Add configurable startup time format

Introduce a new configuration property 'spring.main.log-startup-time-format'
to control how application startup times are displayed in logs. This addresses
concerns about backward compatibility with existing log parsing tools.

The property supports two formats:
- 'decimal' (default): Displays time in seconds with millisecond precision
  (e.g., "3.456 seconds"). This maintains backward compatibility.
- 'human-readable': Displays time in a more intuitive way using appropriate
  units (e.g., "1 minute 30 seconds" or "1 hour 15 minutes").

By defaulting to the existing decimal format, this change ensures no breaking
changes for existing deployments while providing an opt-in mechanism for users
who prefer more readable startup time logs.

Signed-off-by: Huang Xiao <youngledo@qq.com>

core/spring-boot/src/main/java/org/springframework/boot/ApplicationProperties.java

@@ -68,6 +68,11 @@ class ApplicationProperties {
 	 */
 	private boolean logStartupInfo = true;
 
+	/**
+	 * Format used to display application startup time in logs.
+	 */
+	private StartupTimeFormat logStartupTimeFormat = StartupTimeFormat.DEFAULT;
+
 	/**
 	 * Whether the application should have a shutdown hook registered.
 	 */
@@ -139,6 +144,14 @@ class ApplicationProperties {
 		this.logStartupInfo = logStartupInfo;
 	}
 
+	StartupTimeFormat getLogStartupTimeFormat() {
+		return this.logStartupTimeFormat;
+	}
+
+	void setLogStartupTimeFormat(StartupTimeFormat logStartupTimeFormat) {
+		this.logStartupTimeFormat = logStartupTimeFormat;
+	}
+
 	boolean isRegisterShutdownHook() {
 		return this.registerShutdownHook;
 	}

core/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -322,7 +322,8 @@ public class SpringApplication {
 			afterRefresh(context, applicationArguments);
 			Duration timeTakenToStarted = startup.started();
 			if (this.properties.isLogStartupInfo()) {
-				new StartupInfoLogger(this.mainApplicationClass, environment).logStarted(getApplicationLog(), startup);
+				new StartupInfoLogger(this.mainApplicationClass, environment, this.properties.getLogStartupTimeFormat())
+					.logStarted(getApplicationLog(), startup);
 			}
 			listeners.started(context, timeTakenToStarted);
 			callRunners(context, applicationArguments);

core/spring-boot/src/main/java/org/springframework/boot/StartupInfoLogger.java

@@ -44,9 +44,16 @@ class StartupInfoLogger {
 
 	private final Environment environment;
 
+	private final StartupTimeFormat startupTimeFormat;
+
 	StartupInfoLogger(@Nullable Class<?> sourceClass, Environment environment) {
+		this(sourceClass, environment, StartupTimeFormat.DEFAULT);
+	}
+
+	StartupInfoLogger(@Nullable Class<?> sourceClass, Environment environment, StartupTimeFormat startupTimeFormat) {
 		this.sourceClass = sourceClass;
 		this.environment = environment;
+		this.startupTimeFormat = startupTimeFormat;
 	}
 
 	void logStarting(Log applicationLog) {
@@ -87,16 +94,18 @@ class StartupInfoLogger {
 		message.append(startup.action());
 		appendApplicationName(message);
 		message.append(" in ");
-		message.append(startup.timeTakenToStarted().toMillis() / 1000.0);
+		message.append(formatDuration(startup.timeTakenToStarted().toMillis()));
-		message.append(" seconds");
 		Long uptimeMs = startup.processUptime();
 		if (uptimeMs != null) {
-			double uptime = uptimeMs / 1000.0;
+			message.append(" (process running for ").append(formatDuration(uptimeMs)).append(")");
-			message.append(" (process running for ").append(uptime).append(")");
 		}
 		return message;
 	}
 
+	private String formatDuration(long millis) {
+		return this.startupTimeFormat.format(millis);
+	}
+
 	private void appendAotMode(StringBuilder message) {
 		append(message, "", () -> AotDetector.useGeneratedArtifacts() ? "AOT-processed" : null);
 	}

core/spring-boot/src/main/java/org/springframework/boot/StartupTimeFormat.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot;
+
+import java.time.Duration;
+
+/**
+ * Format styles for displaying application startup time in logs.
+ *
+ * @author Huang Xiao
+ * @since 3.5.0
+ */
+public enum StartupTimeFormat {
+
+	/**
+	 * Default format displays time in seconds with millisecond precision (e.g., "3.456
+	 * seconds"). This maintains backward compatibility with existing log parsing tools.
+	 */
+	DEFAULT {
+
+		@Override
+		public String format(long millis) {
+			return String.format("%.3f seconds", millis / 1000.0);
+		}
+
+	},
+
+	/**
+	 * Human format displays time in a more intuitive way using appropriate units (e.g.,
+	 * "1 minute 30 seconds" or "1 hour 15 minutes"). Times under 60 seconds still use the
+	 * default format for consistency.
+	 */
+	HUMAN {
+
+		@Override
+		public String format(long millis) {
+			Duration duration = Duration.ofMillis(millis);
+			long seconds = duration.getSeconds();
+			if (seconds < 60) {
+				return String.format("%.3f seconds", millis / 1000.0);
+			}
+			long hours = duration.toHours();
+			int minutes = duration.toMinutesPart();
+			int secs = duration.toSecondsPart();
+			if (hours > 0) {
+				return String.format("%d hour%s %d minute%s", hours, (hours != 1) ? "s" : "", minutes,
+						(minutes != 1) ? "s" : "");
+			}
+			return String.format("%d minute%s %d second%s", minutes, (minutes != 1) ? "s" : "", secs,
+					(secs != 1) ? "s" : "");
+		}
+
+	};
+
+	/**
+	 * Format the given duration in milliseconds according to this format style.
+	 * @param millis the duration in milliseconds
+	 * @return the formatted string
+	 */
+	public abstract String format(long millis);
+
+}

