EL access a map value by Integer key

Question

I have a Map keyed by Integer. Using EL, how can I access a value by its key?

Map<Integer, String> map = new HashMap<Integer, String>(); map.put(1, "One"); map.put(2, "Two"); map.put(3, "Three"); 

I thought this would work but it doesn't (where map is already in the request's attributes):

<c:out value="${map[1]}"/> 

Follow up: I tracked down the problem. Apparently ${name[1]} does a map lookup with the number as a Long. I figured this out when I changed HashMap to TreeMap and received the error:

java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.Long 

If I change my map to be:

Map<Long, String> map = new HashMap<Long, String>(); map.put(1L, "One"); 

then ${name[1]} returns "One". What's with that? Why does <c:out> treat a number as a long. Seems counterintuitive to me (as int is more commonly used than long).

So my new question is, is there a EL notation to access a map by an Integer value?

Answer 1

Initial answer (EL 2.1, May 2009)

As mentioned in this java forum thread:

Basically autoboxing puts an Integer object into the Map. ie:

map.put(new Integer(0), "myValue") 

EL (Expressions Languages) evaluates 0 as a Long and thus goes looking for a Long as the key in the map. ie it evaluates:

map.get(new Long(0)) 

As a Long is never equal to an Integer object, it does not find the entry in the map.
That's it in a nutshell.

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Update since May 2009 (EL 2.2)

Dec 2009 saw the introduction of EL 2.2 with JSP 2.2 / Java EE 6, with a few differences compared to EL 2.1.
It seems ("EL Expression parsing integer as long") that:

you can call the method intValue on the Long object self inside EL 2.2:

<c:out value="${map[(1).intValue()]}"/> 

That could be a good workaround here (also mentioned below in Tobias Liefke's answer)

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Original answer:

EL uses the following wrappers:

Terms                  Description               Type null                   null value.               - 123                    int value.                java.lang.Long 123.00                 real value.               java.lang.Double "string" ou 'string'   string.                   java.lang.String true or false          boolean.                  java.lang.Boolean 

JSP page demonstrating this:

 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>   <%@ page import="java.util.*" %>   <h2> Server Info</h2> Server info = <%= application.getServerInfo() %> <br> Servlet engine version = <%=  application.getMajorVersion() %>.<%= application.getMinorVersion() %><br> Java version = <%= System.getProperty("java.vm.version") %><br> <%   Map map = new LinkedHashMap();   map.put("2", "String(2)");   map.put(new Integer(2), "Integer(2)");   map.put(new Long(2), "Long(2)");   map.put(42, "AutoBoxedNumber");    pageContext.setAttribute("myMap", map);     Integer lifeInteger = new Integer(42);   Long lifeLong = new Long(42);   %>   <h3>Looking up map in JSTL - integer vs long </h3>    This page demonstrates how JSTL maps interact with different types used for keys in a map.   Specifically the issue relates to autoboxing by java using map.put(1, "MyValue") and attempting to display it as ${myMap[1]}   The map "myMap" consists of four entries with different keys: A String, an Integer, a Long and an entry put there by AutoBoxing Java 5 feature.           <table border="1">     <tr><th>Key</th><th>value</th><th>Key Class</th></tr>     <c:forEach var="entry" items="${myMap}" varStatus="status">     <tr>             <td>${entry.key}</td>       <td>${entry.value}</td>       <td>${entry.key.class}</td>     </tr>     </c:forEach> </table>      <h4> Accessing the map</h4>         Evaluating: ${"${myMap['2']}"} = <c:out value="${myMap['2']}"/><br>     Evaluating: ${"${myMap[2]}"}   = <c:out value="${myMap[2]}"/><br>         Evaluating: ${"${myMap[42]}"}   = <c:out value="${myMap[42]}"/><br>          <p>     As you can see, the EL Expression for the literal number retrieves the value against the java.lang.Long entry in the map.     Attempting to access the entry created by autoboxing fails because a Long is never equal to an Integer     <p>      lifeInteger = <%= lifeInteger %><br/>     lifeLong = <%= lifeLong %><br/>     lifeInteger.equals(lifeLong) : <%= lifeInteger.equals(lifeLong) %> <br>