Java Servlets

1
Java Servlets

• CS-422

2
Application Mapping

• Your servlet application will be mapped to a
  directory structure
• myapp maps to some directory C/docs/apps/myapp
• in the myapp directory create a directory called
  Web-inf
• in Web-inf create
• classes
• jsp
• lib - use this for common things like JDBC
  drivers
• sessions
• these directories are used for the various
  components of your application
• when invoking your servlet
• http//www.myserver.com/myapp/servlet/servletname
• the magic name myapp/setvlet will really refer
  to
• cdocs/apps/myapp/Web-inf/classes

3
Deploying your application

• To deploy a servlet based application create a
  .war (web archive) file containing all of the
  files needed for the application and place it on
  the server
• the servlet container will work from the web
  archive extracting files as needed
• the base JVM has all of the classes it needed for
  working with files in the various versions of
  zipped files.
• Use the JDK JAR utility to create your .war file
• ex cd myapp jar -cvf myapp.war (make sure that
  JDKnnn/bin is in your path and all of the files
  in the current directory will be placed into the
  file myapp.war
• copy the .war file to the webapp directory of
  your server and its work
• make sure to back-up both your development
  directory and your deployed war file.

4
Servlet Life

• A servlet can come into existence for two
  reasons
• it was configured to be loaded on start-up of the
  servlet engine
• a user request called for it
• a servlet object is created on the main thread
• init( ) is started on a secondary thread
• the servlets init( ) method is guaranteed to be
  called once (and only once) for the life of a
  given servlet.
• init( ) is guaranteed to complete before any
  service methods are invoked.
• the main thread for the servlet will terminate at
  the end of the init( )
• when a request for the servlet is received the
  servlet engine spawns a new thread and calls the
  appropriate service( ) method
• in the case of http this will be
• doGet
• doPost
• doDelete
• doOptions
• doPut
• doTrace

5
Servlet Life (more)

• Once the servlets life cycle us up (when all
  associated threads quiesce) the destroy( ) method
  will automatically be run

6
Servlet APIs

• The servlet APIs are split into two packages
• javax.servlet
• contains classes and interfaces that implement
  generic, protocol independent servlets, having
  this generiv layer allows it to be extended other
  protocols (like IIOP)
• javax.servlet.http
• extends javax.servlet for the HTTP protocol
• javax implies it is an official java extension
• TOMCAT is the official reference implementation

7
Scope
8
J2EE Application Servers

• Tomcat Apache Foundation Open Source
• JRUN Macromedia
• WebSphere IBM
• BEA Weblogic BEA
• Sun Java System Application Server SUN
• Oracle Application Server Oracle Corp.

9
Deployment

• Tomcat v.4 (Apache Foundation, Jakarta Project)
• Implements the Servlet 2.3 and JSP 1.2
  Specifications
• Servlet 2.3 Specification
• Outlines requirements for deploying servlets
• Directory Structure
• Deployment Descriptors

10
Directory Structure

• /application
• /application/WEB-INF
• Web.xml (deployment Descriptor)
• /application/WEB-INF/classes
• Compiled class files
• May be a WAR (Web Archive file containing all
  class files) create using the JAR application
  found in the JSDK bin directory

11
Deployment Descriptors

• XML file describing the application
• Used by the server to deploy the application
• DTD is at java.sun.con/j2ee/dtds/web-app_2_2.dtd

12
Web.xml (sample)
ltweb-appgt ltdisplay-namegtCS422Samplelt/display-nam
egt ltdescriptiongtStefliks Sample App for
CS422lt/descriptiongt ltservletgt
ltservlet-namegtBrowserDataServletlt/servlet-namegt
ltservlet-classgtBrowserDataServletlt/servlet-cla
ssgt lt/servletgt ltservlet-mappinggt
ltservlet-namegtBrowserDataServletlt/servlet-namegt
lturl-patterngt/steflik/BrowserDataServletlt/url-
patterngt ltservlet-mappinggt lt/web-appgt
13
Web Application Archive files

• jar cvf mywebapp.war