使用NIO中ByteBuffer.allocateDirect和ByteBuffer.allocate后性能的确不一样。

package com.bxf.NIOTest;

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

public class allocateDirectTest {
public allocateDirectTest(){}

String sfin = "K:\\tmp\\FileIn.txt";
String sfou = "K:\\tmp\\FileOut.txt";
String sfou2 = "K:\\tmp\\FileOut2.txt";

public void copyFileByAllocDir() throws Exception{
FileInputStream fin = new FileInputStream(sfin);
FileChannel fcin = fin.getChannel();

FileOutputStream fout = new FileOutputStream(sfou);
FileChannel fcout = fout.getChannel();

ByteBuffer buffer = ByteBuffer.allocateDirect(1024);

long startTime = System.currentTimeMillis();
while(true){
buffer.clear();
int r = fcin.read(buffer);

if(r == -1)
break;
buffer.flip();
fcout.write(buffer);
}
long endTime = System.currentTimeMillis();
System.out.println("By copyFileByAllocDir Use time : " + (endTime - startTime));
}

// 经测试使用ByteBuffer.allocateDirect(1024)的确要比使用
// ByteBuffer.allocate(1024)快！
public void copyFileByAlloc() throws Exception{
FileInputStream fin = new FileInputStream(sfin);
FileChannel fcin = fin.getChannel();

FileOutputStream fout2 = new FileOutputStream(sfou2);
FileChannel fcout2 = fout2.getChannel();

ByteBuffer buffer = ByteBuffer.allocate(1024);
long startTime = System.currentTimeMillis();
while(true){
buffer.clear();
int r = fcin.read(buffer);

if(r == -1)
break;
buffer.flip();
fcout2.write(buffer);
}
long endTime = System.currentTimeMillis();
System.out.println("By copyFileByAlloc Use time : " + (endTime - startTime));

}
}
// 第一次测试结果：
// By copyFileByAllocDir Use time : 50
// By copyFileByAlloc Use time : 69

// 第二次测试结果：
// By copyFileByAllocDir Use time : 52
// By copyFileByAlloc Use time : 58

如果将buffer调大到：100*1024，差距就更明显了：
//By copyFileByAllocDir Use time : 3
//By copyFileByAlloc Use time : 68

//By copyFileByAllocDir Use time : 2
//By copyFileByAlloc Use time : 60