C# How to identify whether a string is in Json format
C# 如何识别一个字符串是否Json格式 ：
using System;
using System.Collections.Generic;
using System.Text;
namespace CYQ.Data.Tool
{
/// <summary>
/// 分隔Json字符串为字典集合。
/// </summary>
internal class JsonSplit
{
private static bool IsJsonStart(ref string json)
{
if (!string.IsNullOrEmpty(json))
{
json = json.Trim('\r', '\n', ' ');
if (json.Length > 1)
{
char s = json[0];
char e = json[json.Length - 1];
return (s == '{' && e == '}') || (s == '[' && e == ']');
}
}
return false;
}
internal static bool IsJson(string json)
{
int errIndex;
return IsJson(json, out errIndex);
}
internal static bool IsJson(string json, out int errIndex)
{
errIndex = 0;
if (IsJsonStart(ref json))
{
CharState cs = new CharState();
char c;
for (int i = 0; i < json.Length; i++)
{
c = json[i];
if (SetCharState(c, ref cs) && cs.childrenStart)//设置关键符号状态。
{
string item = json.Substring(i);
int err;
int length = GetValueLength(item, true, out err);
cs.childrenStart = false;
if (err > 0)
{
errIndex = i + err;
return false;
}
i = i + length - 1;
}
if (cs.isError)
{
errIndex = i;
return false;
}
}
return !cs.arrayStart && !cs.jsonStart;
}
return false;
}
/// <summary>
/// 获取值的长度（当Json值嵌套以"{"或"["开头时）
/// </summary>
private static int GetValueLength(string json, bool breakOnErr, out int errIndex)
{
errIndex = 0;
int len = 0;
if (!string.IsNullOrEmpty(json))
{
CharState cs = new CharState();
char c;
for (int i = 0; i < json.Length; i++)
{
c = json[i];
if (!SetCharState(c, ref cs))//设置关键符号状态。
{
if (!cs.jsonStart && !cs.arrayStart)//json结束，又不是数组，则退出。
{
break;
}
}
else if (cs.childrenStart)//正常字符，值状态下。
{
int length = GetValueLength(json.Substring(i), breakOnErr, out errIndex);//递归子值，返回一个长度。。。
cs.childrenStart = false;
cs.valueStart = 0;
//cs.state = 0;
i = i + length - 1;
}
if (breakOnErr && cs.isError)
{
errIndex = i;
return i;
}
if (!cs.jsonStart && !cs.arrayStart)//记录当前结束位置。
{
len = i + 1;//长度比索引+1
break;
}
}
}
return len;
}
/// <summary>
/// 字符状态
/// </summary>
private class CharState
{
internal bool jsonStart = false;//以 "{"开始了...
internal bool setDicValue = false;// 可以设置字典值了。
internal bool escapeChar = false;//以"\"转义符号开始了
/// <summary>
/// 数组开始【仅第一开头才算】，值嵌套的以【childrenStart】来标识。
/// </summary>
internal bool arrayStart = false;//以"[" 符号开始了
internal bool childrenStart = false;//子级嵌套开始了。
/// <summary>
/// 【0 初始状态，或 遇到“,”逗号】；【1 遇到“：”冒号】
/// </summary>
internal int state = 0;
/// <summary>
/// 【-1 取值结束】【0 未开始】【1 无引号开始】【2 单引号开始】【3 双引号开始】
/// </summary>
internal int keyStart = 0;
/// <summary>
/// 【-1 取值结束】【0 未开始】【1 无引号开始】【2 单引号开始】【3 双引号开始】
/// </summary>
internal int valueStart = 0;
internal bool isError = false;//是否语法错误。
internal void CheckIsError(char c)//只当成一级处理（因为GetLength会递归到每一个子项处理）
{
if (keyStart > 1 || valueStart > 1)
{
return;
}
//示例 ["aa",{"bbbb":123,"fff","ddd"}]
switch (c)
{
case '{'://[{ "[{A}]":[{"[{B}]":3,"m":"C"}]}]
isError = jsonStart && state == 0;//重复开始错误 同时不是值处理。
break;
case '}':
isError = !jsonStart || (keyStart != 0 && state == 0);//重复结束错误 或者 提前结束{"aa"}。正常的有{}
break;
case '[':
isError = arrayStart && state == 0;//重复开始错误
break;
case ']':
isError = !arrayStart || jsonStart;//重复开始错误 或者 Json 未结束
break;
case '"':
case '\'':
isError = !(jsonStart || arrayStart); //json 或数组开始。
if (!isError)
{
//重复开始 [""",{"" "}]
isError = (state == 0 && keyStart == -1) || (state == 1 && valueStart == -1);
}
if (!isError && arrayStart && !jsonStart && c == '\'')//['aa',{}]
{
isError = true;
}
break;
case ':':
isError = !jsonStart || state == 1;//重复出现。
break;
case ',':
isError = !(jsonStart || arrayStart); //json 或数组开始。
