Advanced Java Server Pages (JSP).pdf

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Advanced Java Server Pages (JSP)(JSP)

JavaTM Education & Technology ServicesCopyright Information Technology Institute http://jets.iti.gov.eg 1

Ch t 1Chapter 1

Custom TagsCustom Tags


Chapter 1 Outline

What are the custom tags?

How to Write Custom Tags?

What is the TLD file?

The Tag Handler Life Cycle.

Using Custom tag in a JSP page.

The role of deployment descriptor.


What are the custom tags?

They are special tags that are used to perform customized actions

You can separate the presentation part of a JSP page from the business rule implementation (Java code)from the business rule implementation (Java code).


What is wrong with java beans?

Only three action elementsjsp:useBean,

jsp:setProperty and getPropertyjsp:setProperty and getProperty.

In some sit ations e ha e to resort to sing code in a In some situations, we have to resort to using code in a JSP page


What is the main idea of custom tags ?

JSP 1.1 defined a new feature: custom tags that can be used to perform custom actions.

Custom tags -unlike java beans - have access to all the objects available to JSP pages and custom tags can beobjects available to JSP pages, and custom tags can be customized using attributes


How to Write Custom Tags?

There are mainly 4 steps1-Design our own Custom Tag2- Create a TLD file named taglib.tld, and save it in

the WEB-INF directory. 3 C il d d l th J l ( t3- Compile, and deploy the Java class (your tag

Handler).4 Create a JSP file import your custom tag then4-Create a JSP file, import your custom tag then

use it.


The deployment descriptor,JSP,and TLD file.


What is the TLD file?

A tag library descriptor (TLD) file is an XML document that defines a tag library and its tags. A TLD file is to custom tag handlers what a Web deployment descriptorcustom tag handlers what a Web deployment descriptor is to servlets.

A TLD file contains the root element ThisA TLD file contains the root element. This element can have the following subelements:

tlibversion jspversion shortname

i f info uri tag


tag

TLD file Elements

Th tlib i l t ifi th i b f The tlibversion element specifies the version number of the tag library in the following format:

([0-9])* (" " [0-9])? (" " [0-9])? (" " [0-9])?([0-9]) ( . [0-9])? ( . [0-9])? ( . [0-9])? The shortname element specifies a short name for the tag library.

The value for this element must begin with a letter and must not contain blank space.

The info element contains the information used for documentation purposes Its default value is an empty stringpurposes. Its default value is an empty string.

The uri element specifies the link to an additional source of documentation for the tag library.

The tag element is the most important element in a tag library. You can specify more than one tag element in the same TLD file.


Tag sub elements

Name (mandatory): specifies an identifier for the tag.T l ( d t ) ifi th f ll lifi d f Tagclass (mandatory): specifies the fully qualified name of the Java class that handles the processing of this tag.

Teiclass : specifies the helper class for this tag, if there is p p g,one

Bodycontent: specifies the type of the body content of the tag if any A body content is what appears between thetag, if any. A body content is what appears between the opening and closing tags. This element can have one of the following values: empty, JSP, or tag dependent

Info: contains an informational description. Attribute : specifies zero or more attributes. The attribute

element can have three subelements: name, required, andelement can have three subelements: name, required, and rtexprvalue. Only name is a required subelement of the attribute


Example

p j j j p g y_ _

1.01 11.1

myTagmylibrary.MyCustomTag


What is Tag Handler ?

I h J l h i li k d d Is the Java class that is linked to a custom tag and gets invoked every time the JSP container encounters the custom tag. The tag handler is so named because it handles the processing of the tag

The tag handler must implement an interface in the javax servlet jsp tagext package or extend one of the classes injavax.servlet.jsp.tagext package or extend one of the classes in the same package.

