java之nio（3）

通道(Channel)


 channel边读边写

package nio;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class ChannelTest {
	public static void main(String[] args) throws Exception{
		ByteBuffer buffer = ByteBuffer.allocate(10);//开辟10个缓冲区
		
		//读文件
		FileInputStream in = new FileInputStream("F:\\1.txt");
		FileChannel inChannel = in.getChannel();
		
		//写文件
		FileOutputStream out = new FileOutputStream("F:\\2.txt");
		FileChannel outChannel = out.getChannel();
		
		String str = "12345";//初始化信息
		buffer.put(str.getBytes());//把初始化信息放入缓冲区
		int temp = 0;
		while((temp=inChannel.read(buffer))!=-1) {//如果还有多余的缓冲区则继续读取直到缓冲区满
			buffer.flip();//每次缓冲区重置（通过改变position=0），必须把内容展示出来
			outChannel.write(buffer);//写入通道
			buffer.clear();//每次必须清空缓冲区，否则while循环每次 read读取的时候的缓冲区已满，read不会再读取新内容，陷入死循环
		}
		inChannel.close();
		in.close();
		outChannel.close();
		out.close();
	}
	
	private static void printInfo(ByteBuffer buffer) {
		while(buffer.hasRemaining()) {
			System.out.print((char)buffer.get()+"、");
		}
		System.out.println();
	}
}

MappedByteBuffer（内存映射流）

 代码：

package nio;

import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class MappedByteBufferTest {
	public static void main(String[] args) throws Exception{
		//读文件
		FileInputStream in = new FileInputStream("F:\\1.txt");
		FileChannel inChannel = in.getChannel();
		
		//开辟内存通道，只读模式，大小为文件大小,MappedByteBuffer只为MapMode.READ_ONLY，如果要操作写模式太危险
		MappedByteBuffer mappedByteBuffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, in.available());
		printInfo(mappedByteBuffer);
		
		inChannel.close();
		in.close();
	}
	
	private static void printInfo(ByteBuffer buffer) {
		while(buffer.hasRemaining()) {
			System.out.print((char)buffer.get()+"、");
		}
		System.out.println();
	}
}