I am working on a project where I will have a binary file. The file is split into multiple sections, each of which represents a list of primitive values. I need a solution where I can have a collection of objects, each of which represents a section of the file. These collections are then all held within a "file" object that represents the file as a whole.
Each collections object will need to provide sequential access to each value in the represented section of the file. What method would provide the fastest data retrieval without loading all the data into memory first?
Also it would be nice if two separate collections of the same "file" object could be accessed by two separate Threads, but this is not as important.
A good approach is to divide the solution into layers, here: one for the file i/o, mapping bytes to Java shorts and ints, another one for the abstraction of the file sections and the entire file.
java.nio's MappedByteBuffer provides a good interface between the "byte array" of a random access file and what you need for getting the Java typed data from that.
As Kayaman has mentioned,
FileChannel.map()returns a MappedByteBuffer and you can navigate easily on that with its methods.The implemention should make use of the OS feature for mapping memory pages to file pages, actually accessing on the file only what you really access in memory. (I've used this recently with Java 8 and Linux, and it performed well on files exceeding even the capacity of a single MappedByteBuffer.)