Questions regarding Disk I/O

Question

Hey there, I have some questions regarding disk i/o and I'm fairly new to Java.
I've got an organized 500MB file and a table like structure (represented by an array) that tells me sections (bytes) within the file. With this I'm currently retrieving blocks of data using the following approach:
// Assume id is just some arbitary int that represents an identifier.
String f = "/scratch/torum/collection.jdx";
int startByte = bytemap[id-1];
int endByte = bytemap[id];
try {
          FileInputStream stream = new FileInputStream(f);
          DataInputStream in = new DataInputStream(stream);
                in.skipBytes(startByte);
          int position = collectionSize - in.available();
          // Keep looping until the end of the block.
          while(position <= endByte) {
              line  = in.readLine();
              // some pocessing here
              String[]entry = line.split(" ");
              String docid = entry[1];
              int tf = Integer.parseInt(entry[2]);
              // update the current position within the file.
              position = collectionSize - in.available();
   } catch(IOException e) {
          e.printStackTrace();
   }This code does EXACTLY what I want it to do but with one complication. It isn't fast enough. I see that using BufferedReader is the choice after reading:
http://java.sun.com/developer/technicalArticles/Programming/PerfTuning/
I would love to use this Class but BufferedReader doesn't have the function, "skipBytes(), which is vital to achieve what I'm trying to do. I'm also aware that I shouldn't really be using the readLine() function of the DataInputStream Class.
So could anyone suggest improvements to this code?
Thanks
null

Answer 1

Okay I've got some results and turns out DataInputStream is faster...
EDIT: I was wrong. RandomAccessFile becomes a bit faster according to my test code when the block size to read is large.
So I guess I could write two routines in my program, RAF for when the block size is larger than an arbitary value and FileInputStream for small blocks.
Here is the code:
public void useRandomAccess() {
     String line = "";
     long start = 1385592, end = 1489808;
     try {
         RandomAccessFile in = new RandomAccessFile(f, "r");
         in.seek(start);
         while(start <= end) {     
          line = in.readLine();     
          String[]entry = line.split(" ");
          String docid = entry[1];
          int tf = Integer.parseInt(entry[2]);
          start = in.getFilePointer();
     } catch(FileNotFoundException e) {
         e.printStackTrace();
     } catch(IOException ioe) {
         ioe.printStackTrace();
public void inputStream() {
     String line = "";
     int startByte = 1385592, endByte = 1489808;
     try {
         FileInputStream stream = new FileInputStream(f);
         DataInputStream in = new DataInputStream(stream);
         in.skipBytes(startByte);
         int position = collectionSize - in.available();
         while(position <= endByte) {
          line  = in.readLine();
          String[]entry = line.split(" ");
          String docid = entry[1];
          int tf = Integer.parseInt(entry[2]);
          position = collectionSize - in.available();
     } catch(IOException e) {
         e.printStackTrace();
    }and the main looks like this:
   public static void main(String[]args) {
     DiskTest dt = new DiskTest();
     long start = 0;
     long end = 0;
     start = System.currentTimeMillis();
     dt.useRandomAccess();
     end = System.currentTimeMillis();
     System.out.println("Random: "+(end-start)+"ms");
     start = System.currentTimeMillis();
     dt.inputStream();
     end = System.currentTimeMillis();
     System.out.println("Stream: "+(end-start)+"ms");
    }The result:
Random: 345ms
Stream: 235ms
Hmmm not the kind of result I was hoping for... or is it something I've done wrong?