Add reactive transaction support SPI

This commit adds SPI interfaces to support reactive transactions
through spring-tx with optional dependencies to Project Reactor and
supportive implementations for TransactionalOperator and
AbstractReactiveTransactionManager.

Author: mp911de

spring-tx/spring-tx.gradle

@@ -1,5 +1,11 @@
 description = "Spring Transaction"
 
+dependencyManagement {
+	imports {
+		mavenBom "io.projectreactor:reactor-bom:${reactorVersion}"
+	}
+}
+
 dependencies {
 	compile(project(":spring-beans"))
 	compile(project(":spring-core"))
@@ -10,8 +16,10 @@ dependencies {
 	optional("javax.resource:javax.resource-api:1.7.1")
 	optional("javax.transaction:javax.transaction-api:1.3")
 	optional("com.ibm.websphere:uow:6.0.2.17")
+	optional