*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	 * 
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	 * @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	 * 
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	 * @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	 * 
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	 * @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 	 * 
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	 * @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;	}