Java拷贝文件的4种方式

java.io.File class doesn’t have any shortcut method to copy file from source to destination. Here we will learn about four different ways we can copy file in java.

1. Using Stream: This is the conventional way of file copy in java, here we create two Files, source and destination. Then we create InputStream from source and write it to destination
file using OutputStream.

Here is the method that can be used to copy file using streams.

private static void copyFileUsingStream(File source, File dest) throws IOException {
InputStream is = null;
OutputStream os = null;
try {
is = new FileInputStream(source);
os = new FileOutputStream(dest);
byte[] buffer =new byte[1024];
int length;
while ((length = is.read(buffer)) > 0) {
os.write(buffer,0, length);
}
} finally{
is.close();
os.close();
}
}

2. Using java.nio.channels.FileChannel: Java NIO classes were introduced in Java 1.4 and FileChannel can be used to copy file in java. According to transferFrom() method
javadoc, this way of copy file is supposed to be faster than using Streams to copy files.

Here is the method that can be used to copy file using FileChannel.

private static void copyFileUsingChannel(File source, File dest) throws IOException {
FileChannel sourceChannel =null;
FileChannel destChannel =null;
try {
sourceChannel =new FileInputStream(source).getChannel();
destChannel = new FileOutputStream(dest).getChannel();
destChannel.transferFrom(sourceChannel,0, sourceChannel.size());
}finally{
sourceChannel.close();
destChannel.close();
}
}

3. Using Apache Commons IO: Apache Commons IO FileUtils.copyFile(File srcFile, File destFile) can be used to copy file in java. If you are already using Apache Commons IO in your
project, it makes sense to use this for code simplicity. Internally it uses Java NIO FileChannel, so you can avoid this wrapper method if you are not already using it for other functions.

Here is the method for using apache commons io for file copy in java.

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

4. Java 7 Files class: If you are working on Java 7, you can use Files class copy() method to copy file in java. It uses File System providers to copy the files.

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

Now to find out which is the fastest method, I wrote a test class and executed above methods one-by-one for copy file of 1 GB. In each call, I used different files to avoid any benefit to later methods because of caching.

Here is the output of above program, note that I commented above code to make sure every time only one method is used for file copy.

Time taken by Stream Copy 1x

Time taken by Channel Copy 2.34x

Time taken by Apache Commons IO Copy 2.43x

Time taken by Java7 Files Copy 2.00x

From the output it’s clear that Stream Copy is the best way to copy File in Java.