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<H4>Provider Implementations of JMS Message Interfaces</H4>
<P>The JMS API provides a set of message interfaces that define the JMS
message
model. It does not provide implementations of these interfaces.
<P>Each JMS provider supplies a set of message factories with its
<CODE>Session</CODE> object for creating instances of messages. This allows
a provider to use message implementations tailored to its specific needs.
<P>A provider must be prepared to accept message implementations that are
not its own. They may not be handled as efficiently as its own
implementation; however, they must be handled.
<P>Note the following exception case when a provider is handling a foreign
message implementation. If the foreign message implementation contains a
<CODE>JMSReplyTo</CODE> header field that is set to a foreign destination
implementation, the provider is not required to handle or preserve the
value of this header field.
<H4>Message Selectors</H4>
<P>A JMS message selector allows a client to specify, by
header field references and property references, the
messages it is interested in. Only messages whose header
and property values
match the
selector are delivered. What it means for a message not to be delivered
depends on the <CODE>MessageConsumer</CODE> being used (see
<A HREF="../../javax/jms/QueueReceiver.html"><CODE>QueueReceiver</CODE></A> and
<A HREF="../../javax/jms/TopicSubscriber.html"><CODE>TopicSubscriber</CODE></A>).
<P>Message selectors cannot reference message body values.
<P>A message selector matches a message if the selector evaluates to
true when the message's header field values and property values are
substituted for their corresponding identifiers in the selector.
<P>A message selector is a <CODE>String</CODE> whose syntax is based on a
subset of
the SQL92 conditional expression syntax. If the value of a message selector
is an empty string, the value is treated as a null and indicates that there
is no message selector for the message consumer.
<P>The order of evaluation of a message selector is from left to right
within precedence level. Parentheses can be used to change this order.
<P>Predefined selector literals and operator names are shown here in
uppercase; however, they are case insensitive.
<P>A selector can contain:
<UL>
<LI>Literals:
<UL>
<LI>A string literal is enclosed in single quotes, with a single quote
represented by doubled single quote; for example,
<CODE>'literal'</CODE> and <CODE>'literal''s'</CODE>. Like
string literals in the Java programming language, these use the
Unicode character encoding.
<LI>An exact numeric literal is a numeric value without a decimal
point, such as <CODE>57</CODE>, <CODE>-957</CODE>, and
<CODE>+62</CODE>; numbers in the range of <CODE>long</CODE> are
supported. Exact numeric literals use the integer literal
syntax of the Java programming language.
<LI>An approximate numeric literal is a numeric value in scientific
notation, such as <CODE>7E3</CODE> and <CODE>-57.9E2</CODE>, or a
numeric value with a decimal, such as <CODE>7.</CODE>,
<CODE>-95.7</CODE>, and <CODE>+6.2</CODE>; numbers in the range of
<CODE>double</CODE> are supported. Approximate literals use the
floating-point literal syntax of the Java programming language.
<LI>The boolean literals <CODE>TRUE</CODE> and <CODE>FALSE</CODE>.
</UL>
<LI>Identifiers:
<UL>
<LI>An identifier is an unlimited-length sequence of letters
and digits, the first of which must be a letter. A letter is any
character for which the method <CODE>Character.isJavaLetter</CODE>
returns true. This includes <CODE>'_'</CODE> and <CODE>'$'</CODE>.
A letter or digit is any character for which the method
<CODE>Character.isJavaLetterOrDigit</CODE> returns true.
<LI>Identifiers cannot be the names <CODE>NULL</CODE>,
<CODE>TRUE</CODE>, and <CODE>FALSE</CODE>.
<LI>Identifiers cannot be <CODE>NOT</CODE>, <CODE>AND</CODE>,
<CODE>OR</CODE>, <CODE>BETWEEN</CODE>, <CODE>LIKE</CODE>,
<CODE>IN</CODE>, <CODE>IS</CODE>, or <CODE>ESCAPE</CODE>.
<LI>Identifiers are either header field references or property
references. The type of a property value in a message selector
corresponds to the type used to set the property. If a property
that does not exist in a message is referenced, its value is
<CODE>NULL</CODE>.
<LI>The conversions that apply to the get methods for properties do not
apply when a property is used in a message selector expression.
