Adobe 38043740 Developing Applications - Page 252

DEVELOPING COLDFUSION 9 APPLICATIONS 247 Developing CFML Applications Using the onRequest method The onRequest method differs from the onRequestStart method in one major way: the onRequest method intercepts the user's request. This difference has two implications: • ColdFusion does not process the request unless you explicitly call it, for example, by using a cfinclude tag. This behavior lets you use the onRequest method to filter requested page content or to implement a switch that determines the pages or page contents to be displayed. • When you use cfinclude to process request, the CFC instance shares the Variables scope with the requested page. As a result, any method in the CFC that executes can set the page's Variables scope variables, and the onRequestEnd method can access any Variable scope values that the included page has set or changed. Therefore, for example, the onRequestStart or onRequest method set variables that are used on the page. To use this method as a filter, place the cfinclude tag inside a cfsavecontent tag, as the following example shows: #replace(content, "report", "MyCompany Quarterly Report", "all")# For more information, see the entry for onRequest in the CFML Reference Using the onRequestEnd method You use the onRequestEnd method for code that should run at the end of each request. (In ColdFusion versions through ColdFusion MX 6.1, you would use the OnRequestEnd.cfm page for such code). Typical uses include displaying dynamic footer pages. For an example, see onSessionEnd in the CFML Reference. Note: If you do not include an onRequest method in Application.cfm file, the onRequestEnd method does not share a Variables scope with the requested page, but it does share Request scope variables. For more information, see the entry for onRequestEnd in the CFML Reference. Handling errors in Application.cfc The following sections briefly describe how you to handle errors in Application.cfc. For more information on error pages and error handling, see "Handling Errors" on page 275 For details on implementing the onError method, see onError in the CFML Reference. Application.cfc error handling techniques Application.cfc handles errors in any combination of the following ways: • Use try/catch error handling in the event methods, such as onApplicationStart or onRequestStart, to handle exceptions that happen in the event methods. • Implement the onError method. This method receives all exceptions that are not directly handled by try/catch handlers in CFML code. The method can use the cfthrow tag to pass any errors it does not handle to ColdFusion for handling. • Use cferror tags in the application initialization code following the cfcomponent tag, typically following the code that sets the application's This scope variables. These tags specify error processing if you do not implement an onError method, or if the onError method throws an error. You could implement an application-specific validation error handler, for example, by placing the following tag in the CFC initialization code: Last updated 1/20/2012