The most important interfaces are : Tag Iteration Tag Body Tag Body Tag


The Tag Interface

C t i th f ll i th d Contains the following methods doStartTag

d E dT doEndTag getParent

setParent setParent setPageContext release release NB:

doStartTag return integers which could be SKIP BODY, g g _ ,EVAL_BODY_INCLUDE.

doEndTag return integers which could be SKIP_PAGE, and EVAL PAGE


and EVAL_PAGE

Exampleimport javax.servlet.jsp.*;import javax.servlet.jsp.tagext.*;public class BasicTagHandler implements Tag {p g p g {public void setParent(Tag t) {}public void setPageContext(PageContext p) {}public void release() {}public Tag getParent() {return null;}

bli i t d St tT () {public int doStartTag() {return EVAL_BODY_INCLUDE;}public int doEndTag() {public int doEndTag() {return EVAL_PAGE;}}


}

The Tag Handler Life Cycle

1. The JSP container obtains an instance of the tag handler from the pool or creates a new one. It then calls the setPageContext passing a PageContextcalls the setPageContext, passing a PageContext object representing the JSP page where the custom tag is found.

2. The JSP container then calls the setParent method. e JS co a e e ca s e se a e e odThis method passes a tag object, which represents the closest tag enclosing the current tag handler.


The Tag Handler Life Cycle (contd)

3.The JSP container then sets all the attributes in the custom tag if any Attributes are handled likecustom tag, if any. Attributes are handled like properties in a JavaBean, namely by using the getter and setter methods.

4. Next, the JSP container calls the doStartTag.5. Regardless of the return value of the doStartTag g g

method, the JSP container next calls the doEndTag method.

6. The release method is the last method that the JSP container calls.Th JSP i h i f h7. The JSP container returns the instance of the tag handler to a pool for future use.


Using Custom tag in a JSP page

fi t d t t lib di ti i you first need to use a taglib directive in your page. %>

The uri attribute specifies an absolute or relative URI that uniquely identifies the tag library descriptor q y g y passociated with this prefix

Next to use it :fi N /

body< T b "12" "13"/>


The role of deployment descriptor

The JSP container can find the name and location of the TLD file by looking up the deployment descriptorThi i f bl b t t bli t This is preferable but not obligatory

Example:t lib /myTld

/WEB INF/taglib tld /WEB-INF/taglib.tld


Complete Example

The tag handler will take the form:public class DoublerTag implements Tag {p g p g {private int number;public void setNumber(int number) {this.number = number;}}PageContext pageContext;public void setParent(Tag t) {}public void setPageContext(PageContext p) {pageContext = p;}public void release() {}public Tag getParent() {return null;}

S () { {public int doStartTag() {try {JspWriter out = pageContext.getOut();out.println("Double of " + number + " is " + (2 * number));}

t h(E ti ) {}catch(Exception e) {}return EVAL_BODY_INCLUDE;}public int doEndTag() throws JspException {return EVAL PAGE;}


return EVAL_PAGE;}

Complete Example (contd)

The TLD file should take the form

1.0< h t >

myTagmylibrary DoublerTagmylibrary.DoublerTag

numbertruetrue


/taglib

Complete Example (contd)

The jsp page should include:


The IterationTag Interface

The IterationTag interface extends the Tag interface. It adds a new method called doAfterBody and a static

fi l i t EVAL BODY AGAINfinal integer EVAL_BODY_AGAIN. This method is invoked after the doStartTag method and

can return either the Tag SKIP BODY orcan return either the Tag.SKIP_BODY or IterationTag.EVAL_BODY_AGAIN.

If the latter is returned the doAfterBody is called again If If the latter is returned, the doAfterBody is called again. If the return value is Tag.SKIP_BODY, the body will be skipped and the JSP container will call the doEndTag pp gmethod.


