Most efficient way to write 4 bytes at the start of any file.

Question

Quick question: I want to write 4 bytes at the start of a file without overriding the current bytes in the file. E.g. push bytes 0-4 along... Is my only option writing the bytes into a new file then writing the rest of the file after? RAF is so close but overrides :(.
Thanks Mel

Answer 1

I revised the code to use a max of 8MB buffers for both the nio and stdio copies...
Looks like NIO is a pretty clear winner... but your milage may vary, lots... you'd need to test this 100's of times, and normalize, to get any "real" metrics... and I for one couldn't be bothered... it's one of those things that's "fast enough"... 7 seconds to copy a 250 MB file to/from the same physical disk is pretty-effin-awesome really, isn't it? ... looks like Vista must be one of those O/S's (mentioned in the API doco) which can channel from a-to-b without going through the VM.
... and BTW, it took the program which produced this file 11,416 millis to write it (from an int-array (i.e. all in memory)).
revised code
package forums;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.channels.FileChannel;
class NioBenchmark1
  private static final double NANOS = Math.pow(10,9);
  private static final int BUFF_SIZE = 8 * 1024 * 1024; // 8
  interface Copier {
    public void copy(File source, File dest) throws IOException;
  static class NioCopier implements Copier {
    public void copy(File source, File dest) throws IOException {
      FileChannel in = null;
      FileChannel out = null;
      try {
        in = (new FileInputStream(source)).getChannel();
        out = (new FileOutputStream(dest)).getChannel();
        final int buff_size = Math.min((int)source.length(),BUFF_SIZE);
        long n = -1;
        int pos = 0;
        while ( (n=in.transferTo(pos, buff_size, out)) == buff_size ) {
          pos += n;
      } finally {
        if(in != null) in.close();
        if(out != null) out.close();
  static class NioCopier2 implements Copier {
    public void copy(File source, File dest) throws IOException {
      if ( !dest.exists() ) {
        dest.createNewFile();
      FileChannel in = null;
      FileChannel out = null;
      try {
        in = new FileInputStream(source).getChannel();
        out = new FileOutputStream(dest).getChannel();
        final int buff_size = Math.min((int)in.size(),BUFF_SIZE);
        long n = -1;
        int pos = 0;
        while ( (n=out.transferFrom(in, 0, buff_size)) == buff_size ) {
          pos += n;
      } finally {
        if(in != null) in.close();
        if(out != null) out.close();
  static class IoCopier implements Copier {
    private byte[] buffer = new byte[BUFF_SIZE];
    public void copy(File source, File dest) throws IOException {
      InputStream in = null;
      FileOutputStream out = null;
      try {
        in = new FileInputStream(source);
        out = new FileOutputStream(dest);
        int count = -1;
        while ( (count=in.read(buffer)) != -1) {
          out.write(buffer, 0, count);
      } finally {
        if(in != null) in.close();
        if(out != null) out.close();
  public static void main(String[] arg) {
    final String filename = "SieveOfEratosthenesTest.txt";
    //final String filename = "PrimeTester_SieveOfPrometheuzz.txt";
    final File src = new File(filename);
    System.out.println("copying "+filename+" "+src.length()+" bytes");
    final File dest = new File(filename+".bak");
    try {
      time(new IoCopier(), src, dest);
      time(new NioCopier(), src, dest);
      time(new NioCopier2(), src, dest);
    } catch (Exception e) {
      e.printStackTrace();
  private static void time(Copier copier, File src, File dest) throws IOException {
    System.gc();
    try{Thread.sleep(1);}catch(InterruptedException e){}
    dest.delete();
    long start = System.nanoTime();
    copier.copy(src, dest);
    long stop = System.nanoTime();
    System.out.println(copier.getClass().getName()+" took "+((stop-start)/NANOS)+" seconds");
output
C:\Java\home\src\forums>"C:\Program Files\Java\jdk1.6.0_12\bin\java.exe" -Xms512m -Xmx1536m -enableassertions -cp C:\Java\home\classes forums.NioBenchmark1
copying SieveOfEratosthenesTest.txt 259678795 bytes
forums.NioBenchmark1$IoCopier took 14.333866455 seconds
forums.NioBenchmark1$NioCopier took 7.712665715 seconds
forums.NioBenchmark1$NioCopier2 took 6.206867074 seconds
Press any key to continue . . .Having said that... The NIO has lost a fair bit of it's charm... testing transferTo's return value and maintaining your own position in the file is "cumbsome" (IMHO)... I'm not even certain that mine is completely correct (?n+=pos or n+=pos+1?).... hmmm..
Cheers. Keiths.