使用JFileChooser处理文件

Question

Hey guys I am running into an issue with my program. I am trying to get the program to only show text files, and once the user selects one, the file information should be displayed in a textbox in the GUI. I am getting this error:

FileChooserDemo3.java:66: error: unreported exception IOException; must be caught or declared to be thrown while ((strLine = br.readLine()) != null) {

Why is this happening? I have a catch statement.. Thanks for any help!

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Scanner;
import java.io.*;

class FileChooserDemo3{

   JLabel jlab;
   JButton jbtnShow;
   JFileChooser jfc;
   JTextArea jta;
   JScrollPane scrollPane;

   FileChooserDemo3() {
      //create new JFrame container.
      JFrame jfrm = new JFrame("JFileChooser Demo");

      //Specify FlowLayout for layout manager
      jfrm.setLayout(new FlowLayout());

      //Give the frame initial size
      jfrm.setSize(800,800);

      //End program when user closes application
      jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      //Create a label to show selected file
      jlab=new JLabel();

      //Create button to show dialog
      jbtnShow = new JButton("Show File Chooser");

      //create textarea with ability to textwrap (p889-891) and scroll (hint:  Use JScrollPane)
      JTextArea textInput = new JTextArea(20, 40);
      textInput.setLineWrap(true);
      JScrollPane scrollPane = new JScrollPane(textInput);




      //Create file chooser starting at default directory
      jfc=new JFileChooser();

      //Show file chooser when show file chooser button pressed
      jbtnShow.addActionListener(new ActionListener()  {
         public void actionPerformed(ActionEvent le) {
            //Pass null for the parent.  This centers the dialog on the screen.
            int result = jfc.showOpenDialog(null);

            if(result==JFileChooser.APPROVE_OPTION){
               jlab.setText("Selected file is:  " + jfc.getSelectedFile().getName());

               //Get selected file stored as a file.




               try{
                  //Do file processing here
                 String strLine;
                 File selectedFile = jfc.getSelectedFile();
                 FileInputStream in = new FileInputStream(selectedFile);
                 BufferedReader br = new BufferedReader(new InputStreamReader(in));
                 while ((strLine = br.readLine()) != null) {
                     textInput.append(strLine + "\n");
                 }
               }

               catch(FileNotFoundException e){
                  System.out.println("Exception");
               }



            }
            else{
               jlab.setText("No file selected.");
            }
         }
      });

         //add the show file chooser button and label to content pane
         jfrm.add(jbtnShow);
         jfrm.add(jlab);


         //Display the frame
         jfrm.setVisible(true);
   }

   public static void main(String[] args){
      //Create GUI on the event dispatching thread.
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            new FileChooserDemo3();
         }
      });
   }
}

Answer 1

You are catching FileNotFoundException, but you also need to catch IOException after your try {} block.

Programmatically, this is because readLine declares throws IOException. Translated, what it's saying is that even after the file is opened, it could still encounter a problem reading from the file.

Answer 2

Whats happening is exactly what it says is happening. "unreported exception IOException." Basically your catch statement is not catching all possible exceptions that can be thrown, change it to catch either IOException, or to make sure it catches every possible excepion, no matter what, make it catch Exception.