I am trying to write $in query with $regex in mongo+java. It's not working in mongo shell either. What I mean is I don't get any results but no query parse error either. Here's the final query I got from Java Debugger at the line where I say collection.find(finalQuery)

{ "$and" : [ 
        { "$or" : 
                [ { "country" : "united states"}]} , 
        { "businesses" : 
                { "$in" : [ { "$regex" : "^.*cardinal.*health.*$"} , { "$regex" :      "^.*the.*hartford.*$"}]}
         }
        ]
}

Java Code snipet for Above query: Set businesses = new HashSet();

for(String st: srchTerms){
    businesses.add(Pattern.compile("^"+st.trim()+"$"));
}
srchTermQuery.append("businesses", new BasicDBObject("$in", businesses ));

However, following query works in mongo shell but I don't know how to write it into java:

{"registering_organization" : {"$in":[/^.*cardinal.*health.*$/,/^.*the.*hartford.*$/]}}

Java Code add double quotes around regex if we try to define it as a string.

For workaround, I can do as someone suggested on StackOverflow using Or in my regex.
Pattern pattern = Pattern.compile("(^aaa$)|(^bbb$)");
srchTermQuery.append("businesses", pattern);

http://stackoverflow.com/questions/17984750/mongodb-java-in-query-with-regex