Package -5 Networking, Applets, Http, Servlet, JSP, Struts

7/30/2019 Package -5 Networking, Applets, Http, Servlet, JSP, Struts

1/86

6/2/20

Networking

Socket Programming

connecting processes


2/86

6/2/20

Introduction to Sockets

Introduction to Sockets Why Sockets?

Used for Interprocess communication.

The Client-Server model

Most interprocess communication uses client-server model

Client & Server are two processes that wants to communicate with each

other

The Client process connects to the Server process, to make a request for

information/services own by the Server.

Once the connection is established between Client process and Server

process, they can start sending / receiving information. What are Sockets?

End-point of interprocess communication.

An interface through which processes can

send / receive information

Socket


3/86


4/86

6/2/20

A generic TCP application

algorithm for TCP client

Find the IP address and port number of server Create a TCP socket

Connect the socket to server (Server must be up and listening for new requests)

Send/ receive data with server using the socket

Close the connection

algorithm for TCP server

Find the IP address and port number of server

Create a TCP server socket

Bind the server socketto server IP and Port number (this is the port to which clients

will connect)

Accept a new connection from client

returns a client socketthat represents the client which is connected

Send/ receive data with client using the client socket

Close the connection with client

A generic UDP application

algorithm for UDP client Find the IP address and port number of server Create a UDP socket Send/ receive data with server using the socket Close the connection

algorithm for UDP server

Find the IP address and port number of server Create a UDP server socket Bind the server socketto server IP and Port number

(this is the port to which clients will send)

Send/ receive data with client using the client socket Close the connection with client


5/86

6/2/20

Programming Client-Server in Java

Programming TCP Client-Server in Java

All the classes related to sockets are in the java.net package, so makesure to import that package when you program sockets.

All the input/output stream classes are in the java.io package, includethis also

How to open a socket? If you are programming a client, then you would create an object of

Socket class Machine name is the machine you are trying to open a connection to, PortNumber is the port (a number) on which the server you are trying

toconnect to is running. select one that is greater than 1,023! Why??

Socket MyClient;

try {

MyClient = new Socket("Machine name",

PortNumber);

}

catch (IOException e) {

System.out.println(e);

}


6/86

6/2/20


If you are programming a server, then this is how you open a socket:

When implementing a server you also need to create a socket object from

the ServerSocket in order to listen for and accept connections from clients.

ServerSocket MyService;

try {

MyServerice = new ServerSocket(PortNumber);

}



}

Socket clientSocket = null;

try {clientSocket = MyService.accept();

}



}

Programming TCP Client-Server in Java How to create an input stream?

On the client side, you can use the DataInputStream class to create aninput stream to receive response from the server:

The class DataInputStream allows you to read lines of text and Java

primitive data types in a portable way. It has methods such as read,readChar, readInt, readDouble, and readLine,. On the server side, you can use DataInputStream to receive input from

the client:

DataInputStream input;

try {

input = new DataInputStream(MyClient.getInputStream());

}



}

DataInputStream input;

try {

input = new

DataInputStream(clientSocket.getInputStream());

}



}


7/86

6/2/20


How to create an output stream? On the client side, you can create an output stream to send information

to the server socket using the class PrintStream or DataOutputStream

of java.io:

The class PrintStream has methods for displaying textual representationof Java primitive data types. Its write and println methods are important.Also, you may want to use the DataOutputStream:

Many of its methods write a single Java primitive type to the output stream.The method writeBytes is a useful one.

PrintStream output;

try {

output = new PrintStream(MyClient.getOutputStream());

}



}

DataOutputStream output;

try {

output = new

DataOutputStream(MyClient.getOutputStream());

}

catch (IOException e) {System.out.println(e);

}

On the server side

you can use the class PrintStream to send information to the

client.

Note: You can use the class DataOutputStream as mentioned

previously.

PrintStream output;

try {

output = new PrintStream(clientSocket.getOutputStream());

}


System.out.println(e);}



8/86

6/2/20


How to close sockets? You should always close the output and input stream before you close

the socket.

On the client side:

On the server side:

try {

output.close();

input.close();

MyClient.close();

}



}

try {

output.close();

input.close();clientSocket.close();

MyService.close();

}



}

HTTP


9/86

6/2/20

Hypertext Transport Protocol\ Language of the Web

protocol used for communication between

web browsers and web servers

TCP port 80

RFC 1945

URI,URN,URL

Uniform Resource Identifier

Information about a resource

Uniform Resource Name

The name of the resource with in a namespace

Uniform Resource Locator

How to find the resource, a URI that says how

to find the resource


10/86

6/2/20

HTTP - URLs

URL

Uniform Resource Locator

protocol (http, ftp, news)

host name (name.domain name)

port (usually 80 but many on 8080)

directory path to the resource

resource name

http://xxx.myplace.com/www/index.html

http://xxx.myplace.com:80/cgi-bin/t.exe

HTTP - methods Methods

GET

retrieve a URL from the server

simple page request

run a CGI program

run a CGI with arguments attached to the URL

POST preferred method for forms processing

run a CGI program

parameterized data in sysin

more secure and private


11/86

6/2/20

HTTP - methods

Methods (cont.)

