web programming in java java servlet...

China Jiliang University

Java Web Applications, Helmut Dispert

Java

Web Programming in Java

Java Servlet Programming



WorkgroupServer

Java TechnologyEnabled Desktop

MicroEdition

StandardEdition

EnterpriseEdition

High-EndServer

Java TechnologyEnabled Devices

JavaCard

Java 2 Platform Editions



Java 2 Platform

Java 2Enterprise

Edition(J2EE)

Core APIs

Java 2Enterprise

Edition(J2EE)

Core APIs

Java 2StandardEdition(J2SE)

Core APIs

Java 2StandardEdition(J2SE)

Core APIs

Java Programming LanguageJava Programming Language

Java HotSpotJava HotSpot Java Virtual Maschine (JVM)Java Virtual Maschine (JVM) KVMKVM Card VMCard VM

Java 2 Micro Edition Core APIsJava 2 Micro Edition Core APIs

TVProfileTV

Profile ScreenPhoneProfile

ScreenPhoneProfile

CarProfileCar

Profile

PersonalProfile

PersonalProfile Mobile InformationDevice Profile

Mobile InformationDevice Profile

SmartCard

Profile

SmartCard

Profile

ProfileProfileProfileProfile

ProfileProfileProfileProfileJava 2 Platform, Micro Edition(J2ME) encompasses VMs and coreAPIs specified via Configurations aswell as vertical or market-specificAPIs specified in Profiles.



Java Technology / Range of Devices



J2EE Platform

ToolsTools Application Programming ModelApplication Programming Model

TransactionsTransactions

MessagingMessaging MailMail

Co

nn

ecto

rsC

on

nec

tors

ContainerContainer

EJBsEJBs JSPsJSPs ServletsServlets

Java 2 SDK, Standard EditionJava 2 SDK, Standard EditionCORBACORBA RMIRMI DatabaseDatabase Naming / DirectoryNaming / Directory

Ap

ple

tsA

pp

lets

Java

Bea

ns

Java

Bea

ns



JAVA 2 EE

Standard platform for web applications J2EE platform released December 1999.

HTML presentation APIs Servlet 2.2

JavaServer Pages 1.1 2008: Servlet 2.5 and JSP 2.1 specifications

Many other subsystems standardized under a single platform

EJB and JDBC technologies JTA, JTS, JMS, JavaMail API, RMI-IIOP

RMI: Remote Method Invocation, JTA: Java Transaction API IIOP: Internet Inter-Orb Protocol, JTS: Java Transaction Service API

JMS: Java Message Service API



Jakarta - Tomcat

Jakarta Project

The goal of the Jakarta Project is to provide commercial-quality server solutions based on the Java Platform that are developed in an open and cooperative fashion.

Jakarta is the "overall" project for many subprojects. For example, Tomcat is the Servlet+JSP Engine which is a subproject of the Jakarta Project.



Jakarta - Tomcat

Jakarta Tomcat

Tomcat is the servlet container that is used in the official Reference Implementation for the Java Servlet and JavaServer Pages technologies. The Java Servlet and JavaServer Pages specifications are developed by Sun under the Java Community Process.

Tomcat is developed in an open and participatory environment and released under the Apache Software License.

21 December 2011 - Jakarta Retired



Standard Services and APIs

ServletJava Server Pages

EJB JDBC

Business LogicPresentation

DataAccess

DataClient

JTS/JTA JNDI JavaMail RMI-IIOP JMS

Java 2 Enterprise Edition APIs



What Are Servlets?

Java technology objects which extend the functionality of an HTTP Server.

Comparable to Netscapes NSAPI, Microsofts ISAPI, or Apache Modules

Platform Independent

Server Independent



What Are Servlets?

Web Server

Servlet Engine Container

BrowserURL2

URL1

Servlet2

Servlet1

Multiple requestsIn a single session

Request

Response

Request

Response



Servlets

Servlets run inside a JVM on the server Requests are handled by separate Threads within the web

server process.

Servlets can interact very closely with the server. Servlets can provide thin-client connectivity to a large

enterprise application. Since servlets reside on the server, they can act as a middleware gateway to legacy systems.

Servlets can provide controlled access to a number of different multi-user applications, such as chat servers, news and file services, discussion databases, and search engines.



Why Servlets?

HTTP is the universal transport of the Internet through restrictive firewalls

Browsers, Web Applications, Java technology-based applets and Applications, and other programs can all use HTTP

Any kind of data can be transmitted over HTTP - not just HTML



Java Servlets

From CGI to Servlet



CGI (Common Gateway Interface) Life Cycle

MainProcess

Request for CGI 1 Child Process for CGI 1



CGI-basedWeb Server

Example: CGI script written in Perl Each request starts a separate Perl interpreter



MainProcess



Request for CGI 1

FastCGI-basedWeb Server

FastCGI creates a single persistent processfor each FastCGI program.

FastCGI Life Cycle



Main Process

Request forServer Extension 1 Server Extension 1

Server Extension 2

Web Server with Server Extension API

Request forServer Extension 2

Request forServer Extension 1

Server Extension APIs Life Cycle



Server Extension APIs

Examples: Netscapes NSAPI (WAI) Microsofts ISAPI

Apache Modules

Server extensions enhance or change the base functionality of the server Proprietary solutions

Server-specific APIs use linked C or C++ code Security and reliability hazards



ASP, JavaScript

Active Server Pages - ASP (Microsoft): Technique for developing dynamic web content;

HTML page contains snippets of embedded code(VBScript, Jscript, etc.);

Supported by Microsoft IIS (Internet Information Server) and other web servers.

Server-side JavaScript - SSJS (Netscape): Technique for developing dynamic web content;

HTML page contains snippets of embedded JavaScript code;

For higher performance the web pages are precompiled.



Main Process

JVM

Java Servlet Life Cycle

Request forServlet 1 Servlet 1

Java Servlet-based Web Server

Servlet 2Request forServlet 2

Request forServlet 1

Thread

Thread

Thread



Servlet Advantages over CGI

Efficient Threads instead of OS processes, one servlet copy,

persistence

Convenient Many high-level utilities

Powerful Sharing data, pooling, persistence

Portable run on virtually all operating systems and servers

Secure No shell escapes, no buffer overflows




Architecturally Faster than CGI Servlets dont fork a new process for each request

Servlets are loaded and ready for each request The same servlet can handle many requests

Easy to Develop Based on Java programming language

No pointer problems like C code No different dialects of development language for

different databases

Object Oriented

Servlets lend themselves to reusable code practices




Extensive Java Libraries Available The functionality of the Java platform libraries make

Servlets the most flexible middle tier Servlets can take advantage of JDBC, EJB, JMS,

JavaMail, JavaIDL, RMI, and more Any third-party Java technology-based library is easily

accessible

Write Once, Run Anywhere Servlets can run on any platform that the Java Runtime

exists The same servlet can run on any brand of server Develop on any small desktop machine, Deploy on the

largest of servers



Free Servlet and JSP engines

Apache Tomcathttp://jakarta.apache.org/tomcat/

SUN JSWDKhttp://java.sun.com/products/servlet/download.html/

IBM WebSphere Application Serverhttp://www.software.ibm.com/webservers

Allaire JRUN

http://www.jrun.com/ Unify ServletExec

http://www.servletexec.com

Gefion Software LiteWebserverhttp://www.gefionsoftware.com/LiteWebServer/

Servlet Engines

http://jakarta.apache.org/tomcat/http://java.sun.com/products/servlet/download.html/http://www.software.ibm.com/webservershttp://www.jrun.com/http://www.servletexec.comhttp://www.gefionsoftware.com/LiteWebServer/



