Reading from and Writing to a Text File in Java

Submitted by mehfuza on Saturday, September 7, 2013 - 01:37.
Introduction: This tutorial demonstrate the method of reading from and writing to a text file in Java. Java has two type of files: Binary and Text. Text file is processed as a sequence of characters where as Binary file is processed a sequence of bytes. This application has 4 JButtons for reading, writing, exiting, and clearing the Display Area. Also It has a display area where we can type the data to be written to text and in the same area content from file are displayed. Step 1: Creating GUI Components Create the four buttons, label, text area and text field. Text field is used to take file name from user.
  1.         JTextArea display=new JTextArea();
  2.         JButton read=new JButton("Read From File");
  3.         JButton write=new JButton("Write To File");
  4.         JButton clear=new JButton("Clear Display Area");
  5.         JButton exit=new JButton("Exit");
  6.        
  7.         JTextField name=new JTextField(20);
  8.         JLabel prompt=new JLabel("File Name : ", JLabel.RIGHT);  
  9.         JPanel commandPanel=new JPanel(); //panel for holding above buttons
  10.        
Step 2: Initializing Constructor In the constructor of class, we add the created components to the frame and add ActionListeners to it. A panel is created with Grid Layout having 2 rows and 3 columns and 1 pixel gap between the components. All the buttons and text field is added to this panel. This panel is added to the North of the main frame. Display area occupies the center area of the frame with scroll pane. Scroll Pane is added when the contents of the component(area) extends the component.
  1. public TextIO(){
  2.                 super("Text IO Demo"); //Title of the frame
  3.                 read.addActionListener(this);
  4.                 write.addActionListener(this);
  5.                 clear.addActionListener(this);
  6.                 exit.addActionListener(this);
  7.                 commandPanel.setLayout(new GridLayout(2,3,1,1)); //grid with two rows and three columns
  8.                 commandPanel.add(prompt);
  9.                 commandPanel.add(name);
  10.                 commandPanel.add(clear);
  11.                 commandPanel.add(read);
  12.                 commandPanel.add(write);
  13.                 commandPanel.add(exit);
  14.                 display.setLineWrap(true);
  15.                 this.setLayout(new BorderLayout());
  16.                 this.add(commandPanel, BorderLayout.NORTH);
  17.                 this.add(new JScrollPane(display));
  18.                 this.add(display,BorderLayout.CENTER);
  19.         }
Step 3: Defining read/write functions The main part is to read and write the data. For reading from a file we require the BufferedReader object which provides buffering for characters input stream(text files). This object takes FileReader object so as to read from a file. try {} catch block is used to handle if there is any error reading the file.
  1. private void readTextFile(JTextArea display, String fileName)
  2.         {
  3.                 try{
  4.                 BufferedReader inStream=new BufferedReader(new FileReader(fileName));
  5.                 String line=inStream.readLine(); //read the next line every time.
  6.                 while(line!=null)
  7.                 {
  8.                         display.append(line + "\n");
  9.                         line=inStream.readLine();
  10.                 }
  11.                 inStream.close();
  12.                 }
  13.                 catch (FileNotFoundException e) {
  14.                        
  15.                         display.setText("IO Error:  " + fileName + " Not Found. "+"\n");
  16.                         e.printStackTrace();
  17.                        
  18.                        
  19.                 }
  20.                 catch (IOException e) {
  21.                         display.setText("IO Error: " + e.getMessage() +"\n");
  22.                         e.printStackTrace();
  23.                        
  24.                 }
  25.         }
write function works similar except that it write the data of the complete text area at one time. FileWriter object is used to write the data to file. This object takes a file name, if file is already there it overrides the file content and if file is not there then new file is created. If the file can not be created then a message is displayed.
  1. try{
  2.                 FileWriter ostream=new FileWriter(fileName);
  3.                 ostream.write(display.getText());
  4.                 JOptionPane.showMessageDialog(null,"Data written to file", "Successful Write Operation",JOptionPane.INFORMATION_MESSAGE);
  5.                 ostream.close();
  6.                 }
  7.                 catch(IOException e){
  8.                         display.setText("IO Error:  " + fileName + " Not Found. "+"\n");
  9.                         e.printStackTrace();
  10.                        
  11.                 }
  12. }
Step 4: Writing Action Listeners for the Buttons When a user clicks on read, write, clear or exit button, appropriate action is performed. When read button is clicked readTextFile() function is called. Similary all other button's events are handled as follows.
  1.                 String fileName=name.getText(); //content of text area
  2.                 if(ae.getSource()==read)// get source of event
  3.                 {
  4.                         display.setText("");
  5.                         readTextFile(display,fileName);
  6.                 }
  7.                 else if(ae.getSource()==write)
  8.                         writeTextFile(display, fileName);
  9.                 else if(ae.getSource()==clear)
  10.                         display.setText(""); //clears the display area
  11.                 else if(ae.getSource()==exit)
  12.                 {
  13.                         System.exit(0);
  14.                        
  15.                 }
Step 5: Writing main() function From here, execution starts, object of the class is created and some properties of frame are set.
Tags
java
Read
write
File

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great u post these small thinks keep it up and post more and more i love u and ur post

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