How to extract row value by using Servlet and JSP?

Question

I am a newbie to JSP. I have created a JSP file which runs on the tomcat server. I have specified my directory location in my program. My program displays all the files from that directory and displays results in a table and creates a delete button after the filename. My program is as follow(JSP file):

<form method="post" action='FileDisplayURL' >
    <h2>Current Collection</h2>
    <table width="100%" border="1">

        <%
          File folder = new File("C:/Apps/eclipse-jee-mars-2-win32-x86_64/eclipse");
          File[] listOfFiles = folder.listFiles();
          for (int i = 0; i < listOfFiles.length; i++) {
        %>
        <tr >
            <%
              if (listOfFiles[i].isFile()) {
            %>
            <td><%=listOfFiles[i].getName()%></td>
            <td><input type="submit" value="delete" name="filename"></td>
            <%
              }
            %>
        </tr>
        <%
          }
        %>
    </table>

</form>

This is my servlet:

@WebServlet("/FileDisplayURL")
public class FileDisplay extends HttpServlet {
  private static final long serialVersionUID = 1L;

  protected void doPost(HttpServletRequest request,
      HttpServletResponse response) throws ServletException, IOException {

    response.setContentType("text/html");

    String deleteFileName = request.getParameter("filename");
    System.out.println("you clicked on " + deleteFileName);

  }

}

This is how my front page looks like :

I am having a problem in getting the name of file when user clicks for delete.

When I run my program on tomcat, the output in terminal looks like this:

INFO: Server startup in 1076 ms
you clicked on delete

"You clicked on delete" doesn't display the name of the file which is clicked. I am very new to Servlet and JSP. I might be missing something obvious. Any help would be appreciated.

First lesson: Don't use scriptlets; use a separate controller and use JSP (or another template system; I prefer Thymeleaf) only to render. — chrylis -cautiouslyoptimistic-, May 23 '16 at 21:07

rekiem87 · Accepted Answer · 2016-05-23T21:54:02.470

It's an HTML error, a button can not have value (and you are not adding a value anyway) you should create a hidden input and put the filename there:

<input type="hidden" value="<%=listOfFiles[i].getName()%>" name="filename"/>

Edit:

I did not realize that you have one form, you need a separate form for each row, since the servlet does not know what value put if several inputs have the same name. So your view should have:

<h2>Current Collection</h2>
<table width="100%" border="1">

    <%
      File folder = new File("C:/Apps/eclipse-jee-mars-2-win32-x86_64/eclipse");
      File[] listOfFiles = folder.listFiles();
      for (int i = 0; i < listOfFiles.length; i++) {
    %>
    <tr >
        <%
          if (listOfFiles[i].isFile()) {
        %>
        <td><%=listOfFiles[i].getName()%></td>
        <td>
            <form method="post" action='FileDisplayURL' >
                <input type="submit" value="delete">
                <input type="hidden" value="<%=listOfFiles[i].getName()%>" name="filename"/>
            </form>
        </td>
        <%
          }
        %>
    </tr>
    <%
      }
    %>
</table>

Edit 2:

Just to clarify your error: When you click the send button, the browser prepares the request adding to the body a key-value list with all the parameters inside the activated form, if you use one form with several fields with the same name the server can not guess which is the correct value:

Body:
filename=a
filename=b
filename=c
filename=d

Which value should be picked? So, you need a form with just one value per name (or maybe brackets for lists)

Thanks for replying. I am able to get the filename. But when I click on delete, it only displays the name of file which I clicked first. When I click on some other file it doesn't display the name of that file. It only displays the first filename which I clicked. Check out my console output: http://i.stack.imgur.com/yAV1z.png — Rose, May 23 '16 at 21:39
Did you check the code after my last edit? with one form for each row? that code should be working — rekiem87, May 23 '16 at 21:42

How to extract row value by using Servlet and JSP?

1 Answers1