Java program that changes a file's extension

I want to write a java program that when executed can take a file or a certain format (say .txt) and give as output the same file, but with the extension changed (say .xml).

How do I go about accomplishing this? Thank you.

The name of a file -including its extension- can be changed by the java.io.File.renameTo method.

Your example is strange, though - an .xml extension implies that the file is valid XML, which wouldn't be the case for just any old .txt file. (Changing the file extension does not change the file type or file contents.)

My example was hypothetical. I actually have the extension .mm (a FreeMind mindmap file), which is valid XML all the time. So I just want to change the file extension for another program to read and parse the XML contained in the file.

Thanks!

split() can be your friend.

I will attempt to implement it and get back if I have any problems. Thank you.

import java.io.*;
 
public class FileRename {
 
 public static void main(String[] args) {
    String targetExtension=".xml";
    if(args.length >= 1 ) {//1
        String ext =args[0].substring(args[0].indexOf("."));
        System.out.println(ext);
        if(ext.equalsIgnoreCase(".txt")) {//2
          File f = new File(args[0]);
          //if the file exists
          // then change the filename
          if(f.exists()) {//3
           args[0]=args[0].replace(ext,targetExtension);
           System.out.println(" "+args[0]);
           File change = new File(args[0]);
           f.renameTo(change);
          }//3
          //if file does not exists then create a new file
          else {//3
                     try {
            f.createNewFile();
            args[0]=args[0].replace(ext,targetExtension);
            System.out.println(" "+args[0]);
 
            File change = new File(args[0]);
 
            f.renameTo(change);
          }//try
          catch(IOException ioe) {
 
          }//catch
 
        }//3
 
      }//2
 
    }//1
 
 }//main
 
}//class

The above program changes the extension of *.txt to *.xml. if ext file is not found , then it creates a file in that name and renames its extension to xml. files with other extension are not renamed or created.

That code is error prone.

First of all, what if there is no extension? indexOf will return -1, which will cause an IndexOutOfBoundsException. Secondly, what if there are multiple dots in the full filename? lastIndexOf will solve that.

And what if the filename contains the extension twice?

Your code, slightly modified:

import java.io.*;
 
public class FileRename
{
    public static void main(String[] args)
    {
        String targetExtension = ".xml";
        if (args.length >= 1 )
        {
            int extIndex = args[0].lastIndexOf(".");
            if (extIndex != -1)
            {
                String ext = args[0].substring(extIndex);
                System.out.println(ext);
                if (ext.equalsIgnoreCase(".txt"))
                {
                    try
                    {
                        File f = new File(args[0]);
                        // no sense in coding the same thing twice;
                        // just create if it doesn't exist, then call the same code just once
                        if (!f.exists())
                        {
                            f.createNewFile();
                        }
                        args[0] = args[0].substring(0, extIndex) + targetExtension;
                        System.out.println(" " + args[0]);
                        File change = new File(args[0]);
                        f.renameTo(change);
                    }
                    catch (IOException e)
                    {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

[ May 28, 2008: Message edited by: Rob Prime ]

import java.io.File;
import java.util.StringTokenizer;

/*Change the extension name of the file recursively
for multiple directories
*/
public class renFile {
static String reName ="";
static StringTokenizer str =null;
static File files[] =null;
static final String ext = ".doc";//Extension to Change to
public void Innundo(String path){
String t;
try {
File file = new File(path);
files = file.listFiles();
for(File fl : files){
if(fl.isDirectory()){
System.out.println("Directory name:"+fl.toString());
Innundo(fl.toString());

}else {
System.out.println("File name:"+fl.toString());
if(fl.isFile()){
t = fl.getName();
str = new StringTokenizer(t,".");
if(str.hasMoreTokens()){
t= str.nextToken();
t= fl.getParent()+"\\"+t+ext;
System.out.println("Changed Name "+t);
fl.renameTo(new File(t));
}
}
else {System.out.println(fl.getName()+" Not A File! ");}
}
}
}catch(Exception e){
e.printStackTrace();

}
}
public static void main(String[] args) {
String path="C:/Path_To_Directory";
renFile re = new renFile();
re.Innundo(path);
}
}
//Internet Resources

Anthony Gomes, don't forget the "Code" button, otherwise your code becomes illegible. Please go back and use the edit button to add code tags.