Object-Oriented Enterprise Application Development

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Object-Oriented Enterprise Application Development

• Tomcat 3.2 Configuration
• Last Updated 03/30/2001

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Topics

• This Tomcat overview examines
• Creating a new server
• Starting and stopping the server
• The web.xml file
• Installing web components
• Running servlets and JavaServer Pages

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Application Servers
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Functions

• A web server is software that provides the
  ability to reference both static and dynamic web
  resources.
• It is really designed to be a repository for all
  web-based business logic.
• This software abstracts the routine mechanics of
  executing this components so that we don't have
  to do it.

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Servlet Engines

• To execute a servlet or JavaServer Page, you must
  have an appropriate engine.
• The engine is the software that handles requests
  for a particular type of resource.
• A servlet engine handles servlet requests.
• A JSP engine handles requests for JavaServer
  Pages.

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Web Connectors

• When a web server receives a request for static
  content such as an HTML document, it handles the
  request itself.
• When a request for dynamic content, such as a
  servlet, is received, the web server must hand
  that request off to the web container for
  processing.
• This is the job of the web connector.

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Jakarta - Tomcat

• Jakarta-Tomcat is the servlet and JavaServer
  Pages engine available from the Apache Group.
• http//jakarta.apache.org/tomcat
• Tomcat is small, installs quickly, and is free.
  The current version is Tomcat 3.2.
• For this class, Tomcat will be acting as both a
  web and application server.

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Server Configuration
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Tomcat Root

• The directory where you installed Tomcat is
  called the lttomcat-rootgt. For instance
• c\apache\jakarta-tomcat
• We'll use the lttomcat-rootgt as our point of
  reference for all Tomcat configuration and
  installation issues.

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Document Root

• Change to the webapps directory under the
  lttomcat-rootgt.
• Create a new directory for this class called
  se452.
• This new directory is the ltdocument-rootgt for the
  new application.

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Directory Structure

• Within your ltdocument-rootgt, create the following
  directory structure
• /WEB-INF
• /WEB-INF/classes
• /WEB-INF/lib
• All directory and file names are case-sensitive.

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Server Configuration(1 of 2)

• Once you've chosen a ltdocument-rootgt for your
  application, you need to make Tomcat aware of it.
• If any part of your configuration is incorrect,
  Tomcat will fail to start.
• Tomcat records the problem in the lttomcat
  rootgt/logs directory.

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Server Configuration(2 of 2)

• All tomcat configuration information is stored in
  lttomcat-rootgt/conf.
• Edit the server.xml file.
• Add a new Context entry to the file
• ltContext path"/se452"
• docBase"webapps/se452"
• debug"9"
• reloadable"true"
• trusted"false"
• lt/Contextgt

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Servlet Installation
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Purpose

• Before we can execute a servlet, it must be
  installed under control of the application
  server. This involves two (2) steps
• Installing the servlet's class files
• Modifying the application's web.xml file.

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Deploying Servlets(1 of 2)

• Servlets are just Java classes.
• The servlet .class file is copied to the
  WEB-INF/classes directory.
• If you're using packages, make sure to install
  them in the WEB-INF/classes directory.

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Deploying Servlets(2 of 2)

• We need to make Tomcat aware of the fact that a
  new servlet has been deployed to the server.
• This is done through the web.xml file.
• The web.xml file contains important configuration
  information relevant to the application.

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Modifying the web.xml File

• Once the servlet class files have been installed
  on the server we need to update the web.xml file.
• This file allows us to map "pretty" names that
  are seen by the application's clients to "ugly"
  names used internally.
• This file uses an XML format to specify the
  servlet properties.

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Modifying web.xml(1 of 2)

• We create a new servlet entry in the web.xml file
  for each servlet
• ltservletgtltservlet-namegt howdylt/servlet-namegtlt
  servlet-classgt HelloWorldlt/servlet-classgt
• lt/servletgt

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Modifying web.xml(2 of 2)

• We next provide a translation from URLs to the
  servlet name slide
• ltservlet-mappinggtltservlet-namegt
  howdylt/servlet-namegtlturl-patterngt
  /greetingslt/url-patterngt
• lt/servlet-mappinggt

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JSP Installation
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Purpose

• Before we can execute a JSP, it must be installed
  under control of the application server.
• In contrast to servlets, this really only
  involves a single step
• Install the JSP files anywhere you would install
  a static HTML document.
• Any embedded Java classes referenced by the JSP
  must exist in the server's CLASSPATH.

