重写java.lang.String IndexOf()方法，实现对字符串以ASCII规则截取

     /**
      * 根据元数据和目标ascii位数截取字符串，失败返回-1
      * @param sourceStr    元数据字符串
      * @param endIndex    截取到第几位
      * @return 结果字符串
      */
     public static String indexOf(String sourceStr,int endIndex){
         int length = ;
         StringBuilder result = new StringBuilder();
         List<String> resultList = new ArrayList<String>();
         for(int i = ; i < sourceStr.length(); i++){
             int ascii = Character.codePointAt(sourceStr,i);
             if(ascii >=  && ascii <=){
                 length++;
                 resultList.add(String.valueOf(ascii));
             }else{
                 length+=;
                 resultList.add(String.valueOf(ascii));
             }
             if(length>){
                 if((length==sourceStr.length() && length <= endIndex) || length == endIndex || length == endIndex-){
                     for (String string : resultList) {
                         result.append(asciiToString(string));
                     }
                     return result.toString();
                 }
             }
         }
         //return String.valueOf("-1");
         /**
          * 根据业务要求，如果传进来的参数为空值的时候默认返回空字符串
          */
         return "";
     }

     /**
      * 将ascii码转换为utf-8
      * @param value ascii编码 多个以,号分割
      * @return 结果字符串
      */
     public static String asciiToString(String value) {
         StringBuffer sbu = new StringBuffer();
         String[] chars = value.split(",");
         for (int i = ; i < chars.length; i++) {
             sbu.append((char) Integer.parseInt(chars[i]));
         }
         return sbu.toString();
     }