el function with generic arraylist return type and with parameter

Question

I want to return ArrayList<HashMap<String,String>> in EL function with three String argument. How to do that?

Answer 1

Actually I think it's perfectly reasonable to have an EL function return some complex object. Of course, there are issues of "architectural style" that might dictate what would and would not be appropriate situations for such a thing, but I'd say that a good example would be some facility for returning some kinds of configuration information that is not specific to any particular action, not really of interest to back-end business logic, and likely to be of use for presentation purposes on many pages.

To do that, what you want is an EL function that returns "Object", or perhaps "Object[]". You can't use the Java generics stuff in your EL declarations (in your .tld file, that is), but that doesn't really matter because the EL environment does type sniffing anyway. What you'd do is declare a public static function in a class somewhere:

public static Object yourFunction(String arg1, String arg2, String arg3) {
    // code code code
    return (ArrayList<HashMap<String, String>>) whatever;
}

In your .tld file, you'll have something like this:

<function>
  <description>Blah blah blah</description>
  <name>yourFunction</name>
  <function-class>your.package.YourClassName</function-class>
  <function-signature>
    java.lang.Object yourFunction(java.lang.String, java.lang.String, java.lang.String)
  </function-signature>
</function>

In your JSP, you'd access the function like this:

<c:set var='result' value='${prefix:yourFunction("Goodbye", "Mr.", "Chips")}'/>