62進数Javaコードサンプル（Base62）

Base62.java

package sample.util;

import java.math.BigInteger;

/**
 * Base62ユーティリティ。
 * [0-9A-Za-z]の順番で0から対応する。ASCIIコードの並び順に合わせて大文字の方が先なので注意。
 * 'Z'は35、'i'は44、'z'は61。
 * @author t-yamo
 */
public final class Base62 {

	private static final String CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
	private static final int BASE = CHARS.length();
	private static final BigInteger BIG_BASE = BigInteger.valueOf(BASE);

	private Base62() {
		// N/A
	}

	/**
	 * longからBase62への変換。
	 * @param num 変換元数値。
	 * @return Base62。
	 */
	public static String encode(long num) {
		if (num <= 0) {
			return "0";
		}
		StringBuilder sb = new StringBuilder();
		while (num > 0) {
			int sup = (int) (num % BASE);
			sb.append(CHARS.charAt(sup));
			num = num / BASE;
		}
		return sb.reverse().toString();
	}

	/**
	 * Base62からlongへの変換。
	 * @param str 変換元Base62。
	 * @return long。
	 */
	public static long decode(String str) {
		BigInteger num = BigInteger.valueOf(0);
		char[] chars = str.toCharArray();
		for (int i = 0; i < chars.length; i++) {
			int index = CHARS.indexOf(chars[chars.length - i - 1]);
			num = num.add(BIG_BASE.pow(i).multiply(BigInteger.valueOf(index)));
		}
		return num.longValue();
	}

}

Base62Test.java

package sample.util;

import org.junit.Assert;
import org.junit.Test;

/**
 * @author t-yamo
 */
public class Base62Test {

	@Test
	public void testEncode() {
		Assert.assertEquals("0", Base62.encode(0));
		Assert.assertEquals("6", Base62.encode(6));
		Assert.assertEquals("Z", Base62.encode(35));
		Assert.assertEquals("i", Base62.encode(44));
		Assert.assertEquals("z", Base62.encode(61));
		Assert.assertEquals("1YsaPe", Base62.encode(1431537942)); // 2015-05-13 17:25:42 UTCの秒
		Assert.assertEquals("PCaRJdA", Base62.encode(1431537942000l)); // 2015-05-13 17:25:42 UTCのミリ秒
		Assert.assertEquals("2FEQDJkH9F", Base62.encode(30400066288418849l));
		Assert.assertEquals("1Zyk6HmZO9", Base62.encode(21392905688514741l));
		Assert.assertEquals("1dqNWdRcwg", Base62.encode(22236810928128038l));
		Assert.assertEquals("6Rhvv3b0J", Base62.encode(1407619700686911l));
	}

	@Test
	public void testDecode() {
		Assert.assertEquals(0, Base62.decode("0"));
		Assert.assertEquals(6, Base62.decode("6"));
		Assert.assertEquals(35, Base62.decode("Z"));
		Assert.assertEquals(44, Base62.decode("i"));
		Assert.assertEquals(61, Base62.decode("z"));
		Assert.assertEquals(1431537942, Base62.decode("1YsaPe")); // 2015-05-13 17:25:42 UTCの秒
		Assert.assertEquals(1431537942000l, Base62.decode("PCaRJdA")); // 2015-05-13 17:25:42 UTCのミリ秒
		Assert.assertEquals(30400066288418849l, Base62.decode("2FEQDJkH9F"));
		Assert.assertEquals(21392905688514741l, Base62.decode("1Zyk6HmZO9"));
		Assert.assertEquals(22236810928128038l, Base62.decode("1dqNWdRcwg"));
		Assert.assertEquals(1407619700686911l, Base62.decode("6Rhvv3b0J"));
	}

}