java复制文件的4种要领：（引荐：java视频教程）
一、运用FileStreams复制
这是最典范的体式格局将一个文件的内容复制到另一个文件中。 运用FileInputStream读取文件A的字节，运用FileOutputStream写入到文件B。 这是第一个要领的代码:
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)) ！= -1) {
output.write(buf, 0, bytesRead);
}
} finally {
input.close();
output.close();
}
}
正如你所看到的我们实行几个读和写操纵try的数据,所以这应当是一个低效率的,下一个要领我们将看到新的体式格局。
二、运用FileChannel复制
Java NIO包含transferFrom要领,依据文档应当比文件流复制的速率更快。 这是第二种要领的代码:
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();
}
}
三、运用Commons IO复制
Apache Commons IO供应拷贝文件要领在其FileUtils类,可用于复制一个文件到另一个处所。它异常方便运用Apache Commons FileUtils类时,您已运用您的项目。基本上,这个类运用Java NIO FileChannel内部。 这是第三种要领的代码:
private static void copyFileUsingApacheCommonsIO(File source, File dest)
throws IOException {
FileUtils.copyFile(source, dest);
}
该要领的中心代码以下：
private static void doCopyFile(File srcFile, File destFile, boolean preserveFileDate) throws IOException {
if (destFile.exists() && destFile.isDirectory()) {
throw new IOException("Destination '" + destFile + "' exists but is a directory");
}
FileInputStream fis = null;
FileOutputStream fos = null;
FileChannel input = null;
FileChannel output = null;
try {
fis = new FileInputStream(srcFile);
fos = new FileOutputStream(destFile);
input = fis.getChannel();
output = fos.getChannel();
long size = input.size();
long pos = 0;
long count = 0;
while (pos < size) {
count = size - pos > FILE_COPY_BUFFER_SIZE ? FILE_COPY_BUFFER_SIZE : size - pos;
pos += output.transferFrom(input, pos, count);
}
} finally {
IOUtils.closeQuietly(output);
IOUtils.closeQuietly(fos);
IOUtils.closeQuietly(input);
IOUtils.closeQuietly(fis);
}
if (srcFile.length() != destFile.length()) {
throw new IOException("Failed to copy full contents from '" +
srcFile + "' to '" + destFile + "'");
}
if (preserveFileDate) {
destFile.setLastModified(srcFile.lastModified());
}
}
因而可知，运用Apache Commons IO复制文件的道理就是上述第二种要领：运用FileChannel复制
四、运用Java7的Files类复制
假如你有一些履历在Java 7中你可能会晓得,能够运用复制要领的Files类文件,从一个文件复制到另一个文件。 这是第四个要领的代码:
private static void copyFileUsingJava7Files(File source, File dest)
throws IOException {
Files.copy(source.toPath(), dest.toPath());
}
五、测试
如今看到这些要领中的哪一个是更高效的,我们会复制一个大文件运用每个在一个简朴的顺序。 从缓存来防止任何机能显著我们将运用四个差别的源文件和四种差别的目的文件。 让我们看一下代码:
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 FileStreamslong start = System.nanoTime();
long end;
copyFileUsingFileStreams(source, dest);
System.out.println("Time taken by FileStreams Copy = "
+ (System.nanoTime() - start));
// copy files using java.nio.FileChannelsource = 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 classsource = 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 iosource = 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
正如您能够看到的FileChannels拷贝大文件是最好的要领。假如你处置惩罚更大的文件,你会注意到一个更大的速率差。
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