聊聊artemis的MessageLoadBalancingType

public enum MessageLoadBalancingType {
   OFF("OFF"), STRICT("STRICT"), ON_DEMAND("ON_DEMAND");

   static {
      // for URI support on ClusterConnection
      BeanSupport.registerConverter(new MessageLoadBalancingTypeConverter(), MessageLoadBalancingType.class);
   }

   static class MessageLoadBalancingTypeConverter implements Converter {

      @Override
      public <T> T convert(Class<T> type, Object value) {
         return type.cast(MessageLoadBalancingType.getType(value.toString()));
      }
   }

   private String type;

   MessageLoadBalancingType(final String type) {
      this.type = type;
   }

   public String getType() {
      return type;
   }

   public static MessageLoadBalancingType getType(String string) {
      if (string.equals(OFF.getType())) {
         return MessageLoadBalancingType.OFF;
      } else if (string.equals(STRICT.getType())) {
         return MessageLoadBalancingType.STRICT;
      } else if (string.equals(ON_DEMAND.getType())) {
         return MessageLoadBalancingType.ON_DEMAND;
      } else {
         return null;
      }
   }
}

public class PostOfficeImpl implements PostOffice, NotificationListener, BindingsFactory {

   //......

   public Pair<RoutingContext, Message> redistribute(final Message message,
                                                     final Queue originatingQueue,
                                                     final Transaction tx) throws Exception {
      Bindings bindings = addressManager.getBindingsForRoutingAddress(originatingQueue.getAddress());

      if (bindings != null && bindings.allowRedistribute()) {
         // We have to copy the message and store it separately, otherwise we may lose remote bindings in case of restart before the message
         // arrived the target node
         // as described on https://issues.jboss.org/browse/JBPAPP-6130
         Message copyRedistribute = message.copy(storageManager.generateID());
         copyRedistribute.setAddress(originatingQueue.getAddress());

         if (tx != null) {
            tx.addOperation(new TransactionOperationAbstract() {
               @Override
               public void afterRollback(Transaction tx) {
                  try {
                     //this will cause large message file to be
                     //cleaned up
                     copyRedistribute.decrementRefCount();
                  } catch (Exception e) {
                     logger.warn("Failed to clean up message: " + copyRedistribute);
                  }
               }
            });
         }

         RoutingContext context = new RoutingContextImpl(tx);

         boolean routed = bindings.redistribute(copyRedistribute, originatingQueue, context);

         if (routed) {
            return new Pair<>(context, copyRedistribute);
         }
      }

      return null;
   }

   //......
}

public final class BindingsImpl implements Bindings {

   //......

   @Override
   public boolean allowRedistribute() {
      return messageLoadBalancingType.equals(MessageLoadBalancingType.ON_DEMAND);
   }

   @Override
   public boolean redistribute(final Message message,
                               final Queue originatingQueue,
                               final RoutingContext context) throws Exception {
      if (messageLoadBalancingType.equals(MessageLoadBalancingType.STRICT) || messageLoadBalancingType.equals(MessageLoadBalancingType.OFF)) {
         return false;
      }

      if (logger.isTraceEnabled()) {
         logger.trace("Redistributing message " + message);
      }

      SimpleString routingName = originatingQueue.getName();

      List<Binding> bindings = routingNameBindingMap.get(routingName);

      if (bindings == null) {
         // The value can become null if it's concurrently removed while we're iterating - this is expected
         // ConcurrentHashMap behaviour!
         return false;
      }

      Integer ipos = routingNamePositions.get(routingName);

      int pos = ipos != null ? ipos.intValue() : 0;

      int length = bindings.size();

      int startPos = pos;

      Binding theBinding = null;

      // TODO - combine this with similar logic in route()
      while (true) {
         Binding binding;
         try {
            binding = bindings.get(pos);
         } catch (IndexOutOfBoundsException e) {
            // This can occur if binding is removed while in route
            if (!bindings.isEmpty()) {
               pos = 0;
               startPos = 0;
               length = bindings.size();

               continue;
            } else {
               break;
            }
         }

         pos = incrementPos(pos, length);

         Filter filter = binding.getFilter();

         boolean highPrior = binding.isHighAcceptPriority(message);

         if (highPrior && binding.getBindable() != originatingQueue && (filter == null || filter.match(message))) {
            theBinding = binding;

            break;
         }

         if (pos == startPos) {
            break;
         }
      }

      routingNamePositions.put(routingName, pos);

      if (theBinding != null) {
         theBinding.route(message, context);

         return true;
      } else {
         return false;
      }
   }

   //......
}