barcode font vb.net Building business logic with session beans in Java

Printing Data Matrix ECC200 in Java Building business logic with session beans

Building business logic with session beans
DataMatrix Maker In Java
Using Barcode creator for Java Control to generate, create Data Matrix 2d barcode image in Java applications.
www.OnBarcode.com
DataMatrix Decoder In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
@Remote(BidManager.class) @Stateless public class BidManagerBean { ... }
Creating Data Matrix In Java
Using Barcode printer for Java Control to generate, create Data Matrix ECC200 image in Java applications.
www.OnBarcode.com
UCC - 12 Printer In Java
Using Barcode encoder for Java Control to generate, create Universal Product Code version A image in Java applications.
www.OnBarcode.com
The preceding code marks the BidManager interface as remote through the bean class itself. This way, if you change your mind later, all you d have to do is change the access type specification in the bean class without ever touching the interface. Next, we move on to discussing the EJB lifecycle in our example.
Creating Code 128B In Java
Using Barcode creation for Java Control to generate, create ANSI/AIM Code 128 image in Java applications.
www.OnBarcode.com
Barcode Generator In Java
Using Barcode generator for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
3.2.4 Using bean lifecycle callbacks
Data Matrix Printer In Java
Using Barcode generation for Java Control to generate, create Data Matrix ECC200 image in Java applications.
www.OnBarcode.com
Code 2/5 Printer In Java
Using Barcode generation for Java Control to generate, create C 2 of 5 image in Java applications.
www.OnBarcode.com
We introduced you to lifecycle callback methods, or callbacks, earlier in the chapter; now let s take a deeper look at how they are used with stateless session beans. As far as EJB lifecycles go, stateless session beans have a simple one, as depicted in figure 3.5. In effect, the container does the following:
Make ECC200 In Visual C#
Using Barcode encoder for Visual Studio .NET Control to generate, create Data Matrix 2d barcode image in VS .NET applications.
www.OnBarcode.com
Generate DataMatrix In Visual Studio .NET
Using Barcode generation for VS .NET Control to generate, create Data Matrix ECC200 image in .NET applications.
www.OnBarcode.com
Figure 3.5 The chicken or the egg the stateless session bean lifecycle has three states: does not exist, idle, or busy. As a result, there are only two lifecycle callbacks corresponding to bean creation and destruction.
ANSI/AIM Code 39 Creator In None
Using Barcode generation for Font Control to generate, create USS Code 39 image in Font applications.
www.OnBarcode.com
Making UPC-A Supplement 2 In None
Using Barcode maker for Font Control to generate, create UCC - 12 image in Font applications.
www.OnBarcode.com
Stateless session beans
UPC A Maker In Visual Basic .NET
Using Barcode creator for Visual Studio .NET Control to generate, create GTIN - 12 image in VS .NET applications.
www.OnBarcode.com
Printing Code39 In .NET Framework
Using Barcode creator for ASP.NET Control to generate, create Code 39 image in ASP.NET applications.
www.OnBarcode.com
1 2 3 4
Make GS1 DataBar Expanded In .NET
Using Barcode printer for VS .NET Control to generate, create GS1 DataBar Stacked image in VS .NET applications.
www.OnBarcode.com
Drawing Barcode In Objective-C
Using Barcode encoder for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
Creates bean instances using the default constructor as needed. Injects resources such as database connections. Puts instances in a managed pool. Pulls an idle bean out of the pool when an invocation request is received from the client (the container may have to increase the pool size at this point). Executes the requested business method invoked through the business interface by the client. When the business method finishes executing, pushes the bean back into the method-ready pool. As needed, retires (a.k.a. destroys) beans from the pool.
Printing Matrix In Visual Basic .NET
Using Barcode drawer for Visual Studio .NET Control to generate, create Matrix 2D Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
UPC-A Creator In Objective-C
Using Barcode generator for iPad Control to generate, create UPC-A Supplement 5 image in iPad applications.
www.OnBarcode.com
An important point to note from the stateless session bean lifecycle is that since beans are allocated from and returned to the pool on a per-invocation basis, stateless session beans are extremely performance friendly and a relatively small number of bean instances can handle a large number of virtually concurrent clients. As you know, there are two types of stateless session bean lifecycle callback methods: (1) callbacks that are invoked when the PostConstruct event occurs immediately after a bean instance is created and set up, and all the resources are injected; and (2) callbacks that are invoked when the PreDestroy event occurs, right before the bean instance is retired and removed from the pool. Note that you can have multiple PostConstruct and PreDestroy callbacks for a given bean (although this is seldom used) in a class or in a separate interceptor class (discussed in chapter 5). In listing 3.1, the lifecycle callback methods embedded in the bean are initialize and cleanup. Callbacks must follow the pattern of void <METHOD>(). Unlike business methods, callbacks cannot throw checked exceptions (any exception that doesn t have java.lang.RuntimeException as a parent). Typically, these callbacks are used for allocating and releasing injected resources that are used by the business methods, which is exactly what we do in our example of BidManagerBean in listing 3.1. In listing 3.1 we open and close connections to the database using an injected JDBC data source. Recall that the addBid method in listing 3.1 inserted the new bid submitted by the user. The method created a java.sql.Statement from an open JDBC connection and used the statement to insert a record into the BIDS table. The JDBC connection object used to create the statement is a classic heavy-duty resource. It is
UPC Code Encoder In Objective-C
Using Barcode creator for iPhone Control to generate, create UPC Symbol image in iPhone applications.
www.OnBarcode.com
Printing Matrix 2D Barcode In .NET Framework
Using Barcode printer for .NET framework Control to generate, create Matrix image in Visual Studio .NET applications.
www.OnBarcode.com
Building business logic with session beans
expensive to open and should be shared across calls whenever possible. It can hold a number of native resources, so it is important to close the JDBC connection when it is no longer needed. We accomplish both these goals using callbacks as well as resource injection. In listing 3.1, the JDBC data source from which the connection is created is injected using the @Resource annotation. We explore injecting resources using the @Resource annotation in chapter 5; for now, this is all that you need to know. Let s take a closer look at how we used the callbacks in listing 3.1. PostConstruct callback The setDataSource method saves the injected data source in an instance variable. After injecting all resources, the container checks whether there are any designated PostConstruct methods that need to be invoked before the bean instance is put into the pool. In our case, we mark the initialize method in listing 3.1 with the @PostConstruct annotation:
@PostConstruct public void initialize() { ... connection = dataSource.getConnection(); ... }
In the initialize method, we create a java.sql.Connection from the injected data source and save it into the connection instance variable used in addBid each time the client invokes the method. PreDestroy callback At some point the container decides that our bean should be removed from the pool and destroyed (perhaps at server shutdown). The PreDestroy callback gives us a chance to cleanly tear down bean resources before this is done. In the cleanup method marked with the @PreDestroy annotation in listing 3.1, we tear down the open database connection resource before the container retires our bean:
@PreDestroy public void cleanup() { ... connection.close(); connection = null; ... }
Since bean instances from the pool are assigned randomly for each method invocation, trying to store client-specific state across method invocations is useless
Copyright © OnBarcode.com . All rights reserved.