request.getParameter("fileName") returning null in post method of servlet . Why?

[Srinivasa Maddi]

Hi
When i try to read one of my html field(of type file) value from within the post method of HttpServlet its returning null.

My html code..

<form action="/FileTransfer/TempServlet" method="post" enctype="multipart/form-data">
File to Push: <input type="file" name="fileName"/>

My servlet code..

public class TempServlet extends HttpServlet {

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) 
                        throws ServletException, IOException {
        doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) 
                        throws ServletException, IOException {
    	String opr = request.getParameter("fileName");
    	System.out.println(opr);
    

Output: null

Any clue for this???

[Freddy Wong]

Are you trying to get the contect of the file or the filename?

Unfortunately, servlet doesn't provide a way to do that. You can take a look at Commons FileUpload.

[Srinivasa Maddi]

just file name and moreover here i was asked not to go with any third party jars.

[Bharat Mehta]

The Servlet and JSP specifications does not provide us with any special feature to handle multipart requests (file uploads).

However,we can use third party libraries or make their own framework for this.Writing our own code to handle this is just like re-inventing the wheel. As Freddy Wong suggested we can use package at http://commons.apache.org/fileupload/.

But somehow it comes to my mind, what if we use PUT method?

[Ulf Dittmer]

If you just want a file name, you can make the input field of type "text", and have the user enter the file name. Also, I would question the request not to use 3rd party libraries. It's a lot of work to recreate a file upload handling library from scratch; what would be the point of that?

what if we use PUT method?

HTML forms do not support PUT (and I'm not sure how that would help, either).

[Frank Eichfelder]

Have you tried to remove enctype="multipart/form-data" from the form tag?
I think you should receive the filename, if you omit the enctype-attribute.

[Bharat Mehta]

Pardon me folks if I am wrong here, as I have just started to take dive in the waters of Servlets.

But I tried with PUT method.... and it did worked. Here is a summary of what I did...

  <form action="WelcomeServlet" method="PUT" enctype="multipart/form-data">  
  File to Push: <input type="file" name="fileName"/>  
  </form>  

and the Servlet code where i override the doPut method goes like this:

   protected void doPut(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//Just to print the name of the file 
		resp.setContentType("text/html");
		PrintWriter out=resp.getWriter();
		out.println(req.getParameter("fileName"));
		
	} 

Any comments/thoughts on this?

[Srinivasa Maddi]

Thanks All,

But my problem still persists.
Question to Bharat : Even i tried the same (to be frank : just copy paste i have done )after you, but the control is not going to my servlet atall. Simply i am getting

The page cannot be displayed
The page you are looking for cannot be displayed because the address is incorrect.


After you submit the form how the url should change?

[Bharat Mehta]

Srinivas , the reason for you getting a "Page can not be displayed" may be some conflicts between what you specified at "action" in your <form> and <url-pattern> in the Deployment Descriptor.

May be you are missing something there. Please check this part . Hope this helps you. And one thing more why have you used a "/" in beginning of <code>action="/FileTransfer/TempServlet"</code>?

[Srinivasa Maddi]

But its working very fine without the enctype attribut , however i am getting the same error inspite of using <form action="TempServlet" method="PUT" enctype="multipart/form-data">

[Bharat Mehta]

How about if we do this like below:

  <form action="FileTransfer/TempServlet" method="PUT" enctype="multipart/form-data">   

since you had used FileTransfer earlier.? It will be a guess since I have no sight of you Deployment Descriptor and the mappings therein

[Srinivasa Maddi]

No it dint work. See my dd

 
<servlet>
    <display-name>TempServlet</display-name>
    <servlet-name>TempServlet</servlet-name>
    <servlet-class>TempServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TempServlet</servlet-name>
    <url-pattern>/TempServlet</url-pattern>
  </servlet-mapping>   

[Ulf Dittmer]

Bharat Mehta wrote:But I tried with PUT method.... and it did worked.
...
Any comments/thoughts on this?

As I said, PUT is not supported by HTML forms. See http://www.w3.org/TR/html401/interact/forms.html#submit-format. What happens if you use it is undefined, and likely to be dependent on the browser.

[Bharat Mehta]

Ok I got you point Ulf . We should not be using 'PUT' here. Thanks

[Bauke Scholtz]

It´s fine that you only need the file name and not the file contents, but realize that you can´t get the file contents in any way by only the file name. Maybe only if both the client and the server runs at physically the same machine, but certainly not another than that.