Java Message Service (JMS) Interview Questions And Answers

JMS is an acronym used for Java Messaging Service. It is Java's answer to creating software using asynchronous messaging. It is one of the official specifications of the J2EE technologies and is a key technology.

In RPC the method invoker waits for the method to finish execution and return the control back to the invoker. Thus it is completely synchronous in nature. While in JMS the message sender just sends the message to the destination and continues it's own processing. The sender does not wait for the receiver to respond. This is asynchronous behavior.

JMS is asynchronous in nature. Thus not all the pieces need to be up all the time for the application to function as a whole. Even if the receiver is down the MOM will store the messages on it's behalf and will send them once it comes back up. Thus at least a part of application can still function as there is no blocking.

Message, TextMessage, BytesMessage, StreamMessage, ObjectMessage, MapMessage are the different messages available in the JMS API.

Publish and Subscribe i.e. pub/suc and Point to Point i.e. p2p.

A topic is typically used for one to many messaging i.e. it supports publish subscribe model of messaging. While queue is used for one-to-one messaging i.e. it supports Point to Point Messaging.

Message is a light weight message having only header and properties and no payload. Thus if theIf the receivers are to be notified abt an event, and no data needs to be exchanged then using Message can be very efficient.

Publish Subscribe model is typically used in one-to-many situation. It is unreliable but very fast. P2P model is used in one-to-one situation. It is highly reliable.

TextMessage contains instance of java.lang.String as it's payload. Thus it is very useful for exchanging textual data. It can also be used for exchanging complex character data such as an XML document.

A MapMessage carries name-value pair as it's payload. Thus it's payload is similar to the java.util.Properties object of Java. The values can be Java primitives or their wrappers

An implementation of the JMS interface for a Message Oriented Middleware (MOM). Providers are implemented as either a Java JMS implementation or an adapter to a non-Java MOM.

An application or process that produces and/or receives messages.

A JMS client that creates and sends messages.

A JMS client that receives messages.

An object that contains the data being transferred between JMS clients.

A staging area that contains messages that have been sent and are waiting to be read. Note that, contrary to what the name queue suggests, messages don't have to be delivered in the order sent. If the message driven bean pool contains more than one instance then messages can be processed concurrently and thus it is possible that a later message is processed sooner than an earlier one. A JMS queue guarantees only that each message is processed only once.

A distribution mechanism for publishing messages that are delivered to multiple subscribers.