myeclipse注册机算法

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class MyEclipseGen {
	private static final String LL = "Decompiling this copyrighted software is a violation of both your license agreement and the Digital Millenium Copyright Act of 1998 (http://www.loc.gov/copyright/legislation/dmca.pdf). Under section 1204 of the DMCA, penalties range up to a $500,000 fine or up to five years imprisonment for a first offense. Think about it; pay for a license, avoid prosecution, and feel better about yourself.";

	public String getSerial(String userId, String licenseNum) {
		Calendar cal = Calendar.getInstance();
		// 过期时间为3年后的昨天
		cal.add(Calendar.YEAR, 3);
		cal.add(Calendar.DAY_OF_YEAR, -1);
		
		NumberFormat nf = new DecimalFormat("000");
		licenseNum = nf.format(Integer.valueOf(licenseNum));
		
		String verTime = new StringBuilder("-").append(
				new SimpleDateFormat("yyMMdd").format(cal.getTime()))
				.append("0").toString();
		
		String type = "YE3MP-";
		String need = new StringBuilder(userId.substring(0, 1)).append(type)
				.append("300").append(licenseNum).append(verTime).toString();
		String dx = new StringBuilder(need).append(LL).append(userId)
				.toString();
		int suf = this.decode(dx);
		String code = new StringBuilder(need).append(String.valueOf(suf))
				.toString();
		
		return change(code);
	}

	private int decode(String s) {
		char[] ac = s.toCharArray();
		
		int i = 0;
		for (int j=0; j<ac.length; j++) {
			i = (31 * i) + ac[j];
		}
		return Math.abs(i);
	}

	private String change(String s) {
		byte[] abyte0 = s.getBytes();
		char[] ac = new char[s.length()];
		for (int i=0; i<abyte0.length; i++) {
			int j = abyte0[i];
			if ((j >= '0') && (j <= '9')) {
				j = (j - '0' + 5) % 10 + '0';
			} else if ((j >= 'A') && (j <= 'Z')) {
				j = ((j - 'A') + 13) % 26 + 'A';
			} else if ((j >= 'a') && (j <= 'z')) {
				j = ((j - 'a') + 13) % 26 + 'a';
			}
			
			ac[i] = (char) j;
		}
		
		return String.valueOf(ac);
	}

	public MyEclipseGen() {
		super();
	}

	public static void main(String[] args) throws UnsupportedEncodingException {
		try {
			System.out.println("please input register name:");
			BufferedReader reader = new BufferedReader(new InputStreamReader(
					System.in));
			String userId = null;
			userId = reader.readLine();
			MyEclipseGen myeclipsegen = new MyEclipseGen();
			String res = myeclipsegen.getSerial(userId, "5");
			System.out.println("Serial:" + res);
			reader.close();
		} catch (IOException ex) {
		}
	}
}