JSTL. JSTL (Java Standard Tag Library) is a collection of custom tags that are developed and maintained by the Jakarta project.

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1 JSTL JSTL (Java Standard Tag Library) is a collection of custom tags that are developed and maintained by the Jakarta project. To use them you need to download the appropriate jar and tld files for the tags. You can find links in You store the.jar files in WEB-INF/lib and the.tld files in your WEB-INF. JSTL 3 February

2 JSTL is one Tag Library but divided into four parts, each with its own tld-file. Core, the basic tags XML processing, xml processing and conversions I18N, internationalization SQL, database access JSTL 3 February

3 To use the taglibs, you need to add taglib definitions to your web.xml file. This shows the core and the xml taglibraries. <taglib> <taglib-uri> </taglib-uri> <taglib-location> /WEB-INF/c.tld </taglib-location> </taglib> <taglib> <taglib-uri> </taglib-uri> <taglib-location> /WEB-INF/x.tld </taglib-location> </taglib> JSTL 3 February

4 And the same in all JSP s that uses these libs: <%@taglib prefix= c uri= %> <%@taglib prefix= x uri= %> c and x are standard prefixes for core and xml. JSTL 3 February

5 Tags in the core library, prefix c. <c:out> Evaluates an expression and outputs the result to a JspWriter. It can take two forms, with or without a body <c:out value= expression [default= defaultvalue ] [escapexml= {true false} ]/> or <c:out value= expression [escapexml= {true false} ]> default value </c:out> JSTL 3 February

6 Examples <c:out value= ${5 + 2*(3.3-2)} /> will output the value 7.6 and (assuming that name has a value) <c:out value= ${name} default= hugobald /> <c:out value= ${names} default= hugobald /> will output Putte hugobald This is because there is an attribute (scoped variable) called name in my page context, but none with the name names. JSTL 3 February

7 <c:out value= ${name == \ Fido\ } default= false /><br> <c:out value= ${names} escapexml= true > <xml-tag> text </xml-endtag> </c:out> will output false <xml-tag> text </xml-endtag> The first example compares the strings Putte and Fido. They are clearly not equal. The second example fails because there is no names attribute. Thus the body will be used as default, the < and > are escaped into < and > to pass through the processing. JSTL 3 February

8 <c:set> Sets the value of a scoped variable within the selected scope The are some versions of this tag: Set the value from an expression <c:set value= value var= varname [scope= {page request session application} ]/> Set the value using the body content <c:set var= varname [scope= {page request session application} ]> value </c:set> Set a property of a target object (bean or map) <c:set value= value target= target property= propertyname /> Same with a body <c:set target= target property= propertyname > value </c:set> JSTL 3 February

9 <c:set value= eberhard var= names /> <c:out value= ${names} default= hugobald /> Will create and set the variable names in the page scope. The output will be: eberhard JSTL 3 February

10 <c:remove> removes a scoped variable <c:remove var= varname [scope= {page request session application} ]/> Example <c:remove var= names /> <c:out value= ${names} default= hugobald /> will output hugobald JSTL 3 February

11 <c:if> Evaluates its body if the expression specified evaluates to true. Without a body, stores the value of the condition in the variable <c:if test= condition var= varname [scope= {page request session application} ]/> With a body <c:if test= condition [var= varname ] [scope= {page request session application} ]> body </c:if> JSTL 3 February

12 Example: <c:set value= ${4.5} var= number /> <c:if test= ${number > 4} > <h2>number is greater than 4</h2> </c:if> <c:if test= ${number < 4} > <h2>number is less than 4</h2> </c:if> Will output <h2>number is greater than 4</h2> JSTL 3 February

13 <c:choose> Provides the context for mutually exclusive conditional expressions. <c:choose> body content, (<when> or <otherwise> subtags) </c:choose> There are one or more <when> subtag in the body, they must occur before the <otherwise> subtag. There are zero or one <otherwise> subtag. Must be the last action. A most one of the subtags in the body will be processed. JSTL 3 February

14 <c:when> subtag in the choose tag <c:when test= condition > body content </c:when> Can only occur directly inside a choose tag. Within a <choose>, the first <when> subtag that evaluates its condition to true will be executed JSTL 3 February

15 <c:otherwise> Represents the optional last alternative in a <choose> tag. <c:otherwise> body content </c:otherwise> Can only occur within a <choose> tag. Must be the last subtag. If none of the preceeding <when> subtags evalutates to true, the <otherwise> subtag will be executed. JSTL 3 February

16 Example <c:choose> <c:when test= ${number < 0} > <h2> number is negative </h2> </c:when> <c:when test= ${number == 0} > <h2> number is zero </h2> </c:when> <c:otherwise> <h2> number is positive </h2> </c:otherwise> </c:choose> Will output <h2>number is positive </h2> Using <choose> you can construct if-then-else tests. JSTL 3 February

