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

• Web application - a dynamic extension of a web or application server

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

Web server diagram

http://www.resultantsys.com/appServer.htm

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

Web server statistics

Web server software vendors statisticshttp://news.netcraft.com/archives/web_server_survey.html

Totals for Active Sites Across All Domains:

Web server statistics

Web server software vendors statisticshttp://news.netcraft.com/archives/web_server_survey.html

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

Application server diagram

http://www.resultantsys.com/appServer.htm

Application servers extend web servers to support dynamic content

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

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

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

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://docs.oracle.com/javaee/7/tutorial/doc/

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

Java EE versions

• J2EE 1.2 (December 12, 1999)

• Java EE 5 (May 11, 2006)

• Java EE 6 (Dec 10, 2009)

• Java EE 7 (May 28, 2013)

Java EE 7 technologies

• Web Application Technologies• Java Servlet 3.1

• JavaServer Pages 2.3

• JavaServer Faces 2.2

• Web Services Technologies• JAX-RS 2.0, JAX-WS 2.2, JAXB 2.2, StAX …

• Enterprise Application Technologies• EJB 3.2, JMS 2.0, JPA 2.1, JTA 1.2, JavaMail 1.5…

http://www.oracle.com/technetwork/java/javaee/tech/index.html

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

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

Java Web Application Technologies

Java Servlet technology is the foundation of all the web application technologies

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)

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

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, css)

• 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 code2. Develop the web application deployment

descriptor3. Compile the web application components and

helper classes referenced by the components4. Optionally package the application into a

deployable unit5. Deploy the application into a web container6. 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: servletsutility classesJavaBeans components

tags: tag files, which are implementations of tag libraries

Configuring Web Applications

• Web applications are configured via (optional) 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

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>

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>

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

<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>

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>

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 http://maven.apache.org/

• Jetty web server http://www.mortbay.org/

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

Maven Web Directory Structure

<root>/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

• Stable release: 9.0.4 / 2013-06-26

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://www.eclipse.org/jetty/documentation/current/jetty-maven-plugin.html

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>8.1.13.v20130916</version>

</plugin>

</plugins>

</build>

Running with Jetty

• Execute mvn jetty:run command>mvn jetty:run

[INFO] Scanning for projects...

. . .

[INFO] --- jetty-maven-plugin:8.1.13.v20130916:run (default-cli)

@ servlet-jpa-app ---

[INFO] Configuring Jetty for project: servlet-jpa-app

[INFO] webAppSourceDirectory not set. Defaulting to

C:\tmp\servlet-jpa-app\src\main\webapp

[INFO] Reload Mechanic: automatic

[INFO] Classes = C:\tmp\servlet-jpa-app\target\classes

[INFO] Context path = /servlet-jpa-app

[INFO] Tmp directory = C:\tmp\servlet-jpa-app\target\tmp

[INFO] Web defaults = org/eclipse/jetty/webapp/webdefault.xml

[INFO] Web overrides = none

[INFO] web.xml file = file:/C:/tmp/servlet-jpa-app/src/main/webapp/WEB-INF/web.xml

[INFO] Webapp directory = C:\tmp\servlet-jpa-app\src\main\webapp

...

[INFO] Started Jetty Server

Stop by Ctrl+C

Opening the Application

Open your web browser to http://localhost:8080/

Context Path Configuration <build>

<finalName>maven2example_webapp</finalName>

<plugins>

<plugin>

<groupId>org.mortbay.jetty</groupId>

<artifactId>jetty-maven-plugin</artifactId>

<version>8.1.13.v20130916</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

Opening the Application

Open your web browser to http://localhost:8080/

Resources

• Introduction to Java Platform, Enterprise Edition 7 http://www.oracle.com/technetwork/java/javaee/javaee7-whitepaper-1956203.pdf

• The Java EE 7 Tutorial http://download.oracle.com/javaee/7/tutorial/doc/

• Article “App server, Web server: What's the difference?”http://www.javaworld.com/javaqa/2002-08/01-qa-0823-appvswebserver.html

Resources

• Building Web Applications with Maven 2 http://today.java.net/pub/a/today/2007/03/01/building-web-applications-with-maven-2.html

• Jetty Maven Pluginhttp://www.eclipse.org/jetty/documentation/current/jetty-maven-plugin.html