The JMS clients send messages to message queues managed by the server (e.g., an email inbox can be a message queue). The message queues are monitored by a special kind of EJBs --Message Driven Beans (MDBs). The MDB processes the incoming messages and perform the services requested by the message. The MDBs are the end-point for JMS service request messages.
JMS客戶端向消息隊列(比如收件箱)發送消息。
消息隊列(收件箱)由MDB監視，MDB處理進來的消息并提供消息所需要的服務
In this trail, the investment calculator application is refactored to use a Message Driven Bean. When you click on the "Calculate" button on the web form, the JSP page (calculator.jsp) sends a message containing the calculation parameters to a message queue. It then forwards to another JSP page (check.jsp) to periodically check whether the calculation result becomes available.
當你點擊頁面中的Calculate按鈕時，JSP會把含有計算所需參數的信息發送到一個消息隊列，然后頁面跳轉到check.jsp, check.jsp不斷刷新自己以定期檢查計算結果是否可用。
The message queue is monitored by a MDB, which retrieves the incoming message, parses its contents, and performs the calculation. After the calculation is done, the MDB saves the result to an application-wide shared cache. The result is then picked up and displayed by the result-monitoring JSP page (i.e., check.jsp).
該消息隊列由一個MDB監控，當它檢索到一條消息后，解析消息內容，然后進行計算，然后把計算 結果放在application中。最后這個結果被check.jsp捕獲并顯示。
1。監聽器 The Message Driven Beans
@MessageDriven(activationConfig?
=
{
??@ActivationConfigProperty(propertyName
=
"
destinationType
"
,
????propertyValue
=
"
javax.jms.Queue
"
),
??@ActivationConfigProperty(propertyName
=
"
destination
"
,
????propertyValue
=
"
queue/mdb
"
)
})
public
?
class
?CalculatorBean?
implements
?MessageListener?{
??
public
?
void
?onMessage?(Message?msg)?{
????
try
?{
??????TextMessage?tmsg?
=
?(TextMessage)?msg;
??????Timestamp?sent?
=
??????????
new
?Timestamp(tmsg.getLongProperty(
"
sent
"
));
??????StringTokenizer?st?
=
??????????
new
?StringTokenizer(tmsg.getText(),?
"
,
"
);
??????
int
?start?
=
?Integer.parseInt(st.nextToken());
??????
int
?end?
=
?Integer.parseInt(st.nextToken());
??????
double
?growthrate?
=
?Double.parseDouble(st.nextToken());
??????
double
?saving?
=
?Double.parseDouble(st.nextToken());
??????
double
?result?
=
??????????calculate?(start,?end,?growthrate,?saving);
??????RecordManager.addRecord?(sent,?result);
????}?
catch
?(Exception?e)?{
??????e.printStackTrace?();
????}
??}
}
MDB用@MessageDriven標注
destinationType 表示所監聽的消息的類型
destination 表示所監聽的消息隊列的名字(比如queue/mdb)
如果這個隊列并不存在, JBoss會在deploy的時候自動創建一個，所以不需要XML配置文件!
2。在客戶端的使用
?
<%
@?page?
import
=
"
trail.mdb.*,?javax.naming.*,?java.text.*,
??????????????????javax.jms.
*
,
??????????????????java.sql.Timestamp
"
%>
?
?
<%
???
if
?(
"
send
"
.equals(request.getParameter?(
"
action
"
)))?{
?
?????QueueConnection?cnn?
=
?
null
;
?????QueueSender?sender?
=
?
null
;
?????QueueSession?sess?
=
?
null
;
?????Queue?queue?
=
?
null
;
?
?????
try
?{
???????InitialContext?ctx?
=
?
new
?InitialContext();
???????queue?
=
?(Queue)?ctx.lookup(
"
queue/mdb
"
);
???????QueueConnectionFactory?factory?
=
???????????(QueueConnectionFactory)?ctx.lookup(
"
ConnectionFactory
"
);
???????cnn?
=
?factory.createQueueConnection();
???????sess?
=
?cnn.createQueueSession(
false
,
???????????????????QueueSession.AUTO_ACKNOWLEDGE);
?
?????}?
catch
?(Exception?e)?{
???????e.printStackTrace?();
?????}
?
?????TextMessage?msg?
=
?sess.createTextMessage(
?????????request.getParameter?(
"
start
"
)?
+
?
"
,
"
?
+
?????????request.getParameter?(
"
end
"
)?
+
?
"
,
"
?
+
?????????request.getParameter?(
"
growthrate
"
)?
+
?
"
,
"
?
+
?????????request.getParameter?(
"
saving
"
)
?????);
?????
//
?The?sent?timestamp?acts?as?the?message's?ID
?????
long
?sent?
=
?System.currentTimeMillis();
?????msg.setLongProperty(
"
sent
"
,?sent);
?
?????sender?
=
?sess.createSender(queue);
?????sender.send(msg);
?????
//
?sess.commit?();
?????sess.close?();
?
%>
To use the message driven bean, the client (i.e, JSP page calculator.jsp in this case) use the standard JMS API to obtain the target message queue to the MDB using the queue name (queue/mdb), and then send the message to the queue.
to be continued