校验一个字符串是否是合法的JSON格式

来源：互联网发布：武汉天行健网络编辑：程序博客网时间：2024/04/29 18:06
public class JsonValidator {
private CharacterIterator it;private char c;private int col;public JsonValidator() {}/** * 验证一个字符串是否是合法的JSON串 * * @param input 要验证的字符串 * @return true-合法 ，false-非法 */public boolean validate(String input) {    input = input.trim();    boolean ret = valid(input);    return ret;}private boolean valid(String input) {    if ("".equals(input)) return true;    boolean ret = true;    it = new StringCharacterIterator(input);    c = it.first();    col = 1;    if (!value()) {        ret = error("value", 1);    } else {        skipWhiteSpace();        if (c != CharacterIterator.DONE) {            ret = error("end", col);        }    }    return ret;}private boolean value() {    return literal("true") || literal("false") || literal("null") || string() || number() || object() || array();}private boolean literal(String text) {    CharacterIterator ci = new StringCharacterIterator(text);    char t = ci.first();    if (c != t) return false;    int start = col;    boolean ret = true;    for (t = ci.next(); t != CharacterIterator.DONE; t = ci.next()) {        if (t != nextCharacter()) {            ret = false;            break;        }    }    nextCharacter();    if (!ret) error("literal " + text, start);    return ret;}private boolean array() {    return aggregate('[', ']', false);}private boolean object() {    return aggregate('{', '}', true);}private boolean aggregate(char entryCharacter, char exitCharacter, boolean prefix) {    if (c != entryCharacter) return false;    nextCharacter();    skipWhiteSpace();    if (c == exitCharacter) {        nextCharacter();        return true;    }    for (; ; ) {        if (prefix) {            int start = col;            if (!string()) return error("string", start);            skipWhiteSpace();            if (c != ':') return error("colon", col);            nextCharacter();            skipWhiteSpace();        }        if (value()) {            skipWhiteSpace();            if (c == ',') {                nextCharacter();            } else if (c == exitCharacter) {                break;            } else {                return error("comma or " + exitCharacter, col);            }        } else {            return error("value", col);        }        skipWhiteSpace();    }    nextCharacter();    return true;}private boolean number() {    if (!Character.isDigit(c) && c != '-') return false;    int start = col;    if (c == '-') nextCharacter();    if (c == '0') {        nextCharacter();    } else if (Character.isDigit(c)) {        while (Character.isDigit(c))            nextCharacter();    } else {        return error("number", start);    }    if (c == '.') {        nextCharacter();        if (Character.isDigit(c)) {            while (Character.isDigit(c))                nextCharacter();        } else {            return error("number", start);        }    }    if (c == 'e' || c == 'E') {        nextCharacter();        if (c == '+' || c == '-') {            nextCharacter();        }        if (Character.isDigit(c)) {            while (Character.isDigit(c))                nextCharacter();        } else {            return error("number", start);        }    }    return true;}private boolean string() {    if (c != '"') return false;    int start = col;    boolean escaped = false;    for (nextCharacter(); c != CharacterIterator.DONE; nextCharacter()) {        if (!escaped && c == '\\') {            escaped = true;        } else if (escaped) {            if (!escape()) {                return false;            }            escaped = false;        } else if (c == '"') {            nextCharacter();            return true;        }    }    return error("quoted string", start);}private boolean escape() {    int start = col - 1;    if (" \\\"/bfnrtu".indexOf(c) < 0) {        return error("escape sequence  \\\",\\\\,\\/,\\b,\\f,\\n,\\r,\\t  or  \\uxxxx ", start);    }    if (c == 'u') {        if (!ishex(nextCharacter()) || !ishex(nextCharacter()) || !ishex(nextCharacter())                || !ishex(nextCharacter())) {            return error("unicode escape sequence  \\uxxxx ", start);        }    }    return true;}private boolean ishex(char d) {    return "0123456789abcdefABCDEF".indexOf(c) >= 0;}private char nextCharacter() {    c = it.next();    ++col;    return c;}private void skipWhiteSpace() {    while (Character.isWhitespace(c)) {        nextCharacter();    }}private boolean error(String type, int col) {    System.out.printf("type: %s, col: %s%s", type, col, System.getProperty("line.separator"));    return false;}
}
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