java復(fù)制文件的方法有幾種

一、使用FileStreams復(fù)制

這是最經(jīng)典的方式將一個(gè)文件的內(nèi)容復(fù)制到另一個(gè)文件中。 使用FileInputStream讀取文件A的字節(jié)，使用FileOutputStream寫入到文件B。 這是第一個(gè)方法的代碼:

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();
    }
}

正如你所看到的我們執(zhí)行幾個(gè)讀和寫操作try的數(shù)據(jù),所以這應(yīng)該是一個(gè)低效率的,下一個(gè)方法我們將看到新的方式。

二、使用FileChannel復(fù)制

Java NIO包括transferFrom方法,根據(jù)文檔應(yīng)該比文件流復(fù)制的速度更快。 這是第二種方法的代碼:

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、使用Commons IO復(fù)制

Apache Commons IO提供拷貝文件方法在其FileUtils類,可用于復(fù)制一個(gè)文件到另一個(gè)地方。它非常方便使用Apache Commons FileUtils類時(shí),您已經(jīng)使用您的項(xiàng)目?；旧?這個(gè)類使用Java NIO FileChannel內(nèi)部。 這是第三種方法的代碼:

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

該方法的核心代碼如下：

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());
        }
    }

由此可見，使用Apache Commons IO復(fù)制文件的原理就是上述第二種方法：使用FileChannel復(fù)制

四、使用Java7的Files類復(fù)制

如果你有一些經(jīng)驗(yàn)在Java 7中你可能會(huì)知道,可以使用復(fù)制方法的Files類文件,從一個(gè)文件復(fù)制到另一個(gè)文件。 這是第四個(gè)方法的代碼:

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

五、測試

現(xiàn)在看到這些方法中的哪一個(gè)是更高效的,我們會(huì)復(fù)制一個(gè)大文件使用每一個(gè)在一個(gè)簡單的程序。 從緩存來避免任何性能明顯我們將使用四個(gè)不同的源文件和四種不同的目標(biāo)文件。 讓我們看一下代碼:

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);
    }

}

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

正如您可以看到的FileChannels拷貝大文件是最好的方法。如果你處理更大的文件,你會(huì)注意到一個(gè)更大的速度差。

以上就是java復(fù)制文件的4種方實(shí)例的詳細(xì)內(nèi)容，更多請關(guān)注億速云其它相關(guān)文章！