type convert exception in spring mvc3 - spring

Question

I am using sping3 mvc in my application.
I have some entities which need the CRUD operation.
When query the record,the pagination may be needed,so I create the class Pagination:
class Pagination{
int page,
int pageSize,
String sort;
}
This is my Dao:
public List<Post> list(Pagination pagination) {
/////
return xxx;
}
In controller:
#RequestMapping(value = "/", method = RequestMethod.GET)
public String list(#RequestParam int page,#RequestParam int pageSize,#RequestParam String sort) {
List<Post> posts=postDao.list(new Pagination(page,pageSize,sort));
return "";
}
Now,if there no page or pageSize parameter in the httprequest,it will throw the typeconvert exception,in fact,I know I can redirect to the exception page but I do not want this. I want to use some default configuation in this case,for example:
http://xx/post/list ==>return all records without pagination
http://xx/post/list?page=1&pageSize=10&sort=id ==>pagination
http://xx/post/list?page=1 ==>pagination with the default pageSize(maybe 10) and sort(id)
http://xx/post/list?page=notnumber&pageSize=10 ==>pagination with page=1
Then I want to know where and how to validate and reset the Pagination parameter?

Answer 1

You can change your parameter datatype of int page and pageSize to String page and String pageSize, and after doing this you can just check whether the passed parameter values is not null. If parameter value is not null use passed value otherwise use default value.
like this
#RequestMapping(value = "/", method = RequestMethod.GET)
public String list(#RequestParam String page,#RequestParam String pageSize,#RequestParam String sort) {
if(page ==null)
page=1; // assign page default value 1 because user didn't pass page value.
if(pageSize==null)
pageSize=10; // assign pageSize default value 10 because user didn't pass pageSize value.
List posts=postDao.list(new Pagination(page,pageSize,sort));
return "";
}

Answer 2

You must understand that the parameters you send for request would be casted from String to int, for it better if you directly receive in String and call your constructor of Pagination.
You can use conditional instruction inline or other logic, up to u.
In this method u would call the constructor Pagination passing the values of request only when will be informed, another way will send default values that u must put in constants.
#RequestMapping(value = "/", method = RequestMethod.GET)
public String list(#RequestParam String page, #RequestParam String pageSize, #RequestParam String sort) {
List posts = postDao.list(new Pagination(
StringUtils.isEmpty(page) ? page : "1",
StringUtils.isEmpty(pageSize) ? pageSize : "15",
StringUtils.isEmpty(sort) ? sort : "asc"));
return "";
}