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.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 = 127572360Time taken by FileChannels Copy = 10449963Time taken by Java7 Files Copy = 10808333Time taken by Apache Commons IO Copy = 17971677
原文：https://www.cnblogs.com/xxjcai/p/11581987.html