qr barcode generator vb.net Using JDBC from a Stateful Session Bean in Software

Drawing QR Code JIS X 0510 in Software Using JDBC from a Stateful Session Bean

Using JDBC from a Stateful Session Bean
Read QR Code In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Make QR-Code In None
Using Barcode encoder for Software Control to generate, create QR Code JIS X 0510 image in Software applications.
PART VI
Decoding QR Code ISO/IEC18004 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
Generate QR Code In C#.NET
Using Barcode printer for VS .NET Control to generate, create QR Code image in .NET applications.
Many web interactions can t live with the limitations imposed by stateless session beans. Consider a more complex web-based form that spans four pages. As the user fills out each page and sends it to the web site, the session bean must accumulate the information and retain it across the four page clicks until all of the data is ready to be captured into a database. The need to retain information across method invocations calls for a stateful session bean.
QR Code Creator In .NET
Using Barcode maker for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
QR Printer In .NET Framework
Using Barcode generator for Visual Studio .NET Control to generate, create QR Code JIS X 0510 image in Visual Studio .NET applications.
Part VI:
QR Code Generator In VB.NET
Using Barcode printer for VS .NET Control to generate, create QR Code JIS X 0510 image in Visual Studio .NET applications.
Paint GS1 - 12 In None
Using Barcode printer for Software Control to generate, create GTIN - 12 image in Software applications.
SQL Today and Tomorrow
Encode ANSI/AIM Code 128 In None
Using Barcode printer for Software Control to generate, create Code-128 image in Software applications.
Create Code 39 Full ASCII In None
Using Barcode creation for Software Control to generate, create Code-39 image in Software applications.
Display ABC Corp. Price: $15.75 Web browser
Barcode Maker In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
Encoding GS1 128 In None
Using Barcode encoder for Software Control to generate, create EAN 128 image in Software applications.
Internet HTTP request HTML results
Painting ISBN - 13 In None
Using Barcode generator for Software Control to generate, create ISBN - 10 image in Software applications.
Bar Code Decoder In Visual Basic .NET
Using Barcode recognizer for .NET framework Control to read, scan read, scan image in VS .NET applications.
Web server AppSvr request Application server Session bean Java code JDBC SQL request SQL results HTML results
Draw Code 39 Extended In C#
Using Barcode creation for VS .NET Control to generate, create Code 39 Extended image in .NET applications.
EAN / UCC - 14 Creator In .NET
Using Barcode drawer for ASP.NET Control to generate, create EAN128 image in ASP.NET applications.
Database server(s)
Paint Barcode In .NET
Using Barcode drawer for Visual Studio .NET Control to generate, create bar code image in .NET framework applications.
Paint Data Matrix 2d Barcode In Java
Using Barcode printer for Eclipse BIRT Control to generate, create Data Matrix 2d barcode image in BIRT applications.
FIGURE 22-4
Matrix 2D Barcode Creator In .NET
Using Barcode creation for Visual Studio .NET Control to generate, create 2D Barcode image in .NET framework applications.
Decode Code 128 Code Set C In VB.NET
Using Barcode recognizer for .NET framework Control to read, scan read, scan image in VS .NET applications.
Database calls from a stateless session bean
Another example in which a stateful session bean is appropriate is a commercial web site where a user shops online and accumulates a list of items to be purchased in an online shopping cart. After 40 or 50 clicks through the web site, the user may have accumulated five or six items in the shopping cart. If the user then clicks a button requesting display of the current shopping cart contents, those contents are probably most easily maintained as a session bean state. In both of these examples, the session bean requires continuity of database access to effectively accomplish its tasks. Figure 22-5 shows the pattern, in contrast to the pattern of interactions in Figure 22-4. Even if the bean can be implemented without instance variables (for example, by storing all of its state information in a back-end database), it needs one continuous database session to carry out its database access. The client-side API for the DBMS maintains this session, and the API itself will need to maintain session-state information across session bean method invocations.
22:
SQL and Application Servers
Display Shopping cart Items pants skirt shorts shoes Web browser
Internet
Multiple calls add to shopping cart Application server Stateful session bean Java code
Web server
Instance variables (shopping cart contents) JDBC SQL request SQL results
Database server(s)
FIGURE 22-5
Database calls from a stateful session bean
Entity Bean Database Access
It s possible to implement complete, sophisticated web site applications using session beans deployed on a J2EE application server. However, programming an application using session beans tends to produce more procedural, less object-oriented code. The object-oriented philosophy is to have object classes (in this case, EJB classes) represent real-world entities, such as customers or offices, and to have object instances represent individual customers or offices. But session beans don t represent any of those entities; they represent currently active user sessions. When database interaction is handled directly by session beans, the representation of real-world entities is basically left in the database; it doesn t have an object counterpart. Entity beans provide the object counterpart for real-world entities and the rows in a relational database table that represent them. Entity bean classes embody customers and offices; individual entity bean instances represent individual customers and individual offices. Other objects (such as session beans) within the application server can interact with customers and offices using object-oriented techniques, by invoking the methods of the entity beans that represent them.
PART VI
Part VI:
SQL Today and Tomorrow
To maintain this object-oriented model, there must be very close cooperation between the entity-bean representations of entities and their database representations. If a session bean invokes a customer entity bean method that changes a customer s credit limit, that change must be reflected in the database, so that an order-processing application using the database will use the new limit. Similarly, if an inventory management application adds to the quantity on hand for a particular product in the database, that product s entity bean in the application server must be updated. Just as an application server will passivate and reactivate session beans as necessary, it will passivate and reactivate entity beans repeatedly in response to a heavy workload. Before the application server passivates an entity bean, the bean s state must be saved in a persistent way, by updating the database. Similarly, when the application server reactivates an entity bean, its instance variables must be set to their values just before it was passivated, by reloading those values from the database. The entity bean class defines callback methods that an entity bean must provide to implement this synchronization. There is close correspondence between actions carried out on entity beans and database actions, as shown in Table 22-1. The J2EE specification provides two alternative ways to manage this coordination: Bean-managed persistence The entity bean itself is responsible for maintaining synchronization with the database. The application programmer who develops the entity bean and codes its implementation methods must use JDBC to read and write data in the database when necessary. The application server container notifies the bean when it takes actions that require database interaction. Container-managed persistence The EJB container provided by the application server is responsible for maintaining synchronization with the database. The container monitors interaction with the entity bean, and automatically uses JDBC to read and write data in the database and to update the instance variables within the bean when needed. The application programmer who develops the entity bean and codes its implementation methods can focus on the business logic in the bean, and assume that its instance variables will accurately represent the state of the data in the database.
Database Statement INSERT EJB Method ejbCreate(), ejbPostCreate() EJB/Database Action Creates a new entity bean instance; initial state of the bean is specified by parameters in the create() call. A new row with these values must be inserted into the database. Loads instance variable values, reading them from the persistent data in the database. Stores instance variable values, saving them persistently in the database. Removes an entity bean instance; the corresponding row in the database must be deleted.
Copyright © OnBarcode.com . All rights reserved.