Switch Jackson write-dates-as-timestamps default

Update `JacksonAutoConfiguration` so that `write-dates-as-timestamps`
now defaults to `false`.

Fixes gh-11079

Author: philwebb

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

@@ -20,16 +20,18 @@
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.TimeZone;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.databind.Module;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.PropertyNamingStrategy;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.datatype.joda.cfg.JacksonJodaDateFormat;
 import com.fasterxml.jackson.datatype.joda.ser.DateTimeSerializer;
@@ -70,12 +72,21 @@
  * @author Marcel Overdijk
  * @author Sebastien Deleuze
  * @author Johannes Edmeier
+ * @author Phillip Webb
  * @since 1.1.0
  */
 @Configuration
 @ConditionalOnClass(ObjectMapper.class)
 public class JacksonAutoConfiguration {
 
+	private static final Map<?, Boolean> FEATURE_DEFAULTS;
+
+	static {
+		Map<Object, Boolean> featureDefaults = new HashMap<>();
+		featureDefaults.put(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
+		FEATURE_DEFAULTS = Collections.unmodifiableMap(featureDefaults);
+	}
+
 	@Bean
 	public JsonComponentModule jsonComponentModule() {
 		return new JsonComponentModule();
@@ -228,6 +239,7 @@ public void customize(Jackson2ObjectMapperBuilder builder) {
 				if (this.jacksonProperties.getTimeZone() != null) {
 					builder.timeZone(this.jacksonProperties.getTimeZone());
 				}
+				configureFeatures(builder, FEATURE_DEFAULTS);
 				configureFeatures(builder, this.jacksonProperties.getDeserialization());
 				configureFeatures(builder, this.jacksonProperties.getSerialization());
 				configureFeatures(builder, this.jacksonProperties.getMapper());
@@ -241,14 +253,16 @@ public void customize(Jackson2ObjectMapperBuilder builder) {
 
 			private void configureFeatures(Jackson2ObjectMapperBuilder builder,
 					Map<?, Boolean> features) {
-				for (Entry<?, Boolean> entry : features.entrySet()) {
-					if (entry.getValue() != null && entry.getValue()) {
-						builder.featuresToEnable(entry.getKey());
-					}
-					else {
-						builder.featuresToDisable(entry.getKey());
+				features.forEach((feature, value) -> {
+					if (value != null) {
+						if (value) {
+							builder.featuresToEnable(feature);
+						}
+						else {
+							builder.featuresToDisable(feature);
+						}
 					}
-				}
+				});
 			}
 
 			private void configureDateFormat(Jackson2ObjectMapperBuilder builder) {

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

@@ -22,6 +22,7 @@
 import java.util.Date;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.TimeZone;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonCreator.Mode;
@@ -42,6 +43,7 @@
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.databind.util.StdDateFormat;
+import com.fasterxml.jackson.datatype.joda.cfg.FormatConfig;
 import com.fasterxml.jackson.module.paramnames.ParameterNamesModule;
 import org.joda.time.DateTime;
 import org.joda.time.DateTimeZone;
@@ -448,6 +450,18 @@ public void customParameterNamesModuleCanBeConfigured() {
 				ParameterNamesModuleConfig.class, JacksonAutoConfiguration.class);
 	}
 
+	@Test
+	public void writeDatesAsTimestampsDefault() throws Exception {
+		this.context.register(JacksonAutoConfiguration.class);
+		this.context.refresh();
+		ObjectMapper mapper = this.context.getBean(ObjectMapper.class);
+		DateTime dateTime = new DateTime(1988, 6, 25, 20, 30, DateTimeZone.UTC);
+		String expected = FormatConfig.DEFAULT_DATETIME_PRINTER.rawFormatter()
+				.withZone(DateTimeZone.forTimeZone(TimeZone.getTimeZone("UTC")))
+				.print(dateTime);
+		assertThat(mapper.writeValueAsString(dateTime)).isEqualTo("\"" + expected + "\"");
+	}
+
 	private void assertParameterNamesModuleCreatorBinding(Mode expectedMode,
 			Class<?>... configClasses) {
 		this.context.register(configClasses);