通道Channel获取四种方法

package com.hp.buffer;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

import org.junit.Test;

public class TextChannel {

	@Test //获得通道方法一：用getChannel()方法（非直接缓冲区）
	public void text1() throws IOException {

		FileInputStream fis = null;
		FileOutputStream fos = null;
		FileChannel inChannel = null;
		FileChannel outChannel = null;
		long start = System.currentTimeMillis();
		try {
			//输入输出流
			fis = new FileInputStream("D:\\6.jpg");
			fos = new FileOutputStream("D:\\8.jpg");
			//通道
			inChannel = fis.getChannel();
			outChannel = fos.getChannel();
			//缓冲区
			ByteBuffer buffer = ByteBuffer.allocate(1024);

			//把通道里面的数据，读出来，放缓冲区里面
			while(inChannel.read(buffer)!= -1) {
				//把缓冲区里面的数据，写入，到通道里面
				buffer.flip();
				outChannel.write(buffer);
				buffer.clear();//清空缓存区
			}

		} catch (Exception e) {
			e.printStackTrace();
		}finally {
			//对通道和流进行关闭
			  if(outChannel!=null) {
				  outChannel.close();
			  }
			  if(inChannel!=null) {
				  outChannel.close();
			  }
			  if(fos!=null) {
				  fos.close();
			  }
			  if(fis!=null) {
				  fis.close();
			  }
		}
		long end = System.currentTimeMillis();
		System.out.println(end-start);
	}	

	//获得通道方法二：静态open()方法，获取FileChannel对象，
	//(直接缓冲区:不用写在应用程序的内存里面，直接写在物理地址上面)
	@Test
	public void test2() throws Exception {

		FileChannel	 inChannel = FileChannel.open(Paths.get("D:\\6.jpg"), StandardOpenOption.READ);

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

		FileChannel	 outChannel = FileChannel.open(Paths.get("D:\\9.jpg"), StandardOpenOption.READ,StandardOpenOption.WRITE,StandardOpenOption.CREATE_NEW);

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

		long start = System.currentTimeMillis();
		//对缓冲区域的数据进行操作
		byte[] dst = new byte[inmap.limit()];
		inmap.get(dst);
		outmap.put(dst);

		outChannel.close();
		inChannel.close();

		long end = System.currentTimeMillis();
		System.out.println(end-start);
	}

	//transferTo() /transferForm()  (直接缓冲区)
	@Test
	public void test3() throws Exception {

		FileChannel inFile = FileChannel.open(Paths.get("D:\\6.jpg"), StandardOpenOption.READ);

		FileChannel outFile = FileChannel.open(Paths.get("D:\\10.jpg"), StandardOpenOption.READ,StandardOpenOption.WRITE,StandardOpenOption.CREATE);

		inFile.transferTo(0, inFile.size(), outFile);

		outFile.close();
		inFile.close();
	}

	  @Test //从流中获取通道,采用allocateDirect方式（直接缓冲区）
	public void test4() throws Exception {

	  FileChannel inFile = FileChannel.open(Paths.get("D:\\6.jpg"),
	  StandardOpenOption.READ);

	  FileChannel outFile = FileChannel.open(Paths.get("D:\\11.jpg"),
	  StandardOpenOption.READ,StandardOpenOption.WRITE,StandardOpenOption.CREATE);

	  ByteBuffer buffer = ByteBuffer.allocateDirect((int)inFile.size());

	  inFile.read(buffer);
	  buffer.flip();  //切换
	  outFile.write(buffer);

	  outFile.close();
	  inFile.close();
	}

}

原文地址：https://www.cnblogs.com/zxrxzw/p/10933021.html