Compiling and Invoking Servlets

Set CLASSPATH Servlet JAR file (e.g. servlet.jar)

JSP JAR file (e.g. jasper.jar, jspengine.jar, jsp.jar)

top of your package hierarchy

Put servlet class path on proper location(location depends on server) e.g.: TOMCAT:

host/webapps/ROOT/WEB-INF/classes

Invoke servlets: http://host/servlet/ServletName

http://host/servlet/ServletName



Servlet Engines for Existing Servers

Standalone Servlet Engines Servers with built-in support for servlets:

Sun Microsystem Java Web Server, Netscape Enterprise Server, W3C Jigsaw Server, O'Reilly WebSite Pro

Add-on Servlet Engines Plug-in to an existing server:

Apache Tomcat, WAICoolRunner for Netscape,Life Software JRun

Embeddable Servlet Engines Lightweight servlet platform that can be embedded in

another application:Sun Microsystem JavaServer Engine



Three-tier Architecture

Web ServerContent Level

RelationalDatabaseData and Service Level

PresentationLevel

Clients

Three-tier architecture for application service providers (ASP):focused on accessing information.



Multitier Architecture

Multitier (Internet-based) architecture for application service providers (ASP):focused on accessing application services.

Web ServerContent Level

Clients

PresentationLevel

Relational Databases

Data andService Level

Other Systems

Application LevelApplicationServer



Three-tier servlet model

DBServer

CustomAS

ORB

Java WebServer

Servlet

Servlet

ServletWeb Clients

DB: Database ServerAS: Application ServerORB: Object Request Broker



Java Servlets

DatabaseHTTP-ServerClient

AppletsBrowsers

ServletsServers



Java Servlets

Operating System

Server

Servicee.g. HTTP

Servicee.g. FTP

Servlet

Servlet

Servlet

Servlet



Servlet Package / Servlet API

The javax.servlet package provides interfaces and classes for writing servlets.

All servlets implement the Servlet interface.

Most common way:extending a class that implements the Servlet interface(e.g. HttpServlet).



The Servlet Interface

ServletServlet

GenericServletGenericServlet

HttpServletHttpServlet

MyServletMyServlet Servlet Documentation



Client Interaction

ServletClient

Servlet receives two objects:1. ServletRequest:

encapsulates the communication from the client to the server.

2. ServletResponse:encapsulates the communication from the servlet back to the client.

Call

ServletRequest and ServletResponse are interfaces defined by the javax.servlet package



HTTP Hypertext Transport Protocol

HTTP: Stateless protocol (simple) Client specifies HTTP command (method)

request also specifies URL and HTTP version

Example: GET command

GET /example.html HTTP/1.0

URL(address)

Protocolversion



HTTP Request

After the initial request the client can send optional information about the request (software, content type, etc.):

Optional header information

Example:

User-Agent: Mozilla/4.0 (compatible; MSIE 4.0; Windows 95)Accept: image/gif, image/jpeg, text/*, */*

User-Agent header: Information about the client software

Accept header: Specification of the media (MIME)



HTTP Request

Request Information Example

Method: GET

Request URI:/dispert/servlet/RequestInfoExample

Protocol: HTTP/1.0

Path Info: null

Remote Address: 149.222.10.2



HTTP Request

Request Header ExampleHost 149.222.51.80:8080Referer http://149.222.51.80:8080/

dispert/servlets/index.htmlAccept-Encoding gzipAccept image/gif, image/x-xbitmap,

image/jpeg, image/pjpeg,image/png, */*

Connection Keep-AliveAccept-Charset iso-8859-1,*,utf-8User-Agent Mozilla/4.7 [en] (Win98; U)Accept-Language en

Ref.: W3CThe Referer request-header field allows the client to specify, for the server's benefit, the address (URI) of the resource from which the Request-URI was obtained (the "referrer", although the header field is misspelled.)

http://149.222.51.80:8080/



HTTP Request

After the headers, the client sends a blank line.

The client can also send additional data, if this is appropriate for the method being used (e.g. with the POST method).

After the client sends the request, the server processes it and sends back a response

The first line is a status line that specifies the server's HTTP version, a status code and the code description, e.g.:

HTTP/1.0 200 OK



HTTP Response

Response Header: Status code (line), status description

Examples:

HTTP/1.0 200 OKStatus code: 200

Request was successful

HTTP/1.0 404 Not FoundStatus code: 404

Requested document was not found



HTTP Response

Response Headers: Software running on server

Content type of server response

Date: Sunday 16-June-2013 04:14:12 GMT

Server: JavaWebServer/1.1.1

MIME-Version: 1.0

Content-type: text/html

Content-length:1029

Last-modified: Thursday 9-May-2013 12:15:35 GMT

Example:



HTTP Methods

GETMethod for getting information (e.g. document, DB query result)

POSTMethod for posting (sending) information (e.g. credit card information, DB data)

HEADsimilar to get, used to receive only the response headers

PUT DELETE

TRACE OPTIONS



GET / POST - Requests

GET query string limited to (about) 240 characters

should not be used for critical applications (e.g. place orders, update a databases).

POST used to send megabytes of information (work

around problems with overly-long URLs). URL does not change

cannot be bookmarked or emailed (security)



Other HTTP Requests

HEAD Client sees only header of response to determine size,

etc.

PUT used to place documents directly on server

DELETE Opposite of PUT

TRACE Debugging aid returns to client contents of it's request

OPTIONS returns options that are available on server



HEAD Method

The HTTP HEAD method is similar to the HTTP GET method, except that the server only returns the header information.

HEAD is often used to check: The last-modified date of a document on the server for

caching purposes The size of a document before downloading (so the

browser can present progress information) The server type, allowing the client to customize

requests for that server The type of the requested document, so the client can

be sure it supports it



HTTP Response Codes

Code Groups:

2xx - Success

3xx - Redirection

4xx - Client error

5xx - Server error



HTTP Response Codes

No Response

Partial Information

Accepted

Created

OK

Function

Used for scripts that don't return a visible result.

204

Returned information may be cached or private.

203

Request accepted for asynchronous processing.

202

Following a POST command, this indicates success, but the text of the response line indicates the URL of the new document.

201

200

DescriptionCode

200-series HTTP response codes indicate that the request was processed without any error conditions. The 200-series responses other than 200 are seldom seen in practice.



HTTP Response Codes

Not modified

Method

Found

Moved

Function

Use the local copy if you cached it. Often seen when using the HEAD method, rather than the GET method.

304

Same as found, but a different method may be used to access the document; details about the method are sent in the message body.

303

Same as move, except that linking to the found address doesn't make much sense, since the document URL is expected to change. This is the code that the httpd returns for a cgi script whose output contained a Location: header.

