Adobe 38043740 Developing Applications - Page 281

DEVELOPING COLDFUSION 9 APPLICATIONS 276 Developing CFML Applications • How to use the cferror tag to specify error-handling pages • How to log errors • How to handle ColdFusion exceptions Note: Information about using the cftry and cfcatch tags is provided, but not the equivalent CFScript try and catch statements. The general discussion of exception handling applies to tags and CFScript statements. However, the code that you use and the information available in CFScript differs from the information in the tags. For more information on handling exceptions in CFScript, see "Handling errors in UDFs" on page 166. Understanding errors You can look at errors in many ways; for example, you can look at errors by their causes. You can also look at them by their effects, particularly by whether your application can recover from them. You can also look at them the way ColdFusion does, as follows: About error causes and recovery Errors can have many causes. Depending on the cause, the error can be recoverable. A recoverable error is one for which your application can identify the error cause and take action on the problem. Some errors, such as time-out errors, are recoverable without indicating to the user that an error was encountered. An error for which a requested application page does not exist is not recoverable, and the application can only display an error message. Errors such as validation errors, for which the application cannot continue processing the request, but can provide an error-specific response, can also be considered recoverable. For example, an error that occurs when a user enters text where a number is required can be considered recoverable, because the application can recognize the error and redisplay the data field with a message providing information about the cause of the error and telling the user to reenter the data. Some types of errors are recoverable in some, but not all circumstances. For example, your application can retry a request following a time-out error, but it must also be prepared for the case where the request always times out. Error causes fall in the broad categories listed in the following table: Category Program errors Data errors System errors Description Can be in the code syntax or the program logic. The ColdFusion compiler identifies and reports program syntax errors when it compiles CFML into Java classes. Errors in your application logic are harder to locate. For information on debugging tools and techniques, see "Debugging and Troubleshooting Applications" on page 378. Unlike ColdFusion syntax errors, SQL syntax errors are only caught at runtime. Are typically user data input errors. You use validation techniques to identify errors in user input data and enable the user to correct the errors. Can come from a variety of causes, including database system problems, time-outs due to excessive demands on your server, out-of-memory errors in the system, file errors, and disk errors. Although these categories do not map completely to the way ColdFusion categorizes errors they provide a useful way of thinking about errors and can help you in preventing and handling errors in your code. ColdFusion error types Before you can effectively manage ColdFusion errors, you must understand how ColdFusion classifies and handles them. ColdFusion categorizes errors as detailed in the following table: Last updated 1/20/2012