java中文件复制的4种方式分析

访客 阅读:177 2020-05-08 10:25:19 评论:0

      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。
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.jb51.net/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:\\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
 

 

标签:java
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