302

Browsers with link editing capabilities should automatically link to the new reference. The response contains one or more header lines of the form URI: url string CrLf which specify alternative addresses for the object in question. The string is an optional comment field.

301

DescriptionCode

300-series response codes indicate that the document requested has moved to some other location, or that the browser is being redirected for some other reason.



HTTP Response Codes

Authorization will not helpForbidden403

Request should be retried with proper charge-to header.

Payment Required402

Not found

Unauthorized

Bad Request

Function

A document with that URL doesn't exist. 404

Request should be retried with proper authorization header. This is the response which triggers the browser to pop up the dialog requesting your username and password.

401

Impossible request or syntax error 400

DescriptionCode

400-series messages indicate that the browser did something wrong.



HTTP Response Codes

Not in the HTTP spec, but implemented by some HTTP servers.

Timed out502

Not implemented

Internal Error

Function

Another rather ambiguous message, typically meaning that you tried to execute something that was not executable, or POST to someting that was not a CGI program, or something similar.

501

A rather meaningless catch-all message that indicates that the site admin goofed on their CGI program.

500

DescriptionCode

500-series messages indicate that something went wrong on the server. Usually associated with CGI problems.

Hypertext Transfer Protocol -- HTTP/1.1http://www.w3.org/Protocols/http://www.w3.org/Protocols/rfc2616/rfc2616.txt

http://www.w3.org/Protocols/http://www.w3.org/Protocols/rfc2616/rfc2616.txt



HTTP Response Codes

Example:



The Servlet API

HTTP Servlets:Servlets use classes and interfaces from the following two packages:

javax.servletsupports generic, protocol-independent servlets

javax.servlet.httpadds HTTP-specific functionality to servlets

javax:top-level package name to indicate a standard extension



Generic and HTTP Servlet

Servlet construction:Every servlet must implement the

javax.servlet.Servletinterface.

Possibilities:a) Protocol-independent servlet:

Extend (subclass) the classjavax.servlet.GenericServlet

b) HTTP-Servlet:Extend (subclass) the classjavax.servlet.http.HttpServlet



Generic and HTTP Servlet

Servlet properties: Similar to an applet

a servlet does not have a "main() method" The server invokes certain methods When the server dispatches a request to the servlet the

"service() method" is invoked

Generic Servlet: overrides

the "service() method" to handle requests

HTTP Servlet: overrides the "doGet() method" to handle GET requests overrides the "doPost() method" to handle POST

requests



Servlet Function

Read data sent by the user from HTTP form, applet, or custom HTTP client

Look up HTTP request information Browser capabilities, cookies, requesting host, etc

Generate the results JDBC API, RMI, direct computation

Format the results inside a document HTML, excel, etc.

Send HTTP response parameters MIME types, cookies, compression, etc.

Send the document to the client



Request and Response

Request

HTTP request header

InputStream or Reader

Form data, CGI data

Response

HTTP response header

OutputStream or Writer

Setting cookies, redirect, or error pages



The Request Object

Encapsulates all information from the client

Allows access to:

request headers

InputStream or Reader

CGI like information

Form data



Frequently Used Request Methods

javax.servlet.ServletRequest {

Enumeration getParameterNames();

String getParameter(String paramName);

String getRemoteAddr();

}

javax.servlet.http.HttpServletRequest {

String getRequestURI();

Enumeration getHeaderNames();

String getHeader(String headerName);

HttpSession getSession();

Cookie[] getCookies();

}

Enumeration



Retrieving Information

HttpServletRequest offers several methods to access information about:

initialization parameters

the server

the client

request parameters



The Response Object

Encapsulates all communication to client

Allows access to:

response headers

an OutputStream or Writer

to setting cookies

Methods for sending redirects, error pages, etc.



Frequently Used Response Methods

javax.servlet.ServletResponse {

ServletOutputStream getOuputStream();

PrintWriter getWriter();

void setContentType(String type);

void setContentLength(int length);

}

javax.servlet.http.HttpServletResponse {

void addCookie(Cookie cookie);

void setStatus(int statusCode);

void sendError(int statusCode);

void sendRedirect(String url);

}



HttpServletResponse

HttpServletResponse Object

getWriter() returns a Writer for text

getOutputStream() returns ServletOutputStream for binary

Set header data before above IO set

setContentType in header



Reasons for NOT overriding Service()

Possible to add support for other services later by adding doPut, doTrace, etc.

Not possible with service() override

Possible to add a getLastModified method, in order to add support for modification dates

Built-in version provides automatic support for

HEAD requests

OPTION requests

TRACE requests



GenericServlet subclassServer

service()

Generic Servlet

Request

Response

implemented by subclass



Servlet Life-Cycle

Three phases of the Servlet Life-Cycle: Initialization:

accepts configuration and initializes the state; Service:

processes user requests, returns output;

Destruction:preparations for shutdown, release of memory resources.



Servlet Life-Cycle

Create

Initialize

AvailableFor

Service

UnavailableFor

Service

ServicingRequests

Destroy

Unload

Initialization failed

UnavailableExceptionthrown



Servlet Life-Cycle

Life-Cycle Methods: init (ServletConfig)

service (ServletRequest, ServletResponse) destroy ()

Additional Methods: getServletConfig ()

getServletInfo ()



Servlet Life-Cycle

Comparison Applet Life-Cycle: init ()

start () stop ()

destroy ()

Similarity between servlets and applets is intentional.Servlets are to web servers what applets are to web browsers.



Methods of Servlet

init (ServletConfig config)This method is invoked when the servlet is loaded the first time. The ServletConfig object provides initialization arguments for the servlet.

servlet (ServletRequest req,ServletResponse res)

This method is the main method of the servlet. Each request from a client results in a call to servlet().The objects ServletRequest and ServletResponse represent the data from the client and to the client.

destroy ()This method is called before the servlet is unloaded (e.g. for cleanup purposes).



SampleServlet

import java.io.*;import javax.servlet.*;

public class SampleServlet implements Servlet{

private ServletConfig config;

public void init (ServletConfig config) throws ServletException{

this.config = config;}public void destroy() {} // no action

public ServletConfig getServletConfig(){

return config;}

public String getServletInfo(){

return " First simple servlet";} continued



SampleServlet

public void service (ServletRequest req, ServletResponse res)

throws ServletException, IOException

{

res.setContentType ("text/html");

PrintWriter out = res.getWriter();

out.println ("Helmut Dispert - Sample Servlet");

out.println ("Fachbereich Informatik und Elektrotechnik");

out.println ("First Sample Servlet");

out.println ("");

out.close();

}

}



Initializing Servlets

Common in real-life servlets

e.g. Initializing database connection pools

There are two version of init()

Version 1: takes no parameter

Version 2: takes a ServletConfig

ServletConfig.getInitParameteris used to read initialization parameters

init should be used even when no initialization parameters are read



ServletConfig - Initialization Information

During servlet start-up initialization information (name/value pairs) is made available and passed to the servlet via the ServletConfig parameter of the init() method

String message;

public void init(ServletConfig config)

{

message =config.getInitParameter("message");

}

ServletConfighttp://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/ServletConfig.html

http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/ServletConfig.html



ServletConfig- Initialization Information

messageFH-Kiel

repeats5

Initialization with Jakarta-Tomcat: web.xml

(partial listing)

http://java.sun.com/j2ee/dtds/web-app_2_2.dtd



Servlet Context Information

public abstract interface ServletContextDefines a set of methods that a servlet uses to communicate withits servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file. There is one context per "web application" per Java Virtual Machine. (A "web application" is a collection of servlets and content installed under a specific subset of the server's URL namespace such as /catalog and possibly installed via a .war file.) In the case of a web application marked "distributed" in its deployment descriptor, there will be one context instance for each virtual machine. In this situation, the context cannot be used as a location to share global information (because the information won't be truly global). Use an external resource like a databaseinstead. The ServletContext object is contained within the ServletConfigobject, which the Web server provides the servlet when the servlet is initialized.

