Find if a String in a list of Strings is in another list of Strings in Esper

Question

I'm working with Esper + Mule and I am trying to define a POJO and an Event, but after reading the documentation of Espero I haven't found what I really need.

My event, represented by a POJO, has a property like this:

List<String> Words;

What I would like to do is use the keyword IN to compare it with another list of words, so the pattern would look like this:

... Words in ('word1', 'word2', 'word3) ...

But I get this error:

Collection or array comparison is not allowed for the IN, ANY, SOME or ALL keywords

Is there any way to achieve this?

Thank you very much

Answer 1

One way is to create a method to do what you want, register that method with esper, and reference that method from your EPL statement:

Create helper class (for this example, I use EsperUtils.java):

package my.package;

class EsperUtils {
  public static boolean contains(List<String> list1, List<String> list2) {

    // Check for list1 and list2 to contain same word
    for (String s1 : list1) {
      for (String s2 : list2) {
        if (s1.equals(s2)) return true;
      }
    }
    return false;
  }
}

Register method with esper in aem.esper.config.xml:

<plugin-singlerow-function name="contains" function-class="my.package.EsperUtils" function-method="contains" />

Use the helper method in your EPL:

select * from myEvent where contains(Words,AnotherListOfWords)

You could also add the helper method to your event POJO instead of a helper class.

Answer 2

You'd want to look at enumeration methods, see http://esper.codehaus.org/esper-4.9.0/doc/reference/en-US/html_single/index.html#enumerationreference It seems that "intersect" and "countOf" in combination would suit.