PUT

Used to transfer a file from the client to the server

HEAD

requests URLs status header only

used for conditional URL handling for performance

enhancement schemes

retrieve URL only if not in local cache or date is morerecent than cached copy

HTTP Request Packets

Sent from client to server

Consists of HTTP header

header is hidden in browser environment

contains:

content type / mime type content length

user agent - browser issuing request

content types user agent can handle

and a URL


12/86

6/2/20

HTTP Request Headers

Precede HTTP Method requests headers are terminated by a blank line

Header Fields:

From

Accept

Accept-Encoding

Accept Language

HTTP Request Headers (cont.)

Referer

Authorization

Charge-To

If-Modified-Since Pragma


13/86

6/2/20

From:

In internet mail format, the requesting user

Does not have to correspond to requesting

host name (might be a proxy)

should be a valid e-mail address

Accept-Encoding

Like Accept but list is a list of acceptable

encoding schemes

Ex

Accept-Encoding: x-compress;x-zip


14/86

6/2/20

User-Agent

Software product used by original client

= User-Agent:

= [/]

=

Ex.

User-Agent: IBM WebExplorer DLL /v960311

Referer

For Servers benefit, client lists URL od

document (or document type) from which

the URL in request was obtained.

Allows server to generate back-links,logging, tracing of bad links

Ex.

Referer: http:/www.w3.com/xxx.html


15/86

6/2/20

Authorization:

For Password and authentication schemes

Ex.

Authorization: user fred:mypassword

Authorization: kerberos kerberosparameters

ChargeTo:

Accounting information

Accounting system dependent


16/86

6/2/20

Pragma:

Same format as accept

for servers

should be passed through proxies, but used

by proxy

only pragma currently defined is no-cache;

proxy should get document from owningserver rather than cache

Modified-Since:

Used with GET to make a conditional GET

if requested document has not been

modified since specified date a Modified

304 header is sent back to client instead ofdocument

client can then display cached version


17/86

6/2/20

Response Packets

Sent by server to client browser in response to a

Request Packet

Status Header

HTTP/1.0 sp code

Codes:

1xx - reserved for future use

2xx - successful, understood and accepted 3xx - further action needed to complete

4xx - bad syntax in client request

5xx - server cant fulfill good request


18/86

6/2/20

HTTP Response Headers

Sent by server to client browser

Status Header

Entities Content-Encoding:

Content-Length:

Content-Type:

Expires:

Last-Modified: extension-header

Body content (usually html)

Status Codes

200 OK

201 created

202 accepted

204 no content

301 moved perm.

302 moved temp

304 not modified

400 bad request

401 unauthorized

403 forbidden

404 not found

500 int. server

error

501 not impl.

502 bad gateway

503 svc not avail


19/86

6/2/20

Statelessness

Because of the Connect, Request,

Response, Disconnect nature of HTTP it is

said to be a stateless protocol

i.e. from one web page to the next there is

nothing in the protocol that allows a web

program to maintain program state (like a

desktop program).

state can be maintained by witchery ortrickery if it is needed

Maintaining program state

Hidden variables (

Sessions

Special header tags interpreted by the server

Used by ASP, PHP, JSP

Implemented at the language api level


20/86

6/2/20

Servlets

50% - Mtl Already there

Evolution of Enterprise Applications - Single Tier

Easy to manage - client side management is NOT required

Data consistency is easy and simple to achieve, as all components a

one place

As application size grows, difficult to maintain and reuse

DumbTerminal 1

DumbTerminal 2

DumbTerminal 3

Contains

Business log

Presentatio

logic and da

access

Clients used only for data gathering

and output display

Mainframe


21/86

6/2/20

Evolution of Enterprise Applications - Two Tier (Client/Server)

1. Order fulfillment Application accessing Customer Information2. Customer care operations accessing same Customer DB

Database product independence

Difficult to maintain and update

Database Server

Data Access Layer

Business Logic and

Presentation Logic Layer

Evolution of Enterprise Applications - Three Tier

ExampleDART Application

Business logic can change more easily

Complexity introduced in the middle tier

Database

Server

Data Access LayerPresentation Logic Layer Business Logic


22/86

6/2/20

Evolution of Enterprise Applications - n Tier

Example - Wep Apps on Sparsh, like Leave System , Harmony

More loosely coupled

More reusable

Zero client management

Complexity in the middle tier

Database

Server

Data Access LayerPresentation Logic Business LogicThin Clients

Working of a Web Application

Internet uses Client/Server technology for its working

The world wide web uses the Browser as the client softwaand Web Server as the server software

The user types the required URL in the browser

The IP Address of the Server is found from the URL

The Web Server will be listening in that Server (machine) a

Port No 80

The browser connects to Port No 80 of the specified Serve

Based on the request, the Web Server will deliver theappropriate page to the browser


23/86

6/2/20

Web Application model

Client Tier Middle TierEnterprise Information

System (EIS) Tier

application

browser

Web Container

ServletServlet

JSP

Database

SQL

Filesystem

Introduction

Servlets are modules that extend request/response-oriented servers, such as Java-enabled web servers.

