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Building a Java servlet framework using reflection, Part 1

Reflective code provides more functionality in fewer lines of code.

By Michael Cymerman, JavaWorld.com, 11/22/99

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Common Gateway Interface (CGI) scripting languages like Perl may offer as many features as the Java Servlet API, but servlets significantly outperform their CGI cousins when compared on any given functionality.

Building a Java servlet framework using reflection: Read the whole series!



Many developers who have made the transition from CGI scripting to Java servlets have continued the CGI development style in Java, even though that style may not be the most efficient option available to them. Consider this example: programmers typically use servlets to interpret the input of a Web browser, determine an appropriate course of action, and then display results to the user. The process the servlet handles is thus fourfold: control, business logic, data access, and presentation. In the CGI framework, a single CGI script handled this entire process. Those who continue to program in a CGI style often create monolithic servlets to handle all four of these actions.

It doesn't need to be that way. This article will provide a tool which developers can use to create efficient, easy-to-maintain, server-side Java code.

Framework overview

The actions usually performed in a request-response model have four general characteristics:

Controller: Coordinates all of the other components

Business logic: Executes business rules, like validation, in order to satisfy the request

Data logic: Provides access to any necessary databases, CORBA services, EJBs, or other back-office persistence mechanisms

Presentation logic: Displays the results to the client



This framework does not depend on the presence of Java servlets. All it needs is agreement among developers on the contracts among objects. Some developers should be responsible for the controller code, which can be servlets, CORBA or RMI servers, or Netscape Application Server AppLogics. The other development teams need not be bothered about the specific implementation of those controller components; they need only use the methods provided by the controller objects.

How to create a servlet framework

You can create a servlet framework by assigning responsibilities to various system components. This in turn requires establishing a coding interfaces. The boundary lines between component groups must be drawn so that no object of one group can be used by any object outside that group. For example, be sure that no platform-specific object (like HttpservletRequest) or method is used by any noncontroller component.

A segmented system can be completely self-contained. For example, the team developing the data components can work to make it satisfy the following interface (a simple case), or something similar: 

public interface DataInterface
{
    public void initializeDataObject();
    public void beginTransaction();
    public void commitTransaction();
    public void rollbackTransaction();
    public void executeSQL(String sqlString);
}


This is a simple interface for logging user actions or accepting user inputs to a database. Because all DataObjects must satisfy the DataInterface, it is possible for a single object to perform the duties associated with the database interaction. Again, no component outside of the data functionality should have to deal with connection pooling or database parameters.

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