DATAGRAPH-1363 - Provide Predicate for retryable exceptions.

The `RetryExceptionPredicate` is is provided to help users checking for retryable exceptions, i.e. for use with Resilience4j.

src/main/java/org/springframework/data/neo4j/core/support/RetryExceptionPredicate.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2011-2020 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.data.neo4j.core.support;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.function.Predicate;
+
+import org.apiguardian.api.API;
+import org.neo4j.driver.exceptions.ServiceUnavailableException;
+import org.neo4j.driver.exceptions.SessionExpiredException;
+import org.neo4j.driver.exceptions.TransientException;
+import org.springframework.dao.TransientDataAccessResourceException;
+
+/**
+ * A predicate indicating {@literal true} for {@link Throwable throwables} that can be safely retried and {@literal false}
+ * in any other case. This predicate can be used for example with Resilience4j.
+ *
+ * @author Michael J. Simons
+ * @soundtrack The Kleptones - 24 Hours
+ * @since 6.0
+ */
+@API(status = API.Status.STABLE, since = "6.0")
+public final class RetryExceptionPredicate implements Predicate<Throwable> {
+
+	private static final Set<String> RETRYABLE_ILLEGAL_STATE_MESSAGES = Collections.unmodifiableSet(new HashSet<>(
+			Arrays.asList("Transaction must be open, but has already been closed.",
+					"Session must be open, but has already been closed.")));
+
+	@Override
+	public boolean test(Throwable throwable) {
+
+		if (throwable instanceof IllegalStateException) {
+			String msg = throwable.getMessage();
+			return RETRYABLE_ILLEGAL_STATE_MESSAGES.contains(msg);
+		}
+
+		Throwable ex = throwable;
+		if (throwable instanceof TransientDataAccessResourceException) {
+			ex = throwable.getCause();
+		}
+
+		if (ex instanceof TransientException) {
+			String code = ((TransientException) ex).code();
+			return !("Neo.TransientError.Transaction.Terminated".equals(code) ||
+					"Neo.TransientError.Transaction.LockClientStopped".equals(code));
+		} else {
+			return ex instanceof SessionExpiredException || ex instanceof ServiceUnavailableException;
+		}
+	}
+}

src/test/java/org/springframework/data/neo4j/core/support/RetryExceptionPredicateTest.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2011-2020 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.data.neo4j.core.support;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.junit.platform.commons.util.ReflectionUtils;
+import org.neo4j.driver.exceptions.ServiceUnavailableException;
+import org.neo4j.driver.exceptions.SessionExpiredException;
+import org.springframework.dao.TransientDataAccessResourceException;
+
+/**
+ * @author Michael J. Simons
+ * @soundtrack Die Toten Hosen - Opium fürs Volk
+ */
+class RetryExceptionPredicateTest {
+
+	@ParameterizedTest
+	@ValueSource(strings = { "Transaction must be open, but has already been closed.",
+			"Session must be open, but has already been closed." })
+	void shouldRetryOnSomeIllegalStateExceptions(String msg) {
+
+		RetryExceptionPredicate predicate = new RetryExceptionPredicate();
+		assertThat(predicate.test(new IllegalStateException(msg))).isTrue();
+	}
+
+	@Test
+	void shouldNotRetryOnRandomIllegalStateExceptions() {
+
+		RetryExceptionPredicate predicate = new RetryExceptionPredicate();
+		assertThat(predicate.test(new IllegalStateException())).isFalse();
+	}
+
+	@ParameterizedTest
+	@ValueSource(classes = { SessionExpiredException.class, ServiceUnavailableException.class })
+	void shouldRetryOnObviousRetryableExceptions(Class<? extends Exception> typeOfException) {
+
+		RetryExceptionPredicate predicate = new RetryExceptionPredicate();
+		assertThat(predicate.test(ReflectionUtils.newInstance(typeOfException, "msg"))).isTrue();
+	}
+
+	@ParameterizedTest
+	@ValueSource(classes = { TransientDataAccessResourceException.class, NullPointerException.class })
+	void shouldNotRetryOnRandomExceptions() {
+
+		RetryExceptionPredicate predicate = new RetryExceptionPredicate();
+		assertThat(predicate.test(new IllegalStateException())).isFalse();
+	}
+
+	@Test
+	void shouldExtractCause() {
+
+		TransientDataAccessResourceException ex = new TransientDataAccessResourceException("msg",
+				new ServiceUnavailableException("msg"));
+
+		RetryExceptionPredicate predicate = new RetryExceptionPredicate();
+		assertThat(predicate.test(ex)).isTrue();
+	}
+}