Unit 5: Servlets

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Unit 5 Servlets
Instructor Note To hide Instructor Notes, select
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• Building J2EE Applications in SilverStream

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Section Objectives

• Defining Servlets
• Coding Servlets
• Packaging Web Components
• Deploying Web Components

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What are they?

• From the Servlet Specification
• A servlet is a web component, managed by a
  container, that generates dynamic content.
  Servlets are small, platform independent Java
  classes compiled to an architecture neutral byte
  code that can be loaded dynamically into and run
  by a web server. Servlets interact with web
  clients via a request response paradigm
  implemented by the servlet container. This
  request-response model is based on the behavior
  of the Hypertext Transfer Protocol (HTTP).

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Comparing Servlets

• CGI
• First Generation
• Many different languages
• Vendor neutral
• ISAPI
• Microsoft Standard
• Faster than CGI
• Proprietary
• NSAPI
• Netscape standard
• Faster
• Proprietary

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Java Alternative Servlets

• Faster than CGI
• Vendor/platform neutral
• All the advantages of Java

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From the Browser

• The browser issues a request to a particular URL
• That request might include parameters

Instructor Note You can move through these
slides quickly if the class understands the
basics of HTTP.
HTML client
HTTP request
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To the Servlet

• The SilverStream Server has an integrated HTTP
  server that listens for HTTP requests.
• When the request is received, the server
  interrogates the URL to determine the correct web
  application component

Server runningthe servlet
HTTP request
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HTTP Requests

• Get
• Post
• Put
• Delete

Instructor Note A good way to check
understanding is to ask students how to issue a
Get and/or a Post from the browser
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And Back to the Browser

• The servlet generates the content dynamically and
  returns in a response to the browser.

Server runningthe servlet
HTML client
HTTP response
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Section Objectives

• Defining Servlets
• Coding Servlets
• Packaging Web Components
• Deploying Web Components

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Servlet Methods

• init
• service
• doGet
• doPost
• destroy
• getServletConfig
• getServletInfo

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service() Method

• Early servlet specifications only included this
  method for the request handling.
• Latest specifications include do methods for
  the different HTTP requests.
• Most common HTTP requests
• doGet
• doPost
• Request
• Response
• Session Management

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Request Parameter
Entire query string
req parameter
Cookie info
?
Client user info
Session info
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Retrieving Parameters

• To get the parameter names, use
• Enumeration getParameterNames()
• To retrieve the values, use
• String getParameter(String name)
• Or
• String getParameterValues(name)

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Retrieving Headers

• To get the clients address
• String getRemoteAddr()
• To get the clients domain
• String getRemoteHost()
• To determine HTTP or HTTPS
• String getProtocol()

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Retrieving Session Information

• To get a reference to the clients session
• HttpSession getSession()
• To check is session is still valid
• boolean isRequestedSessionIdValid()

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Response Parameter
Set output file MIME-type
res parameter
Write to the output stream
Add cookies
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Streaming Data to the Client

• Use the ServletOutputStream or PrintWriter to
  send data back to the client
• Get a reference to the stream from the Response
  parameter
• ServletOutputStream out response.getOutputStream
  ()
• Get a reference to the writer from the Response
  parameter
• PrintWriter out response.getWriter()
• Write the output to the stream
• Out.println(ltHTMLgtHello Worldlt/HTMLgt)
• Close the writer
• out.close()

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Setting MIME Type and Status

• When interacting directly with a browser, you
  must identify the type of data generated.
• response.setContentType(text/html)
• response.setContentType(application/pdf)
• You can also control the HTTP status codes.
• For example, 404 Resource Not Found
• response.setStatus()

Segue Now that weve talked about the methods
and parameters, lets look at some examples
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doGet Example

• An HTTP Get request
• lta hrefdisplayName.html?nameSolomongtDisplay
  Solomonlt/agt
• Appearance in the browser

Display Solomon
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doGet Code Example

• public void doGet(HttpServletRequest req,
  HttpServletResponse res) String inName
  req.getParameter("name")
• PrintWriter out res.getWriter()
• res.setContentType("text/html")
• out.println("lthtmlgtltcentergtlth1gtYour name
  is")
• out.println(inName)
• out.println("lt/centergtlt/h1gtlt/htmlgt")
  out.close()

• The servlet output

Your name is Solomon
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doPost Example
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Post HTML Source
lthtmlgt ltbody bgcolor"FFFFFF"gt ltform
action"DisplayName.html" method"post" gt
ltpgtPlease enter your namelt/pgt ltpgt ltinput
type"text" name"nameField"gt lt/pgt ltpgt
ltinput type"submit" name"Submit"
value"Submit"gt ltinput type"reset"
name"Reset" value"Reset"gt lt/pgt lt/formgt lt/bodygt
lt/htmlgt
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doPost Code Example

