DbForms application JSPs contain tags for building the application functionality. These tags are defined in the tag library document, not in this section.

The application web deployment descriptor file web.xml must contain specific content for DbForms. See Section 4.3, “Building your own DbForms-capable applications” and, in particular, Section 4.3.1, “Edit deployment descriptor web.xml” for more information about the requirements for web.xml.

The other key application configuration file is dbforms-config.xml which is the subject of the remainder of this chapter. Errors in this file often cause errors in the execution of a DbForms web application. Whenever a change is made to this file, it is wise to check the servlet engine log files for any errors listed there.

The dbforms-config.xml is read when the servlet container is started or when the web application is reloaded. If there are any errors in this file, the DbForms parser will abort with an exception. The web application will then be left in an indeterminate state. Typically, the servlet engine (such as Tomcat) will continue to service requests for the web application but these will encounter a error such as a Java "No DbConnection object configured with name 'null'" exception.

Setting up the configuration file dbforms-config.xml is an important part of creating a DbForms application. This file defines the set of database tables to be used, defines the database connectivity needed to perform operations, and supplies information and parameters for more advanced capabilities such as interceptors and defined queries. The DevGui tool described in Chapter 5, DevGui provides an easy way to create an initial version of dbforms-config.xml. DevGui uses JDBC to connect with your database and automatically extract table definitions needed for DbForms.

The top level structure of the dbforms-config.xml file is shown below. The root element is <dbforms-config> and this, of course, occurs only one time. The seven subelements shown inside of the root element must appear in the order shown.

   <dbforms-config>
     <table></table>  
     <query></query>  
     <events></events>  
     <dbconnection></dbconnection>  
     <DOMFactoryClass></DOMFactoryClass>  
     <DefaultEscaperClass></DefaultEscaperClass>  
     <interceptors></interceptors>  
   </dbforms-config>

The first four subelements, with tags <table> through <dbconnection>, can appear zero or more times. The remaining subelements, tags <DOMFactoryClass> through <interceptors>, may occur zero or one time. Since all subelements are optional, an empty root tag is valid although not useful.