title: How can I check if the file is an excel file?
body: <p>I'm writing a program, and the have to select an excel file, that will be read by the program. My question is now, how can I prove, if the file is an excel file or not?.</p>
  
  <p>The file is selected in this method:</p>
  
  <pre><code>JButton btnFile = new JButton("Select Excel File");
  btnFile.setPreferredSize(new Dimension(40, 40));
  btnFile.addActionListener(new ActionListener() {
      // Handle open button action.
      public void actionPerformed(ActionEvent e) {
          final JFileChooser fc = new JFileChooser();
          int returnVal = fc.showOpenDialog(frame);
          if (returnVal == JFileChooser.APPROVE_OPTION) {
              file = fc.getSelectedFile();
              // This is where a real application would open the file.
              System.out.println("File: " + file.getName() + ".");
          } else {
              System.out.println("Open command cancelled by user.");
          }
          System.out.println(returnVal);
      }
  });
  </code></pre>