21.Explain how does the JMS work with the J2EE?

The application client like enterprise JavaBeans components and web components can send or receive JMS message synchronously. In addition, the application clients can also receive message asynchronously. With the help of message-driven beans, JMS provider can optionally implement the processing of messages. Message-driven beans are a type of enterprise bean that enables the asynchronous consumption of messages.
The operation of sending and receiving message is carried out in distributed operation, which allows JMS operations and database accesses within a single transaction.

22.What are the types of messages that are supported by JMS?

The types of messages that are supported by JMS are

• Stream Messages
• Text Messages
• Map Messages
• Bytes Messages
• Object Messages

23.What is MOM in reference to JMS?

The MOM ( Message Oriented Middleware) is a software that works as an intermediate between two communicating components. It is placed between the client and server, MOM provides the facility of passing message by using the technique queuing. Until the client does not request to read the message, the messages will be stored in queue. By using this technique, the software component can work independently of time.

24.How you can deliver a java message to a non-java client?

First of all, after receiving the message from Topic or Queue, the message has to be converted into a non-java client according to their specification. The message once converted to non-java client, it can be delivered.

25.For sending messages through JMS, what encryption options are there?

The encryption and decryption of the messages is handled by JMS provider and not JMS specifications. Sonic MQ by Progress Software is a leading JMS provider and they do encryption through encryption mechanisms called Quality of Protection.

26.What is JMS?

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.

27.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.

28.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.

29.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.All the J2EE compliant application servers come built with thier own implementation of JMS.

30.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.

31.What are the different messaging paradigms JMS supports?

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

32.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.

33.What is the role of JMS in enterprise solution development?

A: JMS is typically used in the following scenarios

• Enterprise Application Integration: - Where a legacy application is integrated with a new application via messaging.
• 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.
• Geographically dispersed units: - JMS can ensure safe exchange of data amongst the geographically dispersed units of an organization.
• One to many applications: - The applications that need 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.

34.What is the use of Message object?

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.

35.What is the basic difference between Publish Subscribe model and P2P model?

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.

36.What is the use of BytesMessage?

BytesMessage 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. Whenever you store any primitive type, it is converted into it's byte representation and then stored in the payload. There is no boundary line between the different data types stored. Thus you can even read a long as short. This would result in erroneous data and hence it is advisable that the payload be read in the same order and using the same type in which it was created by the sender.

37.What is the use of StreamMessage?

StreamMessage carries a stream of Java primitive types as it's payload. It contains some conveient methods for reading the data stored in the payload. However StreamMessage prevents reading a long value as short, something that is allwed in case of BytesMessage. This is so because the StreamMessage also writes the type information alonwgith the value of the primitive type and enforces a set of strict conversion rules which actually prevents reading of one primitive type as another.

38.What is the use of TextMessage?

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.

39.What is the use of ObjectMessage?

ObjectMessage contains a Serializable java object as it's payload. Thus it allows exchange of Java objects between applications. This in itself mandates that both the applications be Java applications. The consumer of the message must typecast the object received to it's appropriate type. Thus the consumer should before hand know the actual type of the object sent by the sender. Wrong type casting would result in ClassCastException. Moreover the class definition of the object set in the payload should be available on both the machine, the sender as well as the consumer. If the class definition is not available in the consumer machine, an attempt to type cast would result in ClassNotFoundException. Some of the MOMs might support dynamic loading of the desired class over the network, but the JMS specification does not mandate this behavior and would be a value added service if provided by your vendor. And relying on any such vendor specific functionality would hamper the portability of your application. Most of the time the class need to be put in the classpath of both, the sender and the consumer, manually by the developer.

40.What is the use of MapMessage

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.