Best way to read structured binary files with Java

If you would be using Preon, then all you would have to do is this:

public class Header {
    @BoundNumber int version;
    @BoundNumber byte type;
    @BoundNumber int beginOfData;
    @BoundString(size="15") String id;
}

Once you have this, you create Codec using a single line:

Codec<Header> codec = Codecs.create(Header.class);

And you use the Codec like this:

Header header = Codecs.decode(codec, file);

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.

You could use the DataInputStream class as follows:

DataInputStream in = new DataInputStream(new BufferedInputStream(
                         new FileInputStream("filename")));
int x = in.readInt();
double y = in.readDouble();

etc.

Once you get these values you can do with them as you please. Look up the java.io.DataInputStream class in the API for more info.