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pdf417 javascript library See also in Java
See also PDF-417 2d Barcode Printer In Java Using Barcode creation for Java Control to generate, create PDF-417 2d barcode image in Java applications. www.OnBarcode.comRead PDF-417 2d Barcode In Java Using Barcode scanner for Java Control to read, scan read, scan image in Java applications. www.OnBarcode.com6.1 Sending a publish/subscribe JMS message 6.3 Creating a message-driven Enterprise JavaBean 6.9 Filtering messages for a message-driven EJB Encoding QR Code In Java Using Barcode maker for Java Control to generate, create QR Code 2d barcode image in Java applications. www.OnBarcode.comBarcode Drawer In Java Using Barcode creation for Java Control to generate, create Barcode image in Java applications. www.OnBarcode.com6.8 Speeding up message delivery to a message-driven bean
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public class MessageBean implements MessageDrivenBean, MessageListener { private MessageDrivenContext ctx; public void ejbRemove() { } public void ejbActivate() { } public void ejbPassivate() { } public void setMessageDrivenContext(MessageDrivenContext ctx) { this.ctx = ctx; } public void ejbCreate () throws CreateException { } public void onMessage(Message msg) { MapMessage map= (MapMessage) msg; try { String symbol = map.getString("Symbol"); String description = map.getString("Description"); System.out.println("MDB received Symbol : " + symbol + " " + description ); } catch(Exception ex) { ex.printStackTrace(); } } } To ensure a single message is not duplicated across instances in the message-driven bean pool, the message-driven bean instances should use a message queue as the destination type. Listing 6.17 contains the deployment descriptor for the bean. Messaging
Listing 6.17 Deployment descriptor
<enterprise-beans> <message-driven> <ejb-name>concurrentMDB</ejb-name> <ejb-class>concurrent.MessageBean</ejb-class> <transaction-type>Container</transaction-type> <message-driven-destination> <destination-type>javax.jms.Queue</destination-type> </message-driven-destination> </message-driven> </enterprise-beans> Message-driven bean instance pools are created in a vendor-specific manner. Listing 6.18 shows how this is accomplished using the Weblogic application server. Notice the vendor XML creates a pool maximum size of five beans, with an initial size of two beans. Listing 6.18 Weblogic deployment descriptor
<weblogic-ejb-jar> <weblogic-enterprise-bean> Sets up the message<ejb-name>concurrentMDB</ejb-name> driven bean pool <message-driven-descriptor> <pool> <max-beans-in-free-pool>5</max-beans-in-free-pool> <initial-beans-in-free-pool>2</initial-beans-in-free-pool> </pool> <destination-jndi-name>BookJMSQueue</destination-jndi-name> </message-driven-descriptor> <jndi-name>concurrent.MBD</jndi-name> </weblogic-enterprise-bean> </weblogic-ejb-jar> Discussion
Using a bean pool is a quick and dirty way to achieve concurrent processing of messages. The pool, combined with a message queue, provides a way to process many messages at once without duplicating messages across instances. Creating an environment like this allows messages to start processing instead of waiting for previous messages to complete. You should use this type of processing only when Filtering messages for a message-driven EJB
concurrent processing of messages will not cause problems in your business logic or invalid states in your data. See also
6.1 Sending a publish/subscribe JMS message 6.3 Creating a message-driven Enterprise JavaBean
6.9 Filtering messages for a message-driven EJB
Problem
You want your message-driven beans to receive only the messages that they are intended to process.
Background
Message-driven beans that subscribe to a topic or receive messages from a queue should be able to handle messages of the wrong type (which should not invoke the message-driven business logic). Beans should just politely discard these messages when they are encountered. This is especially true for message-driven beans that exist in an environment with many different beans that watch a single source for incoming messages. However, it would be more efficient to avoid the execution time used for discarding messages and instead avoid receiving unwanted messages. Recipe
To selectively deliver messages to a message-driven bean, the bean should be deployed with a message selector. The bean source needs no changes in order to use the message selector. Listing 6.19 shows a simple message-driven bean that only wants messages that contain an attribute UserRole set to "BuyerRole". The bean prints out the role of the incoming message for verification. Listing 6.19 MessageBean.java
public class MessageBean implements MessageDrivenBean, MessageListener { private MessageDrivenContext ctx; public void onMessage(Message msg) { MapMessage map=(MapMessage)msg; try { String role = map.getString( "UserRole" ); Messaging
System.out.println("Received Message for Role: " + role); ProcessTheMessage( message ); } catch(Exception ex) { ex.printStackTrace(); } } } In the XML descriptor for the bean, you describe the message selector that filters undesired messages for the message-driven bean. Listing 6.20 shows the partial XML descriptor that describes the simple EJB and its message selector.
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