Servlets and JavaServer Pages

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Servlets and JavaServer Pages

• Milt Epstein
• CITES
• mepstein_at_uiuc.edu

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Outline

• Servlets
• Servlet containers
• JavaServer Pages (JSPs)
• Servlet advantages
• Q/A

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So, whats a servlet?

• Javas answer to CGI
• Run on a web server
• Dynamic content
• Middle layer between browser and
  databases/applications

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Lets look at some example servlets

• examples

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How do I run servlets

• Need a servlet container runs a JVM as a
  separate process to run the servlets
• Tomcat
• part of Apache Jakarta project
• servlet reference implementation
• Many others
• JRun, ServletExec, ...
• Some available free

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Integrating with web server

• Many servlet containers can be run in standalone
  mode
• Typically they are integrated (like a plug-in)
  into the web server
• Some web servers (or more fancy application
  servers) have built-in servlet containers
• Typically this means there are (at least) two
  processes running, the web server itself and the
  servlet container

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Tomcat

• Servlet reference implementation
• Can be run standalone
• Can be integrated with web server
• Apache
• IIS, IES (nee NES), others as well

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Integrating Tomcat with Apache

• Need mod_webapp
• Need to modify httpd.conf

LoadModule webapp_module /usr/local/libexec/mod_we
bapp.so AddModule mod_webapp.c ltIfModule
mod_webapp.cgt WebAppConnection warpConnection
warp localhost8008 WebAppDeploy examples
warpConnection /examples/ WebAppDeploy ROOT
warpConnection /tomcat/ lt/IfModule gt
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A closer look at a servlet

• A Java class that extends HttpServlet
• Compiled and placed in the appropriate directory
  (more on that later)
• When a request for a servlet arrives, the servlet
  container (a JVM)
• checks if an instance of that servlet exists
• if not, it creates/loads an instance
• calls the servlets service() method (which in
  turn may call doGet()/doPost()/doXXX())

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Lets look at some more example servlets

• examples

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OK, so whats a JSP?

• JavaServer Page
• Javas answer to ASP
• A text/html page with embedded Java code
  (scriptlet)

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Lets look at some example JSPs

• examples

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No, really, whats a JSP?

• OK, you caught me
• A JSP is really a servlet!
• The first time a JSP is requested, its
  translated to a servlet, and then compiled
• You want proof? It can get pretty ugly!

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JSP implicit objects

• Objects available automatically within a JSP

request out pageContext response config sessio
n page application exception
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JSP tags

• Comment lt-- comment --gt
• Declaration lt! declaration gt
  (may contain multiple declarations)
• Expression lt expression gt
• Code lt code gt
• Include lt_at_ include filerelativeURL gt
• Page lt_at_ page pageDirectiveAttrList gt

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JSP tags, XML style

• Comment No equivalent
• Declaration ltjspdeclarationgt
• Expression ltjspexpressiongt
• Code ltjspscriptletgt
• Include
  ltjspdirective.include filerelativeURL /gt
• Page
  ltjspdirective.page pageDirectiveAttrList /gt

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If a JSP is really a servlet, why use JSPs at
all?Because they can lead to a more cleanly
designed, and more easily maintained system.
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MVC Model, View, Controller

• Model 1
• Model 2
• Blatantly stolen from
  http//www.javaworld.com/javaworld/jw-12-1999/jw-1
  2-ssj-jspmvc_p.html

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JSPs where to put the code

• Call code directly
• Call code indirectly
• Use beans
• Use custom tags
• Use the MVC architecture

(listed in increasing order of complexity of
application)
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Contexts/web applications

• The servlet spec allows for the concept of a web
  application
• Stored in a war (web application archive), a la
  jar and tar
• Includes all resources that might be needed for
  the web application servlets, JSPs, HTML files,
  text files, images, etc.
• Normally, you can have intra-context
  communication, but not inter-context
• Default/ROOT context

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Attributes

• Objects that can be attached to request,
  session, or context/application (correspond to
  scope in JSPs)
• Allow sharing of resources (such as DB connection
  pools), passing data around

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A closer look at Tomcat

• Directory structure
• Server configuration files
• Context/application configuration files
• Other servlet containers will work differently
  (but perhaps similarly)

bin/ classes/ common/ conf/ lib/ logs/
server/ webapps/ work/
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So, why servlets?

• Efficient
• Persistent
• Convenient
• Powerful/Robust
• Portable
• Secure
• Inexpensive

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The Servlet Life Cycle

• init()
• service()
• doGet()
• doPost()
• doXXX()
• destroy()

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More advanced topics

• Web applications (WARs)
• Database connections (JDBC)
• JSP custom tags
• Filters
• Multi-threading/concurrency
• J2EE/EJB/JMS

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Java Users Group?

• CUJUG

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Any questions?