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java多姿势读写文件

Posted on Edited on In

重温经典，特意看了下为什么读文件非得不让等于 -1

fileChannelIn.read(byteBuffer) != -1

EOF = End Of File，其默认值就是-1

这是一个约定好的结束符，不是认为改变的

代码

建议使用大文件进行测试，看效果比较明显

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@Test
public void testCopy() {
    String oldFileName = "/Users/hisenyuan/hisen/blog/source/_posts/Test-Java-Code.md";
    String newFileName = "/Users/hisenyuan/hisen/test/Test-Java-Code.md";
    nioCopy(oldFileName, newFileName);
    ioCopy(oldFileName, newFileName.replace(".md", ".md.bak"));
    ioCopyByLine(oldFileName,newFileName.replace(".md",".bak." + System.currentTimeMillis()));
}

/**
 * 利用NIO进行读写文件
 *
 * @param oldFileName 原文件的路径
 * @param newFileName 新文件的路径
 */
public static void nioCopy(String oldFileName, String newFileName) {
    try {
        FileChannel fileChannelIn = new FileInputStream(new File(oldFileName)).getChannel();
        FileChannel fileChannelOut = new FileOutputStream(new File(newFileName)).getChannel();
        //获取文件大小
        long size = fileChannelIn.size();
        System.out.printf("文件大小为：%s byte \n", size);
        //缓冲
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

        long start = System.currentTimeMillis();
        while (fileChannelIn.read(byteBuffer) != -1) {
            //准备写
            byteBuffer.flip();
            fileChannelOut.write(byteBuffer);
            //准备读
            byteBuffer.clear();
        }
        long end = System.currentTimeMillis();
        System.out.printf("NIO方式复制完成，耗时 %s 秒\n", (end - start) / 1000);
        //关闭
        fileChannelIn.close();
        fileChannelOut.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

/**
 * IO方式复制文件
 *
 * @param oldFileName
 * @param newFileName
 */
public static void ioCopy(String oldFileName, String newFileName) {
    try {
        FileInputStream fileInputStream = new FileInputStream(new File(oldFileName));
        FileOutputStream fileOutputStream = new FileOutputStream(new File(newFileName));

        long length = new File(oldFileName).length();

        System.out.printf("文件大小为：%s byte \n", length);
        byte[] buffer = new byte[1024];

        long start = System.currentTimeMillis();
        int len = 0;
        //EOF = End Of File，其默认值就是-1
        while ((len = fileInputStream.read(buffer)) != -1) {
            fileOutputStream.write(buffer, 0, len);
        }
        long end = System.currentTimeMillis();
        System.out.printf("IO方式复制完成，耗时 %s 秒\n", (end - start) / 1000);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static void ioCopyByLine(String oldFileName, String newFileName) {
    try {
        BufferedReader reader = new BufferedReader(new FileReader(oldFileName));
        BufferedWriter writer = new BufferedWriter(new FileWriter(newFileName));
        String line;
        while ((line = reader.readLine()) != null) {
            writer.write(line);
            writer.newLine();
            writer.flush();
        }
    } catch (IOException e) {
        System.out.println("error:" + e);
    }
}