Solved

Reading text file in Java

Posted on 2000-05-19
4
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Last Modified: 2010-04-01
I want to read a text file from the FileDialog to the textarea but my read is generating error will u please give me the one which is using readline:

my read look as follows:
________________________________
public void read(String fl) throws IOException
      {
FileInputStream fis = new FileInputStream(fl);
BufferedInputStream bis = new BufferedInputStream(fis);
File F = new File(fl);
int r;
byte [] buf = new byte[64000];
 try
{
while((r = bis.read(buf))!=-1);
r = bis.read(buf);
}
 catch(Exception ex)
{
                JOptionPane.showMessageDialog(null,ex.toString() + String.valueOf("Read Error"));
  }
 ta.setText(new String(buf,0));
 fis.close();
 bis.close();
 throw new IOException();
}
____________________________________
0
Comment
Question by:Xolani
  • 2
4 Comments
 
LVL 3

Accepted Solution

by:
ovidiucraciun earned 50 total points
ID: 2824817
here you have your functin a litle bit modified, and works ;)
/////////////////////////////
package noel.test;

import java.io.*;
import javax.swing.*;
import java.awt.*;

public class FileReadTest
{
  private static JFrame main = new JFrame( "test read file" );
  private static JTextArea ta = new JTextArea();
 
  public void read(String fl) throws IOException
  {
    FileInputStream fis = new FileInputStream(fl);
    BufferedInputStream bis = new BufferedInputStream(fis);
    int r;
    byte [] buf = new byte[64000];
    try
    {
      while( (r = bis.read(buf)) != -1 )
      {
        ta.append( new String( buf, 0, r-1 ) );
      }
    }
    catch(Exception ex)
    {
        System.out.println("Reading error");
    }
    fis.close();
    bis.close();
  }
  public static void main( String args[] )
  {
    main.getContentPane().setLayout( new BorderLayout( ) );
    main.getContentPane().add( new JScrollPane( ta ) );
    main.setSize( 500, 800 );
    main.setVisible( true );
   
    FileReadTest test = new FileReadTest();
    JFileChooser fc = new JFileChooser(".");
    if ( JFileChooser.APPROVE_OPTION == fc.showOpenDialog( main ) )
    {
      try
      {
        test.read( fc.getSelectedFile().getAbsolutePath() );
      }
      catch( IOException ex )
      {
        JOptionPane.showMessageDialog(null,ex.toString() + String.valueOf("error reading file"));
        ex.printStackTrace();
      }
    }
    else
    {
      JOptionPane.showMessageDialog(null,String.valueOf("no file selected"));
    }
  }
}
0
 
LVL 19

Expert Comment

by:Jim Cakalic
ID: 2825614
How about this

try {
    File file = new File(name);
    FileInputStream in = new FileInputStream(file);
    byte[] buf = new byte[file.length()];
    in.read(buf);
    in.close();
} catch (Exception e) {
    // or be more explicit if you want
}
String contents = new String(buf);

Here you create a byte[] sized as large as the file and read the entire file into it. Since your byte[] serves as the buffer, I don't think a BufferedInputStream will help performance at all. In fact, it would have a potential negative effect because of moving data around between internal buffers and your buffer.

Best regards,
Jim Cakalic
   
0
 

Author Comment

by:Xolani
ID: 2825961
I have also learn how to use JFileChooser!!!
I do not understand how your points system works but your answer is good!!
0
 
LVL 3

Expert Comment

by:ovidiucraciun
ID: 2826064
jim, if the file is very large and the system is going to use the swap then your solution will give less performance than reading repeatly in an proper buffer; like the sorting or pattern matching algorithms there are best perfomance in some situations with one algorithm and best perfomance in other situations with other algorithms.
If the file are usualy short in size the your solution is better, but if the file are usualy large I think to repeatly read in a smaller buffer is a better solution. Of course there are other problems, e.g. when you load all large content of the file in JTextArea component but this is another discussion ;)

regards
ovidiu
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