecture and Java Servlet Specification: Web components and static web content files such as images are called web resources A web module is the smallest deployable and usable unit of web resources Web module corresponds to a web application A web module has a specific structure

Web Module Structure The top-level directory of a web module is the document root of the application The document root contains: JSP pages client-side classes client-side archives static web resources

Web Module Structure The document root contains a subdirectory /WEB-INF/ web.xml: web application deployment descriptor lib: JAR archives of libraries called by server-side classes

Web Module Structure classes: server-side classes: servlets utility classes JavaBeans components tags: tag files, which are implementations of tag libraries

Configuring Web Applications Web applications are configured via /WEB-INF/web.xml file Configuration options: Map URLs to web components Set initialization parameters Map errors to error screens Declare welcome files Declare resource references

Mapping URLs to Web Components When a request is received by the web container it must determine which web component should handle the request Need to add a servlet definition and a servlet mapping for each servlet to web.xml file ServletName ServletClass ServletName /path

Initialization Parameters It's possible to pass initialization parameters to the context or to a web component Context parameters: name value Servlet parameters (within servlet definition): name value

Handling Errors Web container generates default error page You can specify custom default page to be displayed instead Steps to handle errors Create appropriate error html pages for error conditions Modify the web.xml accordingly

Example: Setting Error Pages exception.BookNotFoundException /errorpage1.html exception.BooksNotFoundException /errorpage2.html exception.OrderException /errorpage3.html

Example: web.xml Your team project name Team N servlets name_of_context_initialization_parameter value_of_context_initializtion_parameter YourServlet YourServletClass YourServlet /YourServlet

WAR Files A web module can be deployed as an unpacked file structure or can be packaged in a JAR file known as a Web Archive File WAR file can be created by: executing jar command using Ant target using IDE (Eclipse for instance) using Maven

Setting a Context Root A context root identifies a web application in a Java EE server The server is responsible for mapping URL’s that start with a specific prefix to the location of a web application Usually this is done with a web server configuration file

Using Maven & Jetty A convenient way to develop, build, deploy and run Web application is by using: Maven build tool Jetty web server

Creating Directory Structure Maven 2 supports the notion of creating a complete project template with a simple command To create Web project template need to use maven-archetype-webapp archetype mvn archetype:create -DgroupId=com.maven2example -DartifactId=maven2example_webapp -DarchetypeArtifactId=maven-archetype-webapp

Maven Web Directory Structure /src/main/webapp/ - directory structure for a WAR

Packaging Executing the command mvn package creates a WAR file

Running with Jetty It’s easy to run application by using Jetty plugin for Maven Jetty is an open-source, standards-based, full-featured web server implemented entirely in Java First created in 1995 Latest version / July 23, 2007

Running with Jetty Add the Jetty plugin to the pom.xml maven2example_webapp org.mortbay.jetty maven-jetty-plugin 6.0.1

Running with Jetty Execute mvn jetty:run command >mvn jetty:run [INFO] Scanning for projects... [INFO] Searching repository for plugin with prefix: 'jetty'. [INFO] [INFO] Building maven2example_webapp Maven Webapp [INFO] task-segment: [jetty:run] [INFO] [INFO] Starting jetty [INFO] Started Jetty Server Stop by Ctrl+C

Opening the Application Open your web browser to

Opening the Application Valid URL is

Resources J2EE Tutorial “Getting Started with Web applications” /bnadr.html Building Web Applications with Maven 2 uilding-web-applications-with-maven-2.html Filmiņa par Web 2 (5 minūtes)