在 JSTL 中计算 list.include 字符串

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最佳答案

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.

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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

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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}

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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

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<c:if test="${fn:contains(task.subscribers, customer)}">

This works fine for me.

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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>

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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.

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${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>

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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.

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If you are using EL 3.0+, the best approach in this case is as this other answer explained in another topic:

For a Collection it's easy, just use the Colleciton#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. [...]

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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).