java基础之URLDecoder异常解决方法

╰半橙微兮° 2021-08-13 19:11 432阅读 0赞

URLDecoder对参数进行解码时候，代码如：

URLDecoder.decode(param,"utf-8");

有时候会出现类似如下的错误：

> URLDecoder异常Illegal hex characters in escape (%)

这是因为传参有一些特殊字符，比如%号或者说+号，导致不能解析，报错

解决方法是：

public static String replacer(StringBuffer outBuffer) {
          String data = outBuffer.toString();
          try {
             data = data.replaceAll("%(?![0-9a-fA-F]{2})", "%25");
             data = data.replaceAll("\\+", "%2B");
             data = URLDecoder.decode(data, "utf-8");
          } catch (Exception e) {
             e.printStackTrace();
          }
          return data;
       }

URLDecoder源码：

public static String decode(String s, String enc)
            throws UnsupportedEncodingException{
    
            boolean needToChange = false;
            int numChars = s.length();
            StringBuffer sb = new StringBuffer(numChars > 500 ? numChars / 2 : numChars);
            int i = 0;
    
            if (enc.length() == 0) {
                throw new UnsupportedEncodingException ("URLDecoder: empty string enc parameter");
            }
    
            char c;
            byte[] bytes = null;
            while (i < numChars) {
                c = s.charAt(i);
                switch (c) {
                case '+':
                    sb.append(' ');
                    i++;
                    needToChange = true;
                    break;
                case '%':
                    /*
                     * Starting with this instance of %, process all
                     * consecutive substrings of the form %xy. Each
                     * substring %xy will yield a byte. Convert all
                     * consecutive  bytes obtained this way to whatever
                     * character(s) they represent in the provided
                     * encoding.
                     */
    
                    try {
    
                        // (numChars-i)/3 is an upper bound for the number
                        // of remaining bytes
                        if (bytes == null)
                            bytes = new byte[(numChars-i)/3];
                        int pos = 0;
    
                        while ( ((i+2) < numChars) &&
                                (c=='%')) {
                            int v = Integer.parseInt(s.substring(i+1,i+3),16);
                            if (v < 0)
                                throw new IllegalArgumentException("URLDecoder: Illegal hex characters in escape (%) pattern - negative value");
                            bytes[pos++] = (byte) v;
                            i+= 3;
                            if (i < numChars)
                                c = s.charAt(i);
                        }
    
                        // A trailing, incomplete byte encoding such as
                        // "%x" will cause an exception to be thrown
    
                        if ((i < numChars) && (c=='%'))
                            throw new IllegalArgumentException(
                             "URLDecoder: Incomplete trailing escape (%) pattern");
    
                        sb.append(new String(bytes, 0, pos, enc));
                    } catch (NumberFormatException e) {
                        throw new IllegalArgumentException(
                        "URLDecoder: Illegal hex characters in escape (%) pattern - "
                        + e.getMessage());
                    }
                    needToChange = true;
                    break;
                default:
                    sb.append(c);
                    i++;
                    break;
                }
            }
    
            return (needToChange? sb.toString() : s);
        }