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.
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Ques 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.
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Ques 38. What is JMS (Java Messaging Service)?
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.
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Ques 39. 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.
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Ques 40. How the 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.