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 lt Integer  String gt  map   new HashMap lt Integer  String gt     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     lt c out value    map 1     gt    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 lt Long  String gt  map   new HashMap lt Long  String gt     map put 1L   One      then   name 1   returns  One   What s with that  Why does  lt c out gt  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

User · Answer

Just another helpful hint in addition to the above comment would be when you have a string value contained in some variable such as a request parameter. In this case, passing this in will also result in JSTL keying the value of say "1" as a sting and as such no match being found in a Map hashmap.

One way to get around this is to do something like this.

<c:set var="longKey" value="${param.selectedIndex + 0}"/>

This will now be treated as a Long object and then has a chance to match an object when it is contained withing the map Map or whatever.

Then, continue as usual with something like

${map[longKey]}

User · Answer

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     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     lt c out value    map  1  intValue       gt    That could be a good workaround here  also mentioned below in Tobias Liefke s answer     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     lt    taglib prefix  c  uri  http   java sun com jsp jstl core   gt     lt    page import  java util      gt     lt h2 gt  Server Info lt  h2 gt  Server info    lt    application getServerInfo     gt   lt br gt  Servlet engine version    lt     application getMajorVersion     gt   lt    application getMinorVersion     gt  lt br gt  Java version    lt    System getProperty  java vm version     gt  lt br gt   lt     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       gt     lt h3 gt Looking up map in JSTL - integer vs long  lt  h3 gt     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             lt table border  1  gt       lt tr gt  lt th gt Key lt  th gt  lt th gt value lt  th gt  lt th gt Key Class lt  th gt  lt  tr gt       lt c forEach var  entry  items    myMap   varStatus  status  gt       lt tr gt               lt td gt   entry key  lt  td gt         lt td gt   entry value  lt  td gt         lt td gt   entry key class  lt  td gt       lt  tr gt       lt  c forEach gt   lt  table gt        lt h4 gt  Accessing the map lt  h4 gt          Evaluating       myMap  2         lt c out value    myMap  2      gt  lt br gt      Evaluating       myMap 2          lt c out value    myMap 2     gt  lt br gt          Evaluating       myMap 42          lt c out value    myMap 42     gt  lt br gt            lt p gt      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      lt p gt       lifeInteger    lt    lifeInteger   gt  lt br  gt      lifeLong    lt    lifeLong   gt  lt br  gt      lifeInteger equals lifeLong     lt    lifeInteger equals lifeLong    gt   lt br gt

User · Answer

Based on the above post i tried this and this worked fine I wanted to use the value of Map B as keys for Map A    lt c if test    not empty activityCodeMap and not empty activityDescMap   gt   lt c forEach var  valueMap  items    auditMap   gt   lt tr gt   lt td class  activity white  gt  lt c out value    activityCodeMap valueMap value activityCode     gt  lt  td gt   lt td class  activity white  gt  lt c out value    activityDescMap valueMap value activityDescCode     gt  lt  td gt   lt td class  activity white  gt   valueMap value dateTime  lt  td gt   lt  tr gt   lt  c forEach gt   lt  c if gt

User · Answer

If you just happen to have a Map with Integer keys you cannot change  you could write a custom EL function to convert a Long to Integer  This would allow you to do something like    lt c out value    map myLib longToInteger 1      gt

User · Answer

You can use all functions from Long  if you put the number into          That way you can cast the long to an int    lt c out value    map  1  intValue       gt

[java] EL access a map value by Integer key

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