Servlets are to servers what applets are to browsers:an external program invoked at runtime.

Unlike applets, however, servlets have no graphicaluser interface.

Servlets can be embedded in many different serversbecause the servlet API, which you use to writeservlets, assumes nothing about the server'senvironment or protocol.

Servlets are portable.


24/86

6/2/20

Servlet Basics

It runs inside a Java Virtual Machine on a server host. Unlike applets, servlets do not require special support

in the web browser.

The Servlet class is not part of the Java Development

Kit (JDK). You must download the JDSK (Java Servlet

Development Kit).

A servlet is an object. It is loaded and runs in an

object called a servlet engine, or a servlet container.

Providing the functionalities of CGI scripts with a better API

and enhanced capabilities.

Allowing collaboration between people. A servlet can handle

multiple requests concurrently, and can synchronize requests.

This allows servlets to support systems such as on-line

conferencing.

Forwarding requests. Servlets can forward requests to otherservers and servlets. Thus servlets can be used to balance

load among several servers that mirror the same content, and

to partition a single logical service over several servers,

according to task type or organizational boundaries.

Uses for Servlets


25/86

6/2/20

Generic Servlets and HTTP Servlets

Every servlet must implement the javax.servlet.Servletinterface

Most servlets implement the interface by extending

one of these classes

javax.servlet.GenericServlet

javax.servlet.http.HttpServlet

A generic servlet should override the service( )

method to process requests and generate appropriate

responses.

An HTTP servlet overrides the doPost( ) and/or doGet(

) method.

Servlet Architecture Overview

Servlet Interface

methods to manage servlet

GenericServlet

implements Servlet HttpServlet

extends GenericServlet

exposes HTTP-specific

functionality

Servlet

extends

doGet()doPost()

service()

...

Override one or more of:

doGet()

doPost()

service()

...

Clas

s

Interface

Class

Class

Clas

s

extendsHttpServlet

implements

GenericServlet

UserServlet


26/86

6/2/20

Generic and HTTP Servlets

GenericServlet

service ( )

ServerClient

request

response

HTTPServlet

service ( )

HTTP ServerBrowser

request

response

doGet ( )

doPost( )

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 response out = response.getWriter();

out.println("");

out.println(title);

out.println("");

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

out.println("

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

out.close();

}

}


27/86

6/2/20

Servlet Lifecycle: init()

public void init(ServerConfig cfg)

Is called only once

when servlet loads

upon clients request

Do not worry about synchronization

Perform costly setup here, rather than for each

request open database connection

load in persistent data

spawn background threads

init()

init() should be completed before starting to

handle requests

If init() fails, UnavailableException is thrown

Invocation process allows to look-up for the

initialization parameters from a configuration file getInitParameter(paramName) method is used to read

the parameters

init() parameters are set by the administrator

servlet parameters are set by the invocation


28/86

6/2/20

Servlet Lifecycle: service()

After the service loads and initializes the servlet,

the servlet is able to handle client requests

public void service(ServletRequest req,

ServletResponse res)

takes Request and Response objects

called many times, once per request

Each request calls the service() method service() receives the client's request, invokes

appropriate handling method (doPost(), doGet() etc)

and sends the response to the client

service() and concurrency

Servlets can run multiple instances of service()

method concurrently service() must be written in a thread-safe manner

it is developers responsibility to handle synchronized

access to shared resources

It is possible to declare a servlet as single-threaded implement SingleThreadModel (empty) interface

guarantees that no two threads will execute the service()

method concurrently

performance will suffer as multiple simultaneous can not

be processed


29/86

6/2/20

Servlet Lifecycle: destroy()

Servlets run until they are removed

When a servlet is removed, it runs the destroy()method

The destroy() method is run only once the servlet will not run again unless it is reinitialized

public void destroy() takes no parameters

afterwards, servlet may be garbage collected

Servlet Lifecycle: destroy() details

Releasing the resources is the developers

responsibility

close database connections

stop threads

Other threads might be running service requests,so be sure to synchronize, and/or wait for them to

quit

Destroy can not throw an exception use server-side logging with meaningful message to

identify the problem


30/86

6/2/20

3

Servlet Lifecycle


31/86


32/86

6/2/20

3

HttpServletRequest Interface

public String ServletRequest.getQueryString( ); returns the query string ofthe requst.

public String getParameter(String name): given the name of a parameter inthe query string of the request, this method returns the value.

String id = getParameter(id)

public String[ ] GetParameterValues(String name): returns multiple valuesfor the named parameter use for parameters which may have multiplevalues, such as from checkboxes.

