md5.java

一个学生选课系统

package com.student.DB;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5 {
	public static String md5(String text) {
		MessageDigest msgDigest = null;//MessageDigest 类为应用程序提供信息摘要算法的功能,如 MD5 或 SHA 算法

		try {
			msgDigest = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalStateException(
					"System doesn't support MD5 algorithm.");
		}

		msgDigest.update(text.getBytes());

		byte[] bytes = msgDigest.digest();

		byte tb;
		char low;
		char high;
		char tmpChar;

		String md5Str = new String();

		for (int i = 0; i < bytes.length; i++) {
			tb = bytes[i];

			tmpChar = (char) ((tb >>> 4) & 0x000f);

			if (tmpChar >= 10) {
				high = (char) (('a' + tmpChar) - 10);
			} else {
				high = (char) ('0' + tmpChar);
			}

			md5Str += high;
			tmpChar = (char) (tb & 0x000f);

			if (tmpChar >= 10) {
				low = (char) (('a' + tmpChar) - 10);
			} else {
				low = (char) ('0' + tmpChar);
			}

			md5Str += low;
		}

		return md5Str;
	}
}