mapping an entire File into a ByteBuffer read only. - Java java.nio

Java examples for java.nio:ByteBuffer Read

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Description

mapping an entire File into a ByteBuffer read only.

Demo Code


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

import java.nio.channels.FileChannel;

public class Main {
    public static void main(String[] argv) throws Exception {
        File file = new File("Main.java");
        System.out.println(mapReadOnly(file));
    }/*  w  w  w  . java2  s.  c  om*/

    /**
     * This is a convenience method for mapping an entire {@link File} into a
     * {@link ByteBuffer}.
     *
     * @param file The {@link File} to map.
     * @return Returns a new {@link ByteBuffer}.
     * @see #map(File,FileChannel.MapMode)
     * @see #map(File,long,long,FileChannel.MapMode)
     * @see #mapReadOnly(File,long,long)
     * @see #mapReadWrite(File\)
     * @see #mapReadWrite(File,long,long)
     */
    public static ByteBuffer mapReadOnly(File file) throws IOException {
        return mapReadOnly(file, 0, file.length());
    }

    /**
     * This is a convenience method for mapping a {@link File} into a
     * {@link ByteBuffer}.
     *
     * @param file The {@link File} to map.
     * @param position The position within the file at which the mapped region
     * is to start.
     * @param size The size of the region to be mapped.
     * @return Returns a new {@link ByteBuffer}.
     * @see #map(File,FileChannel.MapMode)
     * @see #map(File,long,long,FileChannel.MapMode)
     * @see #mapReadOnly(File)
     * @see #mapReadWrite(File)
     * @see #mapReadWrite(File,long,long)
     */
    public static ByteBuffer mapReadOnly(File file, long position, long size)
            throws IOException {
        return map(file, position, size, FileChannel.MapMode.READ_ONLY);
    }

    /**
     * This is a convenience method for mapping an entire {@link File} into a
     * {@link ByteBuffer}.
     *
     * @param file The {@link File} to map.
     * @return Returns a new {@link ByteBuffer}.
     * @see #map(File,long,long,FileChannel.MapMode)
     * @see #mapReadOnly(File)
     * @see #mapReadOnly(File,long,long)
     * @see #mapReadWrite(File)
     * @see #mapReadWrite(File,long,long)
     */
    public static ByteBuffer map(File file, FileChannel.MapMode mapMode)
            throws IOException {
        return map(file, 0, file.length(), mapMode);
    }

    /**
     * This is a convenience method for mapping a {@link File} into a
     * {@link ByteBuffer}.
     *
     * @param file The {@link File} to map.
     * @param position The position within the file at which the mapped region
     * is to start.
     * @param size The size of the region to be mapped.
     * @param mapMode The {@link FileChannel.MapMode} to use.
     * @return Returns a new {@link ByteBuffer}.
     * @see #map(File,FileChannel.MapMode)
     * @see #mapReadOnly(File)
     * @see #mapReadOnly(File,long,long)
     * @see #mapReadWrite(File)
     * @see #mapReadWrite(File,long,long)
     */
    public static ByteBuffer map(File file, long position, long size,
            FileChannel.MapMode mapMode) throws IOException {
        final String rafMode;
        if (mapMode == FileChannel.MapMode.READ_ONLY)
            rafMode = "r";
        else if (mapMode == FileChannel.MapMode.READ_WRITE)
            rafMode = "rw";
        else
            throw new IllegalArgumentException("unsupported MapMode");

        final RandomAccessFile raf = new RandomAccessFile(file, rafMode);
        try {
            return raf.getChannel().map(mapMode, position, size);
        } finally {
            raf.close();
        }
    }
}

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