randomfile.java

编写程序

/*
 * @(#)randomFile.java	1.5 03/12/19
 * 
 * Copyright (c) 2004 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduce the above copyright notice, 
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 * 
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may 
 * be used to endorse or promote products derived from this software without 
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL 
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST 
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, 
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY 
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, 
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

/* 
 * This program uses JNLP API to write to a file 
 * that is selected by the user. We then read
 * whatever is written in the file and display
 * it in the text area.
 */ 


/*
 * Please note that this application sleeps for 2 seconds
 * everytime some text is added to the text area.
 * This is done purely for demonstration purpose.
 */ 

import java.awt.*; 
import java.awt.event.*; 
import java.io.*; 
import java.lang.*; 
import java.applet.*; 
import javax.swing.*;
import javax.jnlp.*; 

public class randomFile 
{ 
       	FileOpenService fos; 
	JNLPRandomAccessFile raf; 
	FileContents fc; 
	static int count=0; 
        JTextArea textArea;
        java.awt.Container contentPane;
        JFrame t; 

     public randomFile() 
     {
        t = new JFrame("JNLPRandomAccessFile API demo");
        contentPane = t.getContentPane();
        contentPane.setLayout( new FlowLayout() );
        contentPane.setBackground(Color.white);
        textArea = new JTextArea();
        contentPane.add(textArea);
        textArea.setText("Demonstrating usage of random access file. \n");
        textArea.append("It behaves like a large array of bytes stored in the file system \n");
        textArea.append("Pick a file to open on the local system \n");
        t.addWindowListener(new WindowAdapter(){
         public void windowClosing(WindowEvent e) 
         { 
          destroy();
          t.setVisible(false);
          System.exit(0);
         }
   
        });
        t.pack();
        t.setSize(500,400); 
        t.setVisible(true); 


	// Look up a FileOpenService 

	try { 
	fos = (FileOpenService)ServiceManager.lookup("javax.jnlp.FileOpenService"); 
	} catch (UnavailableServiceException e) { 
	fos = null; 
	} 

	if (fos != null) { 
	try { 
	// get a file with FileOpenService 
	fc = fos.openFileDialog(null, null); 

	// If valid file contents 
	if (fc != null) { 
	long grantedLength = fc.getLength(); 
	if (grantedLength + 1024 > fc.getMaxLength()) { 
	// attempt to increase the maximum file size defined by 
	// the client 
	grantedLength = fc.setMaxLength(grantedLength + 1024); 
	   }
 
        // Open the file for read write 
	raf = fc.getRandomAccessFile("rw"); 
        textArea.append("File selected : ");
        textArea.append(fc.getName());
        textArea.append("\n");
        textArea.append("Created a random access file in read/write mode....   \n");
          try
          {
          Thread.sleep(2000);
          } catch (InterruptedException e){
           // the VM doesn't want us to sleep anymore,
           // so get back to work
          }

	} 
	} catch (Exception e) { 
	   e.printStackTrace(); 
	 } 
        } 
      } 


  public void write()
     { 

      String msg="JAVA WEB START CAN STUN YOU.. "; 
       
       if (fos != null && fc != null) { 
       try {
         textArea.append("Seek to the begining of the file for write... \n");
          
          try
          {
          Thread.sleep(2000);
          } catch (InterruptedException e){
           // the VM doesn't want us to sleep anymore,
           // so get back to work
          }
          
           // seek to the beginning and write 
         raf.seek(0);

           /* This message will be written at the begining 
           ** of the file. It will overwrite if it is already
           ** existing.
           */ 
           textArea.append("Writing a string to the file using UTF-8 encoding...   \n");
          
           try
           {
            Thread.sleep(2000);
            } catch (InterruptedException e){
             // the VM doesn't want us to sleep anymore,
             // so get back to work
            }
          
           raf.writeUTF("CONGRATS !!. WRITE & READ PERFORMED SUCCESSFULLY "); 
           raf.seek(raf.length()-1);
           
           textArea.append("Seek to end of the file for next write...   \n");
            try
            {
             Thread.sleep(2000);
            } catch (InterruptedException e){
             // the VM doesn't want us to sleep anymore,
             // so get back to work
            }

           /*
           ** This message will always be written at the end of
           ** file. It will be written once for every write you
           ** make to the file indicating number of times this
           ** message was written to the same file.
           */

           textArea.append("Writing another string as a sequence of bytes  \n");
           try
           {
            Thread.sleep(2000);
           } catch (InterruptedException e){
            // the VM doesn't want us to sleep anymore,
            // so get back to work
           }
           
           raf.writeBytes("\n" + msg + count++); 
           } catch (Exception e) { 
              e.printStackTrace(); 
           } 
        } 

       } 

  public void destroy() { 
      if (fos != null && fc != null) { 
       try { 
           // close the file 
              raf.close(); 
              } catch (Exception e) { 
                e.printStackTrace(); 
              } 
            } 
          } 

    public void read() 
    {
       if (fos != null && fc != null) { 
        try
        { 

 
           textArea.append("Now reading whatever was written..   \n");
           textArea.append("Reading one line at a time from the begining of the File..   \n");
          
             try
             {
             Thread.sleep(2000);
             } catch (InterruptedException e){
              // the VM doesn't want us to sleep anymore,
              // so get back to work
             }
           
        
        /*
        ** Starting from the begining, it will read one line
        ** at a time from the file and append it with newline
        ** character.
        */
           textArea.append("\n");
           raf.seek(0);
           String line = raf.readUTF();
           while (line != null)
           { 
            textArea.append(line);
            textArea.append("\n");
            line = raf.readLine();

           }
           
           textArea.append("\n");
            try
            {
             Thread.sleep(2000);
            } catch (InterruptedException e){
               // the VM doesn't want us to sleep anymore,
               // so get back to work
            }
           
         textArea.append("Thanks for choosing Java Web Start..   \n");
           
         } catch (Exception e) { 
             e.printStackTrace(); 
         }
       } 
     }
        
  public static void main(String args[]) 
     { 

       randomFile randomfile = new randomFile(); 
       randomfile.write(); 
       randomfile.read(); 
       
     } 
}