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Web Applications - Basics

Web Applications - Basics. Introduction to Web. Web features Clent/Server HyperText Transfer Protocol HyperText Markup Language URL addresses Web server - a computer program that is responsible for accepting HTTP requests from clients and serving them HTTP responses

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Web Applications - Basics

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  1. Web Applications - Basics

  2. Introduction to Web • Web features • Clent/Server • HyperText Transfer Protocol • 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 (HTTP) servers • A Web server handles the HTTP protocol • To process a HTTP request, a Web server may • respond with a static HTML page or image • send a redirect • delegate the dynamic response generation to some other program such as • CGI scripts • JSPs (JavaServer Pages), servlets • server-side JavaScripts • or some other server-side technology

  4. Web server diagram http://www.resultantsys.com/appServer.htm

  5. Web server features In practice many web servers implement the following features: • Authentication • Handling of static and dynamic content • HTTPS support (by SSL or TLS) • Content compression (i.e. by gzip encoding) • Virtual hosting • Large file support • Bandwidth throttling

  6. Web server statistics Web server software vendors statistics http://news.netcraft.com/archives/web_server_survey.html Totals for Active Sites Across All Domains:

  7. Web server statistics Web server software vendors statistics http://news.netcraft.com/archives/web_server_survey.html

  8. Application servers • Application server is responsible for handling the business logic of the system • Separation of business logic from the presentation logic and the database logic: 3-tier architecture http://www.cavehill.uwi.edu/fpas/cmp/online/cs14k/client_server_model/webserver.htm

  9. Application server diagram Application servers extend web servers to support dynamic content http://www.resultantsys.com/appServer.htm

  10. Application server features • The application server manages its own resources and may provide features such as: • Security • Transaction management • Database connection pooling • Clustering support • Messaging • Most application servers also contain a Web server

  11. Web Applications & Components • Web application is a dynamic extension of a web or application server • 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

  12. 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

  13. Web Application Interaction

  14. Java Enterprise Edition • Java EE is a comprehensive platform for multi-user, enterprise-wide applications • It is based on Java SE and adds APIs for Internet-based server-side computing http://download.oracle.com/javaee/6/tutorial/doc/

  15. Java EE architecture Java EE defines an architecture for implementing services through the use of a Java EE server as multi-tier applications that deliver the scalability, accessibility, and manageability needed by enterprise-level applications • The business and presentation logic has to be implemented by the developer • The standard system services are provided by the Java EE platform

  16. Java EE versions • J2EE 1.2 (December 12, 1999) • Java EE 5 (May 11, 2006) • Java EE 6 (Dec 10, 2009) • Java EE 7 Roadmap https://blogs.oracle.com/theaquarium/entry/java_ee_7_roadmap • Java EE 7 – spring 2013 • Java EE 8 – spring 2015

  17. Java EE 6 technologies • Web Application Technologies • Java Servlet 3.0 • JavaServer Pages 2.2 • JavaServer Faces 2.0 • Web Services Technologies • JAX-RS 1.1, JAX-WS 2.2, JAXB 2.2, StAX … • Enterprise Application Technologies • EJB 3.1, JMS, JPA, JTA, JavaMail … http://www.oracle.com/technetwork/java/javaee/tech/index.html

  18. Java EE components • Java EE applications are made up of components • A Java EE component is a self-contained functional software unit that is assembled into a Java EE application with its related classes and files and that communicates with other components

  19. Java EE components • Components are compiled in the same way as any program in the Java language • Components are assembled into a Java EE application, are verified to be in compliance with the Java EE specification, and are deployed to production, where they are run and managed by a Java EE server

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

  21. Servlets and JSPs • 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)

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

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

  24. 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

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

  26. 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

  27. 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

  28. 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

  29. 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

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

  31. Configuring Web Applications • Web applications are configured via deployment descriptor /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

  32. 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>

  33. 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>

  34. 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

  35. 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>

  36. Example: web.xml <?xml version="1.0" encoding="ISO-8859-1"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> <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>MyServlet</servlet-name> <servlet-class>com.web.demo.MyServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>/servlet</url-pattern> </servlet-mapping> </web-app>

  37. 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

  38. 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

  39. 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/

  40. Creating Directory Structure • Maven 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 type in a single line: mvn archetype:create -DgroupId=com.maven2example -DartifactId=maven2example_webapp -DarchetypeArtifactId=maven-archetype-webapp

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

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

  43. 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 • Stable release: 8.1.7 / 2012-07-16

  44. Jetty Maven Plugin • Useful for rapid development and testing • You can add it to any webapp project that is structured according to the usual Maven defaults • The plugin can then periodically scan your project for changes and automatically redeploy the webapp if any are found http://wiki.eclipse.org/Jetty/Feature/Jetty_Maven_Plugin

  45. Running with Jetty • Add the Jetty plugin to the pom.xml <build> <finalName>maven2example_webapp</finalName> <plugins> <plugin> <groupId>org.mortbay.jetty</groupId> <artifactId>jetty-maven-plugin</artifactId> <version>8.1.7.v20120910</version> </plugin> </plugins> </build>

  46. Running with Jetty • Execute mvn jetty:run command >mvn jetty:run [INFO] Scanning for projects... [INFO] ------------------------------------------------------- [INFO] Building maven2example_webapp Maven Webapp 1.0-SNAPSHOT [INFO] ------------------------------------------------------- [INFO] >>> jetty-maven-plugin:8.1.7.v20120910:run (default-cli) @ maven2example_webapp >>> ... ... 2012-11-01 05:14:02.035:INFO:oejs.AbstractConnector:Started SelectChannelConnector@0.0.0.0:8080 [INFO] Started Jetty Server Stop by Ctrl+C

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

  48. Configuration <build> <finalName>maven2example_webapp</finalName> <plugins> <plugin> <groupId>org.mortbay.jetty</groupId> <artifactId>jetty-maven-plugin</artifactId> <version>8.1.7.v20120910</version> <configuration> <scanIntervalSeconds>10</scanIntervalSeconds> <webApp> <contextPath>/my-super-app</contextPath> </webApp> </configuration> </plugin> </plugins> </build> Now valid URL is: http://localhost:8080/my-super-app

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

  50. Resources • Article “Introducing the Java EE 6 Platform” http://www.oracle.com/technetwork/articles/javaee/javaee6overview-141808.html • The Java EE 6 Tutorial http://download.oracle.com/javaee/6/tutorial/doc/ • Article “App server, Web server: What's the difference?” http://www.javaworld.com/javaqa/2002-08/01-qa-0823-appvswebserver.html

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