com.github.andyglow.json.JsonParser Maven / Gradle / Ivy
package com.github.andyglow.json;
import java.io.*;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
class JsonParser {
private enum State {
JSON,
OBJECT_BEFORE_COLON,
OBJECT_AFTER_COLON,
ARRAY,
}
private InputStream is;
private JsonHandler handler;
JsonParser(String input, JsonHandler handler) {
this(new ByteArrayInputStream(input.getBytes()), handler);
}
JsonParser(InputStream is, JsonHandler handler) {
this.is = is;
this.handler = handler;
}
public void parse() throws IOException, JsonParseException {
try (
Reader _reader = new InputStreamReader(is);
PushbackReader reader = new PushbackReader(_reader)) {
int r;
ArrayDeque state = new ArrayDeque<>();
state.push(State.JSON);
handler.start();
while ((r = reader.read()) != -1) {
char c = (char) r;
switch(c) {
case '{': {
if (state.peek() == State.OBJECT_BEFORE_COLON) throw new JsonParseException();
state.push(State.OBJECT_BEFORE_COLON);
handler.objectStart();
break;
}
case '}': {
state.pop();
if (state.peek() == State.OBJECT_BEFORE_COLON) state.pop();
handler.objectEnd();
break;
}
case '[': {
state.push(State.ARRAY);
handler.arrayStart();
break;
}
case ']': {
if (state.peek() != State.ARRAY) throw new JsonParseException();
handler.arrayEnd();
state.pop();
break;
}
case 'f': {
if (state.peek() == State.OBJECT_BEFORE_COLON) throw new JsonParseException();
tryParse(reader, "alse", () -> handler.value(false));
break;
}
case 't': {
if (state.peek() == State.OBJECT_BEFORE_COLON) throw new JsonParseException();
tryParse(reader, "rue", () -> handler.value(true));
break;
}
case 'n': {
if (state.peek() == State.OBJECT_BEFORE_COLON) throw new JsonParseException();
tryParse(reader, "ull", () -> handler.nullValue());
break;
}
case '-':
case '.':
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9': {
if (state.peek() == State.OBJECT_BEFORE_COLON) throw new JsonParseException();
reader.unread(c);
tryParseNumber(reader, (sb) -> (dotExists) -> (exponentExists) -> {
String text = sb.toString();
int len = text.length();
if (dotExists) {
handler.value(new BigDecimal(text));
} else {
if (exponentExists || len > 18)
handler.value(new BigDecimal(text).toBigInteger());
else if (len <= 9)
handler.value(Integer.parseInt(text));
else
handler.value(Long.parseLong(text));
}
return null;
});
break;
}
case '"': {
tryParseString(reader, (text) -> {
if (state.peek() == State.OBJECT_BEFORE_COLON) {
handler.name(text.toString());
} else {
handler.value(text.toString());
}
});
break;
}
case ':': {
if (state.peek() == State.OBJECT_AFTER_COLON) throw new JsonParseException();
state.push(State.OBJECT_AFTER_COLON);
break;
}
case ',': {
if (state.peek() == State.ARRAY) break;
if (state.peek() == State.OBJECT_BEFORE_COLON) throw new JsonParseException();
state.pop();
break;
}
default:
if (!Character.isWhitespace(c))
throw new JsonParseException("Unexpected [" + c + "]");
}
}
if (state.peek() != State.JSON) throw new JsonParseException();
handler.end();
}
}
private static void tryParse(PushbackReader reader, String expecting, Runnable cb) throws IOException, JsonParseException {
int len = expecting.length();
char[] buf = new char[len];
if (reader.read(buf, 0, len) == expecting.length()) {
if (new String(buf).equals(expecting)) cb.run(); else throw new JsonParseException();
} else {
throw new JsonParseException();
}
}
private static void tryParseNumber(PushbackReader reader, Function>> cb) throws IOException, JsonParseException {
StringBuilder sb = new StringBuilder();
boolean dotExists = false;
boolean minusExists = false;
boolean exponentExists = false;
int i;
char prev = (char) -1;
while ((i = reader.read()) != -1) {
char c = (char) i;
if (c == 'e') {
if (exponentExists) throw new JsonParseException();
else {
sb.append(c);
exponentExists = true;
}
} else if (Character.isDigit(c)) {
sb.append(c);
} else if (c == '+') {
if (prev == 'e') {
sb.append(c);
} else
throw new JsonParseException();
} else if (c == '-') {
if (!minusExists || prev == 'e') {
sb.append(c);
minusExists = true;
} else throw new JsonParseException();
} else if (c == '.') {
if (!dotExists) {
sb.append(c);
dotExists = true;
} else
throw new JsonParseException();
} else {
cb.apply(sb).apply(dotExists).apply(exponentExists);
reader.unread(i);
return;
}
prev = c;
}
cb.apply(sb).apply(dotExists).apply(exponentExists);
}
private static void tryParseString(PushbackReader reader, Consumer cb) throws IOException, JsonParseException {
StringBuilder sb = new StringBuilder();
int i;
boolean escaped = false;
while ((i = reader.read()) != -1) {
char c = (char) i;
if (c == '\\') {
if (escaped) {
sb.append('\\');
escaped = false;
} else {
escaped = true;
}
} else if (c != '"') {
if (Character.isISOControl(c)) {
if (escaped) sb.append(c);
else throw new JsonParseException();
} else
sb.append(c);
escaped = false;
} else {
if (escaped) {
sb.append('"');
} else {
cb.accept(sb);
return;
}
escaped = false;
}
}
throw new JsonParseException();
}
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