json解析器（java版）

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class JsonParser {
    private String json;
    private int index = 0;
    private Map<Character, Boolean> numChars = new HashMap<>();

    public Object parse(String json) throws Exception {
        char[] chars = {'-', '+', 'e', 'E', '.'};
        for (char c : chars) {
            numChars.put(c, true);
        }
        this.json = json.trim();
        return parseValue();
    }

    private Object parseValue() throws Exception {
        ignoreWhiteSpace();
        switch (json.charAt(index)) {
            case '{':
                return parseObject();
            case '[':
                return parseArray();
            case 'n':
            case 'N':
                return parseNull();
            case 't':
            case 'T':
                return parseTrue();
            case 'f':
            case 'F':
                return parseFalse();
            case '"':
            case '\'':
                return parseString();
            default:
                return parseNumber();
        }
    }

    private Map parseObject() throws Exception {
        index++;
        ignoreWhiteSpace();
        Map<String, Object> map = new HashMap<>();
        while (index < json.length() && json.charAt(index) != '}') {
            String key = parseString();
            ignoreWhiteSpace();
            if (json.charAt(index++) != ':') {
                throw new Exception("illegal json string, while parsing :");
            }
            Object value = parseValue();
            map.put(key, value);
            ignoreWhiteSpace();
            if (json.charAt(index) == ',') {
                index++;
            }
            ignoreWhiteSpace();
        }
        if (json.charAt(index++) != '}') {
            throw new Exception("illegal json string, while parsing object");
        }
        return map;
    }

    private List parseArray() throws Exception {
        index++;
        ignoreWhiteSpace();
        List<Object> arrayList = new ArrayList<>();
        while (index < json.length() && json.charAt(index) != ']') {
            arrayList.add(parseValue());
            if (json.charAt(index) == ',') {
                index++;
            }
            ignoreWhiteSpace();
        }
        if (json.charAt(index++) != ']') {
            throw new Exception("illegal json string, while parsing array");
        }
        return arrayList;
    }

    private Object parseNull() throws Exception {
        if (json.substring(index, index + 4).equals("null")) {
            index += 4;
            return null;
        } else {
            throw new Exception("illegal json string, while parsing null");
        }
    }

    private Boolean parseTrue() throws Exception {
        if (json.substring(index, index + 4).equals("true") || json.substring(index, index + 4).equals("True")) {
            index += 4;
            return true;
        } else {
            throw new Exception("illegal json string, while parsing true");
        }
    }

    private Boolean parseFalse() throws Exception {
        if (json.substring(index, index + 5).equals("false") || json.substring(index, index + 5).equals("False")) {
            index += 5;
            return false;
        } else {
            throw new Exception("illegal json string, while parsing false");
        }
    }

    private String parseString() throws Exception {
        char firstChar = json.charAt(index);
        index++;
        int recordIndex = index;
        for (; index < json.length() && json.charAt(index) != firstChar; index++) {
            if (json.charAt(index) == '\\') {
                if (json.charAt(index + 1) == 'u') {
                    index += 5;
                } else {
                    index++;
                }
            }
        }
        if (json.charAt(index) != firstChar) {
            throw new Exception("illegal json string, while parsing string");
        }
        return json.substring(recordIndex, index++);
    }

    private Object parseNumber() throws Exception {
        ignoreWhiteSpace();
        int recordIndex = index;
        boolean hasDot = false;
        while (index < json.length() && isNumberChar(json.charAt(index))) {
            if(json.charAt(index)=='.'){
                hasDot = true;
            }
            index++;
        }
        ignoreWhiteSpace();
        return hasDot?Double.parseDouble(json.substring(recordIndex, index)):Integer.parseInt(json.substring(recordIndex, index));
    }

    private void ignoreWhiteSpace() throws Exception {
        while (index < json.length()) {
            if (json.charAt(index) <= ' ') {
                index++;
            } else {
                break;
            }
        }
        if (index >= json.length()) {
            throw new Exception("illegal json string, while parsing value ArrayIndexOutOfBounds");
        }
    }

    private Boolean isNumberChar(char c) {
        return numChars.get(c) != null || c <= '9' && c >= '0';
    }
}