GH-441: Introduce PredicateRetryPolicy

Fixes: #441

* Replace `Classifier` with more widely used `Predicate` in `RetryTemplateBuilder`
* Introduce `PredicateRetryPolicy` to avoid backward incompatible changes

src/main/java/org/springframework/retry/policy/PredicateRetryPolicy.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2024-2024 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.retry.policy;
+
+import java.util.function.Predicate;
+
+import org.springframework.retry.RetryContext;
+import org.springframework.retry.RetryPolicy;
+import org.springframework.retry.context.RetryContextSupport;
+import org.springframework.util.Assert;
+
+/**
+ * A policy, that is based on {@link Predicate<Throwable>}. Usually, binary classification
+ * is enough for retry purposes. If you need more flexible classification, use
+ * {@link ExceptionClassifierRetryPolicy}.
+ *
+ * @author Morulai Planinski
+ * @since 2.0.7
+ */
+public class PredicateRetryPolicy implements RetryPolicy {
+
+	private final Predicate<Throwable> predicate;
+
+	public PredicateRetryPolicy(Predicate<Throwable> predicate) {
+		Assert.notNull(predicate, "'predicate' must not be null");
+		this.predicate = predicate;
+	}
+
+	@Override
+	public boolean canRetry(RetryContext context) {
+		Throwable t = context.getLastThrowable();
+		return t == null || predicate.test(t);
+	}
+
+	@Override
+	public void close(RetryContext status) {
+	}
+
+	@Override
+	public void registerThrowable(RetryContext context, Throwable throwable) {
+		((RetryContextSupport) context).registerThrowable(throwable);
+	}
+
+	@Override
+	public RetryContext open(RetryContext parent) {
+		return new RetryContextSupport(parent);
+	}
+
+}

src/main/java/org/springframework/retry/support/RetryTemplateBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2023 the original author or authors.
+ * Copyright 2006-2024 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.
@@ -13,11 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.retry.support;
 
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Predicate;
 
 import org.springframework.classify.BinaryExceptionClassifier;
 import org.springframework.classify.BinaryExceptionClassifierBuilder;
@@ -33,6 +35,7 @@ import org.springframework.retry.policy.AlwaysRetryPolicy;
 import org.springframework.retry.policy.BinaryExceptionClassifierRetryPolicy;
 import org.springframework.retry.policy.CompositeRetryPolicy;
 import org.springframework.retry.policy.MaxAttemptsRetryPolicy;
+import org.springframework.retry.policy.PredicateRetryPolicy;
 import org.springframework.retry.policy.TimeoutRetryPolicy;
 import org.springframework.util.Assert;
 
@@ -75,6 +78,7 @@ import org.springframework.util.Assert;
  * @author Artem Bilan
  * @author Kim In Hoi
  * @author Andreas Ahlenstorf
+ * @author Morulai Planinski
  * @since 1.3
  */
 public class RetryTemplateBuilder {
@@ -87,6 +91,8 @@ public class RetryTemplateBuilder {
 
 	private BinaryExceptionClassifierBuilder classifierBuilder;
 
+	private Predicate<Throwable> retryOnPredicate;
+
 	/* ---------------- Configure retry policy -------------- */
 
 	/**
@@ -462,6 +468,27 @@ public class RetryTemplateBuilder {
 		return this;
 	}
 
+	/**
+	 * Set a {@link Predicate<Throwable>} that decides if the exception causes a retry.
+	 * <p>
+	 * {@code retryOn(Predicate<Throwable>)} cannot be mixed with other {@code retryOn()}
+	 * or {@code noRetryOn()}. Attempting to do so will result in a
+	 * {@link IllegalArgumentException}.
+	 * @param predicate if the exception causes a retry.
+	 * @return this
+	 * @throws IllegalArgumentException if {@link #retryOn} or {@link #notRetryOn} has
+	 * already been used.
+	 * @since 2.0.7
+	 * @see BinaryExceptionClassifierRetryPolicy
+	 */
+	public RetryTemplateBuilder retryOn(Predicate<Throwable> predicate) {
+		Assert.isTrue(this.classifierBuilder == null && this.retryOnPredicate == null,
+				"retryOn(Predicate<Throwable>) cannot be mixed with other retryOn() or noRetryOn()");
+		Assert.notNull(predicate, "Predicate can not be null");
+		this.retryOnPredicate = predicate;
+		return this;
+	}
+
 	/**
 	 * Enable examining exception causes for {@link Throwable} instances that cause a
 	 * retry.
@@ -537,20 +564,24 @@ public class RetryTemplateBuilder {
 	public RetryTemplate build() {
 		RetryTemplate retryTemplate = new RetryTemplate();
 
