diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnection.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnection.java
index c9a7475a1f..513bc5cab7 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnection.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnection.java
@@ -154,6 +154,11 @@ final class JarUrlConnection extends java.net.JarURLConnection {
 		return guessContentTypeFromName(this.entryName);
 	}
 
+	@Override
+	public long getLastModified() {
+		return (this.jarFileConnection != null) ? this.jarFileConnection.getLastModified() : super.getLastModified();
+	}
+
 	@Override
 	public String getHeaderField(String name) {
 		return (this.jarFileConnection != null) ? this.jarFileConnection.getHeaderField(name) : null;
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnection.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnection.java
index 32051123ab..0409fe6e3d 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnection.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnection.java
@@ -28,6 +28,15 @@ import java.net.URL;
 import java.net.URLConnection;
 import java.nio.file.Files;
 import java.security.Permission;
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
 
 import org.springframework.boot.loader.ref.Cleaner;
 
@@ -39,6 +48,9 @@ import org.springframework.boot.loader.ref.Cleaner;
  */
 class NestedUrlConnection extends URLConnection {
 
+	private static final DateTimeFormatter RFC_1123_DATE_TIME = DateTimeFormatter.RFC_1123_DATE_TIME
+		.withZone(ZoneId.of("GMT"));
+
 	private static final String CONTENT_TYPE = "x-java/jar";
 
 	private final NestedUrlConnectionResources resources;
@@ -49,6 +61,8 @@ class NestedUrlConnection extends URLConnection {
 
 	private FilePermission permission;
 
+	private Map<String, List<String>> headerFields;
+
 	NestedUrlConnection(URL url) throws MalformedURLException {
 		this(url, Cleaner.instance);
 	}
@@ -69,6 +83,60 @@ class NestedUrlConnection extends URLConnection {
 		}
 	}
 
+	@Override
+	public String getHeaderField(String name) {
+		List<String> values = getHeaderFields().get(name);
+		return (values != null && !values.isEmpty()) ? values.get(0) : null;
+	}
+
+	@Override
+	public String getHeaderField(int n) {
+		Entry<String, List<String>> entry = getHeaderEntry(n);
+		List<String> values = (entry != null) ? entry.getValue() : null;
+		return (values != null && !values.isEmpty()) ? values.get(0) : null;
+	}
+
+	@Override
+	public String getHeaderFieldKey(int n) {
+		Entry<String, List<String>> entry = getHeaderEntry(n);
+		return (entry != null) ? entry.getKey() : null;
+	}
+
+	private Entry<String, List<String>> getHeaderEntry(int n) {
+		Iterator<Entry<String, List<String>>> iterator = getHeaderFields().entrySet().iterator();
+		Entry<String, List<String>> entry = null;
+		for (int i = 0; i < n; i++) {
+			entry = (!iterator.hasNext()) ? null : iterator.next();
+		}
+		return entry;
+	}
+
+	@Override
+	public Map<String, List<String>> getHeaderFields() {
+		try {
+			connect();
+		}
+		catch (IOException ex) {
+			return Collections.emptyMap();
+		}
+		Map<String, List<String>> headerFields = this.headerFields;
+		if (headerFields == null) {
+			headerFields = new LinkedHashMap<>();
+			long contentLength = getContentLengthLong();
+			long lastModified = getLastModified();
+			if (contentLength > 0) {
+				headerFields.put("content-length", List.of(String.valueOf(contentLength)));
+			}
+			if (getLastModified() > 0) {
+				headerFields.put("last-modified",
+						List.of(RFC_1123_DATE_TIME.format(Instant.ofEpochMilli(lastModified))));
+			}
+			headerFields = Collections.unmodifiableMap(headerFields);
+			this.headerFields = headerFields;
+		}
+		return headerFields;
+	}
+
 	@Override
 	public int getContentLength() {
 		long contentLength = getContentLengthLong();
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnectionTests.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnectionTests.java
index e84ab43521..aa91510356 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnectionTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/jar/JarUrlConnectionTests.java
@@ -27,6 +27,8 @@ import java.net.URL;
 import java.net.URLConnection;
 import java.nio.charset.StandardCharsets;
 import java.security.Permission;
+import java.time.Instant;
+import java.time.temporal.ChronoField;
 import java.util.List;
 import java.util.Map;
 import java.util.jar.JarEntry;
@@ -490,4 +492,22 @@ class JarUrlConnectionTests {
 		assertThat(connection).isNotNull();
 	}
 
+	@Test // gh-38204
+	void getLastModifiedReturnsFileModifiedTime() throws Exception {
+		JarUrlConnection connection = JarUrlConnection.open(this.url);
+		assertThat(connection.getLastModified()).isEqualTo(this.file.lastModified());
+	}
+
+	@Test // gh-38204
+	void getLastModifiedHeaderReturnsFileModifiedTime() throws IOException {
+		JarUrlConnection connection = JarUrlConnection.open(this.url);
+		URLConnection fileConnection = this.file.toURI().toURL().openConnection();
+		assertThat(connection.getHeaderFieldDate("last-modified", 0)).isEqualTo(withoutNanos(this.file.lastModified()))
+			.isEqualTo(fileConnection.getHeaderFieldDate("last-modified", 0));
+	}
+
+	private long withoutNanos(long epochMilli) {
+		return Instant.ofEpochMilli(epochMilli).with(ChronoField.NANO_OF_SECOND, 0).toEpochMilli();
+	}
+
 }
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnectionTests.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnectionTests.java
index 7efcf2b257..488a168523 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnectionTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/net/protocol/nested/NestedUrlConnectionTests.java
@@ -18,11 +18,15 @@ package org.springframework.boot.loader.net.protocol.nested;
 
 import java.io.File;
 import java.io.FilePermission;
+import java.io.IOException;
 import java.io.InputStream;
 import java.lang.ref.Cleaner.Cleanable;
 import java.net.MalformedURLException;
 import java.net.URL;
+import java.net.URLConnection;
 import java.security.Permission;
+import java.time.Instant;
+import java.time.temporal.ChronoField;
 
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
@@ -148,4 +152,23 @@ class NestedUrlConnectionTests {
 		actionCaptor.getValue().run();
 	}
 
+	@Test // gh-38204
+	void getLastModifiedReturnsFileModifiedTime() throws Exception {
+		NestedUrlConnection connection = new NestedUrlConnection(this.url);
+		assertThat(connection.getLastModified()).isEqualTo(this.jarFile.lastModified());
+	}
+
+	@Test // gh-38204
+	void getLastModifiedHeaderReturnsFileModifiedTime() throws IOException {
+		NestedUrlConnection connection = new NestedUrlConnection(this.url);
+		URLConnection fileConnection = this.jarFile.toURI().toURL().openConnection();
+		assertThat(connection.getHeaderFieldDate("last-modified", 0))
+			.isEqualTo(withoutNanos(this.jarFile.lastModified()))
+			.isEqualTo(fileConnection.getHeaderFieldDate("last-modified", 0));
+	}
+
+	private long withoutNanos(long epochMilli) {
+		return Instant.ofEpochMilli(epochMilli).with(ChronoField.NANO_OF_SECOND, 0).toEpochMilli();
+	}
+
 }