ServletContexthttp://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/ServletContext.html

http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/ServletContext.html



Servlet Config Information

public abstract interface ServletConfigA servlet configuration object used by a servlet container used to pass information to a servlet during initialization.





Server Context Information

Server Context information is made available through the ServletContext object.A servlet can obtain this object by calling the getServletContext() method on the ServletConfigobject .This reference should be saved in a private variable within the init() method.

private ServletConfig config;public void init (ServletConfig config) {this.config = config; // store configservletContext sc = config.getServletContext ();sc.log ("Started OK!");}





Methods of ServletContext

getAttribute ()Get server information.

getMimeType ()Return MIME type of a file.

getRealPath ()Translate relative or virtual path to a path relative to the HTML document root location.

getServerInfo ()Return name and version of server.

getServlet ()Return Servlet object of given name.

getServletNames ()Return an enumeration of servlet names.

log ()Write information to a servlet log file (server specific).



Servlet Context during Service Request

Service requests can contain information in form of name/value parameter pairs as a ServletInputStreamor a BufferedReader.This information is available through the ServletRequest object that is passed to the service() method.

BufferedReader reader;String param1, param2;public void service {ServletRequest req,

ServletResponse res) {reader = req.getReader ();param1 = req.getParameter ("First");param2 = req.getParameter ("Second");}



Methods of ServletRequest

getAttribute ()Returns value of a named attribute for this request.

getContentLength()Size of request, if known.

getContentType()Returns MIME type of the request message body.

getInputStream()Returns an InputStream for reading binary data from the body of the request message.

getParameter("name")Returns the value of a request parameter as a String, or null ifthe parameter does not exist.

getParameters ("name")Returns an array of URL-decoded values of all occurrences of name in query string or null if the parameter does not exist.

continued




getParameterNames()Returns an array of strings with the names of all parameters.

getParameterValues()Returns an array of strings for a specific parameter name.

getProtocol()Returns the protocol and version for the request as a string of the form /..

getReader()Returns a BufferedReader to get the text from the body of the request message.

continued

ServletRequesthttp://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/ServletRequest.html

http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/ServletRequest.html




getRemoteHost()Host name of the client machine that sent this request.

getScheme()Returns the scheme used in the URL for this request (for example, https, http, ftp, etc.).

getServerName()Name of the host server that received this request.

getServerPort()Returns the port number used to receive this request

getRealPath()Returns actual path for a specified virtual path.

getRemoteAddr()IP address of the client machine sending this request.



javax.servlet

java.lang

java.io

The javax.servlet package

ServletServlet

GenericServletGenericServletObjectObject

ExceptionException

InputStreamInputStream

OutputStreamOutputStream

ServletInputStreamServletInputStream

ServletOutputStreamServletOutputStreamServletConfigServletConfig

SingleThreadModelSingleThreadModel

ServletContextServletContext

ServletRequestServletRequest

ServletResponseServletResponse

ExceptionException UnavailableExceptionUnavailableException

CLASSCLASS ABSTRACT CLASSABSTRACT CLASS INTERFACEINTERFACE

extends implements

SerializableSerializable

http://java.io



HTTP Support

Very common:Servlets that use HTTP(Hypertext Transport Protocol).

Supporting Package: javax.servlet.http



WebServer

HttpServlet subclass

service()

doGet()

doPost()

HTTP Servlet

implemented by subclass

RequestResponse

GET

RequestResponse

POST



WebServer

HttpServlet subclass

service()

doGet()

doPost()

doHead()

HTTP Servlet (HEAD)

GETRequestResponse

POSTRequestResponse

HEADRequestResponse

Body suppressed

HTTP servlet handling a HEAD request:



Client Interaction

Override methods to handle HTTP requests: doGet:

handling GET, conditional GET and HEAD requests;

doPost:handling POST requests;

doPut:handling PUT requests;

doDelete:handling Delete requests.



javax.http.servlet

javax.servletjava.lang

The javax.http.servlet package

ObjectObject

HttpSessionHttpSession

CLASSCLASS ABSTRACT CLASSABSTRACT CLASS INTERFACEINTERFACE

extends implements

CloneableCloneable

java.io

java.util

HttpSessionContextHttpSessionContext

HttpSessionBindingListenerHttpSessionBindingListener

SerializableSerializable

EventListenerEventListener

CookieCookie

HttpUtilsHttpUtils

ServletServlet

ServletRequestServletRequest

ServletResponseServletResponse HttpServletResponseHttpServletResponse

HttpServletRequestHttpServletRequest

GenericServletGenericServlet HttpServletHttpServlet

HttpSessionBindingEventHttpSessionBindingEventEventObjectEventObject

http://java.io



A Simple Servlet "Hello World"

public class HelloServletextends HttpServlet {

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws ServletException, IOException{response.setContentType("text/plain");PrintWriter out = response.getWriter();out.println("Hello World!");}}



A Simple Servlet "Hello World"

Construction of the "HelloWorld" Servlet:

The Servlet "HelloServlet" extends the HttpServlet class;

HelloServlet overloads the "doGet() method", which is invoked every time the web server receives a GET request;

The objects"HttpServletRequest" and "HttpServletResponse"are passed to the "doGet() method";



A Simple Servlet

public class SimpleServlet extends HttpServlet{ /*** Handle the HTTP GET method by building a simple web page.*/

public void doGet (HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException{PrintWriter out;String title = "Simple Servlet Output";

// set content type and other response header fields firstresponse.setContentType("text/html");

// then write the data of the responseout = response.getWriter();

out.println("");out.println(title);out.println("");out.println("" + title + "");out.println("

This is output from SimpleServlet.");out.println("");out.close();}

}



Servlet Request Headers

import java.io.*;import javax.servlet.*;import javax.servlet.http.*;import java.util.*;

public class ShowReqHd extends HttpServlet{

public void doGet (HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException

{response.setContentType ("text/html");PrintWriter out = response.getWriter();

out.println ("Helmut Dispert - Request Headers");out.println ("HTTP Request Headers");out.println ("Request Method: " + request.getMethod());out.println ("Request URI: " + request.getRequestURI());out.println ("Request Protocol: " + request.getProtocol() + "

");

out.println ("Header NameHeader Value");

Enumeration headerNames = request.getHeaderNames();while (headerNames.hasMoreElements()){

String headerName = (String) headerNames.nextElement();out.println ("" + headerName + "");out.println ("" + request.getHeader(headerName) + "");

}out.println ("");

}}

deflate: http://tools.ietf.org/html/rfc1951

http://tools.ietf.org/html/rfc1951



Servlet Request Headers

accept-encoding SDCH: Shared Dictionary Compression over HTTP(new HTTP 1.1 extension )



Examples: Form Handling with GET/POST

http://149.222.51.81:8180/home-tomcat/servlets/ShowParametersPostForm.html

http://149.222.51.81:8180/home-tomcat/servlets/ShowParametersGetForm.html

Get Request

Post Request

http://149.222.51.81:8180/home-tomcat/servlets/ShowParametersPostForm.htmlhttp://149.222.51.81:8180/home-tomcat/servlets/ShowParametersGetForm.html



URI, URL, URN

URI: Uniform Resource Identifier. The generic set of all

names/addresses that are short strings that refer to resources. URL: Uniform Resource Locator. An informal term (no longer used in

technical specifications) associated with popular URI schemes: http, ftp, mailto, etc.