17 <c:foreach> The <foreach> tag iterates over a java.util.collection (e. g. Vector, Set, LinkedList) or a java.util.map (e. g. HashMap) It can also iterate through an array of objects or primitive types. You can also do a traditional for, i. e. looping from a start value to an end value without an underlying datastructure. With a collection or array <c:foreach [var = varname ] items= collection [varstatus = varstatusname ] [begin= begin ] [end = end ] [step= step ] > body content </c:foreach> or without a collection <c:foreach [var = varname ] [varstatus = varstatusname ] begin= begin end = end [step= step ] > body content </c:foreach> JSTL 3 February

18 Examples: <c:foreach var = i begin= 1 end = 10 step = 2 > <p> looping : <c:out value= ${i} /> </p> </c:foreach> Will print <p>looping : 1</p> <p>looping : 3</p> <p>looping : 5</p> <p>looping : 7</p> <p>looping : 9</p> JSTL 3 February

19 Another example, looping through an array <% %> // create an array of integers int [] intarr = {4, -5, 3, 8, 23, 2, 45}; pagecontext.setattribute( intarr, intarr); <br> <c:foreach var = next items= ${intarr} > looping : <c:out value= ${next} /><br> </c:foreach> We create an array and store it into the page scope, then we iterate through it. It will give us: looping : 4 looping : -5 looping : 3 looping : 8 looping : 23 looping : 2 looping : 45 JSTL 3 February

20 And: <% %> // create a Linkedlist java.util.linkedlist l = new java.util.linkedlist(); l.addlast(new Integer(4)); l.addlast(new Integer(-5)); l.addlast(new Integer(3)); l.addlast(new Integer(8)); l.addlast(new Integer(23)); l.addlast(new Integer(2)); l.addlast(new Integer(45)); pagecontext.setattribute( linked, l); <c:foreach var = next varstatus = status items= ${linked} > <c:out value= ${status.count} /> looping through a linked list : <c:out value= ${next} /><br> </c:foreach> Since I haven t imported java.util I have to use a fully qualified name for LinkedList. I could have used <%@ page import= java.util.* %> at the top of my page JSTL 3 February

21 The output will look like 1 looping through a linked list : 4 2 looping through a linked list : -5 3 looping through a linked list : 3 4 looping through a linked list : 8 5 looping through a linked list : 23 6 looping through a linked list : 2 7 looping through a linked list : 45 The status object contains different iteration control information that you can use. The count attribut show the looping index. JSTL 3 February

22 and one more using a Map <% // create a HashMap java.util.hashmap m = new java.util.hashmap(); m.put( name, Nisse Nilsson ); m.put( address, Storgatan 12A ); m.put( age, new Integer(45)); m.put( smokes, new Boolean(true)); %> pagecontext.setattribute( map, m); <c:foreach var = next varstatus = status items= ${map} > looping through a map : <c:out value= ${next.key} /> : <c:out value= ${next.value} /> <br> </c:foreach> Remember that maps aren t sorted. JSTL 3 February

23 will print looping through a map : age : 45 looping through a map : smokes : true looping through a map : address : Storgatan 12A looping through a map : name : Nisse Nilsson JSTL 3 February

24 <c:fortokens> Iterates over tokes, separated by the supplied delimiters. <c:fortokens items = stringoftokens delims = delimiters [var = varname ] [varstatus = varstatusname ] [begin = begin ] [end = end ] [step = step ] > body content </c:fortokens> JSTL 3 February

25 Example <% %> String numbers = 23,34,43,34,43,-45,-5 ; pagecontext.setattribute( num,numbers); <c:fortokens items = ${num} delims=, var = next > Tokensizing : <c:out value = ${next} /><br> </c:fortokens> will print Tokensizing : 23 Tokensizing : 34 Tokensizing : 43 Tokensizing : 34 Tokensizing : 43 Tokensizing : -45 Tokensizing : -5 JSTL 3 February

26 <c:import> Imports the content of a URL-based resource <c:import url = url [context = context ] [var = varname ] [scope= {page request session application} ] [charencoding = charencoding ]> optional body content for the <c:param> subtags </c:import> JSTL 3 February

27 Examples, an absolut URL <c:import url = /> will include the content of this URL into the current page. or a relative URL <c:import url = index.jsp /> JSTL 3 February

28 <c:url> Builds a URL with the proper rewriting rules applied. Without a body <c:url value = value [context = context ] [var = varname ] [scope= {page request session application} ]/> With a body <c:url value = value [context = context ] [var = varname ] [scope= {page request session application} ]> <c:param> subtags </c:url> JSTL 3 February

29 Examples <c:url value = index.jsp > <c:param name = name value = Donald Duck /> <c:param name = address value = Höganäsgatan 32 /> </c:url> produce this: index.jsp?name=donald+duck&address=h%c3%b6gan%c3%a4sgatan+32 JSTL 3 February

30 The I18n tag library is used to develop applications that can be adapted to various languages and regions. This includes language and different formatting rules. JSTL 3 February

31 The SQL-tags are used to access relational databases through tags. It us usually better to use Beans for this but simple application can use JSP s directly. JSTL 3 February

32 The XML actions are used to work with XML and to translate XML into something else like HTML We will discuss this when discussing XML in general. JSTL 3 February