if (!isError)
{
if (jsonStart)
{
isError = state == 0 || (state == 1 && valueStart > 1);//重复出现。
}
else if (arrayStart)//["aa,] [,] [{},{}]
{
isError = keyStart == 0 && !setDicValue;
}
}
break;
case ' ':
case '\r':
case '\n'://[ "a",\r\n{} ]
case '\0':
case '\t':
break;
default: //值开头。。
isError = (!jsonStart && !arrayStart) || (state == 0 && keyStart == -1) || (valueStart == -1 && state == 1);//
break;
}
//if (isError)
//{
//}
}
}
/// <summary>
/// 设置字符状态(返回true则为关键词，返回false则当为普通字符处理）
/// </summary>
private static bool SetCharState(char c, ref CharState cs)
{
cs.CheckIsError(c);
switch (c)
{
case '{'://[{ "[{A}]":[{"[{B}]":3,"m":"C"}]}]
#region 大括号
if (cs.keyStart <= 0 && cs.valueStart <= 0)
{
cs.keyStart = 0;
cs.valueStart = 0;
if (cs.jsonStart && cs.state == 1)
{
cs.childrenStart = true;
}
else
{
cs.state = 0;
}
cs.jsonStart = true;//开始。
return true;
}
#endregion
break;
case '}':
#region 大括号结束
if (cs.keyStart <= 0 && cs.valueStart < 2 && cs.jsonStart)
{
cs.jsonStart = false;//正常结束。
cs.state = 0;
cs.keyStart = 0;
cs.valueStart = 0;
cs.setDicValue = true;
return true;
}
// cs.isError = !cs.jsonStart && cs.state == 0;
#endregion
break;
case '[':
#region 中括号开始
if (!cs.jsonStart)
{
cs.arrayStart = true;
return true;
}
else if (cs.jsonStart && cs.state == 1)
{
cs.childrenStart = true;
return true;
}
#endregion
break;
case ']':
#region 中括号结束
if (cs.arrayStart && !cs.jsonStart && cs.keyStart <= 2 && cs.valueStart <= 0)//[{},333]//这样结束。
{
cs.keyStart = 0;
cs.valueStart = 0;
cs.arrayStart = false;
return true;
}
#endregion
break;
case '"':
case '\'':
#region 引号
if (cs.jsonStart || cs.arrayStart)
{
if (cs.state == 0)//key阶段,有可能是数组["aa",{}]
{
if (cs.keyStart <= 0)
{
cs.keyStart = (c == '"' ? 3 : 2);
return true;
}
else if ((cs.keyStart == 2 && c == '\'') || (cs.keyStart == 3 && c == '"'))
{
if (!cs.escapeChar)
{
cs.keyStart = -1;
return true;
}
else
{
cs.escapeChar = false;
}
}
}
else if (cs.state == 1 && cs.jsonStart)//值阶段必须是Json开始了。
{
if (cs.valueStart <= 0)
{
cs.valueStart = (c == '"' ? 3 : 2);
return true;
}
else if ((cs.valueStart == 2 && c == '\'') || (cs.valueStart == 3 && c == '"'))
{
if (!cs.escapeChar)
{
cs.valueStart = -1;
return true;
}
else
{
cs.escapeChar = false;
}
}
}
}
#endregion
break;
case ':':
#region 冒号
if (cs.jsonStart && cs.keyStart < 2 && cs.valueStart < 2 && cs.state == 0)
{
if (cs.keyStart == 1)
{
cs.keyStart = -1;
}
cs.state = 1;
return true;
}
// cs.isError = !cs.jsonStart || (cs.keyStart < 2 && cs.valueStart < 2 && cs.state == 1);
#endregion
break;
case ',':
#region 逗号 //["aa",{aa:12,}]
if (cs.jsonStart)
{
if (cs.keyStart < 2 && cs.valueStart < 2 && cs.state == 1)
{
cs.state = 0;
cs.keyStart = 0;
cs.valueStart = 0;
//if (cs.valueStart == 1)
//{
// cs.valueStart = 0;
//}
cs.setDicValue = true;
return true;
}
}
else if (cs.arrayStart && cs.keyStart <= 2)
{
cs.keyStart = 0;
//if (cs.keyStart == 1)
//{
// cs.keyStart = -1;
//}
return true;
}
#endregion
break;
case ' ':
case '\r':
case '\n'://[ "a",\r\n{} ]
case '\0':
case '\t':
if (cs.keyStart <= 0 && cs.valueStart <= 0) //cs.jsonStart &&
{
return true;//跳过空格。
}
break;
default: //值开头。。
if (c == '\\') //转义符号
{
if (cs.escapeChar)
{
cs.escapeChar = false;
}
else
{
cs.escapeChar = true;
return true;
}
}
else
{
cs.escapeChar = false;
}
if (cs.jsonStart || cs.arrayStart) // Json 或数组开始了。
{
if (cs.keyStart <= 0 && cs.state == 0)
{
cs.keyStart = 1;//无引号的
}
else if (cs.valueStart <= 0 && cs.state == 1 && cs.jsonStart)//只有Json开始才有值。
{
cs.valueStart = 1;//无引号的
}
}
break;
}
return false;
}
}
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