Java Servlet

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Java Servlet

• Presented by Hsin-Yi Wu
• http//www.albany.edu/hw8054
• March 13, 2000

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Agenda

• What are Servlets?
• Comparison of CGI, Server Extension APIs, and
  Servlet
• Servlet Basics
• Support for Servlet

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What are Servlets?

• Java servlets are a key component of server-side
  Java development.
• A servlet is a small, pluggable extension to a
  server that enhances the servers functionality.

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Examples of Web Applications

• Create dynamic content for a web page
• keyword search on a document archive
• electronic storefront

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Comparison of CGI,Server Extension APIs, and
Servlet
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CGI

• CGI (Common Gateway Interface)
• one of the first techniques for creating dynamic
  content
• intented purpose
• to define a standard method for a server to talk
  with external applications

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CGI life cycle
Child Process for CGI1
Request for CGI 1
Request for CGI 2
Child Process for CGI2
Request for CGI 1
Child Process for CGI1
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Server Extension APIs

• Proprietary server extension APIsfor example
• Netscape provides an internal API called NSAPI
• Microsoft provides ISAPI
• exist within the main process of a web server
• Run extremely fast and make full use of the
  servers resources

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Server Extension APIs life cycle
Request for Server Extension 1
Request for Server Extension 2
Request for Server Extension 1
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Server Extension APIs (continued)

• difficult to develop and maintain
• pose significant security and reliability hazards
• by crashed server extension

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Java Servlets

• similar to a proprietary server extension, except
  that it runs inside a Java Virtual Machine(JVM)
  on the server
• safe and portable
• handled by separate threads within the web server
  process
• efficient and scalable
• compromise between CGI and native-interface
  applications (ex ISAPI/NSAPI)

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Servlet life cycle
Servlet1
Servlet2
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Interface Response
From the May 5, 1998 issue of PC Magazine
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Comparison of Dynamic Web Interfaces- CGI

• Portability Fair
• Performance Fair
• Pros Can use familiar programming environment.
  
• Cons Slow.
• How it Works The Web server executes the CGI
  application as a separate process.

From the May 5, 1998 issue of PC Magazine
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Comparison of Dynamic Web Interfaces-
NSAPI/ISAPI

• Portability Poor
• Performance Excellent
• Pros Very fast.
• Cons Native API. Programming bugs can crash the
  Web server.
• How it Works The application is part of the Web
  server address space.

From the May 5, 1998 issue of PC Magazine
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Comparison of Dynamic Web Interfaces- Java
Servlet

• Portability Good
• Performance Good
• Pros Portable. Uses the JDK environment.
• Cons New and unstable.
• How it Works The Web server use Java Virtual
  Machine with a servlet add-on to interpret the
  Java applets.

From the May 5, 1998 issue of PC Magazine
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Support for Servlet
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Tools you need

• Java Development Kit (JDK)
• Java Servlet Development Kit(JSDK)
• include packagesjavax.servletjavax.servlet.http
  
• available from http//java.sun.com/products/servl
  et
• Servlet Engine

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Servlet Engines

• Used to test and deploy your servlets
• How to choose a servlet engine you need?
• Depends on the web server(s) you are running
• three flavors of servlet engines
• standalone
• add-on
• embeddable

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Servlet Engines

• Standalone servlet engines
• built-in support for servlets
• hard to keep on with the latest version of servlet

• Add-on servlet engines
• plug-in to an existing server

• Embeddable servlet engines
• lightweight servlet deployment platform that can
  be embedded in another application

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For a list of available servlet engines, see the
official list at

• Http//jserv.java.sun.com/products/java-server/ser
  vlets/environments.html

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Servlet Basics

• Java servlets are the first standard extension to
  Java,including two packages
• javax.servlet
• javax.servlet.http

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Servlet Interface
Servlet interface void init(ServletConfig sc)
throws ServletException void
service(ServletRequest req, ServletResponse
res) throws
ServletException, IOException void
destroy()
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Servlet Interface
Servlet interface void init(ServletConfig sc)
throws ServletException void
service(ServletRequest req, ServletResponse
res) throws
ServletException, IOException void
destroy()
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Servlet Framework
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A GenericServlet handling a request
GenericServlet subclass
Server
request
service( )
response
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An HTTP servlet handling GET and POST request
HttpServlet subclass
Server
Get request
doGet( )
response
service( )
Post request
doPost( )
response
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Servlet life cycle
Init()
Servlet1
service()
Servlet2
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import java.io. import javax.servlet. import
javax.servlet.http. public class
HelloWorldServlet extends HttpServlet
public void doGet (HttpServletRequest req,
HttpServletResponse res) throws
ServletException, IOException
res.setContentType("text/html") ServletOutput
Stream out res.getOutputStream() out.println("
lthtmlgt") out.println("ltheadgtlttitlegtHello
Worldlt/titlegtlt/headgt") out.println("ltbodygt") o
ut.println("lth1gtHello Worldlt/h1gt") out.println("
lt/bodygtlt/htmlgt")
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Saying Hello with JSP (hello.jsp)
ltHTMLgt ltHEADgtltTITLEgtHellolt/TITLEgtlt/HEADgt ltBODYgt ltH
1gt lt out.println(Hello World) gt lt/H1gt lt/BODY
gt ltHTMLgt
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For reference, see my web page http//www.albany.e
du/hw8054
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