java中文件复制的4种方式

发布时间：2020-12-15 07:35:39 所属栏目：Java 来源：网络整理

导读：? ? ? 今天一个同事问我文件复制的问题，他一个100M的文件复制的指定目录下竟然成了1G多，吓我一跳，后来看了他的代码发现是自己通过字节流复制的，定义的字节数组很大，导致复制后目标文件非常大，其实就是空行等一些无效空间。我也是很少用这种方式拷贝问

? ? ? 今天一个同事问我文件复制的问题，他一个100M的文件复制的指定目录下竟然成了1G多，吓我一跳，后来看了他的代码发现是自己通过字节流复制的，定义的字节数组很大，导致复制后目标文件非常大，其实就是空行等一些无效空间。我也是很少用这种方式拷贝问价，大多数用Apache提供的commons-io中的FileUtils，后来在网上查了下，发现还有其他的方式，效率更高，所以在此整理一下，也是自己的一个学习。

1. 使用FileStreams复制

比较经典的一个代码，使用FileInputStream读取文件A的字节，使用FileOutputStream写入到文件B。

public static void copy(String source,String dest,int bufferSize) { InputStream in = null; OutputStream out = null; try { in = new FileInputStream(new File(source)); out = new FileOutputStream(new File(dest)); byte[] buffer = new byte[bufferSize]; int len; while ((len = in.read(buffer)) > 0) { out.write(buffer,0,len); } } catch (Exception e) { Log.w(TAG + ":copy","error occur while copy",e); } finally { safelyClose(TAG + ":copy",in); safelyClose(TAG + ":copy",out); } }  
2.

2、使用FileChannel

Java NIO包括transferFrom方法,根据文档应该比文件流复制的速度更快。

public static void copyNio(String source,String dest) { FileChannel input = null; FileChannel output = null; try { input = new FileInputStream(new File(from)).getChannel(); output = new FileOutputStream(new File(to)).getChannel(); output.transferFrom(input,0,input.size()); } catch (Exception e) { Log.w(TAG + "copyNio","error occur while copy",e); } finally { safelyClose(TAG + "copyNio",input); safelyClose(TAG + "copyNio",output); } }

3、 使用Apache Commons IO复制
Appache Commons IO 提供了一个FileUtils.copyFile(File from,File to)方法用于文件复制，如果项目里使用到了这个类库，使用这个方法是个不错的选择。
它的内部也是使用Java NIO的FileChannel实现的。
commons-io的路径：http://commons.apache.org/proper/commons-io/javadocs/api-release/index.html。里面还有很多实用的方法，如拷贝目录、拷贝指定格式文件等。
FileUtils.copyFile(File from,File to)FileChannel

private static void copyFileByApacheCommonsIO(File source,File dest) throws IOException { FileUtils.copyFile(source,dest); }

4、使用Java7的Files类复制

private static void copyFileUsingJava7Files(File source,File dest) throws IOException { Files.copy(source.toPath(),dest.toPath()); }

我没有亲测，找了下网友的测试程序和输出，性能数据供大家参考（来源：https://www.aspzz.cn/article/70412.htm）

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.nio.channels.FileChannel;

import java.nio.file.Files;

import org.apache.commons.io.FileUtils;

public class CopyFilesExample {

?? public static void main(String[] args) throws InterruptedException,

?????? IOException {

???? File source = new File( "C:Usersnikos7Desktopfilessourcefile1.txt" );

???? File dest = new File( "C:Usersnikos7Desktopfilesdestfile1.txt" );

??

???? // copy file using FileStreams

???? long start = System.nanoTime();

???? long end;

???? copyFileUsingFileStreams(source,dest);

???? System.out.println( "Time taken by FileStreams Copy = "

???????? + (System.nanoTime() - start));

???? // copy files using java.nio.FileChannel

???? source = new File( "C:Usersnikos7Desktopfilessourcefile2.txt" );

???? dest = new File( "C:Usersnikos7Desktopfilesdestfile2.txt" );

???? start = System.nanoTime();

???? copyFileUsingFileChannels(source,dest);

???? end = System.nanoTime();

???? System.out.println( "Time taken by FileChannels Copy = " + (end - start));

???? // copy file using Java 7 Files class

???? source = new File( "C:Usersnikos7Desktopfilessourcefile3.txt" );

???? dest = new File( "C:Usersnikos7Desktopfilesdestfile3.txt" );

???? start = System.nanoTime();

???? copyFileUsingJava7Files(source,dest);

???? end = System.nanoTime();

???? System.out.println( "Time taken by Java7 Files Copy = " + (end - start));

???? // copy files using apache commons io

???? source = new File( "C:Usersnikos7Desktopfilessourcefile4.txt" );

???? dest = new File( "C:Usersnikos7Desktopfilesdestfile4.txt" );

???? start = System.nanoTime();

???? copyFileUsingApacheCommonsIO(source,dest);

???? end = System.nanoTime();

???? System.out.println( "Time taken by Apache Commons IO Copy = "

???????? + (end - start));

?? }

?? private static void copyFileUsingFileStreams(File source,File dest)

?????? throws IOException {

???? InputStream input = null ;

???? OutputStream output = null ;

???? try {

?????? input = new FileInputStream(source);

?????? output = new FileOutputStream(dest);

?????? byte [] buf = new byte [ 1024 ];

?????? int bytesRead;

?????? while ((bytesRead = input.read(buf)) > 0 ) {

???????? output.write(buf, 0 ,bytesRead);

?????? }

???? } finally {

?????? input.close();

?????? output.close();

???? }

?? }

?? private static void copyFileUsingFileChannels(File source,File dest)

?????? throws IOException {

???? FileChannel inputChannel = null ;

???? FileChannel outputChannel = null ;

???? try {

?????? inputChannel = new FileInputStream(source).getChannel();

?????? outputChannel = new FileOutputStream(dest).getChannel();

?????? outputChannel.transferFrom(inputChannel,inputChannel.size());

???? } finally {

?????? inputChannel.close();

?????? outputChannel.close();

???? }

?? }

?? private static void copyFileUsingJava7Files(File source,File dest)

?????? throws IOException {

???? Files.copy(source.toPath(),dest.toPath());

?? }

?? private static void copyFileUsingApacheCommonsIO(File source,File dest)

?????? throws IOException {

???? FileUtils.copyFile(source,dest);

?? }

}

输出：

Time taken by FileStreams Copy = 127572360

Time taken by FileChannels Copy = 10449963

Time taken by Java7 Files Copy = 10808333

Time taken by Apache Commons IO Copy = 17971677

（编辑：李大同）

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