• public void doPost(HttpServletRequest req,
  HttpServletResponse res) String inName
  req.getParameter("nameField")
• PrintWriter out res.getWriter()
• res.setContentType("text/html")
• out.println("lthtmlgtltcentergtlth1gtThe name is
  ")
• out.println(inName)
• out.println("lt/centergtlt/h1gtlt/htmlgt")
  out.close()

• The servlet output

The name is David
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Putting it Together

• import java.io.
• import java.servlet.
• import java.servlet.http.
• public class NameServlet extends HttpServlet
• public void doGet(HttpServletRequest req,
  HttpServletResponse res)
• //code from previous example
• public void doPost(HttpServletRequest req,
  HttpServletResponse res) //code from previous
  example

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Session Management

• Session tracking mechanisms
• Methods of HttpSession

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Session Tracking Mechanisms

• URL Rewriting
• http//localhost/dir/index.htmljsessionid1234
• Cookies
• SSL Sessions

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Methods of HttpSession
Instructor Note As a review, ask students how
to get a reference to HttpSession in a servlet.

• To place values in the session
• setAttribute(name, value)
• To retrieve values from the session
• getAttribute(name)
• To remove the value from the session
• removeAttribute(name)
• To determine attribute names
• getAttributeNames()

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Servlet Lab 1 - Build a Servlet to Retrieve Data
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Section Objectives

• Defining Servlets
• Coding Servlets
• Packaging Web Components
• Deploying Web Components

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web.xml

• Deployment descriptor that describes how the
  components in the web archive operate.
• For example, what URLs a servlet listens on
• Created by both the component developer and
  application assembler.
• The web.xml file needs to be located in the
  WEB-INF directory.

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web.xml (2)

• web.xml contents
• Session parameters
• Servlet and servlet mapping
• Designating home and error pages
• Context parameters and environment entries
• Resource and EJB references
• Security authorization and authentication
• JSP tag libraries
• MIME-type mapping

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web.xml (3)
lt?xml version"1.0" encoding"Cp1252"?gt ltweb-appgt
ltdisplay-namegtSome Namelt/display-namegt ltdescript
iongtsome descriptionlt/descriptiongt lticongt ltsmal
l-icongtsmall.giflt/small-icongt ltlarge-icongtlarge.
giflt/large-icongt ...other sections... lt/web-appgt
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Home and Error Pages

• Welcome FilesWeb page that is displayed if a
  user specifies a URL that is a directory.
• Error PagesWeb page that is displayed if either
• A Web server returns a HTTP error code
• A Java Exception is thrown

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Home and Error Pages
ltwelcome-file-listgt ltwelcome-filegtindex.htmllt/wel
come-filegt lt/welcome-file-listgt lterror-pagegt lter
ror-codegt404lt/error-codegt ltlocationgtoops.htmllt/lo
cationgt lt/error-pagegt lterror-pagegt ltexception-ty
pegt java.lang.NullPointerException lt/exception-
typegt ltlocationgt/nullpointer.htmllt/locationgt lt/er
ror-pagegt
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Session Configuration

• Can specify how long a sessions timeout value is
  (in minutes)

ltsession-configgt ltsession-timeoutgt30lt/session
-timeoutgt lt/session-configgt
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Servlets

• Need to place information about the servlets into
  the web.xml including
• Required Information
• Class file to associate to a servlet
• URL mapping to servlets
• Optional Information
• Whether to load servlet on startup
• Servlet initialization parameters

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Servlets (2)
ltservletgt ltdescriptiongtServlet
Lablt/descriptiongt ltservlet-namegtcustomerservletlt/
servlet-namegt ltservlet-classgtCustomerServletlt/ser
vlet-classgt lt/servletgt ltservlet-mappinggt ltservle
t-namegtcustomerservletlt/servlet-namegt lturl-patter
ngtcustomerlisting.htmllt/url-patterngt lt/servlet-map
pinggt
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Parameters

• context-parameters
• For the servlet/JSP container runtime environment
• Developers gain access via getServletContext()
• environment entries
• Application constants
• Values can be changed at deployment time
• Developers gain access via JNDI
• Environment entries are stored at javacomp/env
  in the JNDI tree

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EJB and External Resources

• Your Web application may use
• Enterprise JavaBeans
• JDBC Data Sources
• Java Mail
• JMS
• URLs
• Others...
• ...But you wont necessarily know the location of
  the resources at development time.
• You can specify a location internally that can be
  changed at deployment time without affecting your
  component.