String[ ] colors = req.getParmeterValues(color);

if (colors != null)

for (int I = 0; I < colors.length; I++ )

out.println(colors[I]); public Enumeration getParameterNames( ): returns an enumeration objectwith a list of all of the parameter names in the query string of the request.

HttpServletResponse Objects

An HttpServletResponse object provides two ways ofreturning data to the user:

The getWritermethod returns a Writer

The getOutputStream method returns aServletOutputStream

Use the getWritermethod to return text data to the

user, and the getOutputStreammethod for binarydata.

Closing the Writer or ServletOutputStream after yousend the response allows the server to know whenthe response is complete.


33/86

6/2/20

3

HttpServletResponse Interface

public interface HttpServletResponse extendsServletResponse: The servlet engine provides an object that

implements this interface and passes it into th servlet through

the servicemethod Java Server Programming

public void setContentType(String type) : this method must be

called to generate the first line of the HTTP response:

setContentType(text/html);

public PrintWriter getWriter( ) throws IOException: returns an

object which can be used for writing the responses, one line

at a time:PrintWriter out = res.getWriter;

out.println(Hello world);

Servlets are Concurrent servers

HTTP servlets are typically capable of serving

multiple clients concurrently.

If the methods in your servlet do work for

clients by accessing a shared resource, then

you must either:

Synchronize access to that resource, or

Create a servlet that handles only one client

request at a time.


34/86

6/2/20

3

Handling GET requests

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

HttpServletResponse response) throws ServletException,IOException{...// set content-type header before accessing the Writerresponse.setContentType("text/html");PrintWriter out = response.getWriter();// then write the responseout.println("" +

"Book Description" + ... );//Get the identifier of the book to displayString bookId = request.getParameter("bookId");if (bookId != null) {// fetch the information about the book and print it ... }out.println("");

out.close(); } ...}

Handling POST Requests

public class ReceiptServlet extends HttpServlet {public void doPost(HttpServletRequest request, HttpServletResponseresponse) throws ServletException, IOException {

...// set content type header before accessing the Writerresponse.setContentType("text/html");PrintWriter out = response.getWriter( );// then write the responseout.println("" + " Receipt " + ...);out.println("Thank you for purchasing your books from us " +request.getParameter("cardname") + ...);out.close();}

...}


35/86

6/2/20

3

The Life Cycle of an HTTP Servlet

The web server loads a servlet when it is calledfor in a web page.

The web server invokes the init( ) method of

the servlet.

The servlet handles client responses.

The server destroys the servlet (at the request

of the system administrator). A servlet is

normally not destroyed once it is loaded.

Session State Information

The mechanisms for state information

maintenance with CGI can also be used for

servlets: hidden-tag, URL suffix, file/database,

cookies.

In addition, a session tracking mechanism is

provided, using an HttpSession object.


36/86

6/2/20

3

Cookies in Java

A cookie has a name, a single value, and optional attributes such as acomment, path and domain qualifiers, a maximum age, and a version

number. Some Web browsers have bugs in how they handle the optional

attributes, so use them sparingly to improve the interoperability of your

servlets.

The servlet sends cookies to the browser by using the

HttpServletResponse.addCookie(javax.servelet.http.Cookie)method,

which adds fields to HTTP response headers to send cookies to the

browser, one at a time. The browser is expected to support 20 cookies for

each Web server, 300 cookies total, and may limit cookie size to 4 KB each.

The browser returns cookies to the servlet by adding fields to HTTP

request headers. Cookies can be retrieved from a request by using theHttpServletRequest.getCookies( )method. Several cookies might have thesame name but different path attributes.

Processing Cookies with Java

A cookie is an object of the javax.servlet.http.cookie class.

Methods to use with a cookie object:

public Cookie(String name, String value): creates a cookiewith the name-value pair in the arguments.

import javax.servlet.http.*

Cookie oreo = new Cookie(id,12345);

public string getName( ) : returns the name of the cookie public string getValue( ) : returns the value of the cookie

public void setValue(String _val) : sets the value of the cookie

public void setMaxAge(int expiry): sets the maximum ageof the cookie in seconds.
http://java.sun.com/products/servlet/2.2/javadoc/javax/servlet/http/HttpServletResponse.htmlhttp://java.sun.com/products/servlet/2.2/javadoc/javax/servlet/http/HttpServletResponse.html


37/86

6/2/20

3

Processing Cookies with Java 2

public void setPath(java.lang.String uri): Specifies a path for the cookieto which the client should return the cookie. The cookie is visible to all thepages in the directory you specify, and all the pages in that directory's

subdirectories. A cookie's path must include the servlet that set the

cookie, for example,/catalog, which makes the cookie visible to all

directories on the server under/catalog.

public java.lang.String getPath(): Returns the path on the server towhich the browser returns this cookie. The cookie is visible to all subpaths

on the server.

public String getDomain( ) : returns the domain of the cookie.

if orea.getDomain.equals(.foo.com)

// do something related to golf

public void setDomain(String _domain):sets the cookies domain.

