Java 内存映射文件 MappedByteBuffer，,package com.

Java 内存映射文件 MappedByteBuffer，,package com.

package com.ronsoft.books.nio.channels;import java.nio.ByteBuffer;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;import java.io.File;import java.io.RandomAccessFile;/** * Test behavior of Memory mapped buffer types.  Create a file, write * some data to it, then create three different types of mappings * to it.  Observe the effects of changes through the buffer APIs * and updating the file directly.  The data spans page boundaries * to illustrate the page-oriented nature of Copy-On-Write mappings. * * Created: April 2002 * @author Ron Hitchens (ron@ronsoft.com) * @version $Id: MapFile.java,v 1.3 2002/05/20 07:24:29 ron Exp $ */public class MapFile{   public static void main (String [] argv)      throws Exception   {      // create a temp file and get a channel connected to it      File tempFile = File.createTempFile ("mmaptest", null);      RandomAccessFile file = new RandomAccessFile (tempFile, "rw");      FileChannel channel = file.getChannel();      ByteBuffer temp = ByteBuffer.allocate (100);      // put something in the file, starting at location 0      temp.put ("This is the file content".getBytes());      temp.flip();      channel.write (temp, 0);      // Put something else in the file, starting at location 8192      // 8192 is 8k, almost certainly a different memory/FS page.      // This may cause a file hole, depending on the      // filesystem page size.      temp.clear();      temp.put ("This is more file content".getBytes());      temp.flip();      channel.write (temp, 8192);      // create three types of mappings to the same file      MappedByteBuffer ro = channel.map (         FileChannel.MapMode.READ_ONLY, 0, channel.size());      MappedByteBuffer rw = channel.map (         FileChannel.MapMode.READ_WRITE, 0, channel.size());      MappedByteBuffer cow = channel.map (         FileChannel.MapMode.PRIVATE, 0, channel.size());      // The buffer states before any modifications      System.out.println ("Begin");      showBuffers (ro, rw, cow);      // modify the Copy-On-Write buffer      cow.position (8);      cow.put ("COW".getBytes());      System.out.println ("Change to COW buffer");      showBuffers (ro, rw, cow);      // Modify the Read/Write buffer      rw.position (9);      rw.put (" R/W ".getBytes());      rw.position (8194);      rw.put (" R/W ".getBytes());      rw.force();      System.out.println ("Change to R/W buffer");      showBuffers (ro, rw, cow);      // Write to the file through the channel, hit both pages      temp.clear();      temp.put ("Channel write ".getBytes());      temp.flip();      channel.write (temp, 0);      temp.rewind();      channel.write (temp, 8202);      System.out.println ("Write on channel");      showBuffers (ro, rw, cow);      // modify the Copy-On-Write buffer again      cow.position (8207);      cow.put (" COW2 ".getBytes());      System.out.println ("Second change to COW buffer");      showBuffers (ro, rw, cow);      // Modify the Read/Write buffer      rw.position (0);      rw.put (" R/W2 ".getBytes());      rw.position (8210);      rw.put (" R/W2 ".getBytes());      rw.force();      System.out.println ("Second change to R/W buffer");      showBuffers (ro, rw, cow);      // cleanup      channel.close();      file.close();      tempFile.delete();   }   // show the current content of the three buffers   public static void showBuffers (ByteBuffer ro, ByteBuffer rw,      ByteBuffer cow)      throws Exception   {      dumpBuffer ("R/O", ro);      dumpBuffer ("R/W", rw);      dumpBuffer ("COW", cow);      System.out.println ("");   }   // dump buffer content, counting and skipping nulls   public static void dumpBuffer (String prefix, ByteBuffer buffer)      throws Exception   {      System.out.print (prefix + ": '");      int nulls = 0;      int limit = buffer.limit();      for (int i = 0; i < limit; i++) {         char c = (char) buffer.get (i);         if (c == '\\u0000') {            nulls++;            continue;         }         if (nulls != 0) {            System.out.print ("|[" + nulls               + " nulls]|");            nulls = 0;         }         System.out.print (c);      }      System.out.println ("'");   }}//该片段来自于http://byrx.net