Reads the contents of the given File into a ByteBuffer. - Java java.nio

Java examples for java.nio:ByteBuffer Read

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Description

Reads the contents of the given File into a ByteBuffer.

Demo Code


//package com.java2s;
import java.io.*;
import java.nio.*;

public class Main {
    public static void main(String[] argv) throws Exception {
        File file = new File("Main.java");
        System.out.println(readFile(file));
    }/* ww  w . jav a  2  s .c  om*/

    /**
     * Reads the contents of the given File into a ByteBuffer.
     * This ByteBuffer is always backed by a byte[] of exactly the file's length (at the time we started to read).
     */
    public static ByteBuffer readFile(File file) throws IOException {
        DataInputStream dataInputStream = null;
        try {
            // FIXME: this is broken for files larger than 4GiB.
            int byteCount = (int) file.length();

            // Always read the whole file in rather than using memory mapping.
            // Windows' file system semantics also mean that there's a period after a search finishes but before the buffer is actually unmapped where you can't write to the file (see Sun bug 6359560).
            // Being unable to manually unmap causes no functional problems but hurts performance on Unix (see Sun bug 4724038).
            // Testing in C (working on Ctags) shows that for typical source files (Linux 2.6.17 and JDK6), the performance benefit of mmap(2) is small anyway.
            // Evergreen actually searches both of those source trees faster with readFully than with map.
            // At the moment, then, there's no obvious situation where we should map the file.
            FileInputStream fileInputStream = new FileInputStream(file);
            dataInputStream = new DataInputStream(fileInputStream);
            final byte[] bytes = new byte[byteCount];
            dataInputStream.readFully(bytes);

            return ByteBuffer.wrap(bytes);
        } finally {
            dataInputStream.close();
        }
    }
}

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