文件通道总是阻塞式的。
文件通道不能创建，只能通过（RandomAccessFile、FileInputStream、FileOutputStream）getChannel()获得，具有与File形同的访问权限。
线程安全。
文件锁：锁的对象是文件。
package org.windwant.nio;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.Channel;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.Selector;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* Created by windwant on 2016/5/13.
*/
public class NIOOpt {
public static void main(String[] args) {
try {
MappedPrivateChannel();
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* MapMode.PRIVATE 写时拷贝（copy-on-write）映射：通过put()修改的任何修改，会导致产生一个私有的数据
* 拷贝，宝贝中的数据只有MappedByteBuffer实例可以看到。不会对底层文件做任何修改。若缓冲区被回收，修改丢
* 失，read/write方式建立通道。
* 做修改，拷贝副本前，其它方式的映射区的修改，会反映到当前区域。映射相互的修改不可见
* 允许父子进程共享内存页
* 处理一个文件多个映射场景。
* 关闭通道，映射会保持。除非丢弃缓冲区本身。
* MappedByteBuffer 对象是直接的，占用的内存位于jvm堆栈之外。
*/
public static void MappedPrivateChannel() 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 8 KB, 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 buffer92
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 ("'");
}
/**
* channel Gather/Scatter 矢量IO
*/
public static void channelGatherScatter(){
ByteBuffer head = ByteBuffer.allocate(4);
ByteBuffer body = ByteBuffer.allocate(100);
RandomAccessFile afile = null;
RandomAccessFile bfile = null;
ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
try {
afile = new RandomAccessFile("hello.txt", "r");
bfile = new RandomAccessFile("hehe.txt", "rw");
readWriteLock.readLock().lock();
FileChannel fileChannel = afile.getChannel();
ByteBuffer[] buffers = {head, body};
while (fileChannel.read(buffers) != -1){
}
head.flip();
body.flip();
System.out.println(new String(head.array()));
System.out.println(new String(body.array()));
readWriteLock.readLock().unlock();
fileChannel.close();
afile.close();
readWriteLock.writeLock().lock();
FileChannel bfileChannel = bfile.getChannel();
while (bfileChannel.write(buffers) > 0){
}
bfileChannel.position(bfileChannel.position() + 10);
bfileChannel.write(ByteBuffer.wrap("THIS IS THE TEST TEXT!".getBytes()));
bfileChannel.truncate(3); //改变文件大小
bfileChannel.force(true); //写入磁盘文件 参数 是否更新文件元数据（所有者、访问权限等）
readWriteLock.writeLock().unlock();
bfileChannel.close();
bfile.close();
}catch (Exception e){
e.printStackTrace();
}
}
/**
* 基于MappedFileChannle的文件复制
* 文件锁
*/
public static void mappedFileChannelLock(){
RandomAccessFile afile = null;
RandomAccessFile bfile = null;
FileChannel fc = null;
FileChannel fcb = null;
try {
afile = new RandomAccessFile("hello.txt", "rw");
fc = afile.getChannel();
long length = fc.size();
FileLock fileLock = fc.tryLock(0, length, true);//true共享锁 false 独占锁 从开始 锁定全部内容 如果获取不到锁会返回null
if(null != fileLock) {
MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, length);
byte[] fbo = new byte[(int) length];
mbb.get(fbo);
System.out.println(new String(fbo, "UTF-8"));
fileLock.release();
bfile = new RandomAccessFile("hehe.txt", "rw");
fcb = bfile.getChannel();
fileLock = fcb.tryLock(0, length, false);
MappedByteBuffer mbbb = fcb.map(FileChannel.MapMode.READ_WRITE, 0, length);
for (int i = 0; i < length; i++) {
mbbb.put(i, fbo[i]);
}
mbbb.flip();
mbbb.force();
fileLock.release();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
fc.close();
fcb.close();
afile.close();
bfile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* MappedByteBuffer map(MapMode mode, long position, long size)
* size大于文件大小，文件会做扩充
* MappedByteBuffer 内存映射缓冲池
* 基于MappedFileChannle的文件复制
* 读写锁
* 直接读取，修改磁盘上的文件。
* 自动缓存内存页，比较高效。
*/
public static void mappedFileChannel(){
RandomAccessFile afile = null;
RandomAccessFile bfile = null;
FileChannel fc = null;
FileChannel fcb = null;
ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
try {
afile = new RandomAccessFile("hello.txt", "rw");
readWriteLock.readLock().lock();
fc = afile.getChannel();
long length = fc.size();
MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_WRITE, 0, length);
byte[] fbo = new byte[(int) length];
mbb.get(fbo);
System.out.println(new String(fbo));
readWriteLock.readLock().unlock();
bfile = new RandomAccessFile("hehe.txt", "rw");
readWriteLock.writeLock().lock();
fcb = bfile.getChannel();
MappedByteBuffer mbbb = fcb.map(FileChannel.MapMode.READ_WRITE, 0, length);
for (int i = 0; i < length; i++) {
mbbb.put(i, fbo[i]);
}
mbbb.flip();
mbbb.force();
readWriteLock.writeLock().unlock();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
fc.close();
fcb.close();
afile.close();
bfile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* FileChannel文件读取
*/
public static void fileChannel(){
try {
RandomAccessFile afile = new RandomAccessFile("hello.txt", "rw");
FileChannel fc = afile.getChannel();
ByteBuffer bb = ByteBuffer.allocate(48);
int byteRead;
while ((byteRead = fc.read(bb)) != -1){//确保读完
System.out.println("read:" + byteRead);
bb.flip();//翻转为读状态
while (bb.hasRemaining()){//直到没有可读的字节
System.out.println(String.valueOf(bb.get()));
}
bb.clear();
}
fc.close();
afile.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 基于FileChannel transferTo transferFrom 方法文件复制
*/
public static void fileTransfer(){
try {
RandomAccessFile afile = new RandomAccessFile("hello.txt", "rw");
RandomAccessFile bfile = new RandomAccessFile("hehe.txt", "rw");
FileChannel ac = afile.getChannel();
FileChannel bc = bfile.getChannel();
long position = 0;
long count = ac.size();
// bc.transferFrom(ac, position, count);
ac.transferTo(position, count, bc);
ac.close();
afile.close();
bc.close();
bfile.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void fileSelector(){
try {
RandomAccessFile afile = new RandomAccessFile("hello.txt", "rw");
Channel c = afile.getChannel();
Selector s = Selector.open();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 基于基本channel buffer的文件复制操作
*/
public static void fileTransferByNormal() {
try {
RandomAccessFile afile = new RandomAccessFile("hello.txt", "rw");
RandomAccessFile bfile = new RandomAccessFile("hehe.txt", "rw");
FileChannel ac = afile.getChannel();
FileChannel bc = bfile.getChannel();
ByteBuffer bf = ByteBuffer.allocateDirect(16 * 1024);
while (ac.read(bf) != -1) {
bf.flip();
while (bf.hasRemaining()) {//确保写完
bc.write(bf);
}
bf.clear();
}
ac.close();
afile.close();
bc.close();
bfile.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}