Java文件大小转换的两种方式小结

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-io</artifactId>
    <version>1.3.2</version>
</dependency>

import org.apache.commons.io.FileUtils;
public class TestFileSize {

    public static void main(String[] args) {
        long fileSize = 33931L;
        String fileSizeStr = FileUtils.byteCountToDisplaySize(fileSize);
        System.out.println("文件大小：" + fileSizeStr);
    }
}

import java.text.DecimalFormat;

import org.apache.commons.io.FileUtils;

public class TestFileSize {

    public static void main(String[] args) {
        long bytes = 33931L;
        String fileSizeStr = FileUtils.byteCountToDisplaySize(bytes);
        System.out.println("文件大小：" + fileSizeStr);

        // 自己定义方法实现
        String fileSizeStr1 = formatFileSize1(bytes);
        System.out.println("文件转换字符转大小方式一：" + fileSizeStr1);
        String fileSizeStr2 = formatFileSize2(bytes);
        System.out.println("文件转换字符转大小方式二：" + fileSizeStr2);
        String fileSizeStr3 = formatFileSize3(bytes);
        System.out.println("文件转换字符转大小方式三：" + fileSizeStr3);
        // 转换为字节
        long fileBytes1 = convertSizeToLong1(fileSizeStr2);
        System.out.println("字节数为：" + fileBytes1);
        long fileBytes2 = convertSizeToLong2(fileSizeStr2);
        System.out.println("字节数为：" + fileBytes2);
    }


    /**
     * 将字节数转换为其他单位的文件大小
     *
     * @param bytes 字节数
     * @return 转换后的文件大小
     */
    public static String formatFileSize1(long bytes) {
        if (bytes < 1024) {
            return bytes + " B";
        } else if (bytes < 1024 * 1024) {
            return Math.round(bytes / 1024.0) + " KB";
        } else if (bytes < 1024 * 1024 * 1024) {
            return Math.round(bytes / (1024.0 * 1024.0)) + " MB";
        } else {
            return Math.round(bytes / (1024.0 * 1024.0 * 1024.0)) + " GB";
        }
    }

    /**
     * 将字节数转换为其他单位的文件大小
     *
     * @param bytes 字节数
     * @return 转换后的文件大小
     */
    private static String formatFileSize2(long bytes) {
        DecimalFormat df = new DecimalFormat("#.00");
        String fileSizeString = "";
        String wrongSize = "0 B";
        if (bytes == 0) {
            return wrongSize;
        }
        if (bytes < 1024) {
            fileSizeString = df.format((double) bytes) + " B";
        } else if (bytes < 1048576) {
            fileSizeString = df.format((double) bytes / 1024) + " KB";
        } else if (bytes < 1073741824) {
            fileSizeString = df.format((double) bytes / 1048576) + " MB";
        } else {
            fileSizeString = df.format((double) bytes / 1073741824) + " GB";
        }
        return fileSizeString;
    }

    /**
     * 将字节数转换为其他单位的文件大小
     *
     * @param bytes 字节数
     * @return 转换后的文件大小
     */
    public static String formatFileSize3(long bytes) {
        String[] units = {"bytes", "KB", "MB", "GB", "TB"};
        int unitIndex = 0;
        while (bytes > 1024 && unitIndex < units.length - 1) {
            bytes /= 1024;
            unitIndex++;
        }
        return bytes + " " + units[unitIndex];
    }

    /**
     * 将其他单位的文件大小转换为字节数
     *
     * @param size 文件大小（带单位）
     * @return 转换后的字节数
     */
    public static long convertSizeToLong1(String size) {
        long factor = 1;
        String unit = size.substring(size.length() - 2).trim().toUpperCase();
        // 截取到小数点最后一位
        long value = Long.parseLong(size.substring(0, size.lastIndexOf(".")).trim());
        if (unit.equals("KB")) {
            factor = 1024;
        } else if (unit.equals("MB")) {
            factor = 1024 * 1024;
        } else if (unit.equals("GB")) {
            factor = 1024 * 1024 * 1024;
        }

        return value * factor;
    }

    /**
     * 将其他单位的文件大小转换为字节数
     *
     * @param size 文件大小（带单位）
     * @return 转换后的字节数
     */
    public static long convertSizeToLong2(String size) {
        long factor = 1;
        size = size.trim().toUpperCase();
        String unit = size.replaceAll("[^A-Za-z]+", "");
        double value = Double.parseDouble(size.replaceAll("[^0-9.]+", "").replace(unit, ""));
        switch (unit) {
            case "KB":
                factor = 1024;
                break;
            case "MB":
                factor = 1024 * 1024;
                break;
            case "GB":
                factor = 1024 * 1024 * 1024;
                break;
        }

        return (long) value * factor;
    }
}