Evaluate list.contains string in JSTL

Question

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.

Answer 1

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" values="${myList}">
  <c:if test="${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.

Answer 2

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"&gt;
<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>

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:

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>

edit: more info regarding the tld file - more info here

Answer 3

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}

Answer 4

You can find this into JSTL functions:

<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%&gt;
<c:if test="${fn:contains(myList, myValue)}">style='display:none;'</c:if>

Answer 5

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