For example, suppose you set a property as a string value, as in the
following:
<PRE>myMessage.setStringProperty("NumberOfOrders", "2");</PRE>
The following expression in a message selector would evaluate to
false, because a string cannot be used in an arithmetic expression:
<PRE>"NumberOfOrders > 1"</PRE>
<LI>Identifiers are case-sensitive.
<LI>Message header field references are restricted to
<CODE>JMSDeliveryMode</CODE>, <CODE>JMSPriority</CODE>,
<CODE>JMSMessageID</CODE>, <CODE>JMSTimestamp</CODE>,
<CODE>JMSCorrelationID</CODE>, and <CODE>JMSType</CODE>.
<CODE>JMSMessageID</CODE>, <CODE>JMSCorrelationID</CODE>, and
<CODE>JMSType</CODE> values may be null and if so are treated as a
<CODE>NULL</CODE> value.
<LI>Any name beginning with <CODE>'JMSX'</CODE> is a JMS defined
property name.
<LI>Any name beginning with <CODE>'JMS_'</CODE> is a provider-specific
property name.
<LI>Any name that does not begin with <CODE>'JMS'</CODE> is an
application-specific property name.
</UL>
<LI>White space is the same as that defined for the Java programming
language: space, horizontal tab, form feed, and line terminator.
<LI>Expressions:
<UL>
<LI>A selector is a conditional expression; a selector that evaluates
to <CODE>true</CODE> matches; a selector that evaluates to
<CODE>false</CODE> or unknown does not match.
<LI>Arithmetic expressions are composed of themselves, arithmetic
operations, identifiers (whose value is treated as a numeric
literal), and numeric literals.
<LI>Conditional expressions are composed of themselves, comparison
operations, and logical operations.
</UL>
<LI>Standard bracketing <CODE>()</CODE> for ordering expression evaluation
is supported.
<LI>Logical operators in precedence order: <CODE>NOT</CODE>,
<CODE>AND</CODE>, <CODE>OR</CODE>
<LI>Comparison operators: <CODE>=</CODE>, <CODE>></CODE>, <CODE>>=</CODE>,
<CODE><</CODE>, <CODE><=</CODE>, <CODE><></CODE> (not equal)
<UL>
<LI>Only like type values can be compared. One exception is that it
is valid to compare exact numeric values and approximate numeric
values; the type conversion required is defined by the rules of
numeric promotion in the Java programming language. If the
comparison of non-like type values is attempted, the value of the
operation is false. If either of the type values evaluates to
<CODE>NULL</CODE>, the value of the expression is unknown.
<LI>String and boolean comparison is restricted to <CODE>=</CODE> and
<CODE><></CODE>. Two strings are equal
if and only if they contain the same sequence of characters.
</UL>
<LI>Arithmetic operators in precedence order:
<UL>
<LI><CODE>+</CODE>, <CODE>-</CODE> (unary)
<LI><CODE>*</CODE>, <CODE>/</CODE> (multiplication and division)
<LI><CODE>+</CODE>, <CODE>-</CODE> (addition and subtraction)
<LI>Arithmetic operations must use numeric promotion in the Java
programming language.
</UL>
<LI><CODE><I>arithmetic-expr1</I> [NOT] BETWEEN <I>arithmetic-expr2</I>
AND <I>arithmetic-expr3</I></CODE> (comparison operator)
<UL>
<LI><CODE>"age BETWEEN 15 AND 19"</CODE> is
equivalent to
<CODE>"age >= 15 AND age <= 19"</CODE>
<LI><CODE>"age NOT BETWEEN 15 AND 19"</CODE>
is equivalent to
<CODE>"age < 15 OR age > 19"</CODE>
</UL>
<LI><CODE><I>identifier</I> [NOT] IN (<I>string-literal1</I>,
<I>string-literal2</I>,...)</CODE> (comparison operator where
<CODE><I>identifier</I></CODE> has a <CODE>String</CODE> or
<CODE>NULL</CODE> value)
<UL>
<LI><CODE>"Country IN (' UK', 'US', 'France')"</CODE>
is true for
<CODE>'UK'</CODE> and false for <CODE>'Peru'</CODE>; it is
equivalent to the expression
<CODE>"(Country = ' UK') OR (Country = ' US') OR (Country = ' France')"</CODE>
<LI><CODE>"Country NOT IN (' UK', 'US', 'France')"</CODE>
is false for <CODE>'UK'</CODE> and true for <CODE>'Peru'</CODE>; it
is equivalent to the expression
<CODE>"NOT ((Country = ' UK') OR (Country = ' US') OR (Country = ' France'))"</CODE>
<LI>If identifier of an <CODE>IN</CODE> or <CODE>NOT IN</CODE>
operation is <CODE>NULL</CODE>, the value of the operation is
unknown.
</UL>
<LI><CODE><I>identifier</I> [NOT] LIKE <I>pattern-value</I> [ESCAPE
<I>escape-character</I>]</CODE> (comparison operator, where
<CODE><I>identifier</I></CODE> has a <CODE>String</CODE> value;
<CODE><I>pattern-value</I></CODE> is a string literal where
<CODE>'_'</CODE> stands for any single character; <CODE>'%'</CODE>
stands for any sequence of characters, including the empty sequence;
and all other characters stand for themselves. The optional
<CODE><I>escape-character</I></CODE> is a single-character string
literal whose character is used to escape the special meaning of the
<CODE>'_'</CODE> and <CODE>'%'</CODE> in
<CODE><I>pattern-value</I></CODE>.)
<UL>
<LI><CODE>"phone LIKE '12%3'"</CODE> is true for
<CODE>'123'</CODE> or <CODE>'12993'</CODE> and false for
<CODE>'1234'</CODE>
<LI><CODE>"word LIKE 'l_se'"</CODE> is true for
<CODE>'lose'</CODE> and false for <CODE>'loose'</CODE>
<LI><CODE>"underscored LIKE '\_%' ESCAPE '\'"</CODE>
is true for <CODE>'_foo'</CODE> and false for <CODE>'bar'</CODE>
<LI><CODE>"phone NOT LIKE '12%3'"</CODE> is false for
<CODE>'123'</CODE> or <CODE>'12993'</CODE> and true for
<CODE>'1234'</CODE>
<LI>If <CODE><I>identifier</I></CODE> of a <CODE>LIKE</CODE> or
<CODE>NOT LIKE</CODE> operation is <CODE>NULL</CODE>, the value
of the operation is unknown.
</UL>
<LI><CODE><I>identifier</I> IS NULL</CODE> (comparison operator that tests
for a null header field value or a missing property value)
<UL>
<LI><CODE>"prop_name IS NULL"</CODE>
</UL>
<LI><CODE><I>identifier</I> IS NOT NULL</CODE> (comparison operator that
tests for the existence of a non-null header field value or a property
value)
<UL>
<LI><CODE>"prop_name IS NOT NULL"</CODE>
</UL>
<P>JMS providers are required to verify the syntactic correctness of a
message selector at the time it is presented. A method that provides a
syntactically incorrect selector must result in a <CODE>JMSException</CODE>.
<P>The following message selector selects messages with a message type
of car and color of blue and weight greater than 2500 pounds:
<PRE>"JMSType = 'car' AND color = 'blue' AND weight > 2500"</PRE>
<H4>Null Values</H4>
<P>As noted above, property values may be <CODE>NULL</CODE>. The evaluation
of selector expressions containing <CODE>NULL</CODE> values is defined by
SQL92 <CODE>NULL</CODE> semantics. A brief description of these semantics
is provided here.
<P>SQL treats a <CODE>NULL</CODE> value as unknown. Comparison or arithmetic
with an unknown value always yields an unknown value.
<P>The <CODE>IS NULL</CODE> and <CODE>IS NOT NULL</CODE> operators convert
an unknown value into the respective <CODE>TRUE</CODE> and
<CODE>FALSE</CODE> values.
<P>The boolean operators use three-valued logic as defined by the
following tables:
<P><B>The definition of the <CODE>AND</CODE> operator</B>
<PRE>
| AND | T | F | U
+------+-------+-------+-------
| T | T | F | U
| F | F | F | F
| U | U | F | U
+------+-------+-------+-------
</PRE>
<P><B>The definition of the <CODE>OR</CODE> operator</B>
<PRE>
| OR | T | F | U
+------+-------+-------+--------
| T | T | T | T
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