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EJB and External Resources (2)

• External resources in J2EE terminology are called
  Resource References.
• When specifying a resource reference you must
  identify the Java class representing the
  resource.
• javax.sql.DataSource
• javax.mail.Session
• java.net.URL
• javax.jms.QueueConnectionFactory
• javax.jms.TopicConnectionFactory

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EJB and Resource References
Instructor Note Mention to the students that we
changed the heading from External Resources to
Resource References because we all want to be
J2EE-proper
ltresource-refgt ltdescriptiongtMy
DataSourcelt/descriptiongt ltres-ref-namegtjdbc/myJDB
Clt/res-ref-namegt ltres-typegtjavax.sql.DataSourcelt/
res-typegt ltres-authgtContainerlt/res-authgt lt/resour
ce-refgt
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Security

• With a Web application there are two types of
  security
• Authentication
• Authorization
• Authentication can either be done by the
  container or by one of our web pages
• In the development of our Web apps we think of
  security logically
• Developers dont specify a real user or group
  name
• Instead we think of roles that are mapped to user
  or group at deployment time

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Security (2)

• Within the web.xml we need to identify
• How a login box is displayed (browser or custom
  form)
• What resources are protected
• What logical security roles there are
• Which roles can access protected resources

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Security (3)
ltlogin-configgt ltauth-methodgtFormlt/auth-methodgt lt
realm-namegtSilverStreamlt/realm-namegt ltform-login-
configgt ltform-login-pagegt somepage.html lt/f
orm-login-pagegt ltform-error-pagegt somepage.ht
ml lt/form-error-pagegt lt/form-login-configgt lt/lo
gin-configgt ltsecurity-rolegt ltdescriptiongtlt/descr
iptiongt ltrole-namegtmyrolelt/role-namegt lt/security-
rolegt
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SecuritySide Note

• Normally when you attempt to access a secure
  resource, SilverStream will send a 401 error
  which informs the browser to popup a login
  window.
• You can have a custom Web page that handles the
  login process.
• The page must have a html form
• Form method must be POST
• Action must be j_security_check
• Need an input field named j_username
• Need an input field named j_password

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SecuritySide Note (2)
lthtmlgt ltbodygt ltform method"POST"
action"j_security_check"gt ltinput type"TEXT"
name"j_username"gt ltinput type"TEXT"
name"j_password"gt ltinput type"SUBMIT"gt lt/formgt lt
/bodygt lt/htmlgt
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Security
ltsecurity-constraintgt ltweb-resource-collectiongt
ltweb-resource-namegt somename lt/web-resource-
namegt ltdescriptiongtlt/descriptiongt lturl-pattern
gtpageslt/url-patterngt lthttp-methodgtGETlt/http-met
hodgt lthttp-methodgtPOSTlt/http-methodgt lt/web-reso
urce-collectiongt ...continues...
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Security
ltauth-constraintgt ltdescriptiongtlt/descriptiongt
ltrole-namegtsomerolelt/role-namegt
lt/auth-constraintgt ltuser-data-constraintgt ltde
scriptiongtlt/descriptiongt lttransport-guaranteegt
NONE lt/transport-guaranteegt lt/user-data-const
raintgt lt/security-constraintgt
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MIME Mappings

• There needs to be a MIME mapping for each type of
  data that your Web application will send back to
  the client
• Most common MIME mappings are defined for you
• Text files
• HTML
• Graphic formats (gif, jpeg, png, etc)

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Sample web.xml
lt?xml version"1.0"?gt ltweb-appgt ltdisplay-namegtJ2E
E Sample Applt/display-namegt ltsession-configgt lt
session-timeoutgt30lt/session-timeoutgt lt/session-co
nfiggt ltwelcome-file-listgt ltwelcome-filegtwel
come.htmllt/welcome-filegt lt/welcome-file-listgt
lterror-pagegt lterror-codegt404lt/error-codegt ltloc
ationgt/oops.htmllt/locationgt lt/error-pagegt
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Sample web.xml (2)
ltservletgt ltdescriptiongtServlet
Lablt/descriptiongt ltservlet-namegtcustomerservletlt/
servlet-namegt ltservlet-classgtCustomerServletlt/ser
vlet-classgt lt/servletgt ltservlet-mappinggt ltservle
t-namegtcustomerservletlt/servlet-namegt lturl-patter
ngtcustomerlisting.htmllt/url-patterngt lt/servlet-map
pinggt ltresource-refgt ltdescriptiongtMy Data
Sourcelt/descriptiongt ltres-ref-namegtjdbc/myJDBClt/r
es-ref-namegt ltres-typegtjavax.sql.DataSourcelt/res-
typegt ltres-authgtContainerlt/res-authgt lt/resource-r
efgt
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Servlet Lab 2 Packaging Web Components Package
the Servlet
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Section Objectives

