BasicJsonParser Class — spring-boot Architecture

Source Code

core/spring-boot/src/main/java/org/springframework/boot/json/BasicJsonParser.java lines 42–203

public class BasicJsonParser extends AbstractJsonParser {

	private static final int MAX_DEPTH = 1000;

	@Override
	public Map<String, Object> parseMap(@Nullable String json) {
		return tryParse(() -> parseMap(json, (jsonToParse) -> parseMapInternal(0, jsonToParse)), Exception.class);
	}

	@Override
	public List<Object> parseList(@Nullable String json) {
		return tryParse(() -> parseList(json, (jsonToParse) -> parseListInternal(0, jsonToParse)), Exception.class);
	}

	private List<Object> parseListInternal(int nesting, String json) {
		List<Object> list = new ArrayList<>();
		json = trimEdges(json, '[', ']').trim();
		for (String value : tokenize(json)) {
			list.add(parseInternal(nesting + 1, value));
		}
		return list;
	}

	private Object parseInternal(int nesting, String json) {
		if (nesting > MAX_DEPTH) {
			throw new IllegalStateException("JSON is too deeply nested");
		}
		if (json.startsWith("[")) {
			return parseListInternal(nesting + 1, json);
		}
		if (json.startsWith("{")) {
			return parseMapInternal(nesting + 1, json);
		}
		if (json.startsWith("\"")) {
			return trimEdges(json, '"', '"');
		}
		return parseNumber(json);
	}

	private Map<String, Object> parseMapInternal(int nesting, String json) {
		Map<String, Object> map = new LinkedHashMap<>();
		json = trimEdges(json, '{', '}').trim();
		for (String pair : tokenize(json)) {
			String[] split = StringUtils.split(pair, ":");
			@Nullable String[] values = (split != null) ? StringUtils.trimArrayElements(split) : null;
			Assert.state(values != null, () -> "Unable to parse '%s'".formatted(pair));
			String rawKey = values[0];
			String rawValue = values[1];
			Assert.state(rawKey != null, () -> "rawKew is null in '%s'".formatted(pair));
			Assert.state(rawKey.startsWith("\"") && rawKey.endsWith("\""),
					"Expecting double-quotes around field names");
			String key = trimEdges(rawKey, '"', '"');
			Assert.state(rawValue != null, () -> "rawValue is null in '%s'".formatted(pair));
			Object value = parseInternal(nesting, rawValue);
			map.put(key, value);
		}
		return map;
	}

	private Object parseNumber(String json) {
		try {
			return Long.valueOf(json);
		}
		catch (NumberFormatException ex) {
			try {
				return Double.valueOf(json);
			}
			catch (NumberFormatException ex2) {
				return json;
			}
		}
	}

	private static String trimTrailingCharacter(String string, char c) {
		if (!string.isEmpty() && string.charAt(string.length() - 1) == c) {
			return string.substring(0, string.length() - 1);
		}
		return string;
	}

	private static String trimLeadingCharacter(String string, char c) {
		if (!string.isEmpty() && string.charAt(0) == c) {
			return string.substring(1);
		}
		return string;
	}

	private static String trimEdges(String string, char leadingChar, char trailingChar) {
		return trimTrailingCharacter(trimLeadingCharacter(string, leadingChar), trailingChar);
	}

	private List<String> tokenize(String json) {
		List<String> list = new ArrayList<>();
		Tracking tracking = new Tracking();
		StringBuilder build = new StringBuilder();
		int index = 0;
		while (index < json.length()) {
			char ch = json.charAt(index);
			if (tracking.in(Tracked.ESCAPE)) {
				build.append(ch);
				index++;
				tracking.set(Tracked.ESCAPE, 0);
				continue;
			}
			switch (ch) {
				case '{' -> tracking.update(Tracked.OBJECT, +1);
				case '}' -> tracking.update(Tracked.OBJECT, -1);
				case '[' -> tracking.update(Tracked.LIST, +1);
				case ']' -> tracking.update(Tracked.LIST, -1);
				case '"' -> tracking.toggle(Tracked.VALUE);
			}
			if (ch == ',' && !tracking.in(Tracked.OBJECT, Tracked.LIST, Tracked.VALUE)) {
				list.add(build.toString());
				build.setLength(0);
			}
			else if (ch == '\\') {
				tracking.set(Tracked.ESCAPE, 1);
			}
			else {
				build.append(ch);
			}
			index++;
		}
		if (!build.isEmpty()) {
			list.add(build.toString().trim());
		}
		return list;
	}

	private static final class Tracking {

		private final int[] counts = new int[Tracked.values().length];

		boolean in(Tracked... tracked) {
			return Arrays.stream(tracked).mapToInt(this::get).anyMatch((i) -> i > 0);
		}

		void toggle(Tracked tracked) {
			set(tracked, (get(tracked) != 0) ? 0 : 1);
		}

		void update(Tracked tracked, int delta) {
			set(tracked, get(tracked) + delta);
		}

		private int get(Tracked tracked) {
			return this.counts[tracked.ordinal()];
		}

		void set(Tracked tracked, int count) {
			this.counts[tracked.ordinal()] = count;
		}

	}

	private enum Tracked {

		OBJECT, LIST, VALUE, ESCAPE

	}

}