Merge branch '2.2.x'

Closes gh-19435

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java

@@ -88,6 +88,7 @@ public class JacksonAutoConfiguration {
 	static {
 		Map<Object, Boolean> featureDefaults = new HashMap<>();
 		featureDefaults.put(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
+		featureDefaults.put(SerializationFeature.WRITE_DURATIONS_AS_TIMESTAMPS, false);
 		FEATURE_DEFAULTS = Collections.unmodifiableMap(featureDefaults);
 	}
 

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.autoconfigure.jackson;
 import java.io.IOException;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
+import java.time.Duration;
 import java.util.Date;
 import java.util.HashSet;
 import java.util.Set;
@@ -378,6 +379,15 @@ class JacksonAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void writeDurationAsTimestampsDefault() {
+		this.contextRunner.run((context) -> {
+			ObjectMapper mapper = context.getBean(ObjectMapper.class);
+			Duration duration = Duration.ofHours(2);
+			assertThat(mapper.writeValueAsString(duration)).isEqualTo("\"PT2H\"");
+		});
+	}
+
 	@Test
 	void writeWithVisibility() {
 		this.contextRunner