Make JarURLConnection return entry's last modified time

See gh-9893

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/jar/JarURLConnectionTests.java

@@ -35,6 +35,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  *
  * @author Andy Wilkinson
  * @author Phillip Webb
+ * @author Rostyslav Dudka
  */
 public class JarURLConnectionTests {
 
@@ -150,6 +151,14 @@ public class JarURLConnectionTests {
 		assertThat(url.openConnection().getContentLengthLong()).isEqualTo(1);
 	}
 
+	@Test
+	public void getLastModifiedReturnsLastModifiedTimeOfJarEntry() throws Exception {
+		URL url = new URL("jar:file:" + getAbsolutePath() + "!/1.dat");
+		JarURLConnection connection = JarURLConnection.get(url, this.jarFile);
+		assertThat(connection.getLastModified())
+				.isEqualTo(connection.getJarEntry().getTime());
+	}
+
 	private String getAbsolutePath() {
 		return this.rootJarFile.getAbsolutePath().replace('\\', '/');
 	}