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Apache Struts 2 Documentation
Checkbox Interceptor
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`org.apache.struts2.interceptor.CheckboxInterceptor` is in the `defaultStack`. It checks each form parameter submitted to the action and if it finds one with a prefix of `_checkbox` it inserts a value for a parameter whose name is derived from the suffix to `_checkbox` if it does not exist. The default value inserted is `false` but this can be changed by setting the `uncheckedValue` parameter on the interceptor.

This means that a checkbox can be accompanied by a hidden input with the same name but a prefix of `_checkbox` so that if the checkbox is not checked on the form the action will still receive a value rather than the default HTML action of not providing a value for unchecked checkboxes.

## Parameters

- setUncheckedValue - The default value of an unchecked box can be overridden by setting the 'uncheckedValue' property.

## Extending the Interceptor