Java Server Pages(JSP)

8/8/2019 Java Server Pages(JSP)

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J2EE Web 1

Pre-assessment Questions

Which method is invoked only once in the life cycle of a servlet?

1. init()

2. doPost()

3. service()

4. doGet()

Identify the correct feature of servlets.

2. Servlets are client-side components that generates dynamic contents.

3. Servlets by default can service only one client request at a time.

4. Servlets are platform dependent.

5. Servlets can service multiple client requests.


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J2EE Web 2

Pre-assessment Questions (Contd.)

Identify the method called by the Web container after creating a servlet instance.

3. init()

4. service()

5. start()

6. destroy()

Which method is automatically invoked by the Web container when a request

arrives?

4. init()5. service()

6. doPost()

7. doGet()


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J2EE Web 3

Pre-assessment Questions (Contd.)

Identify the method that sends user information as query string appended to theURL.

5. GET

6. POST

7. HEAD

8. DELETE


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J2EE Web 4

Solution to Pre-assessment Questions

a. init() d. Servlets can service multiple client requests. a. init() b. service() a. GET


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J2EE Web 5

Objectives

In this lesson, you will learn about:

Classes and interfaces of Servlet API Servlet lifecycle events Deployment descriptor elements


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J2EE Web 6

The Servlet API

The Servlet API consists of:

javax.servlet package contains:

ServletRequest Interface

ServletResponseInterface

ServletContextInterface

javax.servlet.http package contains: HttpServletRequest Interface

HttpServletResponse Interface

HfttpSession Interface


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The Servlet API (Contd.)

The following table describes the various methods defined in theServletRequest interface:

Method Description

public String getParameter(String

paramName)Returns a String object that specifies thevalue of a particular request parameter.

public String[]

getParameterValues(String

paramName)

Returns an array of String objects that

contains all the values of the request

parameter.

public Enumeration

getParameterNames()Returns an Enumeration containing all

the parameter names as String objects

that a servlet request contains.


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Methods ofServletRequest interface (Contd.):

Method Description

public String getRemoteHost()

Returns a String that specifies the full-qualified name of the computer from which

the request is sent.

public String getRemoteAddr()

Returns a String that specifies the IPaddress of the computer from which the

request is sent.


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J2EE Web 9


The following table describes the various methods defined in theServletResponse interface:Method Description

public ServletOutputStream

getOutputStream() throws

IOException

Returns an object of theServletOutputStream class that

represents an output stream to sendbinary data as response.

public PrintWriter getWriter()

throws IOException

Returns an object of the PrintWriter

class that the servlet uses to sendcharacter data as response.

public void setContentType(String

type)Sets the MIME type for a servlet response,such as text/plain, image/jpeg and

text/html.


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J2EE Web 10


The following table describes the various methods defined in theServletContext interface:

Method Description

public void setAttribute(String,

Object)Binds the object with a name andstores the name/value pair as an

attribute of the ServletContext

object. If an attribute alreadyexists, then this method replaces

the existing attribute.

public Object getAttribute(String

attrname)Returns the Object stored in theServletContext object with the

name passed as a parameter.


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J2EE Web 11


Methods ofServletContext interface (Contd.):

Method Description

public Enumeration getAttributeNames()Returns an Enumeration of String object that

contains names of all the context attributes.

public String getInitParameter(String

pname)Returns the value of the initialization

parameter with the name passed as aparameter.

public Enumeration

getInitParameterNames()Returns an Enumeration of String object thatcontains names of all the initialization

parameters.


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Method Description

public int getMajorVersion()

Returns an integer value that specifies the major

version of the Servlet API that the Webcontainer supports. If your Web container

supports the version 2.4 of the servlet API,

this method will return 2.

public int getMinorVersion() Returns an integer value that specifies the minor

version of the servlet API that the Webcontainer supports. If your Web container

supports the version 2.4 of the servlet API,this method will return 4.

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J2EE Web Components


Methods ofServletContext interface (Contd.):


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J2EE Web 13


The following table describes the various methods defined in theHttpServletRequest interface:

Method Description

public String getHeader(String

fieldname)Returns the value of the request header

field such as Cache-Control and Accept-

Language specified in parameter.

public Enumeration

getHeaders(String sname)Returns all the values associated with a

specific request header as an Enumerationof String objects

public Enumeration

getHeaderNames()Returns the names of all the requestheaders that a servlet can access as an

Enumeration of String objects.


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J2EE Web 14


The following table describes the various methods defined in theHttpServletResponse interface:

Method Description

void setHeader(String hname,

String hvalue)Sets the value of header, hname tohvalue. If the header has already been

set, the new value overwrites theexisting value.

void setIntHeader(String hname,

int hvalue) Sets the value of the header, hname tothe int value, hvalue. If the header has

already been set, the new value

overwrites the existing value.


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J2EE Web 15


Methods ofHttpServletResponse interface (Contd.):

Method Description

void setDateHeader(String hname,

long datev)Sets the value of the header, hname with a

long value datev. The datev represents thenumber of milliseconds since the midnight ofJanuary 1, 1970, GMT.

void addHeader(String hname, String

hvalue)Adds a header, hname with value, hvalue. This

method adds a new header if the header

already exists.void addIntHeader(String hname, int

hvalue)Adds a header, hname with an integer value,hvalue.


