Update `LoadedPemSslStore` to use lazy loading

Update `LoadedPemSslStore` so that it loads content lazily. This
restores the behavior of Spring Boot 3.1 and allows bundles to be
defined with files that don't exist as long as they are never accessed.

Fixes gh-38659

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/ssl/PropertiesSslBundle.java

@@ -16,9 +16,6 @@
 
 package org.springframework.boot.autoconfigure.ssl;
 
-import java.io.IOException;
-import java.io.UncheckedIOException;
-
 import org.springframework.boot.autoconfigure.ssl.SslBundleProperties.Key;
 import org.springframework.boot.ssl.SslBundle;
 import org.springframework.boot.ssl.SslBundleKey;
@@ -99,23 +96,17 @@ public final class PropertiesSslBundle implements SslBundle {
 	 * @return an {@link SslBundle} instance
 	 */
 	public static SslBundle get(PemSslBundleProperties properties) {
-		try {
-			PemSslStore keyStore = getPemSslStore("keystore", properties.getKeystore());
-			if (keyStore != null) {
-				keyStore = keyStore.withAlias(properties.getKey().getAlias())
-					.withPassword(properties.getKey().getPassword());
-			}
-			PemSslStore trustStore = getPemSslStore("truststore", properties.getTruststore());
-			SslStoreBundle storeBundle = new PemSslStoreBundle(keyStore, trustStore);
-			return new PropertiesSslBundle(storeBundle, properties);
-		}
-		catch (IOException ex) {
-			throw new UncheckedIOException(ex);
+		PemSslStore keyStore = getPemSslStore("keystore", properties.getKeystore());
+		if (keyStore != null) {
+			keyStore = keyStore.withAlias(properties.getKey().getAlias())
+				.withPassword(properties.getKey().getPassword());
 		}
+		PemSslStore trustStore = getPemSslStore("truststore", properties.getTruststore());
+		SslStoreBundle storeBundle = new PemSslStoreBundle(keyStore, trustStore);
+		return new PropertiesSslBundle(storeBundle, properties);
 	}
 
-	private static PemSslStore getPemSslStore(String propertyName, PemSslBundleProperties.Store properties)
-			throws IOException {
+	private static PemSslStore getPemSslStore(String propertyName, PemSslBundleProperties.Store properties) {
 		PemSslStore pemSslStore = PemSslStore.load(asPemSslStoreDetails(properties));
 		if (properties.isVerifyKeys()) {
 			CertificateMatcher certificateMatcher = new CertificateMatcher(pemSslStore.privateKey());

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/ssl/pem/LoadedPemSslStore.java

@@ -17,12 +17,16 @@
 package org.springframework.boot.ssl.pem;
 
 import java.io.IOException;
+import java.io.UncheckedIOException;
 import java.security.PrivateKey;
 import java.security.cert.X509Certificate;
 import java.util.List;
+import java.util.function.Supplier;
 
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
+import org.springframework.util.function.SingletonSupplier;
+import org.springframework.util.function.ThrowingSupplier;
 
 /**
  * {@link PemSslStore} loaded from {@link PemSslStoreDetails}.
@@ -34,15 +38,23 @@ final class LoadedPemSslStore implements PemSslStore {
 
 	private final PemSslStoreDetails details;
 
-	private final List<X509Certificate> certificates;
+	private final Supplier<List<X509Certificate>> certificatesSupplier;
 
-	private final PrivateKey privateKey;
+	private final Supplier<PrivateKey> privateKeySupplier;
 
