Introduce a minimal retry functionality as a core framework feature

This commit introduces a minimal core retry feature. It is inspired
by Spring Retry, but redesigned and trimmed to the bare minimum to
cover most cases.

It also adapts the util backoff package with some naming conventions
for consistency with the new core retry feature.

Author: fmbenhassine

framework-docs/modules/ROOT/pages/integration/jms/using.adoc

@@ -234,8 +234,8 @@ with a non-durable subscription with high loads may lead to message loss. Make s
 use a proper cache level in such a case.
 
 This container also has recoverable capabilities when the broker goes down. By default,
-a simple `BackOff` implementation retries every five seconds. You can specify
-a custom `BackOff` implementation for more fine-grained recovery options. See
+a simple `BackOffPolicy` implementation retries every five seconds. You can specify
+a custom `BackOffPolicy` implementation for more fine-grained recovery options. See
 {spring-framework-api}/util/backoff/ExponentialBackOff.html[`ExponentialBackOff`] for an example.
 
 NOTE: Like its sibling (xref:integration/jms/using.adoc#jms-mdp-simple[`SimpleMessageListenerContainer`]),

spring-core/src/main/java/org/springframework/core/retry/RetryCallback.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2002-2025 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.core.retry;
+
+/**
+ * Callback interface for a retryable piece of code. Used in conjunction with {@link RetryOperations}.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 7.0
+ * @param <R> the type of the result
+ * @see RetryOperations
+ */
+public interface RetryCallback<R> {
+
+	/**
+	 * Method to execute and retry if needed.
+	 * @return the result of the callback
+	 * @throws Throwable if an error occurs during the execution of the callback
+	 */
+	R run() throws Throwable;
+
+	/**
+	 * A unique logical name for this callback to distinguish retries around
+	 * business operations.
+	 * @return the name of the callback
+	 */
+	String getName();
+}

spring-core/src/main/java/org/springframework/core/retry/RetryException.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2002-2025 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.core.retry;
+
+import java.io.Serial;
+
+/**
+ * Exception class for exhausted retries.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 7.0
+ * @see RetryOperations
+ */
+public class RetryException extends Exception {
+
+	@Serial
+	private static final long serialVersionUID = 5439915454935047936L;
+
+	/**
+	 * Create a new exception with a message.
+	 * @param message the exception's message
+	 */
+	public RetryException(String message) {
+		super(message);
+	}
+
+	/**
+	 * Create a new exception with a message and a cause.
+	 * @param message the exception's message
+	 * @param cause the exception's cause
+	 */
+	public RetryException(String message, Throwable cause) {
+		super(message, cause);
+	}
+
+}

spring-core/src/main/java/org/springframework/core/retry/RetryExecution.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2002-2025 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.core.retry;
+
+/**
+ * Strategy interface to define a retry execution.
+ *
+ * <p>Implementations do not need to be thread-safe.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 7.0
+ */
+public interface RetryExecution {
+
+	/**
+	 * Specify if the operation should be retried based on the given throwable.
+	 * @param throwable the exception that caused the operation to fail
+	 * @return {@code true} if the operation should be retried, {@code false} otherwise
+	 */
+	boolean shouldRetry(Throwable throwable);
+
+}

spring-core/src/main/java/org/springframework/core/retry/RetryListener.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2002-2025 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.core.retry;
+
+import org.springframework.core.retry.support.listener.CompositeRetryListener;
+
+/**
+ * An extension point that allows to inject code during key retry phases.
+ *
+ * <p>Typically registered in a {@link RetryTemplate}, and can be composed using
+ * a {@link CompositeRetryListener}.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 7.0
+ * @see CompositeRetryListener
+ */
+public interface RetryListener {
+
+	/**
+	 * Called before every retry attempt.
+	 */
+	default void beforeRetry(RetryExecution retryExecution) {
+
+	}
+
+	/**
+	 * Called after the first successful retry attempt.
+	 * @param result the result of the callback
+	 * @param <T> the type of the result
+	 */
+	default <T> void onRetrySuccess(RetryExecution retryExecution, T result) {
+	}
+
+	/**
+	 * Called every time a retry attempt fails.
+	 * @param throwable the throwable thrown by the callback
+	 */
+	default void onRetryFailure(RetryExecution retryExecution, Throwable throwable) {
+	}
+
+	/**
+	 * Called once the retry policy is exhausted.
+	 * @param throwable the last throwable thrown by the callback
+	 */
+	default void onRetryPolicyExhaustion(RetryExecution retryExecution, Throwable throwable) {
+	}
+
+}

spring-core/src/main/java/org/springframework/core/retry/RetryOperations.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2002-2025 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.core.retry;
+
+import org.jspecify.annotations.Nullable;
+
+/**
+ * Main entry point to the core retry functionality. Defines a set of retryable operations.
+ *
+ * <p>Implemented by {@link RetryTemplate}. Not often used directly, but a useful
+ * option to enhance testability, as it can easily be mocked or stubbed.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 7.0
+ * @see RetryTemplate
+ */
+public interface RetryOperations {
+
+	/**
+	 * Retry the given callback (according to the retry policy configured at the implementation level)
+	 * until it succeeds or eventually throw an exception if the retry policy is exhausted.
+	 * @param retryCallback the callback to call initially and retry if needed
+	 * @param <R> the type of the callback's result
+	 * @return the callback's result
+	 * @throws RetryException thrown if the retry policy is exhausted. All attempt exceptions
+	 * should be added as suppressed exceptions to the final exception.
+	 */
+	<R> @Nullable R execute(RetryCallback<R> retryCallback) throws RetryException;
+
+}
+

spring-core/src/main/java/org/springframework/core/retry/RetryPolicy.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2002-2025 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.core.retry;
+
+/**
+ * Strategy interface to define a retry policy.
+ *
+ * @author Mahmoud Ben Hassine
+ * @since 7.0
+ */
+public interface RetryPolicy {
+
+	/**
+	 * Start a new retry execution.
+	 * @return a fresh {@link RetryExecution} ready to be used
+	 */
+	RetryExecution start();
+
+}