話題:假設機器只有500M內存,有一個1.23GB的文件,要從一個目錄複製到另外一個目錄
目的:比較IO與NIO的讀取速度效率
細節:大文件不能一次讀到內存中,否則會內存溢出,只能每次讀取固定大小的數據流
下面進行代碼實現,在實現代碼中,有的代碼是一次性讀取全部內容到內存中,有的是讀取固定大小,分別看看這些方法讀取文件速度的差異
文件大小 1.23GB
1.使用RandomAccessFile讀取文件,FileOutputStream寫文件,耗時:8768ms
2.使用BufferedInputStream讀取文件,BufferedOutputStream寫文件,耗時:2202ms
3.使用Scanner讀文件,FileOutputStream寫文件,耗時:120945ms
4.使用NIO,FileChannel讀寫文件,耗時:
- NIO每次讀取1M,耗時:8947ms
- NIO每次讀取5M,耗時:2976ms
- NIO每次讀取10M,耗時:1802ms
- NIO每次讀取20M,耗時:1279ms
基本上使用NIO和有緩衝區的IO–BufferedInputStream讀寫文件速度最快,通過任務管理器觀察對內存的使用基本在100M上下浮動
package com.zypcy.readbigfile;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.Scanner;
/**
* 讀取大文件
* 分別測試不同文件流IO與NIO讀取的效率
* 因文件很大,機器可用內存較小,無法一次讀取全部內容,需要讀取固定大小的數據
* @author zhuyu
*/
public class Demo {
public static void main(String[] args) {
String filePath = "D:\\project\\java\\workspace\\DemoThread\\src\\com\\zypcy\\readbigfile\\bigdata.zip";
String newPath = "D:\\project\\java\\workspace\\DemoThread\\src\\com\\zypcy\\readbigfile\\output.zip";
try {
File file = new File(filePath);
if(!file.exists()){
return;
}
File newFile = new File(newPath);
//randomAccessRead(file ,newFile);
//測試:讀取1.23GB文件耗時:8768ms
//bufferedRead(file ,newFile);
//測試:讀取1.23GB文件耗時:2202ms
//scannerRead(file ,newFile);
//測試:讀取1.23GB文件耗時:120945ms
fileChannelRead(file ,newFile);
//每次讀取1M,耗時:8947ms
//每次讀取5M,耗時:2976ms
//每次讀取10M,耗時:1802ms
//每次讀取20M,耗時:1279ms
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 使用 RandomAccessFile 讀取文件
* @param file
* @param newFile
*/
public static void randomAccessRead(File file , File newFile){
//測試:讀取1.23GB文件耗時:8768ms
long d1 = System.currentTimeMillis();
RandomAccessFile raf = null;
OutputStream output = null;
try {
raf = new RandomAccessFile(file , "rw");
output = new FileOutputStream(newFile);
int len = 0; //每次讀取內容長度
byte[] data = new byte[1024];//內容緩衝區
while((len = raf.read(data)) != -1){
output.write(data, 0, len);
}
long d2 = System.currentTimeMillis();
System.out.println("randomAccessRead讀取完成,耗時:" + (d2 - d1));
} catch (Exception e) {
e.printStackTrace();
}finally{
try {
if(raf != null){
raf.close();
}
if(output != null){
output.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 使用NIO的FileChannel讀取
* @param file
* @param newFile
*/
public static void fileChannelRead(File file , File newFile){
//1.23GB文件
//每次讀取1M,耗時:8947ms
//每次讀取5M,耗時:2976ms
//每次讀取10M,耗時:1802ms
//每次讀取20M,耗時:1279ms
long d1 = System.currentTimeMillis();
FileInputStream in = null;
FileOutputStream output = null;
FileChannel fic = null;
FileChannel foc = null;
try {
in = new FileInputStream(file);
output = new FileOutputStream(newFile);
fic = in.getChannel();
foc = output.getChannel();
//fic.transferTo(0, fic.size(), foc);
ByteBuffer buf = ByteBuffer.allocate(20480);
while(fic.read(buf) != -1){
buf.flip();//切換到讀取數據模式
foc.write(buf);//將緩衝區的數據寫入通道中
buf.clear();//清空緩衝區
}
long d2 = System.currentTimeMillis();
System.out.println("fileChannelRead讀取完成,耗時:" + (d2 - d1));
} catch (Exception e) {
e.printStackTrace();
}finally{
try {
if(in != null){
in.close();
}
if(output != null){
output.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 使用IO的緩衝區讀取
* @param file
* @param newFile
*/
public static void bufferedRead(File file , File newFile){
//測試:讀取1.23GB文件耗時:2202
long d1 = System.currentTimeMillis();
InputStream in = null;
OutputStream output = null;
try {
in = new BufferedInputStream(new FileInputStream(file)) ;
output = new BufferedOutputStream(new FileOutputStream(newFile));
int len = 0;
byte[] data = new byte[1024];
while((len = in.read(data)) != -1){
output.write(data, 0, len);
}
long d2 = System.currentTimeMillis();
System.out.println("bufferedRead讀取完成,耗時:" + (d2 - d1));
} catch (Exception e) {
e.printStackTrace();
}finally{
try {
if(in != null){
in.close();
}
if(output != null){
output.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 使用Scanner一行一行讀取
* @param file
* @param newFile
*/
public static void scannerRead(File file , File newFile){
//讀取1.23GB文件耗時:120945
long d1 = System.currentTimeMillis();
InputStream in = null;
OutputStream output = null;
try {
in = new FileInputStream(file);
output = new FileOutputStream(newFile);
Scanner sc = new Scanner(in, "UTF-8");
//sc.useDelimiter("\\r\\n");
while(sc.hasNext()){
String content = sc.nextLine();
output.write(content.getBytes("UTF-8"));
}
long d2 = System.currentTimeMillis();
System.out.println("scannerRead讀取完成,耗時:" + (d2 - d1));
} catch (Exception e) {
e.printStackTrace();
}finally{
try {
if(in != null){
in.close();
}
if(output != null){
output.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}