com.github.tnakamot.jscdg.json.parser.JSONParser Maven / Gradle / Ivy
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/*
* Copyright (C) 2020 Takashi Nakamoto .
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see
* Instances of this class are disposal. A new instance must be created
* to parse one sequence of JSON tokens.
*
* @see RFC 8259
*/
public class JSONParser {
private final List tokens;
private final JSONParserErrorMessageFormat errMsgFmt;
private int position;
private static final String stringToken = "A string";
private static final String valueToken
= "A JSON value (object, array, number, string, boolean or null)";
private static final String valueOrEndArrayToken
= String.format("%s or '%s'", valueToken, JSON_END_ARRAY);
private static final String valueSepOrEndArrayToken
= String.format("'%s' or '%s'", JSON_VALUE_SEPARATOR, JSON_END_ARRAY);
private static final String stringOrEndObjectToken
= String.format("%s or '%s'", stringToken, JSON_END_OBJECT);
private static final String valueSepOrEndObjectToken
= String.format("'%s' or '%s'", JSON_VALUE_SEPARATOR, JSON_END_OBJECT);
private static final String nameSepToken
= String.format("'%s'", JSON_NAME_SEPARATOR);
/**
* Create an instance of JSON parse for the given sequence of JSON tokens.
*
* @param tokens a sequence of JSON tokens to parse
* @param errMsgFmt settings of error message format of {@link JSONParserException}
*/
public JSONParser(List tokens, JSONParserErrorMessageFormat errMsgFmt) {
if (tokens == null) {
throw new NullPointerException("tokens cannot be null");
} else if (errMsgFmt == null) {
throw new NullPointerException("errMsgConfig cannot be null");
}
this.tokens = new ArrayList<>(tokens);
this.errMsgFmt = errMsgFmt;
this.position = 0;
}
/**
* Parse the given sequence of JSON tokens and return the root JSON value.
*
* @return the root JSON value, or null if there is no value.
* @throws JSONParserException if there is a semantic error in the sequence of JSON tokens
* @see RFC 8259 - 2. JSON Grammer
*/
public JSONValue parse() throws JSONParserException {
if (tokens.size() == 0) {
return null;
}
JSONValue value = readValue();
if (position < tokens.size()) {
unexpectedToken(popToken(), "EOF");
}
return value;
}
private JSONToken popToken() {
JSONToken token = tokens.get(position);
position += 1;
return token;
}
private JSONToken lastToken() {
return tokens.get(tokens.size() - 1);
}
private void pushBack() {
position -= 1;
}
private void unexpectedEof(String expectedToken) throws JSONParserException {
String msg = String.format("Reached EOF unexpectedly. %s was expected.", expectedToken);
JSONToken lastToken = lastToken();
throw new JSONParserException(
lastToken.source(), lastToken.endLocation(), errMsgFmt, msg);
}
private void unexpectedToken(JSONToken token, String expectedToken)
throws JSONParserException
{
String msg = String.format("Unexpected token '%s'. %s was expected.",
token.text(), expectedToken);
throw new JSONParserException(
token.source(), token.beginningLocation(), errMsgFmt, msg);
}
private JSONValue readValue() throws JSONParserException {
try {
JSONToken token = popToken();
switch (token.type()) {
case BEGIN_ARRAY:
return readArray();
case BEGIN_OBJECT:
return readObject();
case NULL:
return new JSONValueNull(token);
case BOOLEAN:
return new JSONValueBoolean((JSONTokenBoolean)token);
case NUMBER:
return new JSONValueNumber((JSONTokenNumber) token);
case STRING:
return new JSONValueString((JSONTokenString) token);
default:
unexpectedToken(token, valueToken);
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(valueToken);
}
throw new RuntimeException("never reach here");
}
private JSONValueArray readArray() throws JSONParserException {
List array = new LinkedList<>();
// read the first value (or it can be an empty array)
try {
JSONToken token = popToken();
switch(token.type()) {
case END_ARRAY:
// an empty array
return new JSONValueArray(array);
case NULL:
case BOOLEAN:
case NUMBER:
case STRING:
case BEGIN_ARRAY:
case BEGIN_OBJECT:
pushBack();
array.add(readValue());
break;
default:
unexpectedToken(token, valueOrEndArrayToken);
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(valueOrEndArrayToken);
}
while(true) {
// read a next value or an end array
try {
JSONToken token = popToken();
switch (token.type()) {
case END_ARRAY:
return new JSONValueArray(array);
case VALUE_SEPARATOR:
array.add(readValue());
break;
default:
unexpectedToken(token, valueSepOrEndArrayToken);
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(valueSepOrEndArrayToken);
}
}
}
private Map.Entry readMember() throws JSONParserException {
JSONValueString key;
// read a key
try {
JSONToken token = popToken();
if (token.type() == JSONTokenType.STRING) {
key = new JSONValueString((JSONTokenString) token);
} else {
unexpectedToken(token, stringToken);
key = null;
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(stringToken);
key = null;
}
// read a name separator
try {
JSONToken token = popToken();
if (token.type() != JSONTokenType.NAME_SEPARATOR) {
unexpectedToken(token, nameSepToken);
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(nameSepToken);
}
JSONValue value = readValue();
JSONValueString rKey = key;
return new Map.Entry<>() {
@Override
public JSONValueString getKey() {
return rKey;
}
@Override
public JSONValue getValue() {
return value;
}
@Override
public JSONValue setValue(JSONValue jsonValue) {
throw new UnsupportedOperationException();
}
};
}
private JSONValueObject readObject() throws JSONParserException {
LinkedHashMap object
= new LinkedHashMap<>();
// read the first member (or it can be an empty object)
try {
JSONToken token = popToken();
switch(token.type()) {
case END_OBJECT:
// empty object
return new JSONValueObject(object);
case STRING:
pushBack();
Map.Entry member = readMember();
object.put(member.getKey(), member.getValue());
break;
default:
unexpectedToken(token, stringOrEndObjectToken);
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(stringOrEndObjectToken);
}
while(true) {
// read a next member or an end object
try {
JSONToken token = popToken();
switch (token.type()) {
case END_OBJECT:
return new JSONValueObject(object);
case VALUE_SEPARATOR:
Map.Entry member = readMember();
object.put(member.getKey(), member.getValue());
break;
default:
unexpectedToken(token, valueSepOrEndObjectToken);
}
} catch (IndexOutOfBoundsException ex) {
unexpectedEof(valueSepOrEndObjectToken);
}
}
}
}