将文件读取为字节数组的最快方法

Question

What is the fastest way to read a file as a byte array (on Android)? The file is about 4 MB. It's inside the assets directory, which means that it's probably compressed.

Currently, I'm doing something like this:

byte[] buffer = new byte[4 * 1024 * 1024];
context.getAssets().open(FILE_NAME).read(buffer);

On Android, creating the array takes about 40 ms, reading the file about 120 ms. I suspect that the 40 ms consist mostly of filling the array with zeroes. Can I avoid this?

The file is basically a list of about 100,000 items which need to be searched through quickly.

Answer 1

You could avoid creating the byte array by using the RandomAccessFile class, with its read method. The android page isn't too different, but could also be useful. I used RAF for a project to store and retrieve data whenever desired from a specific file. RAF is very useful for these tasks. However, the more you read and write, of course increases the run-time considerably. Here is an example of its usage:

import java.io.RandomAccessFile;
import java.io.FileNotFoundException;

public class RAFTest {

    public static void main(String[] args) {
        RandomAccessFile raf;
        String metadata = "This is a test file.";

        try {

            raf = new RandomAccessFile(args[0], "rw");
            raf.writeUTF(metadata);
            int[] nums = new int[10];
            for(int i = 0; i < b.length; i++) {
                nums[i] = i;
                raf.writeInt(nums[i].getValue());
            }

            raf.seek(0); // force pointer to beginning

            System.out.println(raf.readUTF());
            int[] c = new int[5];
            int byteJump = 4;
            for(int i = 0; i < c.length; i++) {
                raf.seek(raf.getFilePointer() + byteJump);
                c[i] = raf.readInt();
                System.out.println(c[i]);
            }

        } catch(Exception ex) { }
    }
}