Pairs Class — spring-boot Architecture

Source Code

core/spring-boot/src/main/java/org/springframework/boot/logging/structured/ContextPairs.java lines 122–236

	public class Pairs<T> {

		private final Joiner joiner;

		private final List<BiConsumer<T, BiConsumer<String, ?>>> addedPairs;

		Pairs(Joiner joiner, Consumer<Pairs<T>> pairs) {
			this.joiner = joiner;
			this.addedPairs = new ArrayList<>();
			pairs.accept(this);
		}

		/**
		 * Add pairs from map entries.
		 * @param <V> the map value type
		 * @param extractor the extractor used to provide the map
		 */
		@SuppressWarnings("NullAway") // Doesn't detect lambda with correct nullability
		public <V> void addMapEntries(Function<T, Map<String, V>> extractor) {
			add(extractor.andThen(Map::entrySet), Map.Entry::getKey, Map.Entry::getValue);
		}

		/**
		 * Add pairs from an iterable.
		 * @param elementsExtractor the extractor used to provide the iterable
		 * @param pairExtractor the extractor used to provide the name and value
		 * @param <E> the element type
		 */
		public <E> void add(Function<T, @Nullable Iterable<E>> elementsExtractor, PairExtractor<E> pairExtractor) {
			add(elementsExtractor, pairExtractor::getName, pairExtractor::getValue);
		}

		/**
		 * Add pairs from an iterable.
		 * @param elementsExtractor the extractor used to provide the iterable
		 * @param <E> the element type
		 * @param <V> the value type
		 * @param nameExtractor the extractor used to provide the name
		 * @param valueExtractor the extractor used to provide the value
		 */
		public <E, V> void add(Function<T, @Nullable Iterable<E>> elementsExtractor, Function<E, String> nameExtractor,
				Function<E, V> valueExtractor) {
			add((item, pairs) -> {
				Iterable<E> elements = elementsExtractor.apply(item);
				if (elements != null) {
					elements.forEach((element) -> {
						String name = nameExtractor.apply(element);
						V value = valueExtractor.apply(element);
						pairs.accept(name, value);
					});
				}
			});
		}

		/**
		 * Add pairs using the given callback.
		 * @param <V> the value type
		 * @param pairs callback provided with the item and consumer that can be called to
		 * actually add the pairs
		 */
		@SuppressWarnings({ "unchecked", "rawtypes" })
		public <V> void add(BiConsumer<T, BiConsumer<String, V>> pairs) {
			this.addedPairs.add((BiConsumer) pairs);
		}

		void flat(T item, BiConsumer<String, Object> pairs) {
			this.addedPairs.forEach((action) -> action.accept(item, joining(pairs)));
		}

		@SuppressWarnings("unchecked")
		void nested(T item, BiConsumer<String, Object> pairs) {
			LinkedHashMap<String, Object> result = new LinkedHashMap<>();
			this.addedPairs.forEach((addedPair) -> {
				addedPair.accept(item, joining((name, value) -> {
					StringBuilder part = new StringBuilder(name.length());
					int length = (!name.endsWith(".")) ? name.length() : name.length() - 1;
					Map<String, Object> destination = result;
					for (int i = 0; i < length; i++) {
						char ch = name.charAt(i);
						if (i == length - 1) {
							part.append(ch);
							Object previous = destination.put(part.toString(), value);
							assertNotDuplicateNestedPairs(previous == null, name, length);
						}
						else if (ch == '.') {
							Object current = destination.computeIfAbsent(part.toString(),
									(key) -> new LinkedHashMap<>());
							assertNotDuplicateNestedPairs(current instanceof Map, name, i);
							destination = (Map<String, Object>) current;
							part.setLength(0);
						}
						else {
							part.append(ch);
						}
					}
				}));
			});
			result.forEach(pairs);
		}

		private void assertNotDuplicateNestedPairs(boolean expression, String name, int index) {
			Assert.state(expression,
					() -> "Duplicate nested pairs added under '%s'".formatted(name.substring(0, index)));
		}

		private <V> BiConsumer<String, V> joining(BiConsumer<String, V> pairs) {
			return (name, value) -> {
				name = this.joiner.join(ContextPairs.this.prefix, (name != null) ? name : "");
				if (StringUtils.hasLength(name)) {
					pairs.accept(name, value);
				}
			};
		}

	}