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If you are planning to deploy your database application on the Internet or Intranet, very soon you will need to deal with state management.' The stateless nature of Web architecture makes it radically different from the other (traditional) client-server architectures. The servers do not maintain any information on a client after the request is served. NetDynamics offers a solution for such problems. You can develop a fully object-oriented Web application in Java using the NetDynamics system. It supports server side Java for the generation of dynamic Web pages, application logic and database connectivity. It also addresses security, access control and flow control of the user in a Web application.

Installation and Configuration
Thanks to Installshield, installation is easy. The software requires about 20Mb of disk space. For development, it needs a §minimum of 32 Mb RAM on Windows 95/ NT3.51 and 48Mb on NT4.0. On UNIX, 50MB of hard disk and 64 Mb are RAM required. The installation requires HTTP servers. I had installations of Microsoft's Front Page Web Server and Netscape's Fasttrak. The Setup detected both the servers along with their port numbers. It allowed me to select HTTP server and an appropriate connectivity (CGI/NSAPI/ISAPI) to it. Then I could start the Application Server' without any hassle.

System Components, Architecture and Working
The NetDynamics solution is based on a three-tier architecture in which its application server, along with the HTTP server, forms a middle tier. The middle tier implements the business logic processing. The application server is responsible for session state management, automatic queuing, scheduling and load balancing. Since the server is always running, the Web request does not have to share the time overhead of starting and stopping it.

The HTTP server passes the HTTP request to the NetDynamics Application Server through a client connection (CC) interface. The CC can either be a lightweight CGI executable (20K) or you can use the Microsoft ISAPI runtime library or Netscape server API (NSAPI). The CC puts the request in a shared memory-based request queue. A Connection Processor (CP) monitors the queue, validates the access privileges and loads and executes the Java code corresponding to the project on a Java Virtual machine. For every connection, CP interacts with a Persistence Engine (PE) to verify the existence of the user session. For the existing user session, PE maintains the information related to the session and login privileges. The programmers can also store some data at the page level, user session level or global level for all projects. The CP puts a database-related request in another queue. The Data Servers monitor the request queue and interact with RDBMS/DBMS natively (for Oracle, Informix, Sybase) or using ODBC. NetDynamics 3.0, comes with a WebEXTEND module which enables DS to interact with enterprise applications like SAP and PeopleSoft. The DS establishes persistent connections with the database. These persistent connections enhance the performance. The DS then sends the database results to CP. Using this data, CP dynamically generates an HTML page as designed by an application programmer.

As an administrator, you can control the number of CPs and DS's on the application servers. Again, you can distribute application servers over multiple machines. This can make your system scalable and distributed, which I think is a pretty good architecture.

Figure 1
Figure 1: The NetDynamics Architecture

Session Management, Access Control and Flow Control
NetDynamics computes and encrypts a unique session ID to each session and stores it as a hidden field' on every page. It also allows you to store your own data at the page level, user session level or global (to all) level. This facility is very good for designing applications like shopping cart.

They also provide a good security mechanism. You can authenticate the users whenever they log into the application. You can select database tables, Java events or Gradient WebCrusader (third party software) to authenticate the user. It maintains an access privilege list at every page and verifies user access with the list.

Development Process
NetDynamics Studio is a GUI development environment for Rapid Application Development (RAD). If you have used any other visual development tool, you will find yourself on home ground. Using drag-and-drop facility, you can create page templates, data sources, data objects and security objects. You can also use wizards to create all of these objects. The wizards are very useful for creating most commonly required templates. With the page template wizard, you can create single or multiple pages (search, master-detailed or drill-down). Then, you can customize the pages by adding use interface elements like static text box, text box, list box, combo box and radio button. The HTML generator generates an HTML page template that you can customize to add client side Java applets, JavaScript or images. With the Inspector window, you can set the properties of each of these GUI objects. You can bind the display objects, such as text box or radio buttons, to columns of the data objects and you can automatically fill the list box or combo box with data from database tables. The data object itself is derived from single or multiple tables with SQL or stored procedure access. The studio automatically generates Java code for the page.

Figure 2
Figure 2: The NetDynamics Studio

Java API
NetDynamics's Java API is one of the best Java implementations. It is a set of classes organized in different packages - namely CSpider (general), visual, database, session, access and util, for adding your business logic. All classes begin with the characters "CSp", which stands for Spider (the former name of NetDynamics). The company name has changed but it is still stuck to the classes. Today, this is very common. However, it is better not to use thecompany name for API classes and methods!

  • CSpider Package consists of a static class called CSpider and other high level classes like CSpProject, etc. CSpider consists of static methods to access all projects, pages and data objects while creating project-specific information (e.g. session time out).
  • Visual Package consists of all server side classes of the GUI objects that the end user sees. It includes CSpPage, which is a server side container class. CSpPage can contain GUI classes like CSpTextBox, CSPListBox, CSpButton, etc.
  • Database Package contains classes related to relational databases as SQL abstraction (select, insert, update, delete and all), stored procedure abstraction, transaction processing, database schema, etc. You might frequently use methods related to joining tables or adding where clauses, (addDynamicCriterion). Here, I should note that the database API offers a high level abstraction. NetDynamics developed this excellent package well before JDBC was available. Still, if someone needs to access low level database calls, it is yet another API.' I look forward to seeing that JDBC API, which is planned to become an integral part of the existing API.
  • Session Package contains classes that are wrappers over standard Java data types. These classes have serialization and deserialization methods that make them sessionable. You can create your own sessionable objects using these classes.
  • Access package is very important for access control and privileges. It contains classes for security table, user profile, privileges and page flow security.
  • Util Package contains general purpose classes for error logging, encryption, named lists, etc.

The Java API seems to be very impressive. It is flexible and complex and you may need to allow a considerable learning time.

NetDynamics has developed a complex system on a very strong foundation. It provides a user-friendly development tool and excellent Java API. Through its session management capability, it has bridged the gap between the HTTP server and database server. Its security model makes it more suitable for the Web. While deploying your application, it is worth considering using JIT compilers for better performance

About the Author
Khanderao Kand is a Principal Consultant at TekEdge Corp., CA. He has been consulting at Informix and Cisco. Khanderao can be reached at kand@nestors-world.com


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