Java实现自己的Json解析器

package com.xson.test; public class ObjectParser { private final String json; private int pos = 0 ; public ObjectParser(String json) { this.json = json; } public int getPos() { return pos; } public Object nextObject(){ if(pos >= json.length()){ throw new JsonException("unexpected string end."); } char c = getChar(); switch (c){ case 't': case 'T'://可能是true pos++; if(checkChars('r','u','e')){ return true; } throw new JsonException("invalid boolean value"); case 'f': case 'F': //可能是false pos++; if(checkChars('a','l','s','e')){ return false; } throw new JsonException("invalid boolean value"); case 'n': case 'N': //可能是null pos++; if(checkChars('u','l','l')){ return null; } throw new JsonException("invalid null value"); } Object number = parseNumber(c); if(number != null){ return number; } if(c == '\"'){ return parseString(c); } if(c == '['){ return parseArray(); } if(c == '{'){ return parseObject(); } throw new JsonException("invalid value : " + c); } //检查是否有剩余字符 private void checkPos(){ if(pos >= json.length()){ throw new JsonException("unexpected string end."); } } public static boolean isSpace(char c){ return c == ' ' || c == '\r' || c == '\n'; } //方法得到当前字符，忽略空格、换行符 private char getChar(){ char c = json.charAt(pos); while(isSpace(c)){ pos++; c = getCurrentChar(); } return c; } //得到当前字符，包括空格、换行符 private char getCurrentChar(){ checkPos(); return json.charAt(pos); } //得到当前字符，包括空格、换行符。将指针指向下一个字符 private char getCurrentCharNext(){ char c = getCurrentChar(); pos++; checkPos(); return c; } //得到当前字符，忽略空格、换行符。将指针指向下一个字符 private char getCharNext(){ char c = getChar(); pos++; checkPos(); return c; } private String parseString(char c){ //字符串 pos++; StringBuilder sb = new StringBuilder(); while (true){ c = getCurrentCharNext(); if(c == '\\'){ //处理转义字符 char next = getCurrentChar(); switch (next){ case 'r':sb.append('\r');break; case 'n':sb.append('\n');break; case 'b':sb.append('\b');break; case 't':sb.append('\t');break; case '\"':sb.append('\"');break; default: throw new JsonException("unknown escape char : " + next); } pos++; }else if(c == '\"'){ break; }else{ sb.append(c); } } return sb.toString(); } private Object parseNumber(char c){ StringBuilder numberBuilder = new StringBuilder(); boolean containsPoint = false; while (c >= '0' && c <= '9' || c == '+' || c == '-' || c == '.'){ if(c == '.'){ containsPoint = true; } numberBuilder.append(c); pos++; c = getCurrentChar(); } if(numberBuilder.length() > 0){ String numberString = numberBuilder.toString(); try{ if(containsPoint){ return Double.valueOf(numberString); }else{ return Integer.valueOf(numberString); } }catch (NumberFormatException e){ throw new JsonException("invalid number value:" + numberString); } } return null; } private JsonArray parseArray(){ pos++; checkPos(); JsonArray jsonArray = new JsonArray(); boolean flag = false; //是否需要用逗号分割 char c = getChar(); while (c != ']'){ if(flag){ if (c != ',') { throw new JsonException("illegal json array."); } pos++; } jsonArray.add(nextObject()); flag = true; if(pos >= json.length()){ throw new JsonException("unexpected string end."); } c = getChar(); } pos++; return jsonArray; } private JsonObject parseObject(){ JsonObject jsonObject = new JsonObject(); boolean flag = false; //是否需要用逗号分割 char c = getCharNext(); while (c != '}'){ if(flag){ if (c != ',') { throw new JsonException("illegal json object."); } pos++; } Object key = nextObject(); if(key == null || !(key instanceof String)){ throw new JsonException("illegal json object.key must be a string:" + key); } c = getCharNext(); if(c != ':'){ throw new JsonException("illegal json object."); } Object value = nextObject(); jsonObject.put((String) key,value); flag = true; c = getChar(); } pos++; return jsonObject; } private boolean checkChars(char ...chars){ for(char ch : chars){ char c = getCurrentCharNext(); if(Character.toLowerCase(ch) != Character.toLowerCase(c)){ return false; } } return true; } }