code: public static IReaction getReactionByReactionID(IReactionSet reactionSet, String id) {
          Iterable<IReaction> reactionIter = reactionSet.reactions();
          for (IReaction reaction : reactionIter) {
              if (reaction.getID() != null && reaction.getID().equals(id)) {
                  return reaction;
              }
          }
          return null;
      }
docs: Gets a reaction from a ReactionSet by ID. If several exist,
  only the first one will be returned.
  
  @param reactionSet The reactionSet to search in
  @param id The id to search for.
  @return The Reaction or null;