Close class resource InputStream in ThrowawayClassLoader

Prior to this commit, ThrowawayClassLoader#loadClassFromResource opened
an InputStream via getResourceAsStream(...) but never closed it. The
stream leaked on both the success path (after defineClass) and the
IOException path, as the surrounding try-block had neither a finally
nor a try-with-resources clause.

This commit adapts the existing inputStream variable as a
try-with-resources resource so that it is closed on every path, leaving
the loading logic unchanged.

Closes gh-36933

Signed-off-by: junhyeong9812 <pickjog@gmail.com>

spring-core/src/main/java/org/springframework/aot/nativex/feature/ThrowawayClassLoader.java

@@ -65,12 +65,11 @@ class ThrowawayClassLoader extends ClassLoader {
 		if (inputStream == null) {
 			return null;
 		}
-		try {
+		try (inputStream) {
 			ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
 			inputStream.transferTo(outputStream);
 			byte[] bytes = outputStream.toByteArray();
 			return defineClass(name, bytes, 0, bytes.length);
-
 		}
 		catch (IOException ex) {
 			throw new ClassNotFoundException("Cannot load resource for class [" + name + "]", ex);

spring-core/src/test/java/org/springframework/aot/nativex/feature/ThrowawayClassLoaderTests.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2002-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.aot.nativex.feature;
+
+import java.io.ByteArrayInputStream;
+import java.io.FilterInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ThrowawayClassLoader}.
+ *
+ * @author Junhyeong Kim
+ */
+class ThrowawayClassLoaderTests {
+
+	@Test
+	void loadingClassFromResourceClosesInputStream() throws Exception {
+		String className = Probe.class.getName();
+		byte[] classBytes = classBytesOf(className);
+		AtomicBoolean closed = new AtomicBoolean();
+
+		// The grandparent resolves bootstrap classes only, so super.loadClass(...)
+		// fails for the probe class and ThrowawayClassLoader falls back to loading it
+		// from the resource stream provided below.
+		ClassLoader resourceLoader = new ClassLoader(new ClassLoader(null) {}) {
+			@Override
+			public InputStream getResourceAsStream(String name) {
+				return new TrackingInputStream(new ByteArrayInputStream(classBytes), closed);
+			}
+		};
+
+		ThrowawayClassLoader classLoader = new ThrowawayClassLoader(resourceLoader);
+		Class<?> loaded = classLoader.loadClass(className);
+
+		assertThat(loaded.getName()).isEqualTo(className);
+		assertThat(closed).as("InputStream closed").isTrue();
+	}
+
+	private static byte[] classBytesOf(String className) throws IOException {
+		String resourceName = className.replace('.', '/') + ".class";
+		try (InputStream in = ThrowawayClassLoaderTests.class.getClassLoader().getResourceAsStream(resourceName)) {
+			assertThat(in).as("class bytes for %s", className).isNotNull();
+			return in.readAllBytes();
+		}
+	}
+
+
+	static class Probe {
+	}
+
+
+	private static final class TrackingInputStream extends FilterInputStream {
+
+		private final AtomicBoolean closed;
+
+		TrackingInputStream(InputStream in, AtomicBoolean closed) {
+			super(in);
+			this.closed = closed;
+		}
+
+		@Override
+		public void close() throws IOException {
+			this.closed.set(true);
+			super.close();
+		}
+	}
+
+}