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Java Server Pages

http://www.vovanhai.wordpress.com

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JSP Basics

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JSP Java Server Page (JSP) is a server side script language

Saved with .jsp extension

A simple, yet powerful Java technology for creating and maintaining

dynamic-content webs pages

JSP page are converted by the web container into a Servlet instance

It focus on the presentation logic of the web application

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Architecture of JSP

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JSP Expression

Includes expression in a scripting language page

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Scriptlet

Refers to code blocks executed for every request.

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Declarations

Defines the variables and methods for a JSP page

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Comments

Explains the functioning of the code

Comments are ignored by the servlet during

compilation

Syntax

...

<!–- HTML comments -->

...

...

<%-- JSP comments --%>

...

...

<% /*Scripting languages comments*/ %>

...

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Directives Controls the structure of the servlet by sending

messages from the JSP page to the JSP container.

Specify the scripting language to used.

Denote the use of custom tag library in a JSP page.

Be used to include the content of another JSP page.

…

Syntax

...

<%directivename attribute = “value”%>

...

Specifies the JSP directive

Refers to the directive attribute9

Directives – Contd…

The types of JSP directives are:

page -Associates the attributes that affect the

entire JSP page

include - Sends message to the JSP container

to include the contents of one file into another

taglib - Enables the use of custom tags in the

JSP page

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page Directive

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include Directive

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taglib Directive

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Standard Actions Tags affecting the behavior of JSP at runtime and the response sent

back to web browser

Syntax:

...

<jsp: standard action>

...

Standard Action Description

<jsp: useBean> Accesses the functions of custom tags

<jsp: param> Provides name and value to the parameters used by the JSP page

<jsp: include> Includes the output from one file into the other files

<jsp: forward> Transfers control from a JSP page to another

<jsp: plugin> Uses a plugin to execute an applet or bean

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JSP Implicit Object

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Implicit Objects

Are loaded by the Web

Container automatically and

maintains them in a JSP page

The names of the implicit

objects are reserved words of

JSP

Access dynamic content

using JavaBeans

Types of implicit objects16

Implicit Objects (cont)

Object Class / Interface

page javax.servlet.jsp.HttpJspPage

config javax.servlet.ServletConfig

request javax.servlet.http.HttpServletRequest

response javax.servlet.http.HttpServletResponse

out javax.servlet.jsp.JspWriter

session javax.servlet.http.HttpSession

application javax.servlet.ServletContext

pageContext javax.servlet.jsp.PageContext

exception java.lang.Throwable

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The request Object

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Represents the request from the client for a Web page

Controls information associated with a request from client

Includes the source, URL, headers, cookies and parameters

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The response Object

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Manages the response generated by JSP container and

sends response to the client

Is passed as a parameter to JSP _jspService() method

The out Object

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Represents the output stream, then it will be sent to the client as a

response for the request

Is has page scope

The session Object

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Provides all the objects

available in the JSP pages

within the session

The application Object

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Is used to share the data

between all application

pages

Can be accessed by any

JSP present in the

application

The pageContext Obbject (1)

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Provides methods to access all attributes

defined by implicit objects in the page.

Provides methods to transfer control

from one web page to another

osetAttribute()

ogetAttribute()

ogetAttributeNamesInScope()

oremoveAttribute()

The pageContext Obbject (2)

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Find the scope or

specify the scope

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Servlet Object (1)

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The page object: is an instance of the servlet

processing the current request in a JSP page.

Servlet Object (2)

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The “config” Object:

oStores the information of

the servlet

oRepresents the

configuration of the servlet

data where a JSP page is

compiled

oIt has page scope

The exception Object

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Is used to handle errors in a

JSP page

Is used to trace the

exception thrown during

the execution

It has page scope

Error handling

<%@page errorpage=“error.jsp”%>

< -- some of code,…-->

index.jsp

error.jsp

<%@page isErrorPage=“true”%>

<%

if(exception!=null){

out.println(exception.getMessage());

}

%>

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Standard Actions

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Standard Actions

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Are XML like tags which take the form of an XML tag

with a name prefixed jsp

Are used for

Forwarding requests and performing includes in page

Embedding the appropriate HTML on pages

Interacting between pages and JavaBeans

Providing additional functionality to tag libraries

Syntax:<jsp:actionName attribute=“value”>...</jsp:actionName>

Some properties

Using <jsp> prefix

The attributes are case sensitive

Value in the attributes must be enclosed in double quotes

Standard actions can be either an empty or a container tag30

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<jsp:include>

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Include either static or dynamic file in jsp file at

the time of page request.

