fix code and add test

hutool-core/src/main/java/org/dromara/hutool/core/classloader/JarClassLoader.java

@@ -14,6 +14,7 @@ package org.dromara.hutool.core.classloader;
 
 import org.dromara.hutool.core.exception.HutoolException;
 import org.dromara.hutool.core.io.IORuntimeException;
+import org.dromara.hutool.core.io.file.FileNameUtil;
 import org.dromara.hutool.core.io.file.FileUtil;
 import org.dromara.hutool.core.net.url.UrlUtil;
 import org.dromara.hutool.core.reflect.method.MethodUtil;
@@ -125,10 +126,9 @@ public class JarClassLoader extends URLClassLoader {
 	 * @param jarFileOrDir jar文件或者jar文件所在目录
 	 * @return this
 	 */
+	@SuppressWarnings("resource")
 	public JarClassLoader addJar(final File jarFileOrDir) {
-		if (isJarFile(jarFileOrDir)) {
+		// loopJar方法中，如果传入的是jar文件，直接返回此文件
-			return addURL(jarFileOrDir);
-		}
 		final List<File> jars = loopJar(jarFileOrDir);
 		for (final File jar : jars) {
 			addURL(jar);
@@ -174,10 +174,8 @@ public class JarClassLoader extends URLClassLoader {
 	 * @since 4.4.2
 	 */
 	private static boolean isJarFile(final File file) {
-		if (!FileUtil.isFile(file)) {
+		return FileUtil.isFile(file) &&
-			return false;
+			FileNameUtil.isType(file.getName(), FileNameUtil.EXT_JAR);
-		}
-		return file.getPath().toLowerCase().endsWith(".jar");
 	}
 	// ------------------------------------------------------------------- Private method end
 }

hutool-core/src/test/java/org/dromara/hutool/core/classloader/ClassLoaderUtilTest.java

@@ -12,10 +12,21 @@
 
 package org.dromara.hutool.core.classloader;
 
+import org.dromara.hutool.core.collection.iter.EnumerationIter;
+import org.dromara.hutool.core.io.file.FileUtil;
+import org.dromara.hutool.core.lang.Console;
 import org.dromara.hutool.core.map.Dict;
+import org.dromara.hutool.core.reflect.ClassUtil;
+import org.dromara.hutool.core.reflect.FieldUtil;
+import org.dromara.hutool.core.reflect.method.MethodUtil;
 import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
+import java.lang.reflect.Field;
+import java.sql.Driver;
+import java.sql.DriverManager;
+
 public class ClassLoaderUtilTest {
 
 	@Test
@@ -61,4 +72,18 @@ public class ClassLoaderUtilTest {
 
 		}
 	}
+
+	@Test
+	@Disabled
+	void loadClassFromJarTest() {
+		final JarClassLoader classLoader = ClassLoaderUtil.getJarClassLoader(
+			FileUtil.file("D:\\m2_repo\\com\\sap\\cloud\\db\\jdbc\\ngdbc\\2.18.13\\ngdbc-2.18.13.jar"));
+
+		final Class<?> aClass = ClassUtil.forName("com.sap.db.jdbc.Driver", true, classLoader);
+		final Field instance = FieldUtil.getField(aClass, "INSTANCE");
+		Console.log(FieldUtil.getFieldValue(null, instance));
+
+		final Field version = FieldUtil.getField(aClass, "JAVA_VERSION");
+		Console.log(FieldUtil.getFieldValue(null, version));
+	}
 }

hutool-core/src/test/java/org/dromara/hutool/core/io/file/FileUtilTest.java

@@ -292,6 +292,13 @@ public class FileUtilTest {
 		}
 	}
 
+	@Test
+	@Disabled
+	public void loopFileTest() {
+		final List<File> files = FileUtil.loopFiles("D:\\m2_repo\\cglib\\cglib\\3.3.0\\cglib-3.3.0.jar");
+		Console.log(files);
+	}
+
 	@Test
 	@Disabled
 	public void loopFilesTest2() {