How Does Struts2 Handle Conversion and Validation Errors and Ensure Proper Input?

Understanding Struts2's INPUT Result and Handling Conversion/Validation Errors

Conversion/Validation Errors: Not Blocking Errors

Struts2 treats conversion and validation errors as input errors rather than blocking errors. This means it doesn't raise exceptions but instead notifies the user and requests a valid input.

How it Works

1. Parameters Interceptor: Attempts to set parameters. If a runtime exception like NumberFormatException occurs, it's handled or logged.
2. Conversion Errors Interceptor: Checks for conversion errors and adds field errors accordingly. Original values are saved to display the correct input on subsequent requests.
3. Validation Interceptor: Performs requested validations and adds field errors for invalid fields.
4. Workflow Interceptor: Checks for field errors. If none, the execution continues. If errors are found, an INPUT result is returned.

Correct Interceptor Order

To ensure the mechanism works, the following interceptors should be present in the Custom Stack in the correct order:

• Parameters Interceptor
• Conversion Error Interceptor
• Validation Interceptor
• Workflow Interceptor

Side Question: Alphabets as Zero

When an alphabet is entered in an integer field, it's the default behavior for the getter of that field to return 0 (if int is used).

Original Value Handling

The Conversion Interceptor claims to save the original values for subsequent requests. However, a bug existed where this behavior was not consistent if the value attribute was used in the JSP tag. This bug has been fixed, so the original value should be displayed correctly in subsequent requests.

Best Practices

• Configure the Interceptor Stack correctly.
• Check the code, especially the use of the value attribute.
• If using the value attribute, use the correct syntax, e.g., value = "%{myIntField}".
• For testing, initially remove the value attribute to confirm the behavior and then debug to find the bug.

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