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The method as a controller in Java that I have written gets an File typed argument like below.
#RequestMapping(value = "/user/insertUser")
public String insertUser(#RequestParam("imageFile") CommonsMultipartFile file,
HttpSession session) throws Exception {
......}
What my problem is that when there is no File argument sent from a JSP , how I can handle it.
I am not sure if my explain was understandable though.

You can set defaultValue to handle null case:
#RequestMapping(value = "/user/insertUser")
public String insertUser(#RequestParam(value = "imageFile", required = false, defaultValue = "/default/path/to/file") CommonsMultipartFile file,
HttpSession session) throws Exception {
......}

I believe you are trying to make it as optional you can do
#RequestParam(value = "imageFile", required = false)

You need to give required = false for imageFile
#RequestMapping(value = "/user/insertUser")
public String insertUser(#RequestParam("imageFile", required = false) CommonsMultipartFile file,HttpSession session) throws Exception {
......}

You can do it as follows:
#RequestMapping(value = "/user/insertUser")
public String insertUser(#RequestParam("imageFile") CommonsMultipartFile file,
HttpSession session) throws Exception {
if(file!=null && !file.isEmpty()) {
//file is uploaded successfully
} else {
//file is not uploaded
}
}

If your question is whether you can provide an optional parameter as request param, you can do that by simply changing your #RequestParam to below.
#RequestParam(value = "imageFile", required = false) CommonsMultipartFile file
If you are using Java 8 you can also do the below.
#RequestParam("imageFile") Optional<CommonsMultipartFile> file
If your question is not this then please provide more details.

Here you can do this parameter as required = false so that you have option to sand this parameter or not.
{
#RequestMapping(value = "/user/insertUser")
public String insertUser(#RequestParam(value="imageFile",required=false) CommonsMultipartFile file,
HttpSession session) throws Exception {
......}
}
using this, if you send "imageFile" then you will get on server, else you have not send "imageFile" then you will get it null.