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JSP Standard Tag Library
JSTL JSP Standard Tag Library 24-Nov-18
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What is JSTL? JSTL (JSP Standard Tag Libraries) is a collection of JSP custom tags developed by Java Community Process, The reference implementation is developed by the Jakarta project, jakarta.apache.org. Full JSTL – Contains many common and useful JSP custom tags – Particularly useful when you are using MVC, but the data contains a varying number of entries – Based on the Struts looping and logic tags. JSTL allows you to program your JSP pages using tags, rather than the scriptlet code that most JSP programmers are already accustomed to. JSTL can do nearly everything that regular JSP scriptlet code can do.
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count to ten Example Using scriptlet:
JSTL was introduced to allow JSP programmers to program using tags rather than Java code. To show why this is preferable, a quick example is in order. We will examine a very simple JSP page that counts to ten. (count1.jsp) We will examine this page both as regular scriptlet-based JSP, and then as JSTL. When the count to ten example is programmed using scriptlet based JSP, the JSP page appears as follows.` <html> <head> <title>title>Count to 10 in JSP scriptlet</title> </head> <body> <% for(int i=1;i<=10;i++) {%> <%= i %><br/> <% } %> </body> </html>
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As you can see from the preceding example, using scriptlet code produces page source code that contains a mix of HTML tags and Java statements. The primary reason that it is not optimal to mix scriptlet and tag- based code is readability. JSTL allows the human programmer to look at a program that consists entirely of HTML and HTML-like tags.
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count to ten Example Using JSTL:
The following code shows how the count to ten example would be written using JSTL. As you can see, this code listing is much more constant, as only tags are used. HTML and JSTL tags are mixed to produce the example. count2.jsp taglib uri=" prefix="c" %> <html> <head> <title>Count to 10 Example (using JSTL)</title> </head> <body> <c:forEach var="i" begin="1" end="10" step="1"> <c:out value="${i}" /> <br /> </c:forEach> </body> </html>
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Count3.jsp – JSTL and GET taglib prefix="c" uri=" %> <HTML> <HEAD> </HEAD> <BODY> <c:set var="n" value="${param.number}" /> Hello ...Printing numbers till N= <c:out value="${n}"/> <br/> <c:forEach var="i" begin="1" end="${n}" step="1"> <c:out value="${i}"/> </c:forEach> </BODY>
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The JSTL Tag Libraries The JavaServer Pages Standard Tag Library (JSTL) is a collection of useful JSP tags which encapsulates core functionality common to many JSP applications. JSTL is often spoken of as a single-tag library. JSTL has support for common, structural tasks such as iteration and conditionals, tags for manipulating XML documents, internationalization tags, and SQL tags. It also provides a framework for integrating existing custom tags with JSTL tags. The JSTL tags can be classified, according to their functions, into following JSTL tag library groups that can be used when creating a JSP page:
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Core Tags Formatting tags SQL tags XML tags JSTL Functions
The JSTL Tag Libraries The JSTL tags can be classified, according to their functions, into following JSTL tag library groups that can be used when creating a JSP page: Core Tags Formatting tags SQL tags XML tags JSTL Functions
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The JSTL Tag Libraries Core Tag Library—Contains tags that are essential to nearly any Web application. Examples of core tag libraries include looping, expression evaluation, and basic input and output. Formatting/Internationalization Tag Library—Contains tags that are used to parse data. Some of these tags will parse data, such as dates, differently based on the current locale. Database Tag Library—Contains tags that can be used to access SQL databases. These tags are normally used only to create prototype programs. This is because most programs will not handle database access directly from JSP pages. Database access should be embedded in EJBs that are accessed by the JSP pages. XML Tag Library—Contains tags that can be used to access XML elements. Because XML is used in many Web applications, XML processing is an important feature of JSTL. JSTL Functions --JSTL includes a number of standard functions, most of which are common string manipulation functions.
