java中文件复制的4种方式

      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