Channel在Java中是一种可以直接与ByteBuffer交互的媒介，它提供了一种基于块的I/O操作模式，有助于提高大数据量的读写效率。
一、Java Channel概述
Channel是Java中的一个接口，它继承了Closeable和InterruptibleChannel两个接口。它允许从缓冲区直接读取和写入数据。FileChannel、DatagramChannel、Channel的具体实现是SocketChannel和ServerSocketChannel。
import java.nio.channels.Channel;
import java.nio.ByteBuffer;
public class Main {
public static void main(String[] args){
Channel channel;
ByteBuffer buffer;
}
}二、Channel的使用
让我们以FileChannel为例，展示如何使用Channel。FileChannel用于读取、写入、映射和操作文件。首先，我们使用FileInputStream。、FileOutputStream或RandomAccessFile获得FileChannel。然后，我们可以通过调用read()和write()来读取和写入数据。
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
public static void main(String[] args) throws Exception {
FileInputStream fin = new FileInputStream("test.txt");
FileChannel fc = fin.getChannel();
ByteBuffer buffer = ByteBuffer.allocate(1024);
int bytesRead = fc.read(buffer); // 读取数据
while (bytesRead != -1) {
buffer.flip();
while (buffer.hasRemaining()) {
System.out.print((char) buffer.get());
}
buffer.clear();
bytesRead = fc.read(buffer);
}
fin.close();
String str = "Hello, World!";
FileOutputStream fout = new FileOutputStream("test.txt");
FileChannel fcout = fout.getChannel();
ByteBuffer buffer1 = ByteBuffer.allocate(1024);
buffer1.clear();
buffer1.put(str.getBytes());
buffer1.flip();
while (buffer1.hasRemaining()) {
fcout.write(buffer1); // 写入数据
}
fout.close();
}
}三、Channel的特性
Channel除了基本的读写操作外，还支持transferTo()和transferFrom()等传输操作，可以直接将数据从一个Channel(例如FileChannel)传输到另一个Channel。这通常比先读后写更有效。
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
public class Main {
public static void main(String[] args) throws Exception {
FileInputStream fin = new FileInputStream("src.txt");
FileOutputStream fout = new FileOutputStream("dest.txt");
FileChannel finChannel = fin.getChannel();
FileChannel foutChannel = fout.getChannel();
long transferred = finChannel.transferTo(0, finChannel.size(), foutChannel);
System.out.println("Bytes transferred = " + transferred);
fin.close();
fout.close();
}
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