Question 1 :
What is the difference between Message producer and Message consumer?
Messaging systems provide a host of powerful advantages over other conventional distributed computing models. Primarily, they encourage "loose coupling" between message consumers and message producers. There is a high degree of anonymity between producer and consumer: to the message consumer, it doesn't matter who produced the message, where the producer lives on the network, or when the message was produced.
In Publish/Subscribe model:
A publish/subscribe (pub/sub) messaging system supports an event driven model where information consumers and producers participate in the transmission of messages. Producers "publish" events, while consumers "subscribe" to events of interest, and consume the events. Producers associate messages with a specific topic, and the messaging system routes messages to consumers based on the topics the consumers register interest in.
In Point-To-Point model:
In point to point messaging systems, messages are routed to an individual consumer which maintains a queue of "incoming" messages. Messaging applications send messages to a specified queue, and clients retrieve messages from a queue.
In Point-To-Point model, one client can send message to the another client through the Destination.
There is a guarantee to recieve the message whenever reciever is connected.
example:your telephone answering machine ,outer send a message to u,but you can recieve those msg whenever u coonected to answering machine.
In pub/sub model. one publisher,many no.of clients willbe there,publisher publish the message,subscriber or consumer can recieve those messages when he got subscription through the topic.There is no guarantee consumer can recieve the messages send by the publisher.
Question 2 :
What is JMS application ?
One or more JMS clients that exchange messages.
Question 3 :
What type messaging is provided by JMS ?
Both synchronous and asynchronous are provided by JMS.
Question 4 :
How JMS is different from RPC?
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.
Question 5 :
What Is the JMS API?
The Java Message Service is a Java API that allows applications to create, send, receive, and read messages. Designed by Sun and several partner companies, the JMS API defines a common set of interfaces and associated semantics that allow programs written in the Java programming language to communicate with other messaging implementations.
The JMS API minimizes the set of concepts a programmer must learn to use messaging products but provides enough features to support sophisticated messaging applications. It also strives to maximize the portability of JMS applications across JMS providers in the same messaging domain.
The JMS API enables communication that is not only loosely coupled but also
* Asynchronous. A JMS provider can deliver messages to a client as they arrive; a client does not have to request messages in order to receive them.
* Reliable. The JMS API can ensure that a message is delivered once and only once. Lower levels of reliability are available for applications that can afford to miss messages or to receive duplicate messages.
The JMS Specification was first published in August 1998. The latest version of the JMS Specification is Version 1.1, which was released in April 2002. You can download a copy of the Specification from the JMS Web site, http://java.sun.com/products/jms/.
Question 6 :
What is JMS client ?
A Java language program that sends or receives messages.
Give an example of using the point-to-point model
The point-to-point model is used when the information is specific to a single client. For example, a client can send a message for a print out, and the server can send information back to this client after completion of the print job.
Question 7 :
What is Producer and Consumer?
Messaging lets a servlet delegate processing to a batch process either on the same machine or on a separate machine. The servlet creates a message and sends it to a queue. The servlet immediately completes and when the batch process is ready, it processes the message.
Messaging is therefore comprised of three main components:
A Producer creates messages and sends them to a Queue. The Producer could be something like a Servlet.
A Queue stores the messages from the Produces and provides them to a Consumer when ready. The Queue is implemented by the messaging provider.
A Consumer processes messages as they become available in the Queue. The Consumer is typically a bean implementing the MessageListener interface.
A producer is the client application that plays the role of a message sender in JMS API.
A consumer is the client application that plays the role of a message receiver in JMS API.
Question 8 :
Can JMS utilities automatically re-establish a connection if one side of the communication link (i.e. an application that's sending/receiving messages) goes down and is restarted? Are there APIs to help detect that the other side broke a connection (went down)?
Yes. You can write a snooper files to detect the service and restart the node upon node fail and a server instance fail.
Question 9 :
What is the Role of the JMS Provider?
The JMS provider handles security of the messages, data conversion and the client triggering. The JMS provider specifies the level of encryption and the security level of the message, the best data type for the non-JMS client.
Question 10 :
What is JMS provider?
A messaging system that implements the Java Message Service as well as other administrative and control functionality needed in a full-featured messaging product.
Question 11 :
What is Byte Message ?