-	LoadedPemSslStore(PemSslStoreDetails details) throws IOException {
+	LoadedPemSslStore(PemSslStoreDetails details) {
 		Assert.notNull(details, "Details must not be null");
 		this.details = details;
-		this.certificates = loadCertificates(details);
-		this.privateKey = loadPrivateKey(details);
+		this.certificatesSupplier = supplier(() -> loadCertificates(details));
+		this.privateKeySupplier = supplier(() -> loadPrivateKey(details));
+	}
+
+	private static <T> Supplier<T> supplier(ThrowingSupplier<T> supplier) {
+		return SingletonSupplier.of(supplier.throwing(LoadedPemSslStore::asUncheckedIOException));
+	}
+
+	private static UncheckedIOException asUncheckedIOException(String message, Exception cause) {
+		return new UncheckedIOException(message, (IOException) cause);
 	}
 
 	private static List<X509Certificate> loadCertificates(PemSslStoreDetails details) throws IOException {
@@ -77,12 +89,12 @@ final class LoadedPemSslStore implements PemSslStore {
 
 	@Override
 	public List<X509Certificate> certificates() {
-		return this.certificates;
+		return this.certificatesSupplier.get();
 	}
 
 	@Override
 	public PrivateKey privateKey() {
-		return this.privateKey;
+		return this.privateKeySupplier.get();
 	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/ssl/pem/PemSslStore.java

@@ -16,7 +16,6 @@
 
 package org.springframework.boot.ssl.pem;
 
-import java.io.IOException;
 import java.security.KeyStore;
 import java.security.PrivateKey;
 import java.security.cert.X509Certificate;
@@ -92,9 +91,8 @@ public interface PemSslStore {
 	 * {@link PemSslStoreDetails}.
 	 * @param details the PEM store details
 	 * @return a loaded {@link PemSslStore} or {@code null}.
-	 * @throws IOException on IO error
 	 */
-	static PemSslStore load(PemSslStoreDetails details) throws IOException {
+	static PemSslStore load(PemSslStoreDetails details) {
 		if (details == null || details.isEmpty()) {
 			return null;
 		}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/ssl/pem/PemSslStoreBundle.java

@@ -17,7 +17,6 @@
 package org.springframework.boot.ssl.pem;
 
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.security.KeyStore;
 import java.security.KeyStoreException;
 import java.security.NoSuchAlgorithmException;
@@ -66,13 +65,8 @@ public class PemSslStoreBundle implements SslStoreBundle {
 	 */
 	@Deprecated(since = "3.2.0", forRemoval = true)
 	public PemSslStoreBundle(PemSslStoreDetails keyStoreDetails, PemSslStoreDetails trustStoreDetails, String alias) {
-		try {
-			this.keyStore = createKeyStore("key", PemSslStore.load(keyStoreDetails), alias);
-			this.trustStore = createKeyStore("trust", PemSslStore.load(trustStoreDetails), alias);
-		}
-		catch (IOException ex) {
-			throw new UncheckedIOException(ex);
-		}
+		this.keyStore = createKeyStore("key", PemSslStore.load(keyStoreDetails), alias);
+		this.trustStore = createKeyStore("trust", PemSslStore.load(trustStoreDetails), alias);
 	}
 
 	/**

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/ssl/pem/LoadedPemSslStoreTests.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2012-2023 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.boot.ssl.pem;
+
+import java.io.UncheckedIOException;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+/**
+ * Tests for {@link LoadedPemSslStore}.
+ *
+ * @author Phillip Webb
+ */
+class LoadedPemSslStoreTests {
+
+	@Test
+	void certificatesAreLoadedLazily() {
+		PemSslStoreDetails details = PemSslStoreDetails.forCertificate("classpath:missing-test-cert.pem")
+			.withPrivateKey("classpath:test-key.pem");
+		LoadedPemSslStore store = new LoadedPemSslStore(details);
+		assertThatExceptionOfType(UncheckedIOException.class).isThrownBy(store::certificates);
+	}
+
+	@Test
+	void privateKeyIsLoadedLazily() {
+		PemSslStoreDetails details = PemSslStoreDetails.forCertificate("classpath:test-cert.pem")
+			.withPrivateKey("classpath:missing-test-key.pem");
+		LoadedPemSslStore store = new LoadedPemSslStore(details);
+		assertThatExceptionOfType(UncheckedIOException.class).isThrownBy(store::privateKey);
+	}
+
+}