SwiftMQ provides the possibility to define topic hierarchies in the form <roottopic>.<subtopic>.<subsubtopic> etc.
Example:
iit.sales.EU
iit.sales.US
iit.projects.swiftmq.users
news.weather.forecasts
sports.formula1.MichaelSchumacher
Publishing and subscribing rules to nodes in a hierarchy:
As an extension to the normal topic node- and subnode-addressing scheme, SwiftMQ provides SQL-Like predicate topic addressing. So every subnode could be a SQL-Like predicate. A SQL-Like predicate could contain wildcards which match a single character (the underscore '_'), or any characters (the percent sign '%'). Escape character is '\'.
Root nodes cannot be addressed as a predicate; i. e. it is not possible to specify i%.%.swiftmq.
Predicate topics are normal topic destinations and are not available via JNDI lookups. To create a predicate topic, one has to use the createTopic() method from a TopicSession.
Example:
Topic allSwiftMQ = topicSession.createTopic("iit.%.US");
msg.setJMSDestination(allSwiftMQ);
publisher.publish(msg);
Access to predicate topics must be granted by the Authentication Swiftlet just like normal topics.
What means "Indirect Subscriber Selection"? The topic name inside the message is a SQL-Like predicate. It is used to select those topic names which are defined at the Topic Manager Swiftlet configuration. This is the first step. The next step is to use those matched topics and match it against subscribers. Subscribers are also using SQL-Like predicates. Therefore, in this mode, a topic hierarchy needs to be declared in the Topic Manager configuration in order to work. This is the price for the flexibility and sometimes a disadvantage. For this reason we introduced "Direct Subscriber Selection" in SwiftMQ 7.3.0 (see next section).
This feature does not interpret the topic name in the message as SQL-Like predicate but as a string. Therefore it is possible to select the subscribers directly by matching the subscriber's SQL-Like predicates against the topic name of the message. You don't need to declare the topics in the Topic Manager Swiftlet configuration.
Because it is a very rare case that someone uses a predicate as a topic name when sending a message, e.g. send to "iit.%.US", the direct subscriber selection is the default mode starting with SwiftMQ 7.3.0 but can be disabled:
