message.html

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 <P>JMSX properties defined in the specification as "set by provider on 
 send" are available to both the producer and the consumers of the message. 
 JMSX properties defined in the specification as "set by provider on 
 receive" are available only to the consumers.

 <P><CODE>JMSXGroupID</CODE> and <CODE>JMSXGroupSeq</CODE> are standard 
 properties that clients 
 should use if they want to group messages. All providers must support them.
 Unless specifically noted, the values and semantics of the JMSX properties 
 are undefined.

 <P>The JMS API reserves the <CODE>JMS_<I>vendor_name</I></CODE> property 
 name prefix for provider-specific properties. Each provider defines its own 
 value for <CODE><I>vendor_name</I></CODE>. This is the mechanism a JMS 
 provider uses to make its special per-message services available to a JMS 
 client.

 <P>The purpose of provider-specific properties is to provide special 
 features needed to integrate JMS clients with provider-native clients in a 
 single JMS application. They should not be used for messaging between JMS 
 clients.

 <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" title="interface in javax.jms"><CODE>QueueReceiver</CODE></A> and 
 <A HREF="../../javax/jms/TopicSubscriber.html" title="interface in javax.jms"><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&nbsp;BETWEEN&nbsp;15&nbsp;AND&nbsp;19"</CODE> is 
         equivalent to 
         <CODE>"age&nbsp;>=&nbsp;15&nbsp;AND&nbsp;age&nbsp;<=&nbsp;19"</CODE>
     <LI><CODE>"age&nbsp;NOT&nbsp;BETWEEN&nbsp;15&nbsp;AND&nbsp;19"</CODE> 
         is equivalent to 
         <CODE>"age&nbsp;<&nbsp;15&nbsp;OR&nbsp;age&nbsp;>&nbsp;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&nbsp;IN&nbsp;('&nbsp;UK',&nbsp;'US',&nbsp;'France')"</CODE>
         is true for 
         <CODE>'UK'</CODE> and false for <CODE>'Peru'</CODE>; it is 
         equivalent to the expression 
         <CODE>"(Country&nbsp;=&nbsp;'&nbsp;UK')&nbsp;OR&nbsp;(Country&nbsp;=&nbsp;'&nbsp;US')&nbsp;OR&nbsp;(Country&nbsp;=&nbsp;'&nbsp;France')"</CODE>
     <LI><CODE>"Country&nbsp;NOT&nbsp;IN&nbsp;('&nbsp;UK',&nbsp;'US',&nbsp;'France')"</CODE> 
         is false for <CODE>'UK'</CODE> and true for <CODE>'Peru'</CODE>; it 
         is equivalent to the expression 
         <CODE>"NOT&nbsp;((Country&nbsp;=&nbsp;'&nbsp;UK')&nbsp;OR&nbsp;(Country&nbsp;=&nbsp;'&nbsp;US')&nbsp;OR&nbsp;(Country&nbsp;=&nbsp;'&nbsp;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&nbsp;LIKE&nbsp;'12%3'"</CODE> is true for 
         <CODE>'123'</CODE> or <CODE>'12993'</CODE> and false for 
         <CODE>'1234'</CODE>
     <LI><CODE>"word&nbsp;LIKE&nbsp;'l_se'"</CODE> is true for 
         <CODE>'lose'</CODE> and false for <CODE>'loose'</CODE>
     <LI><CODE>"underscored&nbsp;LIKE&nbsp;'\_%'&nbsp;ESCAPE&nbsp;'\'"</CODE>
          is true for <CODE>'_foo'</CODE> and false for <CODE>'bar'</CODE>
     <LI><CODE>"phone&nbsp;NOT&nbsp;LIKE&nbsp;'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&nbsp;IS&nbsp;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&nbsp;IS&nbsp;NOT&nbsp;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>.
 JMS providers may also optionally provide some semantic checking at the time
 the selector is presented. Not all semantic checking can be performed at
 the time a message selector is presented, because property types are not known.
 
 <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&nbsp;=&nbsp;'car'&nbsp;AND&nbsp;color&nbsp;=&nbsp;'blue'&nbsp;AND&nbsp;weight&nbsp;>&nbsp;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: