java中文件复制的4种方式，java文件的复制

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。

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。

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:\\Users\\nikos7\\Desktop\\files\\sourcefile1.txt");

File dest =new File("C:\\Users\\nikos7\\Desktop\\files\\destfile1.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:\\Users\\nikos7\\Desktop\\files\\sourcefile2.txt");

dest =new File("C:\\Users\\nikos7\\Desktop\\files\\destfile2.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:\\Users\\nikos7\\Desktop\\files\\sourcefile3.txt");

dest =new File("C:\\Users\\nikos7\\Desktop\\files\\destfile3.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:\\Users\\nikos7\\Desktop\\files\\sourcefile4.txt");

dest =new File("C:\\Users\\nikos7\\Desktop\\files\\destfile4.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,0, 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

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