c# 实现json解析器 c# 怎样实现一个简单的json解析器

  /// <summary>
  /// JSON解析类型
  /// </summary>
  public static class JsonConvert
  {
    /// <summary>
    /// 解析JSON
    /// </summary>
    /// <param name="text">待解析的JSON字符串</param>
    /// <returns>解析完成的JSON结构对象</returns>
    public static JsonElement AnalysisJson(string text)
    {
      var index = 0;
      //读取到非空白字符
      ReadToNonBlankIndex(text, ref index);
      if (text[index++] == '[')
        //解析数组
        return AnalysisJsonArray(text, ref index);
      //解析对象
      return AnalysisJsonObject(text, ref index);
    }

    /// <summary>
    /// 解析JSON对象
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引位置</param>
    /// <returns>JSON对象</returns>
    private static JsonObject AnalysisJsonObject(string text, ref int index)
    {
      var jsonArray = new JsonObject();
      do
      {
        ReadToNonBlankIndex(text, ref index);
        if (text[index] != '"') throw new JsonAnalysisException($"不能识别的字符“{text[index]}”！应为“\"”",index);
        index++;
        //读取字符串
        var name = ReadString(text, ref index);
        ReadToNonBlankIndex(text, ref index);
        if (text[index] != ':') throw new JsonAnalysisException($"不能识别的字符“{text[index]}”！",index);
        index++;
        ReadToNonBlankIndex(text, ref index);
        if (jsonArray.ContainsKey(name)) throw new JsonAnalysisException($"已经添加键值：“{name}”",index);
        //读取下一个Element
        jsonArray.Add(name, ReadElement(text, ref index));
        //读取到非空白字符
        ReadToNonBlankIndex(text, ref index);
      } while (text[index++] != '}');

      return jsonArray;
    }

    /// <summary>
    /// 解析JSON数组
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引位置</param>
    /// <returns>JSON数组</returns>
    private static JsonArray AnalysisJsonArray(string text, ref int index)
    {
      var jsonArray = new JsonArray();
      do
      {
        ReadToNonBlankIndex(text, ref index);
        //读取下一个Element
        jsonArray.Add(ReadElement(text, ref index));
        //读取到非空白字符
        ReadToNonBlankIndex(text, ref index);
      } while (text[index++] != ']');

      return jsonArray;
    }

    /// <summary>
    /// 读取JSONElement
    /// </summary>
    /// <param name="text">字符串</param>
    /// <param name="index">开始下标</param>
    /// <returns>下一个Element</returns>
    private static JsonElement ReadElement(string text, ref int index)
    {
      switch (text[index++])
      {
        case '[':
          return AnalysisJsonArray(text, ref index);
        case '{':
          return AnalysisJsonObject(text, ref index);
        case '"':
          return new JsonString(ReadString(text, ref index));
        case 't':
          return ReadJsonTrue(text, ref index);
        case 'f':
          return ReadJsonFalse(text, ref index);
        case 'n':
          return ReadJsonNull(text, ref index);
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
          return ReadJsonNumber(text, ref index);
        default:
          throw new JsonAnalysisException($"未知Element“{text[index]}”应该为【[、{{、\"、true、false、null】", index);
      }
    }

    /// <summary>
    /// 读取值类型
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引</param>
    /// <returns>JSON数值类型</returns>
    private static JsonNumber ReadJsonNumber(string text, ref int index)
    {
      var i = index;
      while (i < text.Length && char.IsNumber(text[i]) || text[i] == '.') i++;
      if (double.TryParse(text.Substring(index - 1, i - index + 1), out var value))
      {
        index = i;
        return new JsonNumber(value);
      }

      throw new JsonAnalysisException("不能识别的数字类型！", i);
    }

    /// <summary>
    /// 读取NULL
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引</param>
    /// <returns>读取NULL</returns>
    private static JsonNull ReadJsonNull(string text, ref int index)
    {
      if (text[index++] == 'u' &&
        text[index++] == 'l' &&
        text[index++] == 'l')
      {
        return new JsonNull();
      }

      throw new JsonAnalysisException("读取null出错！", index);
    }

    /// <summary>
    /// 读取FALSE
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引</param>
    /// <returns>布尔值-假</returns>
    private static JsonBoolean ReadJsonFalse(string text, ref int index)
    {
      if (text[index++] == 'a' &&
        text[index++] == 'l' &&
        text[index++] == 's' &&
        text[index++] == 'e')
      {
        return new JsonBoolean(false);
      }

      throw new JsonAnalysisException("读取布尔值出错！", index);
    }

    /// <summary>
    /// 读取TRUE
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引</param>
    /// <returns>布尔值-真</returns>
    private static JsonBoolean ReadJsonTrue(string text, ref int index)
    {
      if (text[index++] == 'r' &&
        text[index++] == 'u' &&
        text[index++] == 'e')
      {
        return new JsonBoolean(true);
      }
      throw new JsonAnalysisException("读取布尔值出错！",index);
    }

    /// <summary>
    /// 读取字符串
    /// </summary>
    /// <param name="text">JSON字符串</param>
    /// <param name="index">开始索引</param>
    /// <returns>字符串值</returns>
    private static string ReadString(string text, ref int index)
    {
      //是否处于转义状态
      var value = new StringBuilder();
      while (index < text.Length)
      {
        var c = text[index++];
        if (c == '\\')
        {
          value.Append('\\');
          if (index >= text.Length)
            throw new JsonAnalysisException("未知的结尾！",index);
          c = text[index++];
          value.Append(c);
          if (c == 'u')
          {
            for (int i = 0; i < 4; i++)
            {
              c = text[index++];
              if (IsHex(c))
              {
                value.Append(c);
              }
              else
              {
                throw new JsonAnalysisException("不是有效的Unicode字符！",index);
              }
            }
          }
        }
        else if (c == '"')
        {
          break;
        }
        else if (c == '\r' || c == '\n')
        {
          throw new JsonAnalysisException("传入的JSON字符串内容中不允许有换行！",index);
        }
        else
        {
          value.Append(c);
        }
      }

      return value.ToString();
    }

    /// <summary>
    /// 判断是否为16进制字符
    /// </summary>
    private static bool IsHex(char c)
    {
      return c >= '0' && c <= '9' || c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z';
    }

    /// <summary>
    /// 读取到非空白字符
    /// </summary>
    /// <param name="text">字符串</param>
    /// <param name="index">开始下标</param>
    /// <returns>非空白字符下标</returns>
    private static void ReadToNonBlankIndex(string text, ref int index)
    {
      while (index < text.Length && char.IsWhiteSpace(text[index])) index++;
    }
  }