java随机字符串+校验位

package com.g4m;

import java.util.Stack;  


public class JingzhiTest {  
	private final static String _str="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";  
	private static char[] charSet = _str.toCharArray();    
    private static int len = _str.length(); 
    private static int checkNum = 10; 
    
	/** 
	 * 将10进制转化为62进制  
	 * @param number  
	 * @return 
	 */  
	public static String numTo62String(long number){  
		Long rest=number;  
		Stack<Character> stack=new Stack<Character>();  
		StringBuilder result=new StringBuilder(0);  
		while(rest!=0){  
			stack.add(charSet[new Long((rest-(rest/62)*62)).intValue()]);  
			rest=rest/62;  
		}  
		for(;!stack.isEmpty();){  
			result.append(stack.pop());  
		}  
		return result.toString();  
	}  
    
	/**
	 * 生成长度为length的字符串,length > 1
	 * @param length
	 * @return
	 */
	public static String createRandom(int length) {
		if(length < 2) {
			return "";
		}
		StringBuffer str = new StringBuffer();
		for (int i = 0; i < length-1; i++) {
			int a = (int) (Math.random()*62); //0-1,等于0,不等于1
			str.append(charSet[a]);
		}
		return str.toString() + getCheckCode(str.toString());
	}
	/**
	 * 生成长度为length的字符串,length > 1
	 * @param length
	 * @return
	 */
	public static String createStringById(long id,int length) {
		String strNum = numTo62String(id);
		StringBuffer str = new StringBuffer();
		for (int i = strNum.length(); i < length-1; i++) {
			str.append(0);
		}
		return getCheckCode(str.toString()+strNum)+str.toString()+strNum;
	}
	/**
	 * 生成长度为length的字符串,length > 1
	 * @param length
	 * @return
	 */
	public static String createStringById(long id) {
		return createStringById(id,6);
	}
	
	/**
	 * 添加校验位
	 * @param string
	 * @return
	 */
    private static char getCheckCode(String string) {
    	long unm = toNum(string)+checkNum;
		int a = (int) (unm%62);
		return charSet[a];
	}

    /**
     * 字符串转数字
     * @param s
     * @return
     */
	public static long toNum(String s) {  
        int a = s.length()-1;  
        long val=0;  
        for(int i=a;i>=0;i--){  
            char c = s.charAt(i);  
            val += (_str.indexOf(c)*Math.pow(len, a-i));  
        }  
        return val;  
    }  
	
	
	/**
	 * 校验短链是否正确
	 * @param link
	 * @return
	 */
	public static boolean checkShortLink(String link) {
		if(link==null) {
			return false;
		}
		if(link.length()<2) {
			return true;
		}
		String substring = link.substring(1, link.length());
		char charAt = link.charAt(0);
		char checkCode = getCheckCode(substring);
		if((int)charAt == (int)(checkCode)) {
			return true;
		}
		return false;
	}
	
	/** 
	 * @param args 
	 */  
	public static void main(String[] args) {
		String createStringById = createStringById(1l);
		System.out.println("id:"+createStringById);
		
		boolean checkShortLink = checkShortLink(createStringById);
		System.out.println("check:"+checkShortLink);
		
		//生成随机字符串
		String createRandom = createRandom(6);
		System.out.println(createRandom);
		
		//校验随机字符串
		boolean checkShortLink1 = checkShortLink("YB0mEmm");
		System.out.println(checkShortLink1);
	}
}