-		// Exception classifier
-
-		BinaryExceptionClassifier exceptionClassifier = this.classifierBuilder != null ? this.classifierBuilder.build()
-				: BinaryExceptionClassifier.defaultClassifier();
-
 		// Retry policy
 
 		if (this.baseRetryPolicy == null) {
 			this.baseRetryPolicy = new MaxAttemptsRetryPolicy();
 		}
 
+		RetryPolicy exceptionRetryPolicy;
+		if (this.retryOnPredicate == null) {
+			BinaryExceptionClassifier exceptionClassifier = this.classifierBuilder != null
+					? this.classifierBuilder.build() : BinaryExceptionClassifier.defaultClassifier();
+			exceptionRetryPolicy = new BinaryExceptionClassifierRetryPolicy(exceptionClassifier);
+		}
+		else {
+			exceptionRetryPolicy = new PredicateRetryPolicy(this.retryOnPredicate);
+		}
+
 		CompositeRetryPolicy finalPolicy = new CompositeRetryPolicy();
-		finalPolicy.setPolicies(new RetryPolicy[] { this.baseRetryPolicy,
-				new BinaryExceptionClassifierRetryPolicy(exceptionClassifier) });
+		finalPolicy.setPolicies(new RetryPolicy[] { this.baseRetryPolicy, exceptionRetryPolicy });
 		retryTemplate.setRetryPolicy(finalPolicy);
 
 		// Backoff policy

src/test/java/org/springframework/retry/support/RetryTemplateBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2023 the original author or authors.
+ * Copyright 2006-2024 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.
@@ -22,9 +22,9 @@ import java.time.Duration;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.function.Predicate;
 
 import org.junit.jupiter.api.Test;
-
 import org.springframework.classify.BinaryExceptionClassifier;
 import org.springframework.retry.RetryListener;
 import org.springframework.retry.RetryPolicy;
@@ -38,6 +38,7 @@ import org.springframework.retry.policy.BinaryExceptionClassifierRetryPolicy;
 import org.springframework.retry.policy.CompositeRetryPolicy;
 import org.springframework.retry.policy.MapRetryContextCache;
 import org.springframework.retry.policy.MaxAttemptsRetryPolicy;
+import org.springframework.retry.policy.PredicateRetryPolicy;
 import org.springframework.retry.policy.TimeoutRetryPolicy;
 import org.springframework.retry.util.test.TestUtils;
 
@@ -56,6 +57,7 @@ import static org.springframework.retry.util.test.TestUtils.getPropertyValue;
  * @author Kim In Hoi
  * @author Gary Russell
  * @author Andreas Ahlenstorf
+ * @author Morulai Planinski
  */
 public class RetryTemplateBuilderTests {
 
@@ -93,8 +95,9 @@ public class RetryTemplateBuilderTests {
 			.build();
 
 		PolicyTuple policyTuple = PolicyTuple.extractWithAsserts(template);
-
-		BinaryExceptionClassifier classifier = policyTuple.exceptionClassifierRetryPolicy.getExceptionClassifier();
+		assertThat(policyTuple.exceptionClassifierRetryPolicy).isInstanceOf(BinaryExceptionClassifierRetryPolicy.class);
+		BinaryExceptionClassifierRetryPolicy retryPolicy = (BinaryExceptionClassifierRetryPolicy) policyTuple.exceptionClassifierRetryPolicy;
+		BinaryExceptionClassifier classifier = retryPolicy.getExceptionClassifier();
 		assertThat(classifier.classify(new FileNotFoundException())).isTrue();
 		assertThat(classifier.classify(new IllegalArgumentException())).isTrue();
 		assertThat(classifier.classify(new RuntimeException())).isFalse();
@@ -176,7 +179,9 @@ public class RetryTemplateBuilderTests {
 	}
 
 	private void assertDefaultClassifier(PolicyTuple policyTuple) {
-		BinaryExceptionClassifier classifier = policyTuple.exceptionClassifierRetryPolicy.getExceptionClassifier();
+		assertThat(policyTuple.exceptionClassifierRetryPolicy).isInstanceOf(BinaryExceptionClassifierRetryPolicy.class);
+		BinaryExceptionClassifierRetryPolicy retryPolicy = (BinaryExceptionClassifierRetryPolicy) policyTuple.exceptionClassifierRetryPolicy;
+		BinaryExceptionClassifier classifier = retryPolicy.getExceptionClassifier();
 		assertThat(classifier.classify(new Exception())).isTrue();
 		assertThat(classifier.classify(new Exception(new Error()))).isTrue();
 		assertThat(classifier.classify(new Error())).isFalse();
@@ -203,6 +208,28 @@ public class RetryTemplateBuilderTests {
 			.notRetryOn(Collections.<Class<? extends Throwable>>singletonList(OutOfMemoryError.class)));
 	}
 