URN: Uniform Resource Name.

- An URI that has an institutional commitment to persistence, availability, etc. This sort of URI may also be a URL (example: PURI).

- A particular scheme, urn:, specified by RFC2141 and related documents, intended to serve as persistent, location-independent, resource identifiers.

RFC 2396 - Uniform Resource Identifiers (URI): Generic Syntax



URI, URL, URN

UR* Terms

URIs

URLs

URNs

http:ftp:...

urn:



URI, URL, URN

Both URLs and URNs are URIs

Expansions:

PURL - Persistent Uniform Resource Locatorhttp://purl.oclc.org/

URC: Uniform Resource Characteristics URA: Uniform Resource Agent PURL

PURLs are Persistent Uniform Resource Locators (URLs). A URL is simply an address on the World Wide Web. A Persistent URL is an address on the World Wide Web that points to other Web resources. If a Web resource changes location (and hence URL), a PURL pointing to it can be updated. A user of a PURL always uses the same Web address, even though the resource in question may have moved.

http://purl.oclc.org/

http://purl.oclc.org/http://purl.oclc.org/



Unicode, UCS, and UTF-8

http://www.unicode.org/






UCS and ISO 10646 (ISO/IEC 10646-1)The international standard ISO 10646 defines the Universal Character Set (UCS). UCS is a superset of all other characterset standards.

UCS and Unicode are code tables that assign integer numbers to characters.

UCS-2 and UCS-4:store Unicode text as sequences of either 2 or 4 bytes.




The Unicode Standard

http://www.unicode.org/unicode/reports/tr27/

The Unicode Standard is a character coding system designed to support the worldwide interchange, processing, and display of the written texts of the diverse languages of the modern world. In addition, it supports classical and historical texts of many written languages.

The Unicode Standard, Version 3.1

The primary feature of Unicode 3.1 is the addition of 44,946 new encoded characters. Together with the 49,194 already existing characters in Unicode 3.0, that comes to a grand total of 94,140encoded characters in Unicode 3.1.The new characters cover several historic scripts, several sets of symbols, and a very large collection of additional CJK ideographs. Unicode 3.1 also features new Unicode character properties, and assignments of property values for the much expanded repertoire of characters.

http://www.unicode.org/unicode/reports/tr27/




ASCII or Latin-1 can be transformed into UCS-2 by inserting a 0x00 byte in front of every ASCII byte. In case of UCS-4 three 0x00 bytes have to be inserted before every ASCII byte.

8 8

0 0 0 0 00 00 0 0 0 0 00 00 0 0 0 0 00 00 0 x x x xx xx

8 8

UCS-4

ASCII

0 0 0 0 00 00 0 x x x xx xxUCS-2

ISO 10646 is designed as a 31-bit character set (with possible code positions ranging from \u00000000 to \u7FFFFFFF),.

Basic Multilingual Plane (BMP):First 216 (64k) character positions (ISO 10646-2, Unicode 3.1).UCS-4 can represent all UCS and Unicode characters, UCS-2 can represent only those from the BMP (\u0000 to \uFFFF).



ISO-8859-1 (Latin-1)

Unicode\uFFFF

\u0000

ISO-8859-1

#0

#255

(diagrams are not to scale)

\u0000

\u00FF



8859-15

8859-1

0xBE0xBD0xBC0xB80xB40xA80xA60xA4Position

Differences between Latin-1 and Latin-9

ISO-8859-15 (Latin-9)

The ISO Latin 9 (ISO 8859-15) character set differs from ISO Latin 1 (ISO 8859-1) character set in a few positions only. The Euro sign and some national letters used e.g. in French and Finnish have been introduced and some rarely used special characters omitted.



UTF-8

Properties of UTF-8 (UCS Transformation Format): UCS characters \u0000 to \u007F (ASCII) are encoded as bytes 0x00

to 0x7F (ASCII compatibility). Therefore files and strings whichcontain only 7-bit ASCII characters have the same encoding under both ASCII and UTF-8.

All UCS characters > \u007F are encoded as a sequence of several bytes, each of which has the most significant bit set. Therefore, no ASCII byte (0x00-0x7F) can appear as part of any other character.

The first byte of a multibyte sequence that represents a non-ASCII character is always in the range 0xC0 to 0xFD and it indicates how many bytes follow for this character. All further bytes in a multibyte sequence are in the range 0x80 to 0xBF. This allows easy resynchronization and makes the encoding stateless and robust against missing bytes.

UTF-8 encoded characters may theoretically be up to six bytes long, however 16-bit BMP characters are only up to three bytes long.

The bytes 0xFE and 0xFF are never used in the UTF-8 encoding.

RFC 2279: UTF-8, a transformation format of ISO 10646



UTF-8

UTF-8 definition (from RFC 2279):

In UTF-8, characters are encoded using sequences of 1 to 6 octets.

The only octet of a "sequence" of one has the higher-order bit set to 0, the remaining 7 bits being used to encode the character value.

In a sequence of n octets, n>1, the initial octet has the n higher-order bits set to 1, followed by a bit set to 0. The remaining bit(s) of that octet contain bits from the value of the character to be encoded. The following octet(s) all have the higher-order bit set to 1 and the following bit set to 0, leaving 6 bits in each to contain bits from the character to be encoded.



