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ATIJ EL + JSTL 1/32

EL + JSTL

Advanced Topics in Java

Khalid Azim [email protected]

http://www.ii.uib.no/~khalid/atij/

Version date: 2006-09-04

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Overview

Accessing Java Code using JSP Expression Language (EL)

Introduction to using JSP Standard Tag Library (JSTL) in JSP Pages


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Accessing Java Code using JSP Expression Language (EL)

Simplifies using the "Pull Model".

Provides a navigational notation to pull information from the model and into a JSPpage.

Makes using the server state easier in a JSP page. The expression language automatically handles typecasting, nullvalues, and error

handling.

Notation for evaluating and returning the textual representation of values that arestored in the standard scopes:

${ expression }

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Topics on JSP EL

Activating EL Evaluation

Accessing Attributes in the Standard Scopes

Accessing Properties of Beans stored as Attributes in the Standard Scopes

Accessing Collections stored as Attributes in the Standard Scopes

Using EL Implicit Objects

Using EL Operators

EL Conditional Evaluation


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Activating EL Evaluation

The web.xmlfile should be compatible with JSP 2.0:

Shopping ...

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EL Syntax

Syntax: ${ expression }

The result of expression evaluation replaces the expression and its delimiters.

EL expressions are comprised of literals, operators and variables.

Used in template text and within tags:

Thevalue of an attribute stored in a scopecan be accessed in an EL expression.

The value of an attribute in tags/elementscan be specified by an EL expression.

Functionscan also be called from EL expressions (covered later in these notes). To escape ${, use \${.


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Accessing Attributes in the Standard Scopes

The variables in EL expressions can reference attributes that are stored in thestandard scopes.

The variable is looked up in the standard scopes in the following order: page, request,

session, or application. The first match is returned. If no match, return null.

The value of the variable is converted to a string if necessary by calling thetoString()method.

User name: ${username}

User name: ${sessionScope.username}

are equivalent to:

User name:

Standard Scope EL Implicit Object with Attributes from the Standard Scope (Maps)

page pageScope

request requestScope

session sessionScope

application applicationScope

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Accessing Properties of Beans stored as Attributes in the StandardScopes

Syntax: ${ beanAttr.prop1.prop2. ....propk}

All propiare legal Java identifier.

The dot operator allows navigating from one property to another every time it is usedin an expression.

${userinfo.username}

${userinfo.address.street}

${userinfo.address.zipcode}


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Accessing Collections stored as Attributes in the Standard Scopes

If the attribute is an array, a List or a Map, then the following syntax can be used:

${ beanAttr[indexValue] }

${userTab[0]}

${userTab["0"]}

${userTab.0}

${itemList[0]}

${callMap["Monday"]}

${callMap[Monday]}


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EL Implicit Object (cont.)

Getting the HTTP request method.

${request.method} ${requestScope.method}

${pageContext.request.method}


Using EL Operators

Used for simple tasks related to presentation logic.

Operators have the standard precedence and associativity rules.

EL expressions with only literals and operators are evaluated as arithmeticexpressions.

Predefined EL literals: true, false, null.

Type of

Operators Operators Example Result

Indexing [].( )

${initparam["dt_table"]}${array["0"]}${initparam.dt_table}${ 2 * (3 + 4)}

Arithmetic -* / div% mod+ -

${1 + 2 * 3}${"10" + 2}${100 % 98}${var * 2}

7122var coerced to number beforeoperation


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Relational == eq!= ne< lt

> gt= ge

${obj == obj}${2 == 3}${obj == null}

${bigI == bigJ}${obj1 == obj2}${"10" < "2"}

truefalsefalse

dep. on compareTo(bigI, bigJ)value of obj1.equals(obj2)true

Logical && and|| or! not

${obj1 != null && obj2 != null}${!(2 == 3)} true

The EmptyOperator

empty ${empty null}${empty attr.prop}

true

trueif attr.propis null, an emptystring, an empty array, an emptymap, or an empty collection, i.e

an empty container.The TernaryOperator

test ?trueExpr :falseExpr

${(shopping.total > 1000)? "Esteemed Customer": "Dear Customer" }

Dependent on the test.

Type ofOperators

Operators Example Result


null-friendly JSP EL

In expressions containing dot or []operators, an undefined variable is treated ashaving the nullvalue.

In arithmetic and relational expressions, an undefined variable is treated as 0(zero).

In logical expressions, an undefined variable is treated as false.

${ying}

${ying.yang}

${10 - yang}

${10 / yang}

${10 % yang}

${10 < yang}

${not yang}


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Implementing JSP EL Functions

1. Implement a Java class with a publicstaticmethod.

Can have a non-empty parameter list, and is normally declared as non-void.

The class file is installed in /WEB-INF/classesdirectory

2. Create a Tag Library Descriptor (TLD) file specifies a mapping between the functionand the JSP page.

The element is used to specify the pertinent information.

A subelement specifies the name that will be used in a JSP page.

A subelement specifies the name () that will be used to invokethe function from a JSP page, the class of the function () , thesignature of the method () .

