O'Reilly - Java Message Service

Java Message Service
Table 3.1 shows the conversion rules for each type. The left column shows the type
written, and the right column shows how that type may be read. A JMSException is thrown
by the accessor methods to indicate that the original type could not be converted to the
type requested. This is the exception that would be thrown if you attempted to read long as
a short.
write( ) read( )
boolean boolean, String
Table 3.1. Type Conversion Rules
byte byte, short, int, long, String
short short, int, long, String
char char, String
Long long, String
Int int, long, String
float float, double, String
double double, String
String String, boolean, byte, short, int, long, float, double
byte [] byte []
String values can be converted to any primitive data type if they are formatted correctly. If
the String value cannot be converted to the primitive type requested, a
java.lang.NumberFormatException is thrown. However, most primitive values can be
accessed as a String using the readString( ) method. The only exceptions to this rule are
char values and byte arrays, which cannot be read as String values.
The writeObject( ) method follows the rules outlined for the similar method in the
BytesMessage class. Primitive wrappers are converted to their primitive counterparts. The
readObject( ) method returns the appropriate object wrapper for primitive values, or a
String or a byte array, depending on the type that was written to the stream. For example,
if a value was written as a primitive int, it can be read as a java.lang.Integer object.
The StreamMessage also allows null values to be written to the stream. If a JMS client
attempts to read a null value using the readObject( ) method, null is returned. The rest of
the primitive accessor methods attempt to convert the null value to the requested type
using the valueOf( ) operations. The readBoolean( ) method returns false for null
values, while the other primitive property methods throw the
java.lang.NumberFormatException. The readString( ) method returns null or possibly an
empty String ("") depending on the implementation. The readChar( ) method throws a
NullPointerException.
If an exception is thrown while reading the StreamMessage, the pointer in the stream is
reset to the position it had just prior to the read operation that caused the exception. This
allows the JMS client to recover gracefully from exceptions without losing the pointer's
position in the stream.
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