今天一個同事問我文件復制的問題，他一個100M的文件復制的指定目錄下竟然成了1G多，嚇我一跳，后來看了他的代碼發現是自己通過字節流復制的，定義的字節數組很大，導致復制后目標文件非常大，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，后來在網上查了下，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復制
比較經典的一個代碼，使用FileInputStream讀取文件A的字節，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復制的速度更快。
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復制
Appache Commons IO 提供了一個FileUtils.copyFile(File from, File to)方法用於文件復制，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。里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類復制
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序和輸出，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