• Defining Servlets
• Coding Servlets
• Packaging Web Components
• Deploying Web Components

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Deploying Web Components

• Once a web application has been properly
  packaged, the deployer will deploy the
  application.
• The deployer resolves dependencies and vendor
  specific constructs in a deployment plan
• SilverStreams deployment plan for web components
  is an XML file
• Based on deploy_war.dtd
• SilverStreams deployment tool is SilverCmd

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SilverCmd

• Command-line interface
• SILVERSTREAM_HOME/bin/SilverCmd.exe
• Standard format
• SilverCmd command arguments
• Day-to-day administration, and deployment
• Example
• SilverCmd DeployWar localhost SilverBooksBegin
  myapp.war
• -f myapp-deployment.xml v5

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Deploying Web Components (2)

• The deployer will review the deployment
  descriptor (web.xml) to determine what is needed
  in the deployment plan
• Once a deployment plan is written, SilverCmd is
  used to deploy the web component into the server.
• If there are any unresolved dependencies,
  SilverCmd will report an error

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Deploying Web Components (3)

• What happens when you deploy?
• Dependencies get resolved
• New JNDI names get created
• JSP pages get compiled into servlets

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War Deployment Plan

• Basic War Deployment Plan

ltwarJarOptions isObjecttruegt ltwarJar
isObjecttruegt ltsessionTimeoutgt300lt/sessionTi
meoutgt ltURLgt/myapplt/URLgt lt/warJargt lt/warJarOpt
ionsgt
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War Deployment Plan Options

• Environment Entries
• Bean References

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War Deployment Plan Options (2)

• Resource References Options

ltresourceReferenceList isObjecttruegt ltresource
Reference isObjecttruegt ltnamegtjdbc/myJDBClt/na
megt lttypegtjavax.sql.DataSourcelt/typegt ltdataSou
rcegtSilverBooksBeginlt/dataSourcegt lt/resourceRefer
encegt lt/resourceReferenceListgt
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War Deployment Plan Options (3)

• Security Role Map Options

ltobj_roleMapgt ltobj_roleMappinggt ltnamegtname_as_i
n_war.xmllt/namegt ltuserOrGroupNamegt some-user-
or-group lt/userOrGroupNamegt lt/obj_roleMappinggt
lt/obj_roleMapgt
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Sample War Deployment Plan
lt?xml version"1.0"?gt ltwarJarOptions
isObjecttruegt ltwarJar isObjecttruegt
ltsessionTimeoutgt300lt/sessionTimeoutgt
ltURLgt/myapplt/URLgt ltresourceReferenceList
isObjecttruegt ltresourceReference
isObjecttruegt ltnamegtjdbc/myJDBClt/namegt
lttypegtjavax.sql.DataSourcelt/typegt
ltdataSourcegtSilverBooksBeginlt/dataSourcegt
lt/resourceReferencegt lt/resourceReferenceListgt
lt/warJargt lt/warJarOptionsgt
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SilverCmd DeployWAR
SilverCmd DeployWAR serverport
database warJar-f deploymentPlan
options Options include -o overwrite -i
ignore errors -U userid -P password -v verbose
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SilverCmd QuickDeployWAR
SilverCmd QuickDeployWAR serverport
database warJar-f deploymentPlan -s
rootdirectory options Options include -o
overwrite -i ignore errors -U userid -P
password -v verbose
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Servlet Lab 3 Deploying Web Components Deploy
the Servlet
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Servlet Lab 4 Configure Servlet Look at
Deployment
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Unit Summary

• What is the benefit of servlets over similar
  technologies?
• What two methods contain most of the code for a
  servlet?
• What must be defined in the web.xml file for a
  servlet?
• What is the difference between DeployWar and
  QuickDeployWar?

Instructor Note -- Faster than CGI, more open
than ISAPI or NSAPI -- doGet( ) and doPost( ) --
The servlet name, implementation class, and
URL -- QuickDeployWar looks for changed JSPs and
only deploys those
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Unit Summary

• Defining Servlets
• Coding Servlets
• Packaging Web Components
• Deploying Web Components