File文件读写操作代码,Java代码库,德仔网

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【Java】 File文件读写操作
作者:汶纡 / 发布于2014/11/18/ 397

	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&mdash;&mdash;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&mdash;&mdash;start_time:"+df.format(start_time));
	 System.out.println("==============第一种方式&mdash;&mdash;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&mdash;&mdash;start_time:"+df.format(start_time));
	 System.out.println("==================第二种方式&mdash;&mdash;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&mdash;&mdash;start_time:"+df.format(start_time));
	 System.out.println("======================第三种方式&mdash;&mdash;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&mdash;&mdash;start_time:"+df.format(start_time));
	 System.out.println("======================第一种文件复制方式&mdash;&mdash;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&mdash;&mdash;start_time:"+df.format(start_time));
	 System.out.println("======================第二种文件复制方式&mdash;&mdash;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");
	 }
	 }
	}
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