doGet Method using cookies

public void doGet(HttpServletResponse req, HttpServletResponse res)

throws ServletException, IOExceiption{

res.setContentType(text/html);

PrintWriter out = res.getWriter( );

out.println (Contents of your shopping cart:);

Cookie cookies[ ];

cookies = req.getCookies( );

if (cookies != null) {

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

if (cookies*i+.getName( ).startWith(Item))

out.println( cookies*i+.getName( ) : cookies*i+.getValue( ));

out.close( );

}


38/86

6/2/20

3

Servlet & Cookies Example

See Servlet\cookies folder in code sample: Cart.html: web page to allow selection of items

Cart.java: Servlet invoked by Cart.html; it instantiates

a cookie object for each items selected.

Cart2.html: web page to allow viewing of items

currently in cart

Cart2.java: Servlet to scan cookies received with the

HTTP request and display the contents of each cookie.

HTTP Session Objects

Thejavax.servlet.http package provides a

public interface HttpSession: Provides a way to

identify a user across more than one page request or

visit to a Web site and to store information about that

user.

The servlet container uses this interface to create asession between an HTTP client and an HTTP server.

The session persists for a specified time period, across

more than one connection or page request from the

user. A session usually corresponds to one user, who

may visit a site many times.


39/86

6/2/20

3

HTTP Session Object 2

This interface allows servlets to View and manipulate information about a session, such as

the session identifier, creation time, and last accessed time

Bind objects to sessions, allowing user information to

persist across multiple user connections

Session object allows session state information to be

maintained without depending on the use of cookies

(which can be disabled by a browser user.)

Session information is scoped only to the current webapplication (ServletContext), so information stored

in one context will not be directly visible in another.

The Session object

A Session object

servelet engine

web server

Server host

Client host

request/response

servlet


40/86

6/2/20

4

Obtaining an HTTPSession Object

A session object is obtained using the getSession( ) method of the

HttpServletRequest object (from doPost or doGet) public HTTPSession getSession(boolean create): Returns the

current HttpSession associated with this request or, if if there is nocurrent session and create is true, returns a new session. Ifcreate isfalse and the request has no valid HttpSession, this method returnsnull.

To make sure the session is properly maintained, you must call this

method before the response is committed.public class ShoppingCart extends HttpServlet {

public void doPost(HttpServletRequest req, HttpServletRespnse res)

throws ServletException, IOException

// get session object

HttpSession session = req.getSession(true)

if (session != null) {

}

The HTTPSession Object methods

public java.lang.String getId( ): returns a string containingthe unique identifier assigned to this session. The identifier isassigned by the servlet container and is implementationdependent.

public java.lang.ObjectgetAttribute(java.lang.String name): returns the objectbound with the specified name in this session, or null if no

object is bound under the name. public java.util.Enumeration getAttributeNames( ): returns

an Enumeration ofString objects containing the names of allthe objects bound to this session.

public void removeAttribute(java.lang.String name):removes the object bound with the specified name from thissession. If the session does not have an object bound with thespecified name, this method does nothing.


41/86

6/2/20

4

Session Object example

See Servlet\Session folder in code sample: Cart.html: web page to allow selection of items

Cart.java: Servlet invoked by Cart.html; it instantiates

a session object which contains descriptions of items

selected.

Cart2.html: web page to allow viewing of items

currently in cart

Cart2.java: Servlet to display items in the shoppingcart, as recorded by the use a session object in the

Cart servlet

For state information maintenance:

hidden form fields

cookies

the servlets instance variables may hold global

data

a session object can be used to hold session data


42/86

6/2/20

4

Inter-Servlet Communication

Allows servlets that are executing on the

same Web server to:

Communicate with each other

Share resources amongst each other

The RequestDispatcher interface

can be used to invoke a servlet from the

other

Inter servlet Communication

Inter-Servlet Communication (Contd.)

The RequestDispatcher interface:

Can be used to delegate a request to other

resources that are existing on the Web

server, such as a:

HTML page

Servlet

JSP page

Encapsulates the URL of a resource that

exists in a particular servlet context


43/86

6/2/20

4

Inter-Servlet Communication (Contd.)

The following are few methods that can be

used for communication between servletsMethod name Descr ipt ion

getServletContext() This method belongs to the interfacejavax.servlet.ServletConfig

public abstractServletContextgetServletContext()

This function returns the context of the servlet.

getRequestDispatcher() public abstract RequestDispatchergetRequestDispatcher(String urlpath)

This method is used to get a reference to a servlet

through an URL that is specified as the parameter. The

dispatcher that is returned is used to invoke the

servlet. If a dispatcher cannot be obtained for the URL

specified, this function returns a null.

Method name Descript ion

forward() public abstract void

forward(ServletRequest

request,ServletResponse response)

throws ServletException,

IOException

This method belongs to the RequestDispatcher

interface and can be used to forward a request

from one servlet to another. This method must

be used when the output is completely

generated by the second servlet or the servlet

that is invoked.

include() public abstract void

include(ServletRequest

request,ServletResponse response)

throws ServletException,

IOException

This function is also used to invoke one servlet

from another like the forward() function.

