mmap和sendfile

package read;

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

public class FormerReader {
    public static void main(String [] f) throws Exception {

        File fileIn = new File("/Users/joyce/Downloads/java.pdf"); //打开源文件
        File fileOut = new File("/Users/joyce/Downloads/target.pdf");

        // 普通stream方式
        long formerStart = System.currentTimeMillis();
        FileInputStream streamln = new FileInputStream (fileIn);
        FileOutputStream streamOut = new FileOutputStream (fileOut);
        int c;
        while ((c = streamln.read()) != -1) {
            streamOut.write(c);
        }
        streamln.close();
        streamOut.close();
        long formerEnd = System.currentTimeMillis();
        System.out.println((formerStart-formerEnd)/1000);


        // randomaccessFile
        formerStart = System.currentTimeMillis();
        RandomAccessFile randomAccessFileR = new RandomAccessFile(fileIn, "r");
        RandomAccessFile randomAccessFileW = new RandomAccessFile(fileOut, "rw");
        byte[] buf = new byte[1024];
        while((randomAccessFileR.read(buf)) != -1) {
            randomAccessFileW.write(buf);
        }
        formerEnd = System.currentTimeMillis();
        System.out.println((formerStart-formerEnd)/1000);


        // nio FileChannel
        formerStart = System.currentTimeMillis();
        FileChannel fileChannelIn = new RandomAccessFile(fileIn, "r").getChannel();
        FileChannel fileChannelOut = new RandomAccessFile(fileOut, "rw").getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(48);

        int bytesRead = fileChannelIn.read(buffer);
        while(bytesRead != -1){
            buffer.flip();
            fileChannelOut.write(buffer);
            buffer.clear();
            bytesRead = fileChannelIn.read(buffer);
        }

        formerEnd = System.currentTimeMillis();
        System.out.println((formerStart-formerEnd)/1000);


        // nio MappedByteBuffer
        // 将FileChannle对于的文件的一部分直接映射到内存。（这里的内存是堆外内存）
        formerStart = System.currentTimeMillis();
        long len = fileIn.length();
        MappedByteBuffer mappedByteBuffer = new RandomAccessFile(fileIn, "r").getChannel().map(FileChannel.MapMode.READ_ONLY, 0, len);
        MappedByteBuffer mappedByteBufferout = new RandomAccessFile(fileOut, "rw").getChannel().map(FileChannel.MapMode.READ_WRITE, 0, len);

        for (int offset = 0; offset < len; offset++) {
            byte b = mappedByteBuffer.get();
            mappedByteBufferout.put(b);
        }

        formerEnd = System.currentTimeMillis();
        System.out.println((formerStart-formerEnd)/1000);
    }
}

 @volatile
      protected var mmap: MappedByteBuffer = {
        // 第1步：创建索引文件
        val newlyCreated = file.createNewFile()
        // 第2步：以writable指定的方式（读写方式或只读方式）打开索引文件
        val raf = if (writable) new RandomAccessFile(file, "rw") else new RandomAccessFile(file, "r")
        try {
          if(newlyCreated) {
            if(maxIndexSize < entrySize) // 预设的索引文件大小不能太小，如果连一个索引项都保存不了，直接抛出异常
              throw new IllegalArgumentException("Invalid max index size: " + maxIndexSize)
            // 第3步：设置索引文件长度，roundDownToExactMultiple计算的是不超过maxIndexSize的最大整数倍entrySize
            // 比如maxIndexSize=1234567，entrySize=8，那么调整后的文件长度为1234560
            raf.setLength(roundDownToExactMultiple(maxIndexSize, entrySize))
          }
    
    
          // 第4步：更新索引长度字段_length
          _length = raf.length()
          // 第5步：创建MappedByteBuffer对象
          val idx = {
            if (writable)
              raf.getChannel.map(FileChannel.MapMode.READ_WRITE, 0, _length)
            else
              raf.getChannel.map(FileChannel.MapMode.READ_ONLY, 0, _length)
          }
          /* set the position in the index for the next entry */
          // 第6步：如果是新创建的索引文件，将MappedByteBuffer对象的当前位置置成0
          // 如果索引文件已存在，将MappedByteBuffer对象的当前位置设置成最后一个索引项所在的位置
          if(newlyCreated)
            idx.position(0)
          else
            idx.position(roundDownToExactMultiple(idx.limit(), entrySize))
          // 第7步：返回创建的MappedByteBuffer对象
          idx
        } finally {
          CoreUtils.swallow(raf.close(), AbstractIndex) // 关闭打开索引文件句柄
        }
      }