Static case: The content is included in the calling

jsp file.

Dynamic case: it acts on the request and send

back a result that is include in the JSP page.

Syntax:

<jsp:include: page=“webURL”|<%=exp%>

flush=“true”/>

<jsp:forward>

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It’s used to forward the request and response to

another jsp page or servlet

Syntax:

<jsp:forward page=“{webURL|<%=exp%>}”>

<jsp:param name=“{paramName|<%=exp%>”}/>

<jsp:forward>

Allow to pass one or more name/value pairs as parameters to

an included or forwarded resource like a jsp page.

Syntax:

<jsp:param name=“thename” value=“{thevalue|<%=exp%>}”

<jsp:param>

<jsp:plugin>

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Used in the execution of an applet or bean.

Syntax:

<jsp:plugintype=“bean|applet”code=“ClassFileName”codebase=“classFileDirectoryName”<jsp:params>

<jsp:param name=“thename” value=“thevalue”>

</jsp:params>[<jsp:fallback> display message to

user</jsp:fallback>

</jsp:plugin>

<jsp:fallback>

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Display a text message to user if the plug-

in could not start.

Syntax:

<jsp:fallback>

html message

</jsp:fallback>

JavaBeans

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Concept

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JavaBeans are reusable components that can be deployed in java.

Define the interactivity of Java object

Allow creation of graphical components that can be reused in GUI

application.

Can be embedded in multiple applications, servlet and jsp.

Requirements:

o Be a public class

o Have a public constructor with no arguments

o Have get/set methods to read/write bean properties

Components of JavaBeans:

◦ Properties

Getters and setters

◦ Methods

◦ Events

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<jsp:useBean> Is used to create a reference and include an existing bean

component in JSP

The <jsp:useBean> follows to locate or instantiate the

Bean

Attemps to locate a Bean within the scope

Defines an object reference variable with the name

Stores a reference to it in the variable, if it retrieves the

Bean

Instantiates it from the specified class, it is cannot retrieve

the Bean

Syntax: <jsp:useBean id=“name” class=“class”

scope=“page/session/request/application”

/> 37

<jsp:getProperty>

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Using for retrieve properties value of the Bean.

Retrieves a bean property value using the getter

methods and displays the output in a JSP page

The <jsp:getProperty> and expression convert the

value into a string and insert it into an implicit out

object

Some drawbacks

Fails to retrieve the values of indexes property

Fails to directlyaccess enterprise bean components

Syntax:

<jsp:getProperty name=“Bean_Alias”

property=“PropertyName”/>

<jsp:setProperty>

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Retrieves a bean property value using the getter methods and displays the output in a JSP page

The <jsp:getProperty> and expression convert the value into a string and insert it into an implicit out object

Some drawbacks:

◦ Fails to retrieve the values of indexes property

◦ Fails to directly access enterprise bean components

Syntax:

<jsp:setProperty name=“Bean_Alias”

property=“Property_Name”

value=“TheValue” param=“Parameter”/>

JavaBeans & Scriptlets

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JavaBeans can be accessed from scripting element in

different ways. Do it likes in J2SE.

The JSP container converts the string values into non

string values by the attribute values that evaluate the

correct data type to set the propertyvalue

Expression Language

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Expression Language (EL)

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New feature of JSP 2.0

Allows JSP developers to access java objects via a compact, easy-to-use shorthand style (similar to JavaScript)

It can handle both expressions and literals

Developed by two groups JSP Standard Tag Library expert group

JSP 2.0 expert group

Syntax: ${EL Expression}

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EL Implicit Objects

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Implicit Objects

pageContext cookieinitParamparamValuesparam

header headerValues

application

servletContext

request

session

response

Request Headers and Parameters

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param: return a value that maps a request parameter name to

a single string value

ex: "${param.Name}“

paramValues: return an array of values is mapped to the

request parameters from client

ex: “${paramValues.Name[0]}”

header: return a request header name and maps the value to

single string value.

ex: ${header[“host”]}

headerValues: return an array of values is mapped to the

request header

ex: ${headerValues.Name}

cookie: returns the cookies name mapped to the single cookie

object

ex: ${cookie.name.value}

initParam: returns a context initialization parameter name, which is

mapped to a single value.