Example

public class PowerTag implements IterationTag {PageContext pageContext;private int number;private int number;private int power;private int counter;private int result = 1;private int result = 1;public void setNumber(int number) {this.number = number;}

bli id tP (i t ) {public void setPower(int power) {this.power = power;}public void setParent(Tag t) {}public void setPageContext(PageContext p) {pageContext = p;}public void release() {}p () {}public Tag getParent() {return null;}public int doStartTag() {


public int doStartTag() {return EVAL_BODY_INCLUDE;}

Example (contd)

public int doAfterBody() {counter++;result *= number;if (counter == power)return SKIP BODY;return SKIP_BODY;elsereturn EVAL BODY AGAIN;}return EVAL_BODY_AGAIN;}public int doEndTag() throws JspException {System.out.println("doEndTag");try {JspWriter out = pageContext.getOut();out println(number + "^" + power + "=" + result);}out.println(number + ^ + power + = + result);}catch(Exception e) {}return EVAL PAGE;}}


return EVAL_PAGE;}}

Example (contd)

The jsp should take the form :

The tld should take the form :

1.0tlibversion 1.0 /tlibversion


Example (contd)

myTagmypackage PowerTagmypackage.PowerTag

numbername number /nametrue

powertrue


To manipulate body content

A JSP t t h b d t t h th A JSP custom tag can have a body content, such as the following tag: This is the body content

When you use the Tag and IterationTag interfaces, youWhen you use the Tag and IterationTag interfaces, you cannot manipulate the body content. You don't even have access to it.Thi ld b hi d b This could be achieved by: The BodyTag Interface

Th B d C t t Cl The BodyContent Class


To manipulate body content (contd)

BodyTag interface has a similar life cycle of IterationTag interface.

The difference is that the doStartTag method of the tag handler implementing BodyTag can return

SKIP BODY EVAL BODY INCLUDE SKIP_BODY, EVAL_BODY_INCLUDE, or EVAL_BODY_BUFFERED.

If the method returns EVAL BODY INCLUDE theIf the method returns EVAL_BODY_INCLUDE, the body is evaluated as it is in IterationTag. If the method returns EVAL_BODY_BUFFERED, a BodyContent bj t i t d th t t th t t 'object is created that represents the custom tag's

body content Two extra methods are called by the JSP container inTwo extra methods are called by the JSP container in

tag handlers implementing the BodyTag interface: setBodyContent and doInitBody.


The Support Classes

The TagSupport Class Implements the IterationTag interfacep g

The BodyTagSupport ClassE t d T S t i l t B d T Extends TagSupport implements BodyTag interface


Example

import javax.servlet.jsp.*;import javax.servlet.jsp.tagext.*;

bli l C it li T t d B d T S t {public class CapitalizerTag extends BodyTagSupport {public int doAfterBody() {String content = bodyContent getString();String content = bodyContent.getString();try{JspWriter out = bodyContent.getEnclosingWriter();p y g g ()out.print(content.toUpperCase());}

t h(E ti ) {}catch(Exception e) {}return SKIP_BODY;}}}


Lab Exercise


Assignment

Create your own custom tag , and use in in your jsp y j p


Ch t 2Chapter 2

JSTLJSTL


Chapter 2 Outline

What is JSTL ?

JSTL main packages.

Core Package

JSP Expression Language

Database Package.


What is JSTL ?

It stands for JSP Standard Tag Library

What do we need to run JSTL ?

What is wrong with JSP?


How does JSTL fix JSP problems?

JSTL t XML th l l d if l bl d JSTL tags are XML, they cleanly and uniformly blend into a page's HTML markup tags.

The main JSTL tag libraries include most functionalityThe main JSTL tag libraries include most functionality that would be needed in a JSP page.

JSTL tags are easier for non-programmers and inexperienced programmers to use effectively becauseinexperienced programmers to use effectively, because they do not require any knowledge of programming or Java. JSTL t f bj t i th t d JSTL tags can reference objects in the request and session without knowing the object's type and no casting is required.

JSP's EL (Expression Language) makes it easy to call getter and setter methods on Java objects.


