- Home
- Products
- Integration
- Tutorial
- Barcode FAQ
- Purchase
- Company
birt barcode tool Working with message-driven beans in Java
Working with message-driven beans Data Matrix ECC200 Printer In Java Using Barcode maker for Java Control to generate, create Data Matrix 2d barcode image in Java applications. www.OnBarcode.comRecognizing Data Matrix In Java Using Barcode reader for Java Control to read, scan read, scan image in Java applications. www.OnBarcode.comMultithreading Your business application may require multithreaded message consumers that can process messages concurrently. MDBs help you avoid complexity because they handle multithreading right out of the box, without any additional code. They manage incoming messages among multiple instances of beans (in a pool) that have no special multithreading code themselves. As soon as a new message reaches the destination, an MDB instance is retrieved from the pool to handle the message, as figure 4.7 shows. This is popularly known as MDB pooling, which you ll learn about when we discuss the MDB lifecycle later in this chapter. Draw Code-39 In Java Using Barcode encoder for Java Control to generate, create Code39 image in Java applications. www.OnBarcode.comEncoding Quick Response Code In Java Using Barcode encoder for Java Control to generate, create QR Code image in Java applications. www.OnBarcode.comFigure 4.7 As soon as a message arrives at its destination, the container retrieves it and assigns a servicing MDB instance from the pool. Print Code-128 In Java Using Barcode encoder for Java Control to generate, create Code 128 Code Set B image in Java applications. www.OnBarcode.comGS1 - 13 Generation In Java Using Barcode maker for Java Control to generate, create EAN13 image in Java applications. www.OnBarcode.comSimplified messaging code In addition, MDBs relieve you from coding the mechanical aspects of processing messages tasks such as looking up connection factories or destinations, creating connections, opening sessions, creating consumers, and attaching listeners. As you ll see when we build the Turtle message consumer MDB, all these tasks are handled behind the scenes for you. In EJB 3, using sensible defaults for common circumstances eliminates most of the configuration. In the worst-case scenario, you ll have to supply configuration information using simple annotations or through the deployment descriptor. Starting message consumption To start picking up messages from the shipping request queue, someone needs to invoke the appropriate method in your code. In a production environment, it is not clear how this will be accomplished. Starting message consumption through a user-driven manual process obviously is not desirable. In a server environment, almost every means of executing the method on server startup is highly system dependent, not to mention awkward. The same is true about stopping message Linear Generator In Java Using Barcode generation for Java Control to generate, create Linear Barcode image in Java applications. www.OnBarcode.comStandard 2 Of 5 Generation In Java Using Barcode creator for Java Control to generate, create 2 of 5 Industrial image in Java applications. www.OnBarcode.comMessaging and developing MDBs
Paint ECC200 In Objective-C Using Barcode generator for iPhone Control to generate, create Data Matrix 2d barcode image in iPhone applications. www.OnBarcode.comDataMatrix Drawer In None Using Barcode generator for Online Control to generate, create Data Matrix 2d barcode image in Online applications. www.OnBarcode.comreceipt manually. On the other hand, registered MDBs would be bootstrapped or torn down gracefully by the container when the server is started or stopped. We ll continue consolidating these three points as we start investigating a real example of developing MDBs soon. Before we do that, though, let s list the simple rules for developing an MDB. Create PDF 417 In None Using Barcode maker for Software Control to generate, create PDF417 image in Software applications. www.OnBarcode.comRead Code 3/9 In VB.NET Using Barcode decoder for VS .NET Control to read, scan read, scan image in Visual Studio .NET applications. www.OnBarcode.com4.3.2 Programming rules
Universal Product Code Version A Generator In .NET Using Barcode drawer for Reporting Service Control to generate, create UPC-A Supplement 5 image in Reporting Service applications. www.OnBarcode.comUPC-A Supplement 2 Encoder In VS .NET Using Barcode creator for .NET framework Control to generate, create UPCA image in .NET framework applications. www.OnBarcode.comLike all EJBs, MDBs are plain Java objects that follow a simple set of rules and sometimes have annotations. Don t take these rules too seriously yet; simply note them in preparation for going through the code-intensive sections that follow. EAN / UCC - 13 Encoder In Visual Studio .NET Using Barcode encoder for ASP.NET Control to generate, create EAN / UCC - 14 image in ASP.NET applications. www.OnBarcode.comMaking EAN-13 Supplement 5 In Objective-C Using Barcode printer for iPad Control to generate, create GTIN - 13 image in iPad applications. www.OnBarcode.comThe MDB class must directly (by using the implements keyword in the class declaration) or indirectly (through annotations or descriptors) implement a message listener interface. The MDB class must be concrete. It cannot be either a final or an abstract class. The MDB must be a POJO class and not a subclass of another MDB. The MDB class must be declared public. The bean class must have a no-argument constructor. If you don t have any constructors in your Java class, the compiler will create a default constructor. The container uses this constructor to create a bean instance. You cannot define a finalize method in the bean class. If any cleanup code is necessary, it should be defined in a method designated as PreDestroy. You must implement the methods defined in the message listener interface. These methods must be public and cannot be static or final. You must not throw the javax.rmi.RemoteException or any runtime exceptions. If a RuntimeException is thrown, the MDB instance is terminated. Making Data Matrix In None Using Barcode generation for Online Control to generate, create Data Matrix 2d barcode image in Online applications. www.OnBarcode.comBarcode Drawer In None Using Barcode generator for Microsoft Excel Control to generate, create Barcode image in Excel applications. www.OnBarcode.comWe ll apply these rules next in developing our example MDB.
Barcode Maker In Objective-C Using Barcode maker for iPhone Control to generate, create Barcode image in iPhone applications. www.OnBarcode.comRead European Article Number 13 In None Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications. www.OnBarcode.com4.3.3 Developing a message consumer with MDB
Let s now explore developing an MDB by reworking the Turtle server JMS message consumer as an MDB. To make the code a bit more interesting, we ll actually implement the processShippingRequest method mentioned in the JMS code. Listing 4.2 shows the MDB code that first retrieves shipping requests sent to the queue and then saves each request in the Turtle database table named SHIPPING_REQUEST. Note that we re using JDBC for simplicity s sake and because it lets us demonstrate the MDB lifecycle methods for opening and closing JDBC
|
|