core/spring-boot/src/test/java/org/springframework/boot/StartupInfoLoggerTests.java

@@ -109,7 +109,7 @@ class StartupInfoLoggerTests {
 		new StartupInfoLogger(getClass(), this.environment).logStarted(this.log, new TestStartup(1345L, "Started"));
 		then(this.log).should()
 			.info(assertArg((message) -> assertThat(message.toString()).matches("Started " + getClass().getSimpleName()
-					+ " in \\d+\\.\\d{1,3} seconds \\(process running for 1.345\\)")));
+					+ " in \\d+\\.\\d{1,3} seconds \\(process running for 1\\.345 seconds\\)")));
 	}
 
 	@Test
@@ -130,17 +130,79 @@ class StartupInfoLoggerTests {
 				.matches("Restored " + getClass().getSimpleName() + " in \\d+\\.\\d{1,3} seconds")));
 	}
 
+	@Test
+	void startedFormatWithHumanMinutes() {
+		given(this.log.isInfoEnabled()).willReturn(true);
+		new StartupInfoLogger(getClass(), this.environment, StartupTimeFormat.HUMAN).logStarted(this.log,
+				new TestStartup(90000L, "Started", 90000L));
+		then(this.log).should()
+			.info(assertArg(
+					(message) -> assertThat(message.toString()).isEqualTo("Started " + getClass().getSimpleName()
+							+ " in 1 minute 30 seconds (process running for 1 minute 30 seconds)")));
+	}
+
+	@Test
+	void startedFormatWithHumanHours() {
+		given(this.log.isInfoEnabled()).willReturn(true);
+		new StartupInfoLogger(getClass(), this.environment, StartupTimeFormat.HUMAN).logStarted(this.log,
+				new TestStartup(4500000L, "Started", 4500000L));
+		then(this.log).should()
+			.info(assertArg((message) -> assertThat(message.toString()).isEqualTo("Started "
+					+ getClass().getSimpleName() + " in 1 hour 15 minutes (process running for 1 hour 15 minutes)")));
+	}
+
+	@Test
+	void startedFormatWithHumanSingularUnits() {
+		given(this.log.isInfoEnabled()).willReturn(true);
+		new StartupInfoLogger(getClass(), this.environment, StartupTimeFormat.HUMAN).logStarted(this.log,
+				new TestStartup(61000L, "Started", 61000L));
+		then(this.log).should()
+			.info(assertArg((message) -> assertThat(message.toString()).isEqualTo("Started "
+					+ getClass().getSimpleName() + " in 1 minute 1 second (process running for 1 minute 1 second)")));
+	}
+
+	@Test
+	void startedFormatWithHumanZeroSeconds() {
+		given(this.log.isInfoEnabled()).willReturn(true);
+		new StartupInfoLogger(getClass(), this.environment, StartupTimeFormat.HUMAN).logStarted(this.log,
+				new TestStartup(300000L, "Started", 300000L));
+		then(this.log).should()
+			.info(assertArg(
+					(message) -> assertThat(message.toString()).isEqualTo("Started " + getClass().getSimpleName()
+							+ " in 5 minutes 0 seconds (process running for 5 minutes 0 seconds)")));
+	}
+
+	@Test
+	void startedFormatWithDefaultDecimalFormat() {
+		given(this.log.isInfoEnabled()).willReturn(true);
+		new StartupInfoLogger(getClass(), this.environment).logStarted(this.log,
+				new TestStartup(90000L, "Started", 90000L));
+		then(this.log).should()
+			.info(assertArg((message) -> assertThat(message.toString()).matches("Started " + getClass().getSimpleName()
+					+ " in \\d+\\.\\d{1,3} seconds \\(process running for \\d+\\.\\d{1,3} seconds\\)")));
+	}
+
 	static class TestStartup extends Startup {
 
-		private final long startTime = System.currentTimeMillis();
+		private long startTime;
 
 		private final @Nullable Long uptime;
 
 		private final String action;
 
 		TestStartup(@Nullable Long uptime, String action) {
+			this(uptime, action, null);
+		}
+
+		TestStartup(@Nullable Long uptime, String action, @Nullable Long timeTaken) {
 			this.uptime = uptime;
 			this.action = action;
+			if (timeTaken != null) {
+				this.startTime = System.currentTimeMillis() - timeTaken;
+			}
+			else {
+				this.startTime = System.currentTimeMillis();
+			}
 			started();
 		}