UTF-8

Encoding from UCS-4 to UTF-8:

UCS-4 range (hex.) UTF-8 octet sequence (binary)

0000 0000-0000 007F 0xxxxxxx

0000 0080-0000 07FF 110xxxxx 10xxxxxx

0000 0800-0000 FFFF 1110xxxx 10xxxxxx 10xxxxxx

0001 0000-001F FFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

0020 0000-03FF FFFF 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx

0400 0000-7FFF FFFF 1111110x 10xxxxxx ... 10xxxxxx

RFC 2279: UTF-8, a transformation format of ISO 10646



import java.io.*;import javax.servlet.*;import javax.servlet.http.*;

public class HelloSpain extends HttpServlet{

public void doGet (HttpServletRequest req,HttpServletResponse res) throws ServletException, IOException

{res.setContentType ("text/html");PrintWriter out = res.getWriter();res.setHeader ("Content-Language", "es");

out.println("En Espaol");out.println("");out.println(" En Espaol:");out.println(" Hola Mundo!");out.println("");}

}

HTML Character Entities

named character entity




public class HelloSpain2 extends HttpServlet{



out.println("En Espaol");out.println("");out.println(" En Espaol:");out.println(" Hola Mundo!");out.println("");}

}

HTML Character Entities

numbered character entity




public class HelloSpain3 extends HttpServlet{



out.println("En Espa\u00f1ol");out.println("");out.println(" En Espaol:");out.println(" Hola Mundo!");out.println("");}

}

Unicode Escapes

Unicode escape sequence\u00f1



Internationalization - Charsets

PrintWriter uses as the default charsetISO-8859-1 (Latin-1)

Specify alternate charset:

Example: Chinese charset:

res.setContentType ("text/html; charset=gb2312");PrintWriter out = res.getWriter (); // Chinese




ISO-8859-9trTurkish

ISO-8859-5, KOI8-RruRussian

ISO-8859-2plPolish

EUC-KRkoKorean

Shift_JIS, ISO-2022-JP,EUC-JP

jaJapanese

ISO-8859-7elGreek

ISO-8859-1deGerman

ISO-8859-1enEnglish

Big5, gb2312zh-CNzh (TW)

Chinese (Traditional/Taiwan)

CharsetCodeLanguage




import java.io.*;import java.text.*;import java.util.*;import javax.servlet.*;import javax.servlet.http.*;

public class HelloChinaReader extends HttpServlet {

public void doGet(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException {

res.setContentType("text/plain; charset=gb2312");PrintWriter out = res.getWriter();res.setHeader("Content-Language", "zh-CN");

Locale locale = new Locale("zh-CN", "");DateFormat full = DateFormat.getDateTimeInstance(DateFormat.LONG,

DateFormat.LONG,locale);




out.println("In Chinese:");

try {FileInputStream fis = new FileInputStream(

req.getRealPath("HelloWorld.gb2312"));InputStreamReader isr = new InputStreamReader(fis, "gb2312");BufferedReader reader = new BufferedReader(isr);String line = null;while ((line = reader.readLine()) != null) {

out.println(line);}

}catch (FileNotFoundException e) { // No Hello for you}

out.println(full.format(new Date()));}

}



HTTP - continued

HTTP Support ClassesPackage javax.servlet.http to write HTTP servlets.

The abstract class javax.servlet.http.HttpServlet provides an implementation of the javax.servlet.Servlet interface and includes default functionality.Easiest way to write an HTTP servlet:Extend HttpServlet and add custom processing.

The class HttpServlet provides an implementation of the service()method that dispatches the HTTP messages to one of the special methods (i.e. HTTP protocol methods):

doGet() doHead() doDelete() doOptions() doPost() doTrace()



Hosting Server

HttpServlet

HTTP - continued

The service() method interprets each HTTP method and determines if

it is an HTTP GET, HTTP POST, HTTP HEAD, or other protocol method:

Dispatching HTTP requests:

doGet ()doHead ()doDelete ()doOptions ()doPost ()doTrace ()

service ()

HTTPClient



Server-Side Include (SSI) with Servlets

...

...

Servlet1

Request

Response

.shtml fileWeb Server




Time Program

Current local time:

Current time in New York:




import java.io.*;import java.text.*;import javax.servlet.*;import javax.servlet.http.*;import java.util.*;

public class CurrentTime extends HttpServlet{


{PrintWriter out = res.getWriter();Date date = new Date ();DateFormat df = DateFormat.getInstance ();String zone = req.getParameter("zone");if (zone != null){

TimeZone tz = TimeZone.getTimeZone (zone);df.setTimeZone(tz);

}out.println (df.format (date));

}}



Servlet Chaining

Web Server

Servlet1Request

Response

Servlet2

Servlet3

Servlet Chaining:The output from each servlet is passed (piped) as input to the next servlet.



Servlet Filters

http://java.sun.com

Filter Component:A filter dynamically intercepts requests and responses to transform or use the information contained in the requests or responses.

Filters

provide the ability to encapsulate recurring tasks in reusable units (modular code).

can be used to transform the response from a servlet. A common task for the web application is to format data sent back to the client, e.g. when formats other than just HTML are required (for example, WML) .

http://java.sun.com



Servlet Filters

http://java.sun.com

Filter Applications: Authentication: blocking requests based on user

identity. Logging and auditing: tracking users. Image conversion: scaling, etc. Data compression: to reduce download time. Localization (i.e. targeting particular locales). Transformation of XML content (XSL/T ) Encryption. Tokenizing. Triggering resource access events. Mime-type chaining Caching.

http://java.sun.com



Session

SessionSession TrackingCookies



Session Tracking

Background:HTTP is a stateless protocol:

HTTP does not provide any way for a server to recognize that a sequence of requests comes from the same client.

Example (E-Commerce - Shopping cart):Client at an on-line store adds items. How can the server know what is already in the cart?Client proceeds to checkout. How can the server include a previously created shopping cart?

Session Tracking:Maintain state about series of requests from same client over time



Session Tracking

Possible ways for session tracking: Cookies

URL-rewriting

Hidden form fields



Session Tracking

Traditional Approaches: User Authorization

user has to register for an account and then login

getUsername()

Hidden form fields fields are added to an HTML form

URL rewriting http://server:port/servlet/Rewritten

http://server:port/servlet/Rewritten/123 http://server:port/servlet/Rewritten?sessionid=123

http://server:port/servlet/Rewrittenhttp://server:port/servlet/Rewritten/123http://server:port/servlet/Rewritten?sessionid=123



Cookies

Cookie:Small piece of textual information that is sent from a server toa browser. The server can read the information back, in order to get information about the client's previous visit.

Characteristics of Cookies: Key-value pairs Way for server to store information on client Server appends to HTTP response headers Client appends to HTTP request headers Cookies are single-valued



Cookies

Benefits of Cookies: User Identification Storing User ID (Username) and Password Customize a Web-Site Allow client specific (focused) advertising



Cookies

Using Cookies:

Idea Servlet sends a cookie name and value to client

Client returns same name and value when it connects to same site (or same domain, depending on cookie setting)

Typical applications of Cookies Identifying a user during an e-commerce session

(Servlets provide API) Avoiding username and password

Focusing advertising



Using Cookies

To send Cookie instantiate Cookie Object set attributes

send the cookie

Get information from Cookie retrieve all cookies from the users request find cookie with specified name

get values from cookies



Creating a Cookie

Constructor for javax.servlet.http.Cookiecreates a cookie with an initial name and value cookie value can later be changed with the setValue

method.

the value of the cookie can be any String (null value is not guaranteed to work on all browsers).

If the servlet returns a response to the user with a Writer, Cookie has to be created before accessing the Writer.



Cookie Constructor

public Cookie(java.lang.String name, java.lang.String value)

Constructs a cookie with a specified name and value.

The name must conform to RFC 2109. That means it can contain only ASCII alphanumeric characters and cannot contain commas, semicolons, or white space or begin with a $ character. The cookie's name cannot be changed after creation.

