/**
 \* @author: WangZhiJun
 \* @create: 2019-09-21 12:31
 **/
@RestController
@RequestMapping("/api/v1/order")
public class OrderController {
    private static final String SHORT_URL = "shortUrl:";
 
    @Resource
    private RedisTemplate<String, Object> redisTemplate;
 
    /**
     * 系统内生成支付二维码接口
     */
    @GetMapping(value = "/payOrder")
    public String pay(@RequestParam String orderId) {
        String orderName = "XXSuperMarketPay";
        BigDecimal orderMoney = new BigDecimal(100);
        System.out.println("订单"+orderId+orderName+"需支付："+orderMoney+"元");
 
        String wxPayUrl = "http://localhost:8080/wx/pay/pay?orderId="+orderId+"&orderName="+orderName+"&orderMoney="+orderMoney;
        String shortUrl = ShortUrlUtils.shortUrl(wxPayUrl);
        System.out.println("生成的微信支付链接为："+wxPayUrl);
        System.out.println("生成的短链接为："+ shortUrl);
        //存入redis或者数据库,键值为六位数的短链接
        redisTemplate.opsForValue().set(SHORT_URL + shortUrl, shortUrl, 1, TimeUnit.HOURS);
        //这里我的业务场景中是生成二维码，这里简化为链接
        return "http://localhost:8080/url/" + shortUrl;
    }
}

/** 假设这是微信支付的接口
 * @author: WangZhiJun
 * @create: 2019-09-21 12:31
 **/
@RestController
@RequestMapping("/wx/pay")
public class WxPayController {
    /**
     * 模仿微信支付API
     */
    @GetMapping(value = "/pay")
    public void paySuccess(@RequestParam String orderId,
                         @RequestParam String orderMoney,
                         @RequestParam String orderName) {
        System.out.println("订单"+orderId+orderName+"支付："+orderMoney+"元");
        System.out.println("支付成功");
    }
}

/**
 * @description: 短网址转发
 * @author: WangZhiJun
 * @create: 2019-09-21 12:20
 **/
@RestController
@RequestMapping("/url")
public class UrlController {
    private static final String SHORT_URL = "shortUrl:";
 
    @Resource
    private RedisTemplate<String, Object> redisTemplate;
 
    @GetMapping(value = "/{shortUrl}")
    public void getInvoiceUrl(@PathVariable(required = false) String shortUrl,
                              HttpServletResponse response) {
        String url = (String) redisTemplate.opsForValue().get(SHORT_URL + shortUrl);
        try {
            //将短链接映射的长链接取出并重定向到长链接
            response.sendRedirect(url);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.security.MessageDigest;
 
/** 短链接生成工具类
 * @author WangZhiJun
 */
public class ShortUrlUtils {
 
    /**
     * 十六进制下数字到字符的映射数组
     */
    private final static String[] HEXDIGITS = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
    /**把inputString加密*/
    public static String md5(String inputStr){
        return encodeByMD5(inputStr);
    }
 
    /**对字符串进行MD5编码*/
    private static String encodeByMD5(String originString){
        if (originString!=null) {
            try {
                //创建具有指定算法名称的信息摘要
                MessageDigest md5 = MessageDigest.getInstance("MD5");
                //使用指定的字节数组对摘要进行最后更新，然后完成摘要计算
                byte[] results = md5.digest(originString.getBytes());
                //将得到的字节数组变成字符串返回
                String result = byteArrayToHexString(results);
                return result;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }
    /**
     * 轮换字节数组为十六进制字符串
     * @param b 字节数组
     * @return 十六进制字符串
     */
    private static String byteArrayToHexString(byte[] b){
        StringBuffer resultSb = new StringBuffer();
        for(int i=0;i<b.length;i++){
            resultSb.append(byteToHexString(b[i]));
        }
        return resultSb.toString();
    }
 
    /**
     * @param b 字节
     * @return 将一个字节转化成十六进制形式的字符串
     */
    private static String byteToHexString(byte b){
        int n = b;
        if(n<0) {
            n = 256 + n;
        }
        int d1 = n/16;
        int d2 = n%16;
        return HEXDIGITS[d1] + HEXDIGITS[d2];
    }
 
    public static String shortUrl(String url) {
        return shortUrls(url)[0];
    }
 
    public static String[] shortUrls(String url) {
        // 可以自定义生成 MD5 加密字符传前的混合 KEY
        String key = "md5" ;
        // 要使用生成 URL 的字符
        String[] chars = new String[] { "a" , "b" , "c" , "d" , "e" , "f" , "g" , "h" ,
                "i" , "j" , "k" , "l" , "m" , "n" , "o" , "p" , "q" , "r" , "s" , "t" ,
                "u" , "v" , "w" , "x" , "y" , "z" , "0" , "1" , "2" , "3" , "4" , "5" ,
                "6" , "7" , "8" , "9" , "A" , "B" , "C" , "D" , "E" , "F" , "G" , "H" ,
                "I" , "J" , "K" , "L" , "M" , "N" , "O" , "P" , "Q" , "R" , "S" , "T" ,
                "U" , "V" , "W" , "X" , "Y" , "Z"
        };
        // 对传入网址进行 MD5 加密
        String hex = ShortUrlUtils.md5(key + url);
        String[] resUrl = new String[4];
        for ( int i = 0; i < 4; i++) {
            // 把加密字符按照 8 位一组 16 进制与 0x3FFFFFFF 进行位与运算
            String sTempSubString = hex.substring(i * 8, i * 8 + 8);
            // 这里需要使用 long 型来转换，因为 Inteper .parseInt() 只能处理 31 位 , 首位为符号位 , 如果不用 long ，则会越界
            long lHexLong = 0x3FFFFFFF & Long.parseLong (sTempSubString, 16);
            StringBuilder outChars = new StringBuilder();
            for ( int j = 0; j < 6; j++) {
                // 把得到的值与 0x0000003D 进行位与运算，取得字符数组 chars 索引
                long index = 0x0000003D & lHexLong;
                // 把取得的字符相加
                outChars.append(chars[(int) index]);
                // 每次循环按位右移 5 位
                lHexLong = lHexLong >> 5;
            }
            // 把字符串存入对应索引的输出数组
            resUrl[i] = outChars.toString();
        }
        return resUrl;
    }
}