layout: default title: Checkbox Interceptor parent: title: Interceptors url: interceptors.html

Checkbox Interceptor

This interceptor is defined in the defaultStack. It is essential for handling HTML checkboxes, as unchecked checkboxes are not submitted as part of a form. This interceptor ensures that a value is always present for a checkbox, so that in the Action class, the property is not null.

How it works

The interceptor looks for a special hidden field in the form that is associated with the checkbox. This hidden field must have a name that starts with __checkbox_ followed by the name of the checkbox. For example, if your checkbox is named myCheckbox, the hidden field should be named __checkbox_myCheckbox.

When the form is submitted, the CheckboxInterceptor does the following:

  1. It iterates through the request parameters.
  2. If it finds a parameter that starts with __checkbox_, it extracts the name of the checkbox from it (e.g., myCheckbox).
  3. It then checks if a parameter with the checkbox's name (myCheckbox) exists in the request.
  4. If the checkbox parameter does not exist (which means the checkbox was unchecked), the interceptor adds a new parameter to the request with the checkbox's name and a value of false.
  5. Finally, it removes the __checkbox_ prefixed parameters from the request, so they are not processed further.

This ensures that the Action property for the checkbox will be set to false instead of being null.

The <s:checkbox> tag from the Struts UI Tags library automatically generates this hidden field for you.

Parameters

  • uncheckedValue - The default value for an unchecked box is false. You can override this by setting the uncheckedValue property on the interceptor.

Extending the Interceptor

This interceptor does not have any known extension points.

Checkbox lists usage with @StrutsParameter

The <s:checkboxlist> tag is used to render a list of checkboxes. When using this tag, the submitted values are populated into a Collection or an array in your Action. When using @StrutsParameter with a checkbox list, you must place the annotation on the setter method of the collection property.

Example

public class MyAction extends ActionSupport {
    private Collection<String> mySelection;

    @StrutsParameter
    public void setMySelection(Collection<String> mySelection) {
        this.mySelection = mySelection;
    }

    @StrutsParameter
    public Collection<String> getMySelection() {
        return mySelection;
    }
}