Java 评估 JSTL 中的 list.contains 字符串

Evaluate list.contains string in JSTL

提问by OscarRyz

I need to hide an element if certain values are present in the JSP

如果 JSP 中存在某些值，我需要隐藏一个元素

The values are stored in a List so I tried:

这些值存储在一个列表中，所以我试过：

<c:if test="${  mylist.contains( myValue ) }">style='display:none;'</c:if>

But, it doesn't work.

但是，它不起作用。

How can I evaluate if a list contains a value in JSTL, the list and the values are strings.

如何评估列表是否包含 JSTL 中的值，列表和值是否为字符串。

采纳答案by Kaleb Brasee

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:

可悲的是，我认为 JSTL 只支持迭代所有元素来解决这个问题。过去，我使用过核心标签库中的 forEach 方法：

<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.

运行后，如果 myList 包含 myValue，则 ${contains} 将等于“true”。

回答by Chii

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.

没有内置功能可以检查 - 您要做的是编写自己的 tld 函数，该函数接受一个列表和一个项目，并调用列表的 contains() 方法。例如

//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:

然后创建一个名为 Yourclass 的类，并添加一个名为 contains 的静态方法，并具有上述签名。我确信该方法的实现是不言自明的：

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:

然后你可以在你的jsp中使用它：

<%@ 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.

可以从站点中的任何 JSP 使用该标记。

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

编辑：有关 tld 文件的更多信息 - 此处有更多信息

回答by svachon

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}

以下更像是一种解决方法，而不是对您问题的回答，但它可能正是您正在寻找的。如果您可以将您的值放在地图而不是列表中，那将解决您的问题。只需将您的值映射到非空值并执行此操作，<c:if test="${mymap.myValue ne null}">style='display:none;'</c:if>或者您甚至可以映射到style='display:none;并简单地输出${mymap.myValue}

回答by tamersalama

Another way of doing this is using a Map (HashMap)with Key, Value pairs representing your object.

另一种方法是使用Map (HashMap)代表您的对象的键、值对。

Map<Long, Object> map = new HashMap<Long, Object>();
map.put(new Long(1), "one");
map.put(new Long(2), "two");

In JSTL

在 JSTL

<c:if test="${not empty map[1]}">

This should return true if the pair exist in the map

如果这对存在于地图中，这应该返回 true

回答by Vladislav

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

This works fine for me.

这对我来说很好用。

回答by xxg

If you are using Spring Framework, you can use Spring TagLib and SpEL:

如果您使用的是 Spring Framework，则可以使用 Spring TagLib 和 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>

回答by tk_

You need to use the fn:contains()or fn:containsIgnoreCase()function.

您需要使用fn:contains()orfn:containsIgnoreCase()函数。

<%@ 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

或者

<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.

注意：这会起作用mylist.toString().contains("apple")，如果这不是您想要的更好的方法，请使用其他方法。

回答by Tony Hung

${fn:contains({1,2,4,8}, 2)}

OR

或者

  <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>

回答by oOXAam

I found this solution amazing.

我发现这个解决方案很棒。

<%@ 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

上面代码的输出是

My list is [one, two, three]

我的清单是[一、二、三]

My list contains two

我的清单包含两个

My list contains ,

我的清单包含，

I hope it helps someone.

我希望它可以帮助某人。

回答by Lucas Basquerotto

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

如果您使用的是 EL 3.0+，则在这种情况下的最佳方法是另一个主题中解释的其他答案：

For a Collectionit'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. [...]

对于一个Collection很简单，只需使用Colleciton#contains()EL 中的方法。

<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>

对于Object[]（数组），您至少需要 EL 3.0 并利用其新的 Lambda 支持。

<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>

如果您尚未使用 EL 3.0，则需要创建自定义 EL 函数。[...]