The value can be anything the server chooses to send. Its value is probably of interest only to the server. The cookie's value can be changed after creation with the setValue method.

By default, cookies are created according to the Netscape cookie specification. The version can be changed with the setVersion method.

Parameters:

name - a String specifying the name of the cookievalue - a String specifying the value of the cookie

Throws:

java.lang.IllegalArgumentException - if the cookie name contains illegal characters (for example, a comma, space, or semicolon) or it is one of the tokens reserved for use by the cookie protocol

See Also:

setValue(java.lang.String), setVersion(int)



Cookie Constructor

ftp://ftp.rfc-editor.org/in-notes/rfc2109.txt

HTTP State Management Mechanism

Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

1. ABSTRACTThis document specifies a way to create a stateful session with HTTP requests and responses. It describes two new headers, Cookie and Set-Cookie, which carry state information between participating origin servers and user agents. The method described here differs from Netscape's Cookie proposal, but it can interoperate with HTTP/1.0 user agents that use Netscape's method.

RFC2109

ftp://ftp.rfc-editor.org/in-notes/rfc2109.txt



Creating a cookie : Example (Shopping Cart)

public void doGet(HttpServletRequest req,HttpServletResponse res)

throws ServletException, IOException {

//Check for pending adds to the shopping cart

String bookId = req.getParameter("Buy");

// customer wants to add a book to cart:// add a cookie

if (bookId != null) {

Cookie getBook = new Cookie("Buy", bookId);

}

...



Sending a cookie

public void doGet(HttpServletRequest req,HttpServletResponse res)


...


Cookie getBook = new Cookie("Buy", bookId);

getBook.setComment("Customer - Books");

res.addCookie(getBook);

}

...

Cookiehttp://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/http/Cookie.html

http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/http/Cookie.html



Reading/Deleting a cookie: Example

String bookId - req.getParameter("Remove");

...


// Find correct cookie (book)

Cookie[] cookies = req.getCookies();

for (int i = 0; i < cookies.length; i++) {

Cookie c = cookies[i];

if (c.getName().equals("Buy") &&

c.getValue().equals(bookId)) {

// Delete cookie setting maximum age to zero

c.setMaxAge(0);

}getCookies()http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/http/HttpServletRequest.html#getCookies()

http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/http/HttpServletRequest.html#getCookies()



Cookie Methods

getDomain () / setDomain ()Specifies domain to which cookie applies. Current host must be part of domain specified.

getMaxAge () / setMaxAge ()Gets/sets the cookie expiration time (in seconds). If not

set, cookie applies to current browsing session only.

getName () / setName ()Gets/sets the cookie name. For new cookies, name is supplied to constructor.



Cookie Methods

getPath () / setPath ()Gets/sets the path to which cookie applies. If unspecified, cookie applies to URLs that are within

or below directory containing current page.

getSecure () / setSecure ()Gets/sets flag indicating whether cookie should apply only to SSL connections.

getValue () / setValue ()Gets/ sets value associated with cookie.



Problems with Cookies

Problem: privacy - not security Servers can remember previous action Server can link personal information to previous action Servers can share cookie information through use of a

cooperating third party like "doubleclick.net" Badly designed site can store sensitive information

(e.g. credit card numbers) directly in cookie Some browsers allow hostile sites steal cookies

(JavaScript language bugs)

Moral for servlet authors Dont depend on cookie being enabled Dont put sensitive information in cookies

http://doubleclick.net



Cookie Exampleimport java.io.*;import javax.servlet.*;import javax.servlet.http.*;

public class CookieExample extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)throws IOException, ServletException{

response.setContentType("text/html");PrintWriter out = response.getWriter();

// print out cookies

Cookie[] cookies = request.getCookies();for (int i = 0; i < cookies.length; i++) {

Cookie c = cookies[i];String name = c.getName();String value = c.getValue();out.println(name + " = " + value);

}

// set a cookie

String name = request.getParameter("cookieName");if (name != null && name.length() > 0) {

String value = request.getParameter("cookieValue");Cookie c = new Cookie(name, value);response.addCookie(c);

}}

}



Cookie Example - Set Cookiesimport java.io.*;import javax.servlet.*;import javax.servlet.http.*;

public class SetCook extends HttpServlet {public void doGet(HttpServletRequest request,

HttpServletResponse response)throws ServletException, IOException {

for(int i=0; i



Cookie Example - Show Cookiesimport java.io.*;import javax.servlet.*;import javax.servlet.http.*;

public class ShowCook extends HttpServlet {public void doGet(HttpServletRequest request,


response.setContentType("text/html");PrintWriter out = response.getWriter();

out.println("\n" + "" + "Show Cookies" + "\n" +"\n" + "\n" +" Cookie Name\n" + " Cookie Value");

Cookie[] cookies = request.getCookies();if (cookies != null) {Cookie cookie;for(int i=0; i



Cookie Example - Netscape

# Netscape HTTP Cookie File

# http://www.netscape.com/newsref/std/cookie_spec.html# This is a generated file! Do not edit.

149.222.51.80:8080 FALSE /dispert/servlet FALSE 1008271810 Persistent-Cookie-0 Cookie-Value-P0149.222.51.80:8080 FALSE /dispert/servlet FALSE 1008271810 Persistent-Cookie-1 Cookie-Value-P1149.222.51.80:8080 FALSE /dispert/servlet FALSE 1008271810 Persistent-Cookie-2 Cookie-Value-P2.amazon.com TRUE / FALSE 1008489380 session-id-time 1008489600.sun.com TRUE / FALSE 1767225385 SUN_ID 149.222.10.12:113901007762577

persistent cookies

all cookies

http://www.netscape.com/newsref/std/cookie_spec.htmlhttp://.amazon.comhttp://.sun.com



Cookie Example - Internet Explorer

Persistent-Cookie-0Cookie-Value-P0

149.222.51.80/dispert/servlet/0

632833920

29459480

3190006880

29459470*

Persistent-Cookie-1

Cookie-Value-P1

149.222.51.80/dispert/servlet/

0632833920

29459480

3190006880

29459470

*Persistent-Cookie-2

Cookie-Value-P2

149.222.51.80/dispert/servlet/0

63283392029459480

3190006880

29459470

*

filename:helmut dispert@servlet[2].txt

mailto:dispert@servlet[2].txt



Session Tracking API

The Servlet API provides several methods and classes specifically designed to handle session tracking.

Class calls HttpSession

Steps Obtain Session for a user Store or get data from session object Invalidate the session (manual or automatic) Shared by all servlets in application



Session Tracking: Obtainig a session

Example of a Servlet getting a user session :

public class CatalogServlet extends HttpServlet {

public void doGet(HttpServletRequest req,

HttpServletResponse res)


//Get the users session

HttpSession session = req.getSession(true);

...

out = res.getWriter();

}

...

getSession()http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/http/HttpServletRequest.html#getSession()

http://www.rz.e-technik.fh-kiel.de/~dispert/java/servlet-2_3-fcs-docs/javax/servlet/http/HttpServletRequest.html#getSession()



Storing and Getting data from a session

The HttpSession interface provides methods that store and return:

standard session properties, such as a session identifier

application data, which is stored as a name/value pair, where the name is a String and the value is an Object

Important:Because multiple servlets have access to a users session, a naming convention should be adopted for organizing the names associated with application data. This way it can be avoided that servlets accidentally overwrite each others value in the session.



