Delete duplicate numbers from the file

Program:

import java.io.*;
class FileWriterDemo1 
{
  public static void main(String[] args)throws IOException
  {
    BufferedReader br1=
     new BufferedReader(new FileReader("input.txt"));
    PrintWriter out=new PrintWriter("output.txt");
    String target=br1.readLine();
    while(target!=null)
    {
 boolean available=false;
 BufferedReader br2=
          new BufferedReader(new FileReader("output.txt"));
 String line=br2.readLine();
 while(line!=null)
 {
          if(target.equals(line))
   {
     available=true;
     break;
   }
     line=br2.readLine();
 }
 if(available==false)
 {
   out.println(target);
   out.flush();
 }
 target=br1.readLine();
     }
}
}