Improve resource handling for empty files contained in jars

spring-core/src/main/java/org/springframework/core/io/AbstractFileResolvingResource.java

@@ -20,13 +20,15 @@
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.net.HttpURLConnection;
+import java.net.JarURLConnection;
 import java.net.URI;
 import java.net.URL;
 import java.net.URLConnection;
 import java.nio.channels.FileChannel;
 import java.nio.channels.ReadableByteChannel;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.StandardOpenOption;
+import java.util.jar.JarEntry;
 
 import org.springframework.util.ResourceUtils;
 
@@ -114,6 +116,16 @@ boolean checkReadable(URL url) {
 						return false;
 					}
 				}
+				else if (con instanceof JarURLConnection) {
+					JarURLConnection jarCon = (JarURLConnection) con;
+					JarEntry jarEntry = jarCon.getJarEntry();
+					if (jarEntry == null) {
+						return false;
+					}
+					else {
+						return !jarEntry.isDirectory();
+					}
+				}
 				long contentLength = con.getContentLengthLong();
 				if (contentLength > 0) {
 					return true;

spring-core/src/test/java/org/springframework/core/io/ClassPathResourceTests.java

@@ -16,11 +16,19 @@
 
 package org.springframework.core.io;
 
+import java.io.File;
 import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipOutputStream;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
@@ -119,6 +127,34 @@ void directoryNotReadable() {
 		assertThat(jarDir.isReadable()).isFalse();
 	}
 
+	@Test
+	void emptyFileReadable(@TempDir File tempDir) throws IOException {
+		File file = new File(tempDir, "empty.txt");
+		assertThat(file.createNewFile()).isTrue();
+		assertThat(file.isFile());
+
+		ClassLoader fileClassLoader = new URLClassLoader(new URL[]{tempDir.toURI().toURL()});
+
+		Resource emptyFile = new ClassPathResource("empty.txt", fileClassLoader);
+		assertThat(emptyFile.exists()).isTrue();
+		assertThat(emptyFile.isReadable()).isTrue();
+		assertThat(emptyFile.contentLength()).isEqualTo(0);
+
+		File jarFile = new File(tempDir, "test.jar");
+		try (ZipOutputStream zipOut = new ZipOutputStream(new FileOutputStream(jarFile))) {
+			zipOut.putNextEntry(new ZipEntry("empty2.txt"));
+			zipOut.closeEntry();
+		}
+		assertThat(jarFile.isFile());
+
+		ClassLoader jarClassLoader = new URLClassLoader(new URL[]{jarFile.toURI().toURL()});
+
+		Resource emptyJarEntry = new ClassPathResource("empty2.txt", jarClassLoader);
+		assertThat(emptyJarEntry.exists()).isTrue();
+		assertThat(emptyJarEntry.isReadable()).isTrue();
+		assertThat(emptyJarEntry.contentLength()).isEqualTo(0);
+	}
+
 
 	private void assertDescriptionContainsExpectedPath(ClassPathResource resource, String expectedPath) {
 		Matcher matcher = DESCRIPTION_PATTERN.matcher(resource.getDescription());