Storing and Getting data from a session

public class CatalogServlet extends HttpServlet {

public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException, IOException {

//Get the users session and shopping cart

HttpSession session = req.getSession(true);

ShoppingCart cart = (ShoppingCart) session.getValue(session.getId());

// If the user has no cart, create a new one

if (cart == null) {

cart = new ShoppingCart();

session.putValue(session.getId(), cart);

}

...



HttpSession

A session can be designated as new

A new session causes the isNew method of the HttpSession class to return true, indicating that, for example, the client does not yet know about the session.

A new session has no associated data.



HttpSession - Life Cycle

Session do not last for ever. A session either expires automatically or manually(e.g. invalidation of a session when there has been no page request in some period of time).

To invalidate a session means to remove the HttpSession object and its value from the system.

To manually invalidate a session the sessions invalidate method is used:session.invalidate()



HttpSession Methods

getValue (), getAttribute ()Extracts a previously stored value from a session object. Returns null if no value is associated with the given name

putValue (), setAttribute ()Associate a value with a name

removeValue (), removeAttribute ()Removes values associate with name

getValueNames (), getAttributeNames ()Returns names of all attributes in the session

getId ()Returns the unique identifier

continued

Obs.: getValue() and putValue() are deprecated



HttpSession Methods

isNew ()Determines if session is new to client (not page)

getCreationTime ()Returns time at which session was first created

getLastAccessedTime ()Returns time at which the session was last sent fom the client

invalidate ()Invalidate the session and unbind all objects associated with it



HttpSession Example

import java.io.*;import javax.servlet.*;import javax.servlet.http.*;import java.net.*;import java.util.*;

// Session Tracking Example

public class ShowSession extends HttpServlet {public void doGet(HttpServletRequest request,


continued



HttpSession Example

response.setContentType("text/html");PrintWriter out = response.getWriter();HttpSession session = request.getSession(true);String heading;

Integer accessCount =(Integer)session.getAttribute("accessCount");

if (accessCount == null) {accessCount = new Integer(0);heading = "Welcome, Newcomer";

} else {heading = "Welcome Back";accessCount =

new Integer(accessCount.intValue() + 1);}

session.setAttribute("accessCount", accessCount);

continued



HttpSession Example

out.println("\n" + "" + heading + "\n" +"Information on Your Session:\n" +"\n" +"\n" + " Info TypeValue\n" +"\n" + " ID\n" + " " + session.getId() + "\n" +"\n" + " Creation Time\n" +" " + new Date(session.getCreationTime()) + "\n" +"\n" + " Time of Last Access\n" +" " + new Date(session.getLastAccessedTime()) + "\n" +"\n" +" Number of Previous Accesses\n" +" " + accessCount + "\n" +"\n" +"");

continued



HttpSession Example

}

/** Handle GET and POST requests identically. */

public void doPost(HttpServletRequest request,HttpServletResponse response)

throws ServletException, IOException {doGet(request, response);

}}

http://149.222.51.81:8180/home-tomcat/servlet/ShowSession




HttpSession Example





Servlet Exercise

Home directories

URL of the Jakarta-Tomcat Server: 149.222.51.81:8180

Directory for Servlets:$TOMCAT_WEBAPPS/student-servlet/WEB-INF/classes/eop

URLs (Servlets):http://149.222.51.81:8180/student-servlet/servlet/servlet_name

Access via SSH:Server-IP: 149.222.51.81, Port: 22User: student-servlet, Passwd: FH_KielTh

is inf

ormati

on is

not fi

nal y

et for

stud

ents

at

China

Jilia

ng Un

iversi

ty

http://149.222.51.81:8180/student-servlet/servlet/servlet_name



Servlet Exercise - Update

Compiling Servlets:Directory Structure (example)

eop

dispert

eop.dispert

package eop.dispert;

import java.io.*;import javax.servlet.*;import javax.servlet.http.*;import java.net.*;import java.util.*;

// Session Tracking Example

public class ShowSession extends HttpServlet {

javac -target 1.5 ShowSession.java

Servlet API:servlet-api-5.0.18.jar or servlet-api-2.4.jar

Compile for Java (Tomcat) 5.5



Servlet Exercise - Update

Home directories


Directory for Servlets:$TOMCAT_WEBAPPS/student-servlet/WEB-INF/classes/eop

URLs (Servlets):http://149.222.51.81:8180/student-servlet/servlet/servlet_namehttp://149.222.51.81:8180/

student-servlet/servlet/eop.dispert.ShowSession

Access via SSH:Server-IP: 149.222.51.81, Port: 22User: student-servlet, Passwd: FH_Kiel

eop.dispert.ShowSession

Info: http://149.222.51.81:8180/student-servlet/

This

inform

ation

is no

t fina

l yet

for st

uden

ts at

China

Jilia

ng Un

iversi

ty

http://149.222.51.81:8180/student-servlet/servlet/servlet_namehttp://149.222.51.81:8180/http://149.222.51.81:8180/student-servlet/



Servlet Exercise

Home directories


Directory for JSP:$TOMCAT_WEBAPPS/student-jsp/jsp/eop

URLs (JSPs):http://149.222.51.81:8180/student-jsp/jsp/eop/name.jsp

Access via SSH:Server-IP: 149.222.51.81, Port: 22User: student-jsp, Passwd: FH_Kiel

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http://149.222.51.81:8180/student-jsp/jsp/eop/name.jsp



Servlet Exercise

Compiling the servlet using the Jakarta Servlet-API:

a) Download the Servlet-API file "servlet.jar".

b) Install the file in the following directory:"C:\Programme\jdk_dir\jre\lib\ext\"

(with jdk_dir = JDK-directory, e.g. "jdk1.3.0_02").

c) Set the classpath (e.g. using a batch file):set CLASSPATH=

C:\Programme\jdk_dir\jre\lib\ext\servlet.jar

d) Compile the servlet as usual:javac filename.java

http://ikarus.e-technik.fh-kiel.de/index.php?id=277

This

inform

ation

is no

t fina

l yet

for st

uden

ts at

China

Jilia

ng Un

iversi

ty

http://ikarus.e-technik.fh-kiel.de/index.php?id=277



Servlet Exercise

User handling during an e-commerce session

Write a Java Servlet that fulfils the following functions:

New customer:

Welcome this visitor with the message "Welcome to our shop" (or similar).

Offer a form (HTML) to register this new customer asking for the necessary information. Minimum input should be:

first name, last name and address;

preferred product line (using the shop); allow at least four different categories.

The client sends an HTTP POST request with the complete set of data from this HTML form.



Servlet Exercise

Echo the accepted data back to the client in the form of an HTMLtable. The user (client) should receive a non-editable version of the updated information.

Known (old) customer:

Welcome this visitor with the message"Welcome 'first name' 'last name' " followed by basic information about former visits to the shop, like:

last visit,

number of visits (since),

session ID,

Focused advertising:

Send to the known visitor customer-oriented advertisements (banner, e.g. appropriate images that are opened in a separate small window).



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