The relation between JSP and JSTL


JSTL main packages

Plus the function package which is a set of standardized EL functions.


JSTL main packages (Contd)

The core library includes tags for the following uses: Accessing and modifying data in memory Making decisions in your pages Looping over data

The XML library includes tags for the following purposes:e b a y c udes tags o t e o o g pu poses Parsing (that is, reading) XML documents Printing parts of XML documents Making decisions in your page based on the contents of an XMLMaking decisions in your page based on the contents of an XML

document The formatting and internationalization library includes

tags for these uses:tags for these uses: Reading and printing numbers Reading and printing dates (with support for time zones) Helping your application work with more than one language Helping your application work with more than one language

The SQL library helps you read and write data from databases


How to introduce those packages in your code?


Core Package

It depends mainly on Expression Languagep g g


Expression Language

How Expression Language looks like ?It t t ith ${ d d ith } It starts with ${ and ends with }

Example :${ 1+2} ${ 1+2}

NB: Expression Language can be understood inside JSTL Tags and JSP tags as wellinside JSTL Tags and JSP tags as well.

Types of data read by EL? Scoped VariablesScoped Variables Request Parameters


What are scoped variable?

What are types of scoped variables? strings, numbers , booleans and collections which could

be arrays How EL reads Scoped Variables?

${ username }$ ${user.phone}

${header["User-Agent"]}


Expression Language (contd)

The default of scopes: Page-request-session then finally applicationapplication

To be able to specify your variable scope : ${pageScope.username}${p g p } ${requestScope.username} ${sessionScope.username} ${applicationScope.username}

Example:${sessionScope shopping Cart[0]} ${sessionScope.shopping-Cart[0]}

${sessionScope.shoppingCart[1]}


How to read request parameters?

Simply by :${param name} ${param.name}

${paramValues.name} Example Example

Wow, I know a lot about you...Your name is ${param.username}/> Your name is ${param.username}/>.Your password is ${param.pw}/>.You are ${param.gender}/>.p ${p g } p


Accessing other data with EL

Implicit Objects supported by JSTLki JSTL d t i t t ki cookie: JSTL doesnt give you a way to set cookies

(backend job) but u can retrieve cookies. header: read all client headerheader: read all client header headerValues: all values initParam: to access initialization parametersinitParam: to access initialization parameters pageContext: more details about your page


Page Context elements


Page Context elements (contd)


Mathematical operators supported by EL


Comparisons supported by EL


Comparisons supported by EL (contd)

Take care : ${ } must include the entire expression. E l f i lid t t t Example of invalid statments:

${ ${user.weight} gt ${user.IQ} }${user weight} gt ${user IQ} ${user.weight} gt ${user.IQ}

Only we can say : ${user weight gt user IQ}${user.weight gt user.IQ}

Boolean operations and parentheses ${ (param.month == 5 or param.month == 6) and${ (param.month 5 or param.month 6) and

(param.day == 25) }


To check if a certain parameter exists?

Use the keyword : empty Example:

${empty param.choice} ${empty sessionScope.userName}


Core Package (cont.)

Now back to core package.


Used for printing results of expressions Example: Example:

c:out value ${username} default Nobody /

Nothing


Used mainly to create scoped variables Example:p

t l "${4 * 2}"/


Used to delete data E l Example:

Unlike other jstl tags , it will not propagate across scopes if not found.


This action allows you to catch an error in your page,

int zero = 0;

out.write(3/zero);


Controlling flow with conditions

The tag evaluates its test attribute, and if this expression evaluates to false the page skips theexpression evaluates to false, the page skips the body of the tag. On the other hand, if the expression ends up being true.p p g

The body is processed normally. This body can contain any valid JSP code, including text, HTML tags or other JSP tagstags, or other JSP tags.


(contd)

You can use tags anywhere in your pageeven in the middle of an HTML tag.

Example:

color="red"

/c:if


Nested tags

Example:

IIm sorry,

DrDr.

