JMS specifications are built upon the concepts of Topics and Queues, but Apache Pulsar™ has only a general concept of Topics that can model both of those two domains.

In Pulsar there is no concept of a queue: undefined treats Pulsar topics as queues when queue-related JMS API are in use. There is no strict, cluster wide, verification that you are accessing a JMS Queue using the Topic API or vice versa.

In JMS a Topic is written by many Producers and read by many Consumers that share one or many Subscriptions. Subscriptions may be Durable or Non-Durable (meaning the client position not retained on restart), and Shared or Non-Shared determining whether the same message may be received and processed by more than one consumer.

For SharedConsumer and SharedDurableConsumer , set jms.topicSharedSubscriptionType to Key_Shared to use the Key_Shared subscription type.

In JMS a Queue is written by many Producers but only one Consumer eventually processes each message.

In order to emulate that behavior, the first time you create a consumer over a queue, undefined creates a durable subscription named jms-queue at the beginning (initial position = Earliest) of the Pulsar topic.

Every access to the queue passes through the shared subscription and guarantees that only one consumer receives and processes each message.

In order to implement QueueBrowser , undefined uses the Pulsar Reader API, starting from the next message available on the jms-queue subscription. In order to peek at the next message undefined uses the Pulsar Admin API peekMessages .

undefined doesn't deal with schema, and it treats every message as a raw array of bytes, interpreting the content of the message according to the JMS API that is used, and to a special JMSPulsarMessageType property.

JMS specs require that, on the consumer side, you receive a message of the same type sent by the producer:

When the JMS consumer receives a message that has not been produced by undefined itself and lacks the JMSPulsarMessageType property, it converts the message to a BytesMessage .