The TDL file has a .tldextension and can be installed in /WEB-INFdirectory.

3. Create a taglibdirective in the JSP page.

The prefixattribute specifies the namespacefor invoking the method.

The uriattribute value matches the one in the TLD file.

4. Invoke the EL function from the JSP page.

${namespaceInTaglibDirective:nameinTLD()}


Example: JSP EL function (ELFunctionapplication)

The TLD file (DatingFunction.tld) 1.2 /mughal/data dateMe kam.DateWrapper java.util.Date getDate()

The class (DateWrapper.java)implementing the function

package kam;import java.util.Date;public class DateWrapper{ public static Date getDate(){ return new Date(); }}

The JSP file (callingDateFunction.jsp) Calling EL Function Calling EL Function ${kam:dateMe()}


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Introduction to using JSP Standard Tag Library (JSTL) in JSP Pages

The Core Library:

The Formatting Library:

The SQL Library:

The XML Library:


Installing JSTL 1.1

From TOMCAT_HOME\webapps\jsp-examples\WEB-INF\lib, copy the following filesto myApp\WEB-INF\lib:

- jstl.jar

- standard.jar

These jarfiles can also be installed in TOMCAT_HOME\shared\lib, so that allapplications can share them.


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Core JSLT

General purpose

Output:

Set property:

Removing attributes: Exception handling:

Conditionals

Conditional Include:

Multiple Choice: , ,

URL-related

Importing:

URL rewriting:

Redirecting:

Parameter passing:

Iteration

Iteration:

Tokenizing:


The Tag

Version for setting attribute variables:

or

...value inside body...

Version for setting bean propertiesandMap values:

or

...value inside body...

The targetmust evaluate to a reference.


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myJSTLExamples

JSTL Examples

1:

2:

3:

4:

5:

6: ${myShoes}

7:

8:


9:

--%>

10:

Output in browser window:

1: Hello2: Shoes Ekin 999.9 13: Wednesday4: attribute in session5: Shoes sadida 999.9 16: Shoes sadida 999.9 17: Shoes sadida 999.9 18: Shoes sadida 999.9 19: {2=Tuesday, 4=Thursday, 6=Saturday, 1=Monday, 3=Wednesday, 7=Sunday, 5=Friday}

10: {2=Tuesday, 4=Thursday, 6=Saturday, 1=Monday, 3=Wednesday, 7=FREE DAY, 5=Friday}


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The Tag

Used to iterate over the elements in an iterable: an array, Collection, Map, ResultSetor a comma-separated Strings.

${anItem.property}

...

See files forEachTag.jspand kam.Item.javain myJSTLExamplesapplication.

Examples:

The loop

${item}

prints: en

to

tre

fire


The loop

Item no. ${itemLoopCount.count}:

${item.itemName}

${item.itemDescription}

${item.price}

${item.quantity}

prints:Item no. 1: Shoes Ekin 999.9 10

Item no. 2: Shirt Van Heusen 9.9 30

Item no. 3: Shampoo Simple 99.9 15

Item no. 4: Socks Golden Toe 900.0 9

Item no. 5: Suit Armani 49.9 17

An optional attribute called varStatuscan be defined. It provides access to theiteration number.

forEach-loops can be nested.


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The Tag

Allows the contents of its body to be executed or skipped, depending on the testcondition. Note there is no tag.

...if-body...

Example: See file conditionalTags.jspin myJSTLExamplesapplication.

Item no. ${itemLoopCount.count}:

${item.itemName}

${item.itemDescription}

${item.price}

${item.quantity}

Output:Item no. 2: Shirt Van Heusen 9.9 30

Item no. 4: Socks Golden Toe 900.0 9


The Multiple Choice Tags: , ,

Allows the body of only onetag to be executed.

If none of the tags match, the body of the tag is executed.

There is no fall-through.

...

...

...

...

...


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Example: See file conditionalTags.jspin myJSTLExamplesapplication.

The following code:

HOLIDAY

HOLIDAY

${day}

generates:

Monday Tuesday Wednesday Thursday Friday HOLIDAY HOLIDAY


Example: the myELShop application

The myELShopweb application is a rewrite of the myEShopapplication using EL andJSTL.

See the following files for the myELShopweb application:

index.html,WEB-INF\web.xml,WEB-INF\src\kam\shopping\Item.java,WEB-INF\src\kam\shopping\ELShoppingServlet.java,

ELShop.jsp,ELCart.jsp, ELCheckout.jsp,ELError.html myELShop.xml


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JSTL Libraries Overview

CORE LIBRARY FORMATTING LIBRARY XML LIBRARY SQL LIBRARY

GENERAL PURPOSE INTERNATIONALIZATION CORE XML DATABASE

XML FLOW

CONDITIONAL

FORMATTING

URL-RELATED TRANSFORMATION


ITERATION

CORE LIBRARY FORMATTING LIBRARY XML LIBRARY SQL LIBRARY

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Atij More Jsp II 2x1