getNeo4jQueryFunction.java

    //maxRelationLevel is max relation level that you likely use. In your situation, this is 2. Cause, your levels are 1,2,null(ALL)
    public String getQuery(String userId, List<String> userIds, Integer relationLevel, int maxRelationLevel) {
        String startQuery = "start user1=node:node_auto_index(userId = %s), user2=node('name:(%s)')".format(userId, StringUtils.join(userIds,","));
        String whereQuery = ""
        List<String> whereQueryList = new ArrayList<String>();
        if (null != relationLevel) {

            for (i = 1; i <= relationLevel,i++){
                whereQueryList.add("(user1-[knows*%s]->(user2) AND user2.preferedLevel>=%s)".format(i, i);
            }
            whereQuery = StringUtils.join(whereQueryList, " and ");
        } else {
            //relation level must be null when status ALL. If the status is ALL, there will be no preferedLevel field for the record in Neo4J DB.
            whereQueryList.add("not has(user2.preferedLevel)")
            for (i = maxRelationLevel, i >= 0, i--) {
                whereQueryList.add("(user2.preferedLevel=%s and user2-[knows*%s]->(user1))".format(i, i))
            }
            whereQuery = StringUtils.join(whereQueryList, " or ");
        }


        return "%s %s".format(startQuery, whereQuery);
    }