In Struts 1.1, you can change how Struts populates a form by
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Overriding the populate method of the ActionForm
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Overriding the processPopulate method of the Request Processor
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Overriding the populateBean method of the ActionMapping
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None
In Struts 1.1, the form population mechanism was moved from ActionForm to RequestProcessor. To customize how forms are populated, you override the processPopulate() method of RequestProcessor (option B). Option A is incorrect - ActionForm doesn't have a populate method, and C references a non-existent method.
In Struts 1.1, form population from request parameters happens inside RequestProcessor.processPopulate(), which calls form.reset() and then uses BeanUtils.populate() to copy matching request parameters onto the ActionForm's properties. Because this logic lives in the RequestProcessor (not the ActionForm or ActionMapping), overriding processPopulate() in a custom RequestProcessor subclass is the documented way to change how forms get populated — e.g., to add custom type conversion or extra population steps. ActionForm has no populate method and ActionMapping has no populateBean method, so those options are fabricated.