However, you can also include the output of thefirst servlet with the current output.


44/86

6/2/20

4

forward

The forwardmethod of the RequestDispatcherinterface may only be called by the calling servlet if no

output has been committed to the client.

If output exists in the response buffer that has not

been committed, it must be reset (clearing the buffer)

before the target servletsservice method is called.

If the response has been committed, an

IllegalStateExceptionmust be thrown.

importjava.io.*;

importjavax.servlet.*;

importjavax.servlet.http.*;

public class MyServlet extends HttpServlet {

public void doGet (HttpServletRequest req, HttpServletResponse res) throws IOExcep

tion, ServletException

{ServletContext context = getServletContext();

RequestDispatcher dispatcher = context.getRequestDispatcher("/myServlet");

dispatcher.forward(req,res);

}

}


45/86

6/2/20

4

include

The includemethod of the RequestDispatcherinterface may be called at any time. The target servlet

has access to all aspects of the request object, but can

only write information to the response object as well as

the ability to commit a response by either writing

content past the end of the response buffer or explicitly

calling the flush method of the ServletResponse

interface.

The included servlet cannot set headers or call any

method that affects the headers of the response. Anyattempt to do so should be ignored.

importjava.io.*;

importjavax.servlet.*;

importjavax.servlet.http.*;

public class MyServlet extends HttpServlet {

public void doGet (HttpServletRequest req, HttpServletResponse res) throws IOExcep

tion, ServletException

{ServletContext context = getServletContext();

RequestDispatcher dispatcher = context.getRequestDispatcher("/myServlet");

dispatcher.forward(req,res);

}

}


46/86

6/2/20

4

Problem Statement 3.D.2

You need to deposit money into your account. Create a

servlet that accepts the account number and pin number.

The first servlet should also validate the account number

and pass it on to the second servlet. The second servlet

should accept the amount to be deposited from the user.

The third servlet updates the table and displays the

updated balance to the user. In addition, the third servlet

also displays the last 20 transactions for that user. The

fourth servlet should display the last 20 transactions for

that user.

Task List

Identify the mechanism

Write the client interface

Write the code for servlet 1



Write the code for servlet 4 Compile the servlets

Deploy the servlets in J2EE

Verify the servlets


47/86

6/2/20

4

Task 1: Identify the mechanism

The RequestDispatcher interface

must be used:

To invoke one servlet from the other

The reference to a servlet can be

obtained by using:

The servlet context

Task 2: Write the client interface


48/86

6/2/20

4

Task 3: Write code for servlet 1

The first servlet uses the login table to validate theaccount number and the pin number

If the values are valid, an attribute called

accountnumber is created and assigned the value

entered

Else, an error message is displayed to the user

The attribute is created by using thesetAttribute() method

Task 4: Write the code for servlet 2

The second servlet:

Obtains the account number by using thegetAttribute() function

Displays a form in which the user can enter

the amount to be deposited

The third servlet:

Is invoked on the click of the deposit

button in the form


49/86

6/2/20

4


The third servlet:

Accesses the account number by using thegetAttribute() function


The fourth servlet:

Displays the last 20 transactions that were

made by the customers

Displays the balance after the previous

transaction that was made


50/86

6/2/20

5

Summary

In this lesson, you learned that:

RequestDispatcher interface can be used to call

one servlet from the other

The forward() and the include() method can

be used to invoke one servlet from the other

The data, which is common to servlets

can be accessed by using the

ServletContext interface.


51/86

6/2/20

5


52/86

6/2/20

5

Getting attribute value from ServletContext

JSP


53/86

6/2/20

5

Static Web Pages

A Web page author composes an HTML page, and saves it

as an .htm or .html file

A user types a page request via URL into the browser, and

the request is sent from the browser to the Web server

The Web server receives the page request and locates the

.htm/.html page in local file system

The Web server sends the HTML stream back across the

Internet to the client browser

The browser interprets the HTML and displays page

Dynamic Web Pages

Content does not always exist before a page is requested

Content, at least part of it, is generated upon request

For example:

the current time on the Web server

The e-mail system you use: login page, greeting page,

e-mail folders, etc.


54/86

6/2/20

5

Disadvantages of Servlets

Need to be Java programmer

Presentation buried in code

Cant use web page design tools

Creating Dynamic Web Pages with JSP

JSP is a server-side scripting language that produces Web pages that can

be viewed with any browser

You can mix regular HTML tags with JSP script in the same JSP page

The JSP scripts, if any, are interpreted on the Web server (often called the

application server)

The content generated by the execution of JSP code is mixed with HTML

code and the whole content is sent to the client browser

Client never sees JSP part!


