今天一個同事問我文件複製的問題，他一個100M的文件複製的指定目錄下竟然成了1G多，嚇我一跳，後來看了他的代碼發現是自己通過位元組流複製的，定義的位元組數組很大，導致複製後目標文件非常大，其實就是空行等一些無效空間。我也是很少用這種方式拷貝問價，大多數用Apache提供的commons-io中的File ...
今天一個同事問我文件複製的問題，他一個100M的文件複製的指定目錄下竟然成了1G多，嚇我一跳，後來看了他的代碼發現是自己通過位元組流複製的，定義的位元組數組很大，導致複製後目標文件非常大，其實就是空行等一些無效空間。我也是很少用這種方式拷貝問價，大多數用Apache提供的commons-io中的FileUtils，後來在網上查了下，發現還有其他的方式，效率更高，所以在此整理一下，也是自己的一個學習。
1. 使用FileStreams複製
比較經典的一個代碼，使用FileInputStream讀取文件A的位元組，使用FileOutputStream寫入到文件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,根據文檔應該比文件流複製的速度更快。
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複製
Appache Commons IO 提供了一個FileUtils.copyFile(File from, File to)方法用於文件複製，如果項目里使用到了這個類庫，使用這個方法是個不錯的選擇。
它的內部也是使用Java NIO的FileChannel實現的。
commons-io的路徑：http://commons.apache.org/proper/commons-io/javadocs/api-release/index.html。裡面還有很多實用的方法，如拷貝目錄、拷貝指定格式文件等。
private static void copyFileByApacheCommonsIO(File source, File dest) throws IOException {
FileUtils.copyFile(source, dest);
}4、使用Java7的Files類複製
private static void copyFileUsingJava7Files(File source, File dest) throws IOException {
Files.copy(source.toPath(), dest.toPath());
}我沒有親測，找了下網友的測試程式和輸出，性能數據供大家參考（來源：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);
}
}
輸出：
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
