1 / 34

Web Applications Basics

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

alayna
Download Presentation

Web Applications Basics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Web Applications Basics

  2. 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

  3. 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

  4. 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

  5. Web Application Interaction

  6. 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)

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

  8. 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, email APIs

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

  10. 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

  11. 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

  12. Development Cycle • Develop the web component code • Develop the web application deployment descriptor • Compile the web application components and helper classes referenced bythe components • Optionally package the application into a deployable unit • Deploy the application into a web container • Access a URL that references the web application

  13. Web Modules • According to Java EE architecture and Java Servlet Specification: • Web components and static web content files such asimages are called web resources • A web module is the smallest deployable andusable unit of web resources • Web module corresponds to a webapplication • A web module has a specific structure

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

  15. 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

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

  17. 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

  18. 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 <servlet> <servlet-name>ServletName</servlet-name> <servlet-class>ServletClass</servlet-class> </servlet> <servlet-mapping> <servlet-name>ServletName</servlet-name> <url-pattern>/path</url-pattern> </servlet-mapping>

  19. Initialization Parameters • It's possible to pass initialization parameters to the context or to a web component • Context parameters: <context-param> <param-name>name</param-name> <param-value>value</param-value> </context-param> • Servlet parameters (within servlet definition): <init-param> <param-name>name</param-name> <param-value>value</param-value> </init-param>

  20. 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

  21. Example: Setting Error Pages <error-page> <exception-type> exception.BookNotFoundException </exception-type> <location>/errorpage1.html</location> </error-page> <error-page> <exception-type> exception.BooksNotFoundException </exception-type> <location>/errorpage2.html</location> </error-page> <error-page> <exception-type> exception.OrderException </exception-type> <location>/errorpage3.html</location> </error-page>

  22. Example: web.xml <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE web-appPUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN“"http://java.sun.com/dtd/web-app_2_3.dtd"> <web-app> <display-name>Your team project name</display-name> <description>Team N servlets</description> <context-param> <param-name>name_of_context_initialization_parameter</param-name> <param-value>value_of_context_initializtion_parameter</param-value> </context-param> <servlet> <servlet-name>YourServlet</servlet-name> <servlet-class>YourServletClass</servlet-class> </servlet> <servlet-mapping> <servlet-name>YourServlet</servlet-name> <url-pattern>/YourServlet</url-pattern> </servlet-mapping> </web-app>

  23. 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

  24. Setting a Context Root • A context rootidentifies 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

  25. Using Maven & Jetty • A convenient way to develop, build, deploy and run Web application is by using: • Maven build tool http://maven.apache.org/ • Jetty web server http://www.mortbay.org/

  26. 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

  27. Maven Web Directory Structure <root>/src/main/webapp/ - directory structure for a WAR

  28. Packaging • Executing the command mvn package creates a WAR file

  29. 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 6.1.5 / July 23, 2007

  30. Running with Jetty • Add the Jetty plugin to the pom.xml <build> <finalName>maven2example_webapp</finalName> <plugins> <plugin> <groupId>org.mortbay.jetty</groupId> <artifactId>maven-jetty-plugin</artifactId> <version>6.0.1</version> </plugin> </plugins> </build>

  31. 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 6.0.1 ... ... [INFO] Started Jetty Server • Stop by Ctrl+C

  32. Opening the Application Open your web browser to http://localhost:8080/

  33. Opening the Application Valid URL is http://localhost:8080/maven2example_webapp/

  34. Resources • J2EE Tutorial “Getting Started with Web applications” http://java.sun.com/javaee/5/docs/tutorial/doc/bnadr.html • Building Web Applications with Maven 2 http://today.java.net/pub/a/today/2007/03/01/building-web-applications-with-maven-2.html • Filmiņa par Web 2 (5 minūtes) http://www.youtube.com/watch?v=6gmP4nk0EOE

More Related