Best way to read structured binary files with Java

Question

I have to read a binary file in a legacy format with Java.

In a nutshell the file has a header consisting of several integers, bytes and fixed-length char arrays, followed by a list of records which also consist of integers and chars.

In any other language I would create structs (C/C++) or records (Pascal/Delphi) which are byte-by-byte representations of the header and the record. Then I'd read sizeof(header) bytes into a header variable and do the same for the records.

Something like this: (Delphi)

type
  THeader = record
    Version: Integer;
    Type: Byte;
    BeginOfData: Integer;
    ID: array[0..15] of Char;
  end;

...

procedure ReadData(S: TStream);
var
  Header: THeader;
begin
  S.ReadBuffer(Header, SizeOf(THeader));
  ...
end;

What is the best way to do something similar with Java? Do I have to read every single value on its own or is there any other way to do this kind of "block-read"?

Answer 1

To my knowledge, Java forces you to read a file as bytes rather than being able to block read. If you were serializing Java objects, it'd be a different story.

The other examples shown use the DataInputStream class with a File, but you can also use a shortcut: The RandomAccessFile class:

RandomAccessFile in = new RandomAccessFile("filename", "r");
int version = in.readInt();
byte type = in.readByte();
int beginOfData = in.readInt();
byte[] tempId;
in.read(tempId, 0, 16);
String id = new String(tempId);

Note that you could turn the responce objects into a class, if that would make it easier.