read and write in existing file

import java.io.*;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.PrintWriter;
public class tryy
{
    public static void main(String args[])throws IOException
    {
File file=new File("D:\\fold\\myfile.txt");
 PrintWriter writer= new PrintWriter(file, "UTF-8");
String p="fold";
      File dir=new File(p);
      File[]  files=dir.listFiles();
            for(File f : files)
              if(f.isFile())
                 { 
StringBuilder sb=new StringBuilder();

              BufferedReader  ins=null;
             ins=new BufferedReader(new FileReader(f));
               String line;
              writer.print("[");
           writer.print(f.getName());
           writer.println("_DINAMALAR_DATE]\n");
            while((line=ins.readLine())!=null)
                     {
                            writer.println(line);
writer.println(sb.toString());
System.out.println(line);
}
}

   writer.close();
     String inputFile="D:\\fold\\myfile.txt";
String fle=inputFile; 
BufferedReader br = new BufferedReader(new FileReader(inputFile));
 
         String line=null;
         StringBuilder sb = new StringBuilder();
         int count=1;
{
 while((line = br.readLine())!= null){              
     if(line.startsWith("[")){
                    if(sb.length()!=0){
                        File file1= new File(line+".txt");
                        
                            PrintWriter writer1 = new PrintWriter(file1, "UTF-8");
                            
                            writer1.println(line);
                            writer1.println(sb.toString());
                             writer1.close();
                  sb.delete(0, sb.length());

                        count++;
                    }
                    continue;
                }
                sb.append(line);
 }
     }
    }

}