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Method Description

void addDateHeader(String hname,

long datev)Adds a header, hname with valueequal to given date, datev. The value of

datev must be in milliseconds, which starts

since midnight, January 1,1970, GMT.

boolean containsHeader(String hname) Returns true if the header, hname has

already been set with a specific value andfalse, if not.

void sendRedirect(String url) Redirects a request to the specified URL.

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J2EE Web Components


Methods ofHttpServletResponse interface (Contd.):


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J2EE Web 17


The following table describes the various methods defined in the HttpSession

interface:Method Description

public void

setAttribute(String name,

Object value)

Binds the object with a name and stores the

name/value pair as an attribute of theHttpSession object. If an attribute already exists,

then this method replaces the existing attribute.

public Object

getAttribute(String name)Retrieves the String object specified in the

parameter, from the session object. If no object isfound for the specified attribute, then thegetAttribute() method returns null.

public Enumeration

getAttributeNames()Returns an Enumeration that contains the name of

all the objects that are bound as attributes to the

session object.


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J2EE Web 18

Demonstration-Implementing Context

Initialization Parameter

Problem Statement

Smart Softwares wants to develop a Web application that will use

servlets to provide the information about the company. The servlets,

which are created for handling the presentation logic, needs to displayan email-id where an end user can send feedbacks and suggestions.

The company wants to avoid changing the application code, whenever

the email-id of the company changes.


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J2EE Web 19

Demonstration-Implementing Context

Initialization Parameter (Contd.)

Solution

Create a servlet to retrieve initialization parameters.

Specify the initialization parameters.

Access the servlet.


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J2EE Web 20

Servlet Life Cycle API

Types of Events generated during the life cycle of a servlet are:

Servlet Request Events: Relates to changes in the request objects

associated with a Web application.

Servlet Context Events: Relates to changes in thein the context of a

Web application.

HTTP Session Events: Relates to changes in the session object of aservlet application.


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J2EE Web 21

Servlet Life Cycle API (Contd.)

Handling of Servlet Life Cycle Events

The classes that receive notification about the servlet life cycle events are

known as event listeners.

Various event listener interfaces are:

ServletRequestListener Interface

ServletRequestAttributeListener Interface

ServletContextListener interface

ServletContextAttributeListener Interface

HttpSessionListener Interface

HttpSessionAttributeListener Interface

HttpSessionActivationListener Interface


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J2EE Web 22

Demonstration-Implementing Servlet

Life Cycle Events

Problem Statement

David Wong, the administrator at Smart Software Developers want to

create an application that will log the time when request and context

objects are initialized and when attribute is added to the contextobject. At the same time, the application should also log the time

when the attribute is removed from the context object and request

and context objects are destroyed.


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J2EE Web 23

Demonstration-Implementing Servlet

Life Cycle Events (Contd.)

Solution

Create a servlet that adds an attribute to context object.

Create a servlet that logs the time of all the events generated by

first servlet to the server.log file.

Deploy the two servlets. While deploying, register the second servlet

to listen to the events generated by first servlet. Run the program.


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J2EE Web 24

Understanding Elements of

Deployment Descriptor

A deployment descriptor is an XML file with the name web.xml that contains

configuration information of a Web application.

Each Web application contains one web.xml file.

The elements of the web.xml file enable you to specify:

Initialization parameter for the servlet

MIME type for different files

Listener classes

Mapping a URL pattern to a servlet


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J2EE Web 25

Understanding Elements of

Deployment Descriptor (Contd.)

Various deployment descriptors are:


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J2EE Web 26

Summary

In this lesson, you learned:

Java Servlet API consists of two packages:

javax.servlet package

javax.servlet.http package

The various interfaces ofjavax.servlet package are:

ServletRequest interface

ServletContext interface

ServletResponse interface

You can retrieve the request headers by using the various methods of theServletRequest interface.

You can send response to the client request by using the various methods ofServletResponse interface.

You can set a context attribute for a servlet application by using the various

methods ofServletContext interface.


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J2EE Web 27

Summary (Contd.)

The various interfaces ofjavax.servlet.http interface are:

HttpServletRequest interface

HttpServletResponse interface

HttpSession interface

The HttpServletRequest interface provides various methods for retrieving

request parameters sent using HTTP.

The HttpServletResponse interface provides various methods to handle

response and status codes for servlets using HTTP.

The HttpSession interface provides various methods to maintain the state of

an end user across a Web application.

You can initialize servlet applications by using the initialization parameters.

The servlet life cycle events generated within the Web container are:

Servlet request events


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J2EE Web 28

Summary (Contd.)

Servlet context events Servlet session events

The various interfaces for handling servlet life cycle events are:

ServletRequestListener interface

ServletRequestAttributeListener interface

ServletContextListener interface

ServletContextAttributeListener interface

HttpSessionListener interface

HttpSessionAttributeListener interface

HttpSessionActivationListener interface

The various elements of the Web application deployment descriptor are, , , ,

, and .

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