In this tutorial, author discusses how to use java class to copy files.

First example: Copy file using FileWriter

FileWriter is convenience class for writing character files. The constructors of FileWriter  assume that the default character encoding and the default byte-buffer size are acceptable

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class CopyFile {
  public static void main(String[] args) throws IOException {
    File inputFile = new File("inputfile.txt");
    File outputFile = new File("outfile.txt");
    FileReader in = new FileReader(inputFile);
    FileWriter out = new FileWriter(outputFile);
    int c;
    while ((c = in.read()) != -1)
     out.write(c);
    in.close();
    out.close();
  }
}

Second example:copy files using FileChannel class

FileChannel provides a channel for reading, writing, mapping, and manipulating a file.

import java.io.*;
import java.nio.channels.*;
public class FileCopy {
    public static void main(String[  ] args) {
        FileInputStream fin = null;  
        FileOutputStream fout = null;
        try {
            fin = new FileInputStream(args[0]);
            FileChannel in = fin.getChannel( );
            WritableByteChannel out;
            if (args.length > 1) {
                fout = new FileOutputStream(args[1]); 
                out = fout.getChannel( );             
            }
            else {
                out = Channels.newChannel(System.out);
            }
            long numbytes = in.size( );
            in.transferTo(0, numbytes, out);
        }
        catch(IOException e) {
            System.out.println(e);
        }
        finally {
            try {
                if (fin != null) fin.close( );
                if (fout != null) fout.close( );
            }
            catch(IOException e) {  }
        }
    }
}