Scope variables (1)

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Variables are used to store and access values in JSP

program

Variable refers as a attributes that are stored in standard

scope such as page, request, session and application

Dot operator . or square brackets [ ] can be used to

access value of variable

Example

${pageScope.color}

${pageScope[“color”]}

Scope Variables (2)

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EL Operators

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*

/ or div

+

-

% or mod

< or lt

> or gt

< = or le

> = or ge

= = or eq

!= or ne

&& or and

|| or or

! or not

empty

Operators

EmptyLogicalRelationalArithmetic

Example

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JSP Standard Tag Library

(JSTL)

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Concept

JSTL provides a set of reusable standard tag that work for create jsp pages.

JSTL allows programming using tags rather than scriptlet code.

JSTL has tags, such as:◦ Iterators and conditional tags

◦ Internationalization tags

◦ SQL tags

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Types Of Tags Libraries

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JSP Standard Tag Library

(JSTL)

Core Tag

Library

I18N &

Formatting

Tag Library

SQL Tag

Library

XML Tag

Library

Core Tag Library

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General

Purpose Tags

Decision

Making TagsIteration Tags

set remove out forEach forTokensif choose

Core Tag Library

General Purpose Tags

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<c:set>: assigns a value to a variable in scope

<c:remove>: remove a scope variable

<c:out>: evaluate an expression and store a result in the current JspWriter object.

<c:catch>: provides an exception handling functionality, such as try-catch inside jsp pages without using scriptlet

Syntax: <c:set var=“varName” value=“value”

scope=“page|request|session|application” />

<c:remove var=“varName” scope=“page|request|session|application” />

<c:out value=“value|expression” escapeXml=“true|false” default=“defaultValue” />

<c:catch />

Example

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Decision-Making Tags

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<c:if>: used for conditional execution of the code

<c:choose>: similar switch statement in java

Iteration Tags

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<c:forEach>: used to repate the body content over a

collection of objects.

<c:forTokens>: used to iterate over a collection of

tokens separated by user-specified delimiters.

SQL Tag Library

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SQL Tag Library

setDataSource query update paramtransaction

The sql:setDataSource Tag

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The sql:queryTag

The sql:update Tag

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The sql:param Tag

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The sql:transaction Tag

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Internationalization(I18N)

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I18N Basics(1)

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Internationalization

The method of designing an application that can be adapted to

a region or a language without much change in the technology

Helps in creating internationalized Web application that

standardize formatted numeric and date-time output

(supporting multiple languages)

Localization

Is a process of making of product or service language, cultural

and local “look and feel” specific

A Locale is a simple object identifying a specific language and

geographic region (java.lang.Locale)

Is denoted by xx_YY (language code_letter country)

Unicode in Java, is a 16 bit character encoding

Resource Bundles contain locale-specific objects

Internationalizing (1)

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Resource Bundles

Is a set of related classes that inherit from ResourceBundle

The several methods

public static final ResourceBundle getBundle(String baseName,Locale locale)

public abstract Enumeration getKeys()

public Locale getLocale()

public final Object getObject(String key)

public final String getString(String key)

Formatting Dates in Servlets

Using predefined Formats: SHORT, MEDIUM, LONG, FULL

Create a formatter with the getDateInstance() method ofDateFormat class

Invoking the format() method

Customising Formats: Using the SimpleDateFormat class

Internationalizing (2)

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Formatting Currencies

Currency: this class represents currency by ISO 4217 currency codes

public String getCurrencyNode()

public String getSymbol()

public static Currency getInstance(Locale locale)

NumberFormat: this is an abstract base class for all number formats

public final String format(double number)

public Currency getCurrency()

public static final NumberFormat getInstance()

public Number parse(String str) throws ParseException

public void setCurrency(Currency currency)

Formatting Percentages

public static final NumberFormat getPercentInstance()

public static NumberFormat getPercentInstance(Locale inLocale)

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Internationalizing (3)

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Formatting Messages

Using the MessageFormat Objects

The array of objects using the format specifiers

embedded in the pattern formateted by the

MessageFormat.format()

The classes for formatting messages

MessageFormat

MessageFormat.Field