I need to hide an element if certain values are present in the JSP
The values are stored in a List so I tried:
<c:if test="${ mylist.contains( myValue ) }">style='display:none;'</c:if>
But, it doesn't work.
How can I evaluate if a list contains a value in JSTL, the list and the values are strings.
there is no built-in feature to check that - what you would do is write your own tld function which takes a list and an item, and calls the list's contains() method. e.g.
//in your own WEB-INF/custom-functions.tld file add this
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
"http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version="2.0"
>
<tlib-version>1.0</tlib-version>
<function>
<name>contains</name>
<function-class>com.Yourclass</function-class>
<function-signature>boolean contains(java.util.List,java.lang.Object)
</function-signature>
</function>
</taglib>
Then create a class called Yourclass, and add a static method called contains with the above signature. I m sure the implementation of that method is pretty self explanatory:
package com; // just to illustrate how to represent the package in the tld
public class Yourclass {
public static boolean contains(List list, Object o) {
return list.contains(o);
}
}
Then you can use it in your jsp:
<%@ taglib uri="/WEB-INF/custom-functions.tld" prefix="fn" %>
<c:if test="${ fn:contains( mylist, myValue ) }">style='display:none;'</c:if>
The tag can be used from any JSP in the site.
edit: more info regarding the tld file - more info here
Sadly, I think that JSTL doesn't support anything but an iteration through all elements to figure this out. In the past, I've used the forEach method in the core tag library:
<c:set var="contains" value="false" />
<c:forEach var="item" items="${myList}">
<c:if test="${item eq myValue}">
<c:set var="contains" value="true" />
</c:if>
</c:forEach>
After this runs, ${contains} will be equal to "true" if myList contained myValue.
Another way of doing this is using a Map (HashMap) with Key, Value pairs representing your object.
Map<Long, Object> map = new HashMap<Long, Object>();
map.put(new Long(1), "one");
map.put(new Long(2), "two");
In JSTL
<c:if test="${not empty map[1]}">
This should return true if the pair exist in the map
You need to use the fn:contains() or fn:containsIgnoreCase() function.
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%>
...
<c:if test="${not fn:containsIgnoreCase(mylist, 'apple')}">
<p>Doesn't contain 'apple'</p>
</c:if>
or
<c:if test="${not fn:contains(mylist, 'Apple')}">
<p>Contains 'Apple'</p>
</c:if>
Note:
This will work like mylist.toString().contains("apple") and if this is not what you are looking for better use a other approach.
The following is more of a workaround than an answer to your question but it may be what you are looking for.
If you can put your values in a map instead of a list, that would solve your problem. Just map your values to a non null value and do this <c:if test="${mymap.myValue ne null}">style='display:none;'</c:if> or you can even map to style='display:none; and simply output ${mymap.myValue}
${fn:contains({1,2,4,8}, 2)}
OR
<c:if test = "${fn:contains(theString, 'test')}">
<p>Found test string<p>
</c:if>
<c:if test = "${fn:contains(theString, 'TEST')}">
<p>Found TEST string<p>
</c:if>
If you are using EL 3.0+, the best approach in this case is as this other answer explained in another topic:
For a
Collectionit's easy, just use theColleciton#contains()method in EL.<h:panelGroup id="p1" rendered="#{bean.panels.contains('p1')}">...</h:panelGroup> <h:panelGroup id="p2" rendered="#{bean.panels.contains('p2')}">...</h:panelGroup> <h:panelGroup id="p3" rendered="#{bean.panels.contains('p3')}">...</h:panelGroup>For an
Object[](array), you'd need a minimum of EL 3.0 and utilize its new Lambda support.<h:panelGroup id="p1" rendered="#{bean.panels.stream().anyMatch(v -> v == 'p1').get()}">...</h:panelGroup> <h:panelGroup id="p2" rendered="#{bean.panels.stream().anyMatch(v -> v == 'p2').get()}">...</h:panelGroup> <h:panelGroup id="p3" rendered="#{bean.panels.stream().anyMatch(v -> v == 'p3').get()}">...</h:panelGroup>If you're not on EL 3.0 yet, you'd need to create a custom EL function. [...]
you must not use fn:contains(), because it is a string comparison. So suppose your list contains 11,12,13 and you have written fn:contains(list,'1'), it will give you the 'true' result. But I am hoping you are expecting false as 1 is not on the list. You should create your own custom tag to use list.contains(Object o).
If you are using Spring Framework, you can use Spring TagLib and SpEL:
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags" %>
---
<spring:eval var="containsValue" expression="mylist.contains(myValue)" />
<c:if test="${containsValue}">style='display:none;'</c:if>
I found this solution amazing.
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
<%
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
%>
<c:set var="list" value="<%=list%>" />
<html>
<body>
My list is ${list}<br/>
<c:if test='${fn:contains(list, "two")}'>
My list contains two <br/>
</c:if>
<c:if test='${fn:contains(list, ",")}'>
My list contains ,
</c:if>
</body>
</html>
The output for the code above is
My list is [one, two, three]
My list contains two
My list contains ,
I hope it helps someone.
<c:if test="${fn:contains(task.subscribers, customer)}">
This works fine for me.