Byte Messages contains a Stream of uninterrupted bytes. Byte Message contains an array of primitive bytes in it's payload. Thus it can be used for transfer of data between two applications in their native format which may not be compatible with other Message types. It is also useful where JMS is used purely as a transport between two systems and the message payload is opaque to the JMS client.
Question 12 :
What is the difference between Byte Message and Stream Message?
Bytes Message stores data in bytes. Thus the message is one contiguous stream of bytes. While the Stream Message maintains a boundary between the different data types stored because it also stores the type information along with the value of the primitive being stored. Bytes Message allows data to be read using any type. Thus even if your payload contains a long value, you can invoke a method to read a short and it will return you something. It will not give you a semantically correct data but the call will succeed in reading the first two bytes of data. This is strictly prohibited in the Stream Message. It maintains the type information of the data being stored and enforces strict conversion rules on the data being read.
Question 13 :
What are the advantages of JMS?
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.
Question 14 :
Are you aware of any major JMS products available in the market?
IBM's MQ Series is one of the most popular product used as Message Oriented Middleware. Some of the other products are SonicMQ, iBus etc. Weblogic application server also comes with built in support for JMS messaging.
Question 15 :
What are the different types of messages available in the JMS API?
Message, TextMessage, BytesMessage, StreamMessage, ObjectMessage, MapMessage are the different messages available in the JMS API.
Question 16 :
What are the different messaging paradigms JMS supports?
Publish and Subscribe i.e. pub/suc and Point to Point i.e. p2p.
Question 17 :
What is the difference between topic and queue?
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.
Question 18 :
How Does the JMS API Work with the J2EE Platform?
When the JMS API was introduced in 1998, its most important purpose was to allow Java applications to access existing messaging-oriented middleware (MOM) systems, such as MQSeries from IBM. Since that time, many vendors have adopted and implemented the JMS API, so that a JMS product can now provide a complete messaging capability for an enterprise.
Since the 1.3 release of the J2EE platform ("the J2EE 1.3 platform"), the JMS API has been an integral part of the platform, and application developers can use messaging with components using J2EE APIs ("J2EE components").
The JMS API in the J2EE platform has the following features.
* Application clients, Enterprise JavaBeans (EJB) components, and Web components can send or synchronously receive a JMS message. Application clients can in addition receive JMS messages asynchronously. (Applets, however, are not required to support the JMS API.)
* Message-driven beans, which are a kind of enterprise bean, enable the asynchronous consumption of messages. A JMS provider may optionally implement concurrent processing of messages by message-driven beans.
* Message sends and receives can participate in distributed transactions.
The JMS API enhances the J2EE platform by simplifying enterprise development, allowing loosely coupled, reliable, asynchronous interactions among J2EE components and legacy systems capable of messaging. A developer can easily add new behavior to a J2EE application with existing business events by adding a new message-driven bean to operate on specific business events. The J2EE platform's EJB container architecture, moreover, enhances the JMS API by providing support for distributed transactions and allowing for the concurrent consumption of messages.
Another J2EE platform technology, the J2EE Connector Architecture, provides tight integration between J2EE applications and existing Enterprise Information (EIS) systems. The JMS API, on the other hand, allows for a very loosely coupled interaction between J2EE applications and existing EIS systems.
At the 1.4 release of the J2EE platform, the JMS provider may be integrated with the application server using the J2EE Connector Architecture. You access the JMS provider through a resource adapter. For more information, see the Enterprise JavaBeans Specification, v2.1, and the J2EE Connector Architecture Specification, v1.5.
Question 19 :
What is the role of JMS in enterprise solution development?
JMS is typically used in the following scenarios
1. Enterprise Application Integration: - Where a legacy application is integrated with a new application via messaging.
2. B2B or Business to Business: - Businesses can interact with each other via messaging because JMS allows organizations to cooperate without tightly coupling their business systems.
3. Geographically dispersed units: - JMS can ensure safe exchange of data amongst the geographically dispersed units of an organization.
4. One to many applications: - The applications that have to push data in packet to huge number of clients in a one-to-many fashion are good candidates for the use JMS. Typical such applications are Auction Sites, Stock Quote Services etc.
Question 20 :
What is the use of Message object?
Message is a light weight message having only header and properties and no payload. Thus if the received are to be notified abt an event, and no data needs to be exchanged then using Message can be very efficient.