55/86

6/2/20

5

Creating Dynamic Web Pages with JSP

The current date and time on

the Web server are:

The current date and time on

the Web server are:

Mon Jul 16 10:58:09 PDT 2007

JSP file Content sent to client

JSP script executes on the Web

server and the current date and

time are generated

Hello, World JSP Example

Hello World

Hello, World

Its

and all is well.


56/86

6/2/20

5

What Can JSP Do?

Connect to and manipulate a database.Create pages that can display things which will be of interest to a particular

user.

Collect data from users and return information to a visitor based on the

data collected.

Modify the content of a Web page, by updating a text file or the contents

of a database rather than the HTML code itself.

Access file systems via the Internet so that you can read, write, and update

files.

Utilize extensive Java Application Programming Interfaces.

Processing a Request for an HTML Page


57/86

6/2/20

5

Processing a Request for a JSP page

Servlets and JSPWhen a JSP page is requested the first time, it

is compiled into its corresponding servlet

From that point, it is the servlet that handles

all corresponding requests


58/86

6/2/20

5

Servlets and JSP

Why Use JSP?

JSP is built on top of servlets, so it has all the advantages of servlets

JSP is compiled into its corresponding servlet when it is requested

at the first time

The servlet stays in memory, speeding response times

Extensive use of Java API (Applications Programming Interface) for

networking, database access, distributed objects, and others like it

Powerful, reusable and portable to other operating systems and

Web servers (JSP is a specification, not a product)

Separates presentation logic!


59/86

6/2/20

5

Retrieving Form Data

JSP provides request object

one of many objects created and maintained by container

we use to get info

returns query string exactly as would be appended to URL

returns value from Name/Value pair

The Three Kinds of JSP Elements

Directives

do not produce output

control translation and compilation of page

Actions

dynamically generate content upon client request

some built in actions

can create our own

xml syntax


60/86

6/2/20

The Three Kinds of JSP Elements

ScriptsWhat we are using now!

Allow us to insert code into page

creates a scriptlet

is an expression

No space between % and =

Expression is converted to a String and

embedded directly in page

declares things that are

inserted directly into

implementation class in servlet

Form Processing Techniques


61/86


62/86

6/2/20

Sending Output Example

JSP output example 2

Your message is displayed using your preferred font format as

follows:

Storing Form Information

Use request object to get form info

JSP uses variables to store the collected form values

All variables must be declared before you can use them

Date_Type variable_Name

Data types are valid Java types

Variables names are valid Java identifiers

series of characters, digits, and underscores

cannot begin with a digitby convention, use lowercase for first letter, capitalize beginning of

each word

case sensitive!


63/86

6/2/20

Storing Form Information

Your major is

Using Basic JSP Techniques


64/86

6/2/20

Scripting With JSP Elements

Page DirectivesPage directive attributes apply to the entire JSP page:

OR


65/86

6/2/20

Import Attribute

Make Java classes available to the scripting environment

Use Java API to add power to your JSP scriptReference class without specifying package names

Using java.util.Date class

Without import:

If the class imported, then:


66/86

6/2/20

Session Attribute

HTTP is stateless

JSP provides session management

Session attribute specifies whether session should be created

Then, can hold information across multiple requests

Default value is true

If the value is set to false, then no session is created

Session Attribute

A session begins when a user requests a JSP page the first time

Session can be destroyed many different ways

User closes web browser

Server terminates due to inactivity

You can terminate session in code


67/86

6/2/20

Session Object Example

Session attribute

Is this a new session?

Current time:

The session created on :

Session Object Example

Session attribute

Is this a new session?

Current time:

The session created on :


68/86

6/2/20

Buffer Attribute

Specifies the size of the buffer used by the implicit out variable

If a buffer is specified then output is buffered with a buffer size not less than

the specified size

Server may still increase buffer size

Buffer Attribute Example

Buffer attribute

The buffer attribute is set to "16kb"

Let's send some text to the HTML output stream

The content is buffered.

The buffered content is cleared from the buffer.


69/86

6/2/20

Buffer Attribute Example

Buffer attribute

The buffer attribute is set to "none".

Let's send some text to the HTML output stream.

The content is not buffered.

The buffered content is not cleared.

isThreadSafe Attribute

Specify whether to allow more than one thread to execute the JSP code


70/86

6/2/20

7

Include Files

Add content from another file to your page

Could be static content

navigation links

headers and footers

Could be dynamic content

reusable JSP code

Include DirectiveFormat

Alternative format (xml)

Included content is merged into page at translation time!

This is called a static include

Can result in inconsistencies when included file

is updated

Updates are not reflected in already translated

pages!


71/86

6/2/20

7

Include Action

Form

The action does not merge the actual contents

of the specified page at translation time

The page is included each time the JSP page is

requestedUpdates are always reflected

This is an action, not a directive

Performance cost to do this

flush set to true to force current page buffer

to be flushed before new file is included

Variable Duration

The duration of variable (also called its lifetime) is the period during which

the variable exists in memory

Variables of instance duration exist throughout the lifetime that a servlet is

loaded in memory

Variables of local duration exist only during processing of single page


72/86

6/2/20

7

Variable Duration Example

Variable duration

Use the counter variable declared in JSP

declaration

This page has been accessed

time.

times.