+	@Test
+	public void testFailOnPredicateWithOtherMix() {
+		assertThatIllegalArgumentException().isThrownBy(() -> RetryTemplate.builder()
+			.retryOn(Collections.<Class<? extends Throwable>>singletonList(IOException.class))
+			.retryOn(classifiable -> true));
+	}
+
+	@Test
+	public void testRetryOnPredicate() {
+		Predicate<Throwable> predicate = classifiable -> classifiable instanceof IllegalAccessError;
+		RetryTemplate template = RetryTemplate.builder().maxAttempts(10).retryOn(predicate).build();
+
+		PolicyTuple policyTuple = PolicyTuple.extractWithAsserts(template);
+		assertThat(policyTuple.exceptionClassifierRetryPolicy).isInstanceOf(PredicateRetryPolicy.class);
+		RetryPolicy retryPolicy = policyTuple.exceptionClassifierRetryPolicy;
+		assertThat(retryPolicy).isInstanceOf(PredicateRetryPolicy.class);
+		assertThat(policyTuple.baseRetryPolicy).isInstanceOf(MaxAttemptsRetryPolicy.class);
+		assertThat(policyTuple.baseRetryPolicy.getMaxAttempts()).isEqualTo(10);
+		assertThat(getPropertyValue(template, "listeners", RetryListener[].class)).isEmpty();
+		assertThat(getPropertyValue(template, "backOffPolicy")).isInstanceOf(NoBackOffPolicy.class);
+	}
+
 	/* ---------------- BackOff -------------- */
 
 	@Test
@@ -325,7 +352,7 @@ public class RetryTemplateBuilderTests {
 
 		RetryPolicy baseRetryPolicy;
 
-		BinaryExceptionClassifierRetryPolicy exceptionClassifierRetryPolicy;
+		RetryPolicy exceptionClassifierRetryPolicy;
 
 		static PolicyTuple extractWithAsserts(RetryTemplate template) {
 			CompositeRetryPolicy compositeRetryPolicy = getPropertyValue(template, "retryPolicy",
@@ -335,8 +362,8 @@ public class RetryTemplateBuilderTests {
 			assertThat(getPropertyValue(compositeRetryPolicy, "optimistic", Boolean.class)).isFalse();
 
 			for (final RetryPolicy policy : getPropertyValue(compositeRetryPolicy, "policies", RetryPolicy[].class)) {
-				if (policy instanceof BinaryExceptionClassifierRetryPolicy) {
-					res.exceptionClassifierRetryPolicy = (BinaryExceptionClassifierRetryPolicy) policy;
+				if (policy instanceof BinaryExceptionClassifierRetryPolicy || policy instanceof PredicateRetryPolicy) {
+					res.exceptionClassifierRetryPolicy = policy;
 				}
 				else {
 					res.baseRetryPolicy = policy;

src/test/java/org/springframework/retry/support/RetryTemplateTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2023 the original author or authors.
+ * Copyright 2006-2024 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.
@@ -52,6 +52,7 @@ import static org.mockito.Mockito.verify;
  * @author Gary Russell
  * @author Henning Pöttker
  * @author Emanuele Ivaldi
+ * @author Morulai Planinski
  */
 public class RetryTemplateTests {
 
@@ -92,6 +93,38 @@ public class RetryTemplateTests {
 		}
 	}
 
+	@Test
+	public void testRetryOnPredicateWithRetry() throws Throwable {
+		for (int x = 1; x <= 10; x++) {
+			MockRetryCallback callback = new MockRetryCallback();
+			callback.setAttemptsBeforeSuccess(x);
+			callback.setExceptionToThrow(new IllegalStateException("retry"));
+			RetryTemplate retryTemplate = RetryTemplate.builder()
+				.maxAttempts(x)
+				.retryOn(classifiable -> classifiable instanceof IllegalStateException
+						&& classifiable.getMessage().equals("retry"))
+				.build();
+
+			retryTemplate.execute(callback);
+			assertThat(callback.attempts).isEqualTo(x);
+		}
+	}
+
+	@Test
+	public void testRetryOnPredicateWithoutRetry() throws Throwable {
+		MockRetryCallback callback = new MockRetryCallback();
+		callback.setAttemptsBeforeSuccess(0);
+		callback.setExceptionToThrow(new IllegalStateException("no retry"));
+		RetryTemplate retryTemplate = RetryTemplate.builder()
+			.maxAttempts(3)
+			.retryOn(classifiable -> classifiable instanceof IllegalStateException
+					&& classifiable.getMessage().equals("retry"))
+			.build();
+
+		retryTemplate.execute(callback);
+		assertThat(callback.attempts).isEqualTo(1);
+	}
+
 	@Test
 	public void testSuccessfulRecovery() throws Throwable {
 		MockRetryCallback callback = new MockRetryCallback();