java中的File文件读写操作

Java中常用的文件读写方式
1、普通方式
2、内存映射方式

内存映射方式效率更高，速度也更快！

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;




public class FileCopy {


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) {
FileCopy demo = new FileCopy();
// 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 + "test1.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 + "test1.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 + "test1.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 + "test1.txt");
try {
InputStream in = new FileInputStream(f);
OutputStream out = new FileOutputStream("E:" + File.separator
+ "test2.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 + "test1.txt");
try {
FileInputStream in = new FileInputStream(f);
FileOutputStream out = new FileOutputStream("E:" + File.separator
+ "test3.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");
}
}
}