json validator，流事处理，字符事件驱动，状态维护

最新推荐文章于 2024-11-29 20:37:00 发布

原创最新推荐文章于 2024-11-29 20:37:00 发布 · 631 阅读

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本文介绍两种验证JSON字符串有效性的方法。第一种采用状态机思想，通过遍历字符并利用栈来辅助判断。第二种则基于上下文无关文法，设计递归下降解析器实现验证。

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语法字符驱动，状态判断、维护。参考leetcode isValidNum

def isValidJson(json):
	stack, inWord, inKey, inQuote, empty, metaChars, pair = [], False, False, False, True, '[]{},: \t', {'}': '{', ']': '['}
	for c in json:
		if inQuote:
			if c == '"': inQuote = False
		elif c == '"':
			inQuote, inWord, empty = True, True, False
		elif c not in metaChars: inWord, empty = True, False
		elif c == ',':
			if not inWord or inKey: return False
			inWord = False
			if stack[-1] == '{': inKey = True
		elif c == ':':
			if not inWord: return False
			inKey, inWord = False, False
		elif c in '{[':
			stack.append(c)
			inWord, empty = False, True
			if c == '{': inKey = True
		elif c in ']}':
			if len(stack) == 0 or stack[-1] != pair[c]: return False
			if not inWord and not empty: return False
			if c == '}' and inKey and not empty: return False
			stack.pop()
	return len(stack) == 0

方法二：基于上下文无关文法的 RD算法

P -> [(L | e)] | {( D | e)}
L -> E (,L | e)
E -> str | P
D -> F (,D | e)
F -> str:(P | str)

class JsonValidator {
private:
	string s;
	int p;
	enum TOKEN { LEFT_BRACKET, RIGHT_BRACKET, LEFT_BRACE, RIGHT_BRACE, COLON, COMMA, WORD };
	bool term(TOKEN t) {
		if (p == s.size()) return false;
		string m = "[]{}:,";
		if (t < m.size()) {
			while (p < s.size() && s[p] == ' ') ++p;
			return p < s.size() && s[p++] == m[t];
		}
		else {
			for (int start = -1, end = -1; (start < 0 || end < 0) && p < s.size(); ++p) {
				if (m.find(s[p]) != string::npos && start < 0) return false;
				else if (isalnum(s[p])) {
					if (start < 0) start = p;
					if (p == s.size() - 1 || !isalnum(s[p + 1])) end = p;
				}
			}
			return p < s.size();
		}
	}
	bool resume(int i) {
		p = i;
		return true;
	}
	bool e() { return true; }
	bool P() {
		int save = p;
		return resume(save) && term(LEFT_BRACKET) && L() && term(RIGHT_BRACKET)
			|| resume(save) && term(LEFT_BRACKET) && e() && term(RIGHT_BRACKET)
			|| resume(save) && term(LEFT_BRACE) && D() && term(RIGHT_BRACE)
			|| resume(save) && term(LEFT_BRACE) && e() && term(RIGHT_BRACE);
	}

	bool L() {
		int save = p;
		return resume(save) && E() && term(COMMA) && L()
			|| resume(save) && E() && e();
	}

	bool E() {
		int save = p;
		return resume(save) && term(WORD)
			|| resume(save) && P();
	}

	bool D() {
		int save = p;
		return resume(save) && F() && term(COMMA) && D()
			|| resume(save) && F() && e();
	}

	bool F() {
		int save = p;
		return resume(save) && term(WORD) && term(COLON) && term(WORD)
			|| resume(save) && term(WORD) && term(COLON) && P();
	}
public:
	JsonValidator(string s) : s(s), p(0) { isValid = P() && p == s.size(); }
	bool isValid;
};