java中文件复制的4种方式

时间：2022-06-06 19:31:38

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



 
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