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Core Tags: The core group of tags are the most frequently used JSTL tags. Following is the syntax to include JSTL Core library in your JSP: taglib prefix="c" uri=" %> There are following Core JSTL Tags: Tag Description <c:out > Like <%= ... >, but for expressions. <c:set > Sets the result of an expression evaluation in a 'scope' <c:remove > Removes a scoped variable (from a particular scope, if specified). <c:catch> Catches any Throwable that occurs in its body and optionally exposes it. <c:if> Simple conditional tag which evalutes its body if the supplied condition is true. <c:choose> Simple conditional tag that establishes a context for mutually exclusive conditional operations, marked by <when> and <otherwise> <c:when> Subtag of <choose> that includes its body if its condition evalutes to 'true'. <c:otherwise > Subtag of <choose> that follows <when> tags and runs only if all of the prior conditions evaluated to 'false'. <c:import> Retrieves an absolute or relative URL and exposes its contents to either the page, a String in 'var', or a Reader in 'varReader'. <c:forEach > The basic iteration tag, accepting many different collection types and supporting subsetting and other functionality . <c:forTokens> Iterates over tokens, separated by the supplied delimeters. <c:param> Adds a parameter to a containing 'import' tag's URL. <c:redirect > Redirects to a new URL. <c:url> Creates a URL with optional query parameters
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JSP - Expression Language (EL)
A primary feature of JSP technology is its support for an expression language (EL). An expression language makes it possible to easily access application data stored in JavaBeans components. For example, the JSP expression language allows a page author to access a bean using simple syntax such as ${name} for a simple variable or ${name.foo.bar} for a nested property from objects/bean JSP EL allows you to create expressions both (a) arithmetic and (b) logical. Within a JSP EL expression, you can use integers, floating point numbers, strings, the built-in constants true and false for boolean values, and null.
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Simple Syntax: Typically, when you specify an attribute value in a JSP tag, you simply use a string. For example: <jsp:setProperty name="box" property="perimeter" value="100"/> JSP EL allows you to specify an expression for any of these attribute values. A simple syntax for JSP EL is as follows: ${expr} Here expr specifies the expression itself. The most common operators in JSP EL are . and [ ]. These two operators allow you to access various attributes of Java Beans and built-in JSP objects. For example above syntax <jsp:setProperty> tag can be written with an expression like: <jsp:setProperty name="box" property="perimeter" value="${2*box.width+2*box.height}"/> When the JSP compiler sees the ${} form in an attribute, it generates code to evaluate the expression and substitues the value of expresson.
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Simple Syntax: You can also use JSP EL expressions within template text for a tag. For example, the <jsp:text> tag simply inserts its content within the body of a JSP. The following <jsp:text> declaration inserts <h1>Hello JSP!</h1> into the JSP output: <jsp:text> <h1>Hello JSP!</h1> </jsp:text> You can include a JSP EL expression in the body of a <jsp:text> tag (or any other tag) with the same ${} syntax you use for attributes. For example: <jsp:text> Box Perimeter is: ${2*box.width + 2*box.height} </jsp:text> EL expressions can use parentheses to group sub expressions. For example, ${(1 + 2) * 3} equals 9, but ${1 + (2 * 3)} equals 7.
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The test attribute of the following conditional tag is supplied with an EL expression that compares the number of items in the session-scoped bean named cart with 0: <c:if test="${sessionScope.cart.numberOfItems > 0}"> ... </c:if> The JSP expression evaluator is responsible for handling EL expressions, which are enclosed by the ${ } characters and can include literals. Here's an example: <c:if test="${bean1.a < 3}" > ... </c:if> Any value that does not begin with ${ is treated as a literal and is parsed to the expected type using the PropertyEditor for the type: <c:if test="true" > ... </c:if> Literal values that contain the ${ characters must be escaped as follows: <mytags:example attr1="an expression is ${'${'}true}" />
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Basic Operators in EL: JSP Expression Language (EL) supports most of the arithmetic and logical operators supported by Java. Below is the list of most frequently used operators: Operator Description . Access a bean property or Map entry [] Access an array or List element ( ) Group a subexpression to change the evaluation order + Addition - Subtraction or negation of a value * Multiplication / or div Division % or mod Modulo (remainder) == or eq Test for equality != or ne Test for inequality < or lt Test for less than > or gt Test for greater than <= or le Test for less than or equal >= or gt Test for greater than or equal && or and Test for logical AND || or or Test for logical OR ! or not Unary Boolean complement empty Test for null, empty String, array or Collection. func(args) A function call
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Arithmetic operators Few more examples on arithmetic operations.
Before JSP2.0/JSTL <%! int k = 0; %> <% k = ; out.println("value of k is.."+k); Using JSP2.0/JSTL (without using scriptlet) value of k is ${ } Few more examples on arithmetic operations. EL Expression Result ${ } O/P: 30.5 ${ } O/P: -60 ${20 * 2} O/P: 40 ${3/4} O/P: 0.75 ${3 div 4} O/P: 0.75 ${10/0} O/P: Infinity ${50%8} O/P: 2 ${50 mod 8} O/P: 2 ${(10==20) ? "true" : "false"} O/P: false
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guess.jsp – JSTL POST, EL and implicit object if else using JSTL
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JSTL and EL operations jsp:useBean and scope
Page viewpagebean.jsp Request CreateBeanRequestServlet viewrequestbean.jsp Session viewsessionbean.jsp c:forEach and jsp:useBean – populate in table foreachpage.jsp CreateBeanRequestForEachServlet foreachrequest.jsp CreateBeanSessionForEachServlet foreachsession.jsp
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