开始有点跟不上实际思路了，
今天暂停吧。
作个记录。
package com.ronsoft.books.nio.channels;
import java.io.File;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MapFile {
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
File tempFile = File.createTempFile("mmaptest", null);
RandomAccessFile file = new RandomAccessFile(tempFile, "rw");
FileChannel channel = file.getChannel();
ByteBuffer temp = ByteBuffer.allocate(100);
temp.put("This is the file content".getBytes());
temp.flip();
channel.write(temp, 0);
temp.clear();
temp.put("This is more file content".getBytes());
temp.flip();
channel.write(temp, 8192);
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());
System.out.println("Begin");
showBuffers(ro, rw, cow);
cow.position(8);
cow.put("COW".getBytes());
System.out.println("Change to COW buffer");
showBuffers(ro, rw, cow);
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);
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);
cow.position(8207);
cow.put(" COW2".getBytes());
System.out.println("Second change to COW buffer");
showBuffers(ro, rw, cow);
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);
channel.close();
file.close();
tempFile.delete();
}
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("");
}
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("'");
}
}
Begin
R/O: 'This is the file content|[8168 nulls]|This is more file content'
R/W: 'This is the file content|[8168 nulls]|This is more file content'
COW: 'This is the file content|[8168 nulls]|This is more file content'
Change to COW buffer
R/O: 'This is the file content|[8168 nulls]|This is more file content'
R/W: 'This is the file content|[8168 nulls]|This is more file content'
COW: 'This is COW file content|[8168 nulls]|This is more file content'
Change to R/W buffer
R/O: 'This is t R/Wile content|[8168 nulls]|Th R/Ws more file content'
R/W: 'This is t R/Wile content|[8168 nulls]|Th R/Ws more file content'
COW: 'This is COW file content|[8168 nulls]|Th R/Ws more file content'
Write on channel
R/O: 'Channel write le content|[8168 nulls]|Th R/Ws moChannel write t'
R/W: 'Channel write le content|[8168 nulls]|Th R/Ws moChannel write t'
COW: 'This is COW file content|[8168 nulls]|Th R/Ws moChannel write t'
Second change to COW buffer
R/O: 'Channel write le content|[8168 nulls]|Th R/Ws moChannel write t'
R/W: 'Channel write le content|[8168 nulls]|Th R/Ws moChannel write t'
COW: 'This is COW file content|[8168 nulls]|Th R/Ws moChann COW2ite t'
Second change to R/W buffer
R/O: ' R/W2 l write le content|[8168 nulls]|Th R/Ws moChannel R/W2 t'
R/W: ' R/W2 l write le content|[8168 nulls]|Th R/Ws moChannel R/W2 t'
COW: 'This is COW file content|[8168 nulls]|Th R/Ws moChann COW2ite t'
