JSTL ( )

Transcription

1 JSTL JSTL JSTL (Java Standard Tag Library) is a collection of custom tags that are developed by the Jakarta project. Now it is part of the Java EE specication. To use them you need to download the appropriate jar and tld les for the tags. They are provided with IDE's like NetBeans but if you explicitly need them for some reason you can nd links in You store the.jar les in WEB-INF/lib and the.tld les in your WEB-INF. ( )

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

3 To use the taglibs, you need to add taglib denitions to your web.xml le. 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> ( )

4 Note that the <taglib> tag is a subtag of <jsp-cong> and therefore has to be placed within its parent tag. And the same in all JSP's that uses these libs: <%@taglib prex="c" uri=" <%@taglib prex="x" uri=" c and x are standard prexes for core and xml. Note that the URI's are predened that must be used. You cannot change these, you can change the prex. ( )

5 Tags in the core library, prex c. <c:out> Evaluates an expression and outputs the result to a JspWriter. ( )

6 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> ( )

7 Examples <c:out value=${5 + 2*(3.3-2)}" /> will output the value 7.6 ( )

8 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 thename names. ( )

9 <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> ( )

10 The rst 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. ( )

11 <c:set> Sets the value of a scoped variable within the selected scope There are some versions of this tag: Set the value from an expression <c:set value="value" var="varname" [scope="{page request session application}"]/> ( )

12 Set the value using the body content <c:set var="varname" [scope="{page request session application}"]> value </c:set> ( )

13 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> ( )

14 <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 ( )

15 <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 ( )

16 <c:if> Evaluates its body if the expression specied evaluates to true. Without a body, it stores the value of the condition in the variable ( )

17 <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> ( )

18 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> ( )

19 <c:choose> Provides the context for mutually exclusive conditional expressions. <c:choose>} body content, ( <when> or <otherwise> subtags) </c:choose> ( )

20 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. At most one of the subtags in the body will be processed. ( )

21 <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 rst <when> subtag that evaluates its condition to true will be executed. ( )

22 <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. ( )

23 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> ( )

24 Will output <h2>number is positive </h2> Using <choose> you can construct if-then-else tests. ( )

25 <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. ( )

26 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> ( )

27 Examples: <c:foreach var = "i" begin="1" end = "10" step = "2"> <p> looping : <c:out value="${i}"/> </p> </c:foreach> ( )

28 Will print <p>looping : 1</p> <p>looping : 3</p> <p>looping : 5</p> <p>looping : 7</p> <p>looping : 9</p> ( )

29 Another example, looping through an array. We create an array and store it into the page scope, then we iterate through it. <% // 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> ( )

30 It will give us: looping : 4 looping : -5 looping : 3 looping : 8 looping : 23 looping : 2 looping : 45 ( )

31 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> ( )

32 Since I haven't imported java.util I have to use a fully qualied name for LinkedList. I could have used <%@ page import=java.util.*"%> at the top of my page ( )

33 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 dierent iteration control information that you can use. The count attribut show the looping index. ( )

34 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. ( )

35 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 ( )

36 Using this you can for example iterate through the session <c:foreach var = "next" varstatus="status" items="${sessionscope}"> Looping through the session <c:out value="${next.key}"/>: <c:out value="${next.value}"/><br> </c:foreach> ( )

37 <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> ( )

38 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> ( )

39 will print Tokensizing : 23 Tokensizing : 34 Tokensizing : 43 Tokensizing : 34 Tokensizing : 43 Tokensizing : -45 Tokensizing : -5 ( )

40 <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> Can import from outside the application, the jsp:include tag cannot do this. ( )

41 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/> ( )

42 <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}"]/> ( )

43 With a body <c:url value = "value" [context = "context"] [var = "varname"] [scope="{page request session application}"]> <c:param> subtags </c:url> ( )

44 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 ( )

45 The I18n tag library is used to develop applications that can be adapted to various languages and regions. This includes language and dierent formatting rules. ( )

46 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. ( )

47 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. ( )