Add filter, name processor and value processor support to JsonWriter

Update `JsonWriter` to support filtering and processing of names/values.
This update will allow us to offer better customization options with
structured logging.

See gh-42486

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/json/JsonValueWriter.java

@@ -24,9 +24,15 @@
 import java.util.Map;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
+import java.util.function.Predicate;
 
+import org.springframework.boot.json.JsonWriter.MemberPath;
+import org.springframework.boot.json.JsonWriter.NameProcessor;
+import org.springframework.boot.json.JsonWriter.ValueProcessor;
+import org.springframework.boot.util.LambdaSafe;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
 import org.springframework.util.function.ThrowingConsumer;
 
 /**
@@ -40,6 +46,10 @@ class JsonValueWriter {
 
 	private final Appendable out;
 
+	private MemberPath path = MemberPath.ROOT;
+
+	private final Deque<JsonWriterFiltersAndProcessors> filtersAndProcessors = new ArrayDeque<>();
+
 	private final Deque<ActiveSeries> activeSeries = new ArrayDeque<>();
 
 	/**
@@ -50,6 +60,14 @@ class JsonValueWriter {
 		this.out = out;
 	}
 
+	void pushProcessors(JsonWriterFiltersAndProcessors jsonProcessors) {
+		this.filtersAndProcessors.addLast(jsonProcessors);
+	}
+
+	void popProcessors() {
+		this.filtersAndProcessors.removeLast();
+	}
+
 	/**
 	 * Write a name value pair, or just a value if {@code name} is {@code null}.
 	 * @param <N> the name type in the pair
@@ -82,6 +100,7 @@ <N, V> void write(N name, V value) {
 	 * @param value the value to write
 	 */
 	<V> void write(V value) {
+		value = processValue(value);
 		if (value == null) {
 			append("null");
 		}
@@ -119,7 +138,7 @@ else if (value instanceof Number || value instanceof Boolean) {
 	 */
 	void start(Series series) {
 		if (series != null) {
-			this.activeSeries.push(new ActiveSeries());
+			this.activeSeries.push(new ActiveSeries(series));
 			append(series.openChar);
 		}
 	}
@@ -164,8 +183,10 @@ <E> void writeElements(Consumer<Consumer<E>> elements) {
 	<E> void writeElement(E element) {
 		ActiveSeries activeSeries = this.activeSeries.peek();
 		Assert.notNull(activeSeries, "No series has been started");
-		activeSeries.appendCommaIfRequired();
+		this.path = activeSeries.updatePath(this.path);
+		activeSeries.incrementIndexAndAddCommaIfRequired();
 		write(element);
+		this.path = activeSeries.restorePath(this.path);
 	}
 
 	/**
@@ -196,12 +217,17 @@ <N, V> void writePairs(Consumer<BiConsumer<N, V>> pairs) {
 	}
 
 	private <N, V> void writePair(N name, V value) {
-		ActiveSeries activeSeries = this.activeSeries.peek();
-		Assert.notNull(activeSeries, "No series has been started");
-		activeSeries.appendCommaIfRequired();
-		writeString(name);
-		append(":");
-		write(value);
+		this.path = this.path.child(name.toString());
+		if (!isFilteredPath()) {
+			String processedName = processName(name.toString());
+			ActiveSeries activeSeries = this.activeSeries.peek();
+			Assert.notNull(activeSeries, "No series has been started");
+			activeSeries.incrementIndexAndAddCommaIfRequired();
+			writeString(processedName);
+			append(":");
+			write(value);
+		}
+		this.path = this.path.parent();
 	}
 
 	private void writeString(Object value) {
@@ -256,6 +282,48 @@ private void append(char ch) {
 		}
 	}
 
+	private boolean isFilteredPath() {
+		for (JsonWriterFiltersAndProcessors filtersAndProcessors : this.filtersAndProcessors) {
+			for (Predicate<MemberPath> pathFilter : filtersAndProcessors.pathFilters()) {
+				if (pathFilter.test(this.path)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
+	private String processName(String name) {
+		for (JsonWriterFiltersAndProcessors filtersAndProcessors : this.filtersAndProcessors) {
+			for (NameProcessor nameProcessor : filtersAndProcessors.nameProcessors()) {
+				name = processName(name, nameProcessor);
+			}
+		}
+		return name;
+	}
+
+	private String processName(String name, NameProcessor nameProcessor) {
+		name = nameProcessor.processName(this.path, name);
+		Assert.state(StringUtils.hasLength(name), "NameProcessor " + nameProcessor + " returned an empty result");
+		return name;
+	}
+
+	private <V> V processValue(V value) {
+		for (JsonWriterFiltersAndProcessors filtersAndProcessors : this.filtersAndProcessors) {
+			for (ValueProcessor<?> valueProcessor : filtersAndProcessors.valueProcessors()) {
+				value = processValue(value, valueProcessor);
+			}
+		}
+		return value;
+	}
+
+	@SuppressWarnings({ "unchecked", "unchecked" })
+	private <V> V processValue(V value, ValueProcessor<?> valueProcessor) {
+		return (V) LambdaSafe.callback(ValueProcessor.class, valueProcessor, this.path, value)
+			.invokeAnd((call) -> call.processValue(this.path, value))
+			.get(value);
+	}
+
 	/**
 	 * A series of items that can be written to the JSON output.
 	 */
@@ -287,16 +355,27 @@ enum Series {
 	 */
 	private final class ActiveSeries {
 
-		private boolean commaRequired;
+		private final Series series;
+
+		private int index;
+
+		private ActiveSeries(Series series) {
+			this.series = series;
+		}
+
+		MemberPath updatePath(MemberPath path) {
+			return (this.series != Series.ARRAY) ? path : path.child(this.index);
+		}
 
-		private ActiveSeries() {
+		MemberPath restorePath(MemberPath path) {
+			return (this.series != Series.ARRAY) ? path : path.parent();
 		}
 
-		void appendCommaIfRequired() {
-			if (this.commaRequired) {
+		void incrementIndexAndAddCommaIfRequired() {
+			if (this.index > 0) {
 				append(',');
 			}
-			this.commaRequired = true;
+			this.index++;
 		}
 
 	}