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Custom Tags(1 of 2)

• To deploy a custom tag, you need to install the
  two components
• Tag library descriptor
• Tag class
• Each of these elements goes in a separate
  location.

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Custom Tags(2 of 2)

• The tag library descriptor can go in the same
  directory as the HTML and JSP files. This is
  typically the ltdocument-rootgt.
• The tag class package is installed within the
  ltdocument-rootgt/WEB-INF/classes directory.

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Changing JavaServer Pages(1 of 3)

• Tomcat can generally tell if a JSP has changed
  and will recompile the class.
• However, this process is not guaranteed to be
  accurate.
• You may find yourself making changes to a JSP and
  those changes not appearing in your output.

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Changing JavaServer Pages(2 of 3)

• There is a directory called work within your
  lttomcat-rootgt. This directory contains all of the
  translated and compiled JSPs.
• Within this directory there is a directory for
  each ltdocument-rootgt defined to the Tomcat server.

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Changing JavaServer Pages(3 of 3)

• Make sure that Tomcat has been stopped.
• Change to the directory that holds your compiled
  JSPs.
• Delete any of the .java or .class files as
  needed.
• Restart Tomcat.

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Tomcat Administration
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Bouncing the Server

• Whenever you make configuration changes to Tomcat
  you should "bounce" the server.
• "Bouncing" is a term we use to describe the
  process of stopping and then immediately
  restarting a server.
• For tomcat this means issuing the shutdown and
  startup commands located in the lttomcat rootgt/bin
  directory.

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Executing Servlets
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Executing a Servlet(1 of 2)

• To execute a servlet, you need to issue a request
  to Tomcat via a client.
• The most obvious client to use is a web browser.
• By default Tomcat listens for requests on port
  8080. This value can be changed, but for this
  class 8080 should be fine.

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Executing a Servlet(2 of 2)

• To execute the HelloWorld servlet we just entered
  into the web.xml file, use the following URI
• http//localhost8080/se452/greetings
• http//localhost8080/se452/servlet/howdy
• http//localhost8080/se452/servlet/HelloWorld
• This works because of the translations
  established in the web.xml file.

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Initialization Parameters
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Purpose

• Sometimes we want a servlet to initialize itself
  when it's first loaded by the servlet engine.
• For instance we might want to load some
  configuration data before allowing the servlet to
  handle client requests.
• This approach can be useful for testing your code
  without writing HTML pages or complex URLs.

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Modifying web.xml

• Initialization parameters are associated with
  their servlet within the web.xml file
• ltservletgtltservlet-namegthowdylt/servlet-namegtltserv
  let-classgtlt/servlet-classgtltinit-paramgt
  ltparam-namegtparm1lt/param-namegt
  ltparam-valuegtvalue1lt/param-valuegtlt/init-paramgt
• lt/servletgt

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Changing Initialization Parameters

• If you change the name and/or value of an
  initialization parameter you'll need to bounce
  the server.
• Bouncing the server forces it to re-load the
  server.xml and web.xml files.

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Executing JSPs
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Executing a JSP(1 of 2)

• To execute a JSP, you need to issue a request to
  Tomcat via a client.
• The most obvious client to use is a web browser.
• By default Tomcat listens for requests on port
  8080. This value can be changed, but for this
  class 8080 should be fine.

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Executing a JSP(2 of 2)

• To execute the HelloWorld JSP, use the following
  URI
• http//localhost8080/se452/HelloWorld.jsp
• Unlike servlets, there are no intermediate
  translations from logical names to physical JSP
  files.

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Resources

• Tomcat DocumentationYou should plan on spending
  some time reading the configuration and user's
  guides. Most of the problems that you'll
  experience can have their solutions traced
  directly back to one of these two guides.