package com.mahuan.json;import java.util.LinkedList;
import java.util.List;/*** 词法分析*/
public class Tokenizer {// 待分析的字符串private String json;// 读取字符时的索引位置private int index = 0;// 词法分析结果列表private List<Token> tokens = new LinkedList<Token>();// 获取词法分析结果时的索引位置private int tokenIndex = 0;/*** 构造函数，触发词法分析* @param json* @throws Exception*/public Tokenizer(String json) throws Exception {this.json = json;this.init();}/*** 读取字符串中的字符，索引位置加1* @return*/private Character read() {if (index < json.length())return json.charAt(index++);elsereturn null;}/*** 读取字符串中的字符，索引位置减1*/private void unread() {index--;}/*** 进行词法分析* @throws Exception*/private void init() throws Exception {Token token = null;while ((token = token()) != null) {tokens.add(token);}}/*** 按顺序读取字符串，获取词法分析结果* @return* @throws Exception*/private Token token() throws Exception {Character c = read();if (c == null)return null;// 忽略空白字符、换行符等while (isSpace(c)) {c = read();}if (isNull(c))return new Token(TokenType.Null, null);if (c == '{')return new Token(TokenType.ObjectStart, "{");if (c == '}')return new Token(TokenType.ObjectEnd, "}");if (c == '[')return new Token(TokenType.ArrayStart, "[");if (c == ']')return new Token(TokenType.ArrayEnd, "]");if (c == ',')return new Token(TokenType.Comma, ",");if (c == ':')return new Token(TokenType.Colon, ":");if (isTrue(c))return new Token(TokenType.Boolean, "true");if (isFalse(c))return new Token(TokenType.Boolean, "false");if (c == '"')return new Token(TokenType.String, readString());if (isNum(c)) {unread();return new Token(TokenType.Number, readNum());}throw new Exception("");}/*** 读取字符串* @return*/private String readString() {char c = read();StringBuffer sb = new StringBuffer();while (c != '"') {sb.append(c);if (isEscape(c)) {c = read();sb.append(c);}c = read();}return sb.toString();}/*** 读取数字，还未考虑所有数字表达形式* @return*/private String readNum() {char c = read();StringBuffer sb = new StringBuffer();while (c != '"' && c != ':' && c != ',' && c != ']' && c != '}') {sb.append(c);c = read();}unread();return sb.toString();}/*** 判断是否为数字开头的特征* @param c* @return*/private boolean isNum(char c) {if (c == '-' || ('0' <= c && c <= '9'))return true;return false;}/*** 判断是否为转义字符* @param c* @return*/private boolean isEscape(char c) {if (c == '\\')return true;return false;}/*** 是否为true字符串* @param c* @return* @throws Exception*/private boolean isTrue(char c) throws Exception {if (c == 't') {c = read();if (c == 'r') {c = read();if (c == 'u') {c = read();if (c == 'e') {return true;} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {return false;}}/*** 是否为false字符串* @param c* @return* @throws Exception*/private boolean isFalse(char c) throws Exception {if (c == 'f') {c = read();if (c == 'a') {c = read();if (c == 'l') {c = read();if (c == 's') {c = read();if (c == 'e') {return true;} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {return false;}}/*** 是否为null字符串* @param c* @return* @throws Exception*/private boolean isNull(char c) throws Exception {if (c == 'n') {c = read();if (c == 'u') {c = read();if (c == 'l') {c = read();if (c == 'l') {return true;} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {throw new Exception("Invalid JSON input.");}} else {return false;}}/*** 是否为空字符* @param c* @return*/private boolean isSpace(char c) {if (c == '\t')return true;if (c == '\n')return true;if (c == '\r')return true;if (c == '\0')return true;if (c == ' ')return true;return false;}/*** 获取词法分析的下一个结果* @return*/public Token next() {if (tokenIndex + 1 < tokens.size())return tokens.get(++tokenIndex);return null;}/*** 获取当前位置的词法分析结果* @return*/public Token get() {if (tokenIndex < tokens.size())return tokens.get(tokenIndex);return null;}
}/*** 词法分析类型*/
enum TokenType {// object开始
    ObjectStart,// object结束
    ObjectEnd,// 数组开始
    ArrayStart,// 数组结束
    ArrayEnd,// 字符串
    String,// 数字
    Number,// boolean
    Boolean,// 空
    Null,// ,
    Comma,// :
    Colon
}/*** 词法分析单元* @author mahuan* @version 2017年12月13日*/
class Token {public TokenType type;public String value;public Token(TokenType type, String value) {this.type = type;this.value = value;}
}

package com.mahuan.json;import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;/*** 语法分析*/
public class Parser {/*** 分析Object，使用map数据结构标识* @param tokenizer* @return* @throws Exception*/public static Map<String, Object> parserObject(Tokenizer tokenizer) throws Exception {Map<String, Object> map = new HashMap<>();Token token = null;while (true) {token = tokenizer.get();if (token.type == TokenType.ObjectEnd)break;if (token.type == TokenType.ObjectStart) {tokenizer.next();continue;}if (token.type == TokenType.Comma) {tokenizer.next();continue;// 跳过,
            }String key = token.value;token = tokenizer.next();if (token.type != TokenType.Colon)throw new Exception();tokenizer.next();map.put(key, parserValue(tokenizer));}return map;}/*** 分析Array，使用list数据结构标识* @param tokenizer* @return* @throws Exception*/public static List<Object> parserArray(Tokenizer tokenizer) throws Exception {List<Object> list = new LinkedList<>();Token token = null;while (true) {token = tokenizer.get();if (token.type == TokenType.ArrayEnd)break;if (token.type == TokenType.ArrayStart) {tokenizer.next();continue;}if (token.type == TokenType.Comma) {tokenizer.next();continue;}list.add(parserValue(tokenizer));}return list;}/*** 分析值，根据token再判断值的具体类型* @param tokenizer* @return* @throws Exception*/public static Object parserValue(Tokenizer tokenizer) throws Exception {Token token = tokenizer.get();try {if (token.type == TokenType.ObjectStart)return parserObject(tokenizer);else if (token.type == TokenType.ArrayStart)return parserArray(tokenizer);else if (token.type == TokenType.Boolean)return Boolean.valueOf(token.value);else if (token.type == TokenType.String)return token.value;else if (token.type == TokenType.Number)return token.value;else if (token.type == TokenType.Null)return null;throw new Exception("");} finally {// object和array分析完后，要跳过其end的token// 其他类型分析完后，要跳过自身
            tokenizer.next();}}}

package com.mahuan.json;public class Test {public static void main(String[] args) throws Exception {String json = "{  \"success\": true,  \"message\": \"123\",  \"result\": [    -2146464718]}";Tokenizer tokenizer = new Tokenizer(json);Object map = Parser.parserValue(tokenizer);System.out.println(map);}
}