Question

I have a dropdown in my form that has a problem to populate when validation failed. I use xml validation with Preparable interface. To access data for dropdown I need to pass some ID from the form. The problem is when validation failed and prepare()/prepareInput() called, none of the variables in class including ID is set. ID is hidden parameter in the form that does not change. Please advice.
Thank you,
Yuri

Answer 1

prepare() in struts2 is rather synonymous with the role of init() in many other frameworks, that is it is called to initialise the action and fills a role very similar to the constructor.

There seems to be something missing… using the default-stack all the parameters on the action should have been set before validation is called. So if the client is indeed passing in the parameters I can not see why or how any would be missing unless some part of your logic clears them.

Sometimes it is necessary to acquire other objects as fields in your action derived from the values set by a form, or otherwise passed in as parameters. In this case you would like prepare to be called after values are set and then validate, if this scenario applies to you then the params-prepare-params stack is appropriate.

Personally, I would put preparation logic into the actions execute method rather than the prepare method. It is only when I put multiple actions into a single class that the prepare method is most appropriate as it factors out what would be repetition. Then the params-prepare-params is a special case that can crop up although I would argue the if you use DI it may never need to be used.

If this is not helpful please expand your question with the action class/xml mapping(if any) and provide the validation xml as well so we can see why this would be happening.