How Does Struts2 Handle Input Errors and Return an INPUT Result?

How does Input Result Work in Struts2?

Struts2's INPUT result is triggered when the workflow interceptor detects field errors, either from conversion or validation errors. Rather than raising exceptions, these errors are considered input errors, so an INPUT result is returned to request user input correction.

Handling Conversion / Validation Errors

Struts2's error handling mechanism involves several key steps:

1. Parameter Interceptor: Attempts to set parameters. If a runtime exception occurs during conversion (e.g., NumberFormatException), it's swallowed silently or logged with a developer notification.
2. Conversion Errors Interceptor: Identifies any conversion errors and adds field errors to the ActionContext. It also stores original values to ensure they're displayed to the user if the field contains validation errors.
3. Validation Interceptor: Performs validations based on XML, annotations, or action methods. If validation fails, it adds field errors to the ActionContext for each non-complying field.
4. Workflow Interceptor: Checks for field errors from both conversion and validation. If errors exist, it returns an INPUT result; otherwise, it proceeds with the next interceptor.

To enable this mechanism, ensure that the following interceptors are defined in the correct order:

<interceptor-ref name="params"/>
<interceptor-ref name="conversionError"/>
<interceptor-ref name="validation"/>
<interceptor-ref name="workflow"/>

Additional Note on Integer Conversion

To handle the conversion of non-numeric characters to zero, avoid using the value attribute in conjunction with a getter that returns an int data type. This can cause an additional conversion error and result in a value of 0. Instead, use the following syntax:

<s:textfield name="myIntField"/>

Or

<s:textfield name="myIntField" value="%{myIntField}"/>

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