File文件读写操作

acseskd Post at 2014/11/19 22:38:00
package com.file;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
* file operate
* @author ruanpeng
* @time 2014-11-11上午9:14:29
*/
public class OperateFileDemo {

private DateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss:SSS");
private Date start_time = null;//开始时间
private Date end_time = null;//结束时间

public static void main(String[] args) {
OperateFileDemo demo = new OperateFileDemo();
demo.operateFile1();
demo.operateFile2();
demo.operateFile3();
demo.fileCopy1();
demo.fileCopy2();
}

/**
* the first method of reading file
*/
public void operateFile1(){
start_time = new Date();
File f = new File("E:"+File.separator+"test.txt");//File.separator——windows is '\',unix is '/'
try {
//创建一个流对象
InputStream in = new FileInputStream(f);
//读取数据,并将读取的数据存储到数组中
byte[] b = new byte[(int) f.length()];//数据存储的数组
int len = 0;
int temp = 0;
while((temp = in.read()) != -1){//循环读取数据,未到达流的末尾
b[len] = (byte) temp;//将有效数据存储在数组中
len ++;
}

System.out.println(new String(b, 0, len, "GBK"));
in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
end_time = new Date();
System.out.println("==============第一种方式——start_time:"+df.format(start_time));
System.out.println("==============第一种方式——end_time:"+df.format(end_time));
System.out.println("==============第一种方式总耗时:"+(end_time.getTime() - start_time.getTime())+"毫秒");
}
}

/**
* the second method of reading file
*/
public void operateFile2(){
start_time = new Date();
File f = new File("E:"+File.separator+"test.txt");
try {
InputStream in = new FileInputStream(f);
byte[] b = new byte[1024];
int len = 0;
while((len = in.read(b)) != -1){
System.out.println(new String(b, 0, len, "GBK"));
}
in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
end_time = new Date();
System.out.println("==================第二种方式——start_time:"+df.format(start_time));
System.out.println("==================第二种方式——end_time:"+df.format(end_time));
System.out.println("==================第二种方式总耗时:"+(end_time.getTime() - start_time.getTime())+"毫秒");
}
}

/**
* the third method of reading file(文件读取(Memory mapping-内存映射方式))
* 这种方式的效率是最好的,速度也是最快的,因为程序直接操作的是内存
*/
public void operateFile3(){
start_time = new Date();
File f = new File("E:"+File.separator+"test.txt");
try {
FileInputStream in = new FileInputStream(f);
FileChannel chan = in.getChannel();//内存与磁盘文件的通道,获取通道,通过文件通道读写文件。
MappedByteBuffer buf = chan.map(FileChannel.MapMode.READ_ONLY, 0, f.length());
byte[] b = new byte[(int) f.length()];
int len = 0;
while(buf.hasRemaining()){
b[len] = buf.get();
len++;
}
chan.close();
in.close();
System.out.println(new String(b,0,len,"GBK"));
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
end_time = new Date();
System.out.println("======================第三种方式——start_time:"+df.format(start_time));
System.out.println("======================第三种方式——end_time:"+df.format(end_time));
System.out.println("======================第三种方式总耗时:"+(end_time.getTime() - start_time.getTime())+"毫秒");
}
}

/**
* the first method of copying file
*/
public void fileCopy1(){
start_time = new Date();
File f = new File("E:"+File.separator+"test.txt");
try {
InputStream in = new FileInputStream(f);
OutputStream out = new FileOutputStream("F:"+File.separator+"test.txt");
int len = 0;
while((len = in.read()) != -1){
out.write(len);
}
out.close();
in.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
end_time = new Date();
System.out.println("======================第一种文件复制方式——start_time:"+df.format(start_time));
System.out.println("======================第一种文件复制方式——end_time:"+df.format(end_time));
System.out.println("======================第一种文件复制方式总耗时:"+(end_time.getTime() - start_time.getTime())+"毫秒");
}
}

/**
* 使用内存映射实现文件复制操作
*/
public void fileCopy2(){
start_time = new Date();
File f = new File("E:"+File.separator+"test.txt");
try {
FileInputStream in = new FileInputStream(f);
FileOutputStream out = new FileOutputStream("F:"+File.separator+"test2.txt");
FileChannel inChan = in.getChannel();
FileChannel outChan = out.getChannel();
//开辟缓冲区
ByteBuffer buf = ByteBuffer.allocate(1024);
while ((inChan.read(buf)) != -1){
//重设缓冲区
buf.flip();
//输出缓冲区
outChan.write(buf);
//清空缓冲区
buf.clear();
}
inChan.close();
outChan.close();
in.close();
out.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
end_time = new Date();
System.out.println("======================第二种文件复制方式——start_time:"+df.format(start_time));
System.out.println("======================第二种文件复制方式——end_time:"+df.format(end_time));
System.out.println("======================第二种文件复制方式总耗时:"+(end_time.getTime() - start_time.getTime())+"毫秒");
}
}
}

已有 0 位网友发表了看法