,but you have committed a fatal error.


Complex conditional tags

Mutually exclusive conditions with and ,, and . similar to switch statements

The tag is simple: it takes no attributesThe c:choose tag is simple: it takes no attributes and serves only as a container

for and tags. Just as HTMLs g tag makes no sense outside a , and make no sense outside

ha .


Complex conditional tags (contd)

The tag is similar to : it takes a single test attribute.

For each tag, no more than one child tag can succeed tag can succeed.

succeeds only if all its sibling succeeds only if all its sibling tags (those with the same parent tag) have failed.failed.


Example

Error 1 has occurred.



Everything is fine.

/ h i


Rules for using the complex conditional tags

1 h d th i t t1- and tags cannot appear outside a tag.

2- Theres a flip side to this rule: a tag cannot2- There s a flip side to this rule: a tag cannot have any direct children (or nonwhite space text) except or tags.

3- If occurs, it must follow all the tags; it may not come before any of them.

4 Every must have at least one and4- Every must have at least one and no more than one .


Example on Invalid Syntax

hiiiiiiiiiiiiiiiiiii


Controlling flow with loops

lets you loop over nearly any sensible collection of items that the expression language returnsexpression language returns

Example:

accepts: Arrays Arrays Collection variables (including Lists and Sets), Maps, Iterators, and Enumerations. simple strings.simple strings.


Iterating over strings with

We can parse strings as followsf T k it " b " d li " "

can be used with comma delimeter only:


Advanced usage for iteration tags and .

you can determine information about the current items position within the overall loop: is it first, last, or somewhere in the middle?somewhere in the middle?

You can loop over only a part of collection using index


Example

< t l "${l tt }"/>

f E h b i "1" d "5" " t"

/ f E h


Advanced usage for iteration tags and (contd)

Looping tags also support a varStatus attribute that lets you recover information about where you are in the overall iterationthe overall iteration


It supercedes , providing all the functionality of the core JSP tag but also adding new features lets you store the retrieved text in a scopedfeatures, lets you store the retrieved text in a scoped variable instead of printing it.


Example

You can retrieve files from another web application by specifying that web applications name using the

i t t t t tt ib t tags context attribute.


Communicating with imported pages

The tag is used to send parameters to the requested page


To redirect to another resource


Database Package

We have to use : uri="http://java.sun.com/jstl/sql" %>

Sh ld JSP t t t d t b ? Should we use JSP to connect to database?

Wh d b i JSP ? When to use database in JSP ?


Two architectures are available


Setting up a database connection you can decide to expose a scoped variable that

t th d t brepresents the database


Example


Used to perform queries with


Example

SELECT * FROM CUSTOMERS

(contd)

A i t d t t l d Accessing metadata : u can get column names and row count through rowCount, columnNames attributes .

Example:Example:

SELECT NAME, IQ FROM USERS WHERE IQ > 120

tr


Examples

Example


Formatting and internationalizationPackage

Import it using :

Used to Printing numbers Differ than :Differ than :

Provide some control on how numbers are printed tag can automatically sense thefmt:formatNumber tag can automatically sense the

browser locale and customize its output. Example:

The output would be:

United States 500,000.01 France 500 000,01

G 500 000 01 Germany 500.000,01 Switzerland 500'000.01


attributes


Used to print date Used to print date Example

United States May 20, 2002United States May 20, 2002 France 20 mai 2002 Germany 20.05.2002 Netherlands 20-mei-2002 Spain 20-may-2002


Useful only if you need to retrieve a numeric value from a string


Useful to convert a string to a date format


Used to override locales


List of different Locales


Resource bundles

To define a collection of files used for internationalize your website


References & Recommended Reading

Core servlets and JSP

Java for the Web with Servlets, JSP, and EJB

Manning JSTL in Action

Sun presentations

Oracle presentations

SCJWD study guide


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