Evaluate list.contains string in JSTL

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.

Solution 1:

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

Solution 2:

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.