java nio 创建 channel_Java NIO之Channel（通道）入门

Channel(通道)是专用于IO请求的独立处理器。用于在数据源与目标节点之间建立连接。负责缓冲区中数据的传输。

Java NIO的通道类似流，但又有些不同：

既可以从通道中读取数据，又可以写数据到通道。但流的读写通常是单向的。

通道可以异步地读写。

通道中的数据总是要先读到一个Buffer，或者总是要从一个Buffer中写入。

Channel可以看做是铁路，Buffer可以看作是列车，而Data数据可以看做是旅客。

1、Channel的实现

以下是Java NIO中最重要的通道的实现：

FileChannel：用于从文件中读写数据

DatagramChannel：能通过UDP读写网络中的数据

SocketChannel：能通过TCP读写网络中的数据(客户端)

ServerSocketChannel：可以监听新进来的TCP连接(服务端，像Web服务器那样)对每一个新进来的连接都会创建一个SocketChannel

2、Channel UML图

3、Channel使用示例(FileChannel)

3.1、JDK1.7之前

3.1.1、RandomAccessFile

FileChannel readChannel = null;

FileChannel writeChannel = null;

try {

RandomAccessFile sourceFile = new RandomAccessFile("demo.txt", "rw");//指定源文件及操作方式

RandomAccessFile dstFile = new RandomAccessFile("demo2.txt", "rw");//指定目标文件及操作方式

//获取读写通道

readChannel = sourceFile.getChannel();

writeChannel = dstFile.getChannel();

ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

while (-1 != readChannel.read(byteBuffer)) {

byteBuffer.flip();

writeChannel.write(byteBuffer);

byteBuffer.clear();

}

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

} finally {

try {

readChannel.close();

writeChannel.close();

} catch (IOException e) {

e.printStackTrace();

}

}

3.1.2、FileInputStream/FileOutputStream

FileInputStream fips = null;

FileOutputStream fops = null;

FileChannel fipsChannel = null;

FileChannel fopsChannel = null;

try {

fips = new FileInputStream(new File("demo.txt"));

fops = new FileOutputStream(new File("demo2.txt"));

fipsChannel = fips.getChannel();

fopsChannel = fops.getChannel();

ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

while (-1 != fipsChannel.read(byteBuffer)) {

byteBuffer.flip();

fopsChannel.write(byteBuffer);

byteBuffer.clear();

}

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

} finally {

try {

fips.close();

fops.flush();

fops.close();

fipsChannel.close();

fopsChannel.close();

} catch (IOException e) {

e.printStackTrace();

}

}

3.2、JDK1.7开始

通过FileChannel的public static FileChannel open(Path path, OpenOption... options) 静态方法

try {

//获取读写通道 StandardOpenOption.CREATE表示——不存在则创建，存在则覆盖

FileChannel inChannel = FileChannel.open(Paths.get("demo.txt"), StandardOpenOption.READ);

FileChannel outChannel = FileChannel.open(Paths.get("demo2.txt"), StandardOpenOption.WRITE,StandardOpenOption.READ,StandardOpenOption.CREATE);

//使用内存映射文件方式读写数据(只有ByteBuffer支持)

MappedByteBuffer inBuffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());

MappedByteBuffer outBuffer = outChannel.map(FileChannel.MapMode.READ_WRITE, 0, inChannel.size());

//读写数据

byte[] dst = new byte[inBuffer.limit()];

inBuffer.get(dst);

outBuffer.put(dst);

} catch (IOException e) {

e.printStackTrace();

}

4、Channel通信

采用的是直接缓冲区的方式实现

public abstract long transferFrom(ReadableByteChannel src, long position, long count)

public abstract long transferTo(long position, long count, WritableByteChannel target)

try {

FileChannel inChannel = FileChannel.open(Paths.get("demo.txt"), StandardOpenOption.READ);

FileChannel outChannel = FileChannel.open(Paths.get("demo4.txt"), StandardOpenOption.WRITE,StandardOpenOption.READ,StandardOpenOption.CREATE);

//inChannel.transferTo(0, inChannel.size(), outChannel);

outChannel.transferFrom(inChannel,0,inChannel.size());

inChannel.close();

outChannel.close();

} catch (IOException e) {

e.printStackTrace();

}