URLDecoder: Incomplete trailing escape (%) pattern错误处理

解码过程中可能会碰到url中含有普通的%字符的情况，如果直接用URLDecode.decode()则会出现如题的错误，解决方法就是先将’%’编码为’%25’，再对url解码。

public static void main(String[] args) throws Exception{
    String test = "http://www.baidu.com?123%";//随意构造的
    //URLDecoder.decode(test, "utf8");//如直接接就会报如题的错误。
    System.out.println(URLDecoder.decode(test.replaceAll("%", "%25"), "utf8"));
  
}

输出：

1	`http://www.baidu.com?123%`

上述是最简单的一种情况，但是绝大多数情况会掺杂着%为编码的含义，此时只把%替换为%25是不能解出正确的url的，如下：

public static void main(String[] args) throws Exception{
    String test = "http://www.baidu.com?%e4%b8%ad%e5%9b%bd123%";//%e4%b8%ad%e5%9b%bd为中国
    System.out.println(URLDecoder.decode(test.replaceAll("%", "%25"), "utf8")); 
}

输出：

1	`http://www.baidu.com?%e4%b8%ad%e5%9b%bd123%`

解决方法：

public class ConverPercent {
  
    //判断是否为16进制数
    public static boolean isHex(char c){
        if(((c >= '0') && (c <= '9')) || 
                ((c >= 'a') && (c <= 'f')) || 
                ((c >= 'A') && (c <= 'F')))
            return true;
        else
            return false;
    }
  
    public static String convertPercent(String str){
        StringBuilder sb = new StringBuilder(str);
  
        for(int i = 0; i < sb.length(); i++){
            char c = sb.charAt(i);
            //判断是否为转码符号%
            if(c == '%'){
                if(((i + 1) < sb.length() -1) && ((i + 2) < sb.length() - 1)){
                    char first = sb.charAt(i + 1);
                    char second = sb.charAt(i + 2);
                    //如只是普通的%则转为%25
                    if(!(isHex(first) && isHex(second)))
                        sb.insert(i+1, "25");
                }
                else{//如只是普通的%则转为%25
                    sb.insert(i+1, "25");
                }
  
            }
        }
  
        return sb.toString();
    }
  
    public static void main(String[] args) throws UnsupportedEncodingException{
        String test = "http://www.baidu.com?%e4%b8%ad%e5%9b%bd123%";
        //URLDecoder.decode(test, "utf8");//如直接接就会报如题的错误。   
        String url = convertPercent(test);
        System.out.println(url);
        System.out.println(URLDecoder.decode(url,"utf8"));
  
    }
}