Looping over the contents of the file...

[Marcelo Ortega]

Howdy folks,
What would you say is the standard way to loop over the contents of the file?
I do the following but am convinced there is a better way:

 
RandomAccessFile database = ...
long fp = database.getFilePointer();
            
try {
   while (fp < database.length()) {
      ...read bytes...
   }
}
catch(IOException ex) {
  //if we are here it's because we reached the end of the file - not nice
}

Thanks,
Best regards.

[Mike Ngo]

why are you looping?

[Marcelo Ortega]

To read every row...?

[Mike Ngo]

The RandomAccessFile is used to randomly access any byte in a file so typically you would do something like this

RandomAccessFile stream = // open it
// calculate file pointer
long offset = calculateOffset(my_record);
stream.seek(offset)
// read my record

If you don't need to randomly access the data, you can use DataInput/OutputStream.

[Marcelo Ortega]

I see what you mean, but i don't see how you would use RandomAccessFile to read ALL rows? And if the answer is to use a DataInputStream, then how can i read a certain amount of bytes for each field like RandomAccessFile does? How do i read each row with a RandomAccessFile? Or is the trick to mix it with a DataInputStream...?

Kind regards,
Mars.

[Mark Smyth]

Originally posted by Marcelo Ortega:
I see what you mean, but i don't see how you would use RandomAccessFile to read ALL rows? And if the answer is to use a DataInputStream, then how can i read a certain amount of bytes for each field like RandomAccessFile does? How do i read each row with a RandomAccessFile? Or is the trick to mix it with a DataInputStream...?

Kind regards,
Mars.

I think the easyest way is to keep track of how many records (deleted and active) are in the file.

Then you will do something like the following:

 for(int i =0; i<numrecords:i++){
read(i);
}
 

To calculate the number of records would be something like:

numrecords= (fileSize - HeaderLength) / recordLength + 1 //Dont forget about active delete flag