Prevent StackOverflowError when serializing Path using JsonValueWriter

Prior to this commit, serializing `java.nio.file.Path` caused
a StackOverflowError because `Path.iterator()` always returns itself
as the first element of the iterator, which results in a StackOverflowError.

This commit serializes `java.nio.file.Path` as JSON String.

Signed-off-by: Dmytro Nosan <[email protected]>

Author: nosan

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.nio.file.Path;
 import java.util.ArrayDeque;
 import java.util.Arrays;
 import java.util.Deque;
@@ -114,6 +115,10 @@ else if (value instanceof WritableJson writableJson) {
 				throw new UncheckedIOException(ex);
 			}
 		}
+		// https://github.com/spring-projects/spring-boot/issues/44502
+		else if (value instanceof Path p) {
+			writeString(p.toString());
+		}
 		else if (value instanceof Iterable<?> iterable) {
 			writeArray(iterable::forEach);
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/json/JsonValueWriterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.boot.json;
 
+import java.nio.file.Path;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -240,6 +241,18 @@ void endWhenNotStartedThrowsException() {
 			.isThrownBy(() -> valueWriter.end(Series.ARRAY)));
 	}
 
+	// https://github.com/spring-projects/spring-boot/issues/44502
+	@Test
+	void writeJavaNioPathWhenSingleElementShouldNotCauseStackOverflowError() {
+		assertThat(doWrite((valueWriter) -> valueWriter.write(Path.of("overflow")))).isEqualTo(quoted("overflow"));
+	}
+
+	@Test
+	void writeJavaNioPathShouldNotCauseStackOverflowError() {
+		assertThat(doWrite((valueWriter) -> valueWriter.write(Path.of("stack/overflow/error"))))
+			.isEqualTo(quoted("stack\\/overflow\\/error"));
+	}
+
 	private <V> String write(V value) {
 		return doWrite((valueWriter) -> valueWriter.write(value));
 	}

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-structured-logging/src/test/java/smoketest/structuredlogging/SampleStructuredLoggingApplicationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,9 +16,12 @@
 
 package smoketest.structuredlogging;
 
+import java.nio.file.Path;
+
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
+import org.slf4j.LoggerFactory;
 
 import org.springframework.boot.logging.LoggingSystem;
 import org.springframework.boot.logging.LoggingSystemProperty;
@@ -43,6 +46,18 @@ void reset() {
 		}
 	}
 
+	// https://github.com/spring-projects/spring-boot/issues/44502
+	@Test
+	void javaNioPathShouldNotCauseStackOverflowError(CapturedOutput output) {
+		SampleStructuredLoggingApplication.main(new String[0]);
+		LoggerFactory.getLogger(SampleStructuredLoggingApplication.class)
+			.atInfo()
+			.addKeyValue("directory", Path.of("stack/overflow/error"))
+			.log("java.nio.file.Path works as expected");
+		assertThat(output).contains("java.nio.file.Path works as expected").contains("""
+				"directory":"stack\\/overflow\\/error""");
+	}
+
 	@Test
 	void shouldNotLogBanner(CapturedOutput output) {
 		SampleStructuredLoggingApplication.main(new String[0]);

src/checkstyle/checkstyle-suppressions.xml

@@ -12,6 +12,7 @@
 	<suppress files="LogbackLoggingSystemTests\.java" checks="IllegalImport" />
 	<suppress files="LogbackLoggingSystemParallelInitializationTests\.java" checks="IllegalImport" />
 	<suppress files="LogbackConfigurationAotContributionTests\.java" checks="IllegalImport" />
+	<suppress files="SampleStructuredLoggingApplicationTests\.java" checks="IllegalImport" message="LoggerFactory" />
 	<suppress files="MetricsAutoConfigurationMeterRegistryPostProcessorIntegrationTests\.java" checks="IllegalImport" message="LoggerFactory"/>
 	<suppress files="SpringApplicationTests\.java" checks="FinalClass" />
 	<suppress files=".+Configuration\.java" checks="HideUtilityClassConstructor" />