NIO - MappedByteBuffer

转自：http://blog.csdn.net/java2000_wl/article/details/7625021

*MappedByteBuffer的创建

  在FileChannel上调用map方法 返回一个MappedByteBuffer对象  

 

public MappedByteBuffer map(MapMode mode, long position, long size)

  MapMode  映射模式(MapMode 是FileChannel中的一个内部类) 有三个可选值

   1.READ_ONLY    只读映射模式

 

   2.READ_WRITE  读/写映射模式

 

   3.PRIVATE           通过put方法对MappedByteBuffer的修改   不会修改到磁盘文件  只是虚拟内存的修改

 

*MappedByteBuffer在父类ByteBuffer的基础上 新增的几个方法

 

   1.fore缓冲区在READ_WRITE模式下，此方法对缓冲区所做的内容更改强制写入文件
   2.load：将缓冲区的内容载入物理内存，并返回该缓冲区的引用
   3.isLoaded：判断缓冲区的内容是否在物理内存，如果在则返回true，否则返回false

 

private final static Charset charset = Charset.forName("GBK");

    /**
     * 读文件
     * <br>------------------------------<br>
     * @param path
     * @return
     * @throws IOException
     */
    private static String read(String path) throws IOException {
        if (path == null || path.length() == 0) return null;
        FileInputStream fileInputStream =  new FileInputStream(path);
        FileChannel fileChannel =  fileInputStream.getChannel();
        MappedByteBuffer mappedByteBuffer = fileChannel.map(MapMode.READ_ONLY, 0, fileChannel.size());
        fileInputStream.close();
        fileChannel.close();
        String str = charset.decode(mappedByteBuffer).toString();
        mappedByteBuffer = null;
        return str;
    }

    /**
     * 追加内容
     * <br>------------------------------<br>
     * @param path
     * @param str
     * @return
     * @throws IOException
     */
    private static MappedByteBuffer append(String path, String str) throws IOException {
        if (str == null || str.length() == 0) return null;
        RandomAccessFile randomAccessFile = new RandomAccessFile(path, "rw");
        FileChannel fileChannel = randomAccessFile.getChannel();
        byte[] bytes = str.getBytes();
        long size = fileChannel.size() + bytes.length;
        MappedByteBuffer mappedByteBuffer = fileChannel.map(MapMode.READ_WRITE, 0, size);
        fileChannel.close();
        randomAccessFile.close();

        int position = mappedByteBuffer.limit() - bytes.length;
        mappedByteBuffer.position(position);
        mappedByteBuffer.put(bytes);
        mappedByteBuffer.force();
        mappedByteBuffer.flip();
        return mappedByteBuffer;
    }

    /**
     * 文件复制
     * <br>------------------------------<br>
     * @param srcfilePath
     * @param targetPath
     * @throws IOException
     */
    private static void copy(String srcfilePath, String targetPath) throws IOException {
        File file = new File(targetPath);
        if (!file.getParentFile().exists()) {
            file.mkdirs();
        }
        RandomAccessFile inRandomAccessFile = new RandomAccessFile(srcfilePath, "r");
        FileChannel inFileChannel = inRandomAccessFile.getChannel();
        MappedByteBuffer inMappedByteBuffer = inFileChannel.map(MapMode.READ_ONLY, 0, inFileChannel.size());
        inRandomAccessFile.close();
        inFileChannel.close();

        RandomAccessFile outRandomAccessFile = new RandomAccessFile(targetPath, "rw");
        FileChannel outFileChannel = outRandomAccessFile.getChannel();
        MappedByteBuffer outMappedByteBuffer = outFileChannel.map(MapMode.READ_WRITE, 0, inMappedByteBuffer.capacity());
        outMappedByteBuffer.put(inMappedByteBuffer);
        outMappedByteBuffer.force();
        outRandomAccessFile.close();
        outFileChannel.close();
        outMappedByteBuffer.flip();
    }

    /**
     * 不会更新到文件 只会更新虚拟内存
     * <br>------------------------------<br>
     * @param path
     * @param str
     * @return
     * @throws IOException
     */
    private static MappedByteBuffer doTestPrivateMode(String path, String str) throws IOException {
        if (str == null || str.length() == 0) return null;
        RandomAccessFile randomAccessFile = new RandomAccessFile(path, "rw");
        FileChannel fileChannel = randomAccessFile.getChannel();
        byte[] bytes = str.getBytes();
        long size = fileChannel.size() + bytes.length;
        MappedByteBuffer mappedByteBuffer = fileChannel.map(MapMode.PRIVATE, 0, size);
        mappedByteBuffer.put(bytes);
        fileChannel.close();
        randomAccessFile.close();

        mappedByteBuffer.flip();
        System.out.println(charset.decode(mappedByteBuffer));
        return mappedByteBuffer;
    }