Java使用hutool实现文件大小的友好输出

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.8.22</version>
</dependency>

package com.example.demo;

import org.junit.Test;

import cn.hutool.core.io.unit.DataSizeUtil;


public class DataSizeTests {
    @Test
    public void testDataSize() {
        long b = 1L;
        long kb = 1024L + 512L;
        long mb = 1024L * 1024L;
        long gb = 1024L * 1024L * 1024L;
        long tb = 1024L * 1024L * 1024L * 1024L;

        System.out.println(DataSizeUtil.format(b)); // 1 B
        System.out.println(DataSizeUtil.format(kb)); // 1.5 KB
        System.out.println(DataSizeUtil.format(mb)); // 1 MB
        System.out.println(DataSizeUtil.format(gb)); // 1 GB
        System.out.println(DataSizeUtil.format(tb)); // 1 TB
    }
}

package cn.hutool.core.io.unit;

import java.text.DecimalFormat;

/**
 * 数据大小工具类
 *
 * @author looly
 * @since 5.3.10
 */
public class DataSizeUtil {

	/**
	 * 解析数据大小字符串，转换为bytes大小
	 *
	 * @param text 数据大小字符串，类似于：12KB, 5MB等
	 * @return bytes大小
	 */
	public static long parse(String text) {
		return DataSize.parse(text).toBytes();
	}

	/**
	 * 可读的文件大小<br>
	 * 参考 http://stackoverflow.com/questions/3263892/format-file-size-as-mb-gb-etc
	 *
	 * @param size Long类型大小
	 * @return 大小
	 */
	public static String format(long size) {
		if (size <= 0) {
			return "0";
		}
		int digitGroups = Math.min(DataUnit.UNIT_NAMES.length-1, (int) (Math.log10(size) / Math.log10(1024)));
		return new DecimalFormat("#,##0.##")
				.format(size / Math.pow(1024, digitGroups)) + " " + DataUnit.UNIT_NAMES[digitGroups];
	}
}

package com.example.demo;

import java.text.DecimalFormat;

public class DataSizeUtil {

    // 单位大小
    public static final int UNIT_SIZE = 1024;

    // 显示单位
    public static final String[] UNIT_NAMES = new String[]{
            "B", "KB", "MB", "GB", "TB", "PB", "EB"
    };

    /**
     * 可读的文件大小
     *
     * @param size long
     * @return
     */
    public static String format(long size) {
        if (size <= 0) {
            return "0";
        }

        int digitGroups = Math.min(UNIT_NAMES.length - 1, (int) (Math.log10(size) / Math.log10(UNIT_SIZE)));
        String value = new DecimalFormat("#.#").format(size / Math.pow(UNIT_SIZE, digitGroups));
        return String.format("%s %s", value, UNIT_NAMES[digitGroups]);
    }
}

package com.example.demo;

import org.junit.Test;

import java.text.DecimalFormat;

public class DecimalFormatTests {
    @Test
    public void testDecimalFormat(){
        double pi = 3.141592653;

        System.out.println(new DecimalFormat(".0").format(pi)); // 3.1
        System.out.println(new DecimalFormat("0.0").format(pi)); // 3.1
        System.out.println(new DecimalFormat("00.0").format(pi)); // 03.1
        System.out.println(new DecimalFormat(".#").format(pi)); // 3.1
        System.out.println(new DecimalFormat("#.#").format(pi)); // 3.1
        System.out.println(new DecimalFormat("##.#").format(pi)); // 3.1

        System.out.println(new DecimalFormat(".#").format((int)pi)); // 3.0
        System.out.println(new DecimalFormat(".0").format((int)pi)); // 3.0
        System.out.println(new DecimalFormat("0.0").format((int)pi)); // 3.0
        System.out.println(new DecimalFormat("#.#").format((int)pi)); // 3
    }
}