Variable Duration ExampleUse the counter variable declared in JSP sriptlet

This page has been accessed

time.

times.

Reload this page


73/86

6/2/20

7

Implicit Objects

Implicit Objects

Objects created by the servlet container

application

session

request

response

exception

out

Config

pageContext

page


74/86

6/2/20

7

The JSP implicit application object is an instance of a java class thatimplements the javax.servlet.ServletContext interface.

It gives facility for a JSP page to obtain and set information about

the web application in which it is running.

application implicit object

application object example

One.jsp

Two.jsp


75/86

6/2/20

7

The JSP implicit session object is an instance of a java class that implement

the javax.servlet.http.HttpSession interface.

It represents a client specific conversation.

The session implicit object is used to store session state for a single user.

session implicit object

One.jsp

two.jsp


76/86

6/2/20

7

The JSP implicit response object is an instance of a java class that

implements the javax.servlet.http.HttpServletResponse interface.

It represents the response to be given to the client.

The response implicit object is generally used to set

the response content type, add cookie and redirect the response.

response implicit object

One.jsp

response implicit object


77/86

6/2/20

7

The JSP implicit request object is an instance of a java class that

implements the javax.servlet.http.HttpServletRequest interface.

It represents the request made by the client.

The request implicit object is generally used to get request

parameters, request attributes, header information and query string

values.

request implicit object


Login.html

UserName:

Password:


78/86

6/2/20

7


LoginValidation.jsp

The JSP implicit out object is an instance of

the javax.servlet.jsp.JspWriter class.

It represents the output content to be sent to the client.

The out implicit object is used to write the output content.

out implicit object


79/86

6/2/20

7

out implicit object

Login.html

UserName:

Password:

out implicit object

LoginValidation.jsp


80/86

6/2/20

8

The JSP implicit exception object is an instance of

the java.lang.Throwable class.

It is available in JSP error pages only.

It represents the occured exception that caused the control to

pass to the JSP error page.

exception implicit object

The JSP implicit config object is an instance of the java class that implements

javax.servlet.ServletConfig interface.

It gives facility for a JSP page to obtain the initialization parameters available.

config implicit object


81/86

6/2/20

8

config implicit object

The JSP implicit page object is an instance of the java.lang.Object class.

It represents the current JSP page.

That is, it serves as a reference to the java servlet object that implements

the JSP page on which it is accessed.

It is not advisable to use this page implict object often as it consumes large memory.

page implicit object


82/86

6/2/20

8

The JSP implicit pageContext object is an instance of

the javax.servlet.jsp.PageContext abstract class.

It provides useful context information.

That is it provides methods to get and set attributes in different scopes and

for transfering requests to other resources.

Also it contains the reference to to implicit objects.

pageContext implicit object

Scopes of Jsp objects

The availability of a JSP object for use from a particular place of

the application is defined as the scope of that JSP object.

Every object created in a JSP page will have a scope.

Object scope in JSP is segregated into four parts and

they are page

request

session

application.


83/86


84/86

6/2/20

8

session scope means, the JSP object is accessible from pages that belong

to the same session from where it was created.

The JSP object that is created using the session scope is bound

to the session object.

Implicit object session has the session scope.

Session Scope

A JSP object created using the application scope can be accessed from

any pages across the application.

The JSP object is bound to the application object.

Implicit object application has the application scope.

Application scope


85/86

6/2/20

8

JSP Standard actions

JSP Standard action are predefined tags which performsome action based on information that is required at the exact time

the JSP page is requested by a browser.

for instance, access parameters sent with the request to

do a database lookup

The JSP standard actions affect the overall runtime

behavior of a JSP page and also the response sent back to the client.

Action element Description

s Makes a JavaBeans component available in a page

Gets a property value from a JavaBeans

component and adds

it to the response

Sets a JavaBeans component property value

Includes the response from a servlet or JSP page

during the

request processing phase

Forwards the processing of a request to servlet orJSP page

Adds a parameter value to a request handed off to

another servlet

or JSP page using or

Generates HTML that contains the appropriate

browser-dependent

elements (OBJECT or EMBED) needed to execute

an applet with

the Java Plug-in software

JSP Standard actions


86/86

6/2/20

The jsp:include element is processed when a JSP page is executed.The include action allows you to include either a static or a dynamic resource in a JSP file.

The results of including static and dynamic resources are quite different.

If the resource is static, its content is inserted into the calling JSP file.

If the resource is dynamic, the request is sent to the included resource,

the included page is executed,

and then the result is included in the response from the calling JSP page.

The syntax for the jsp:include element is:

Date post:	14-Apr-2018
Category:	Documents
Upload:	sunil-kumar
View:	227 times
Download:	0 times

Package -5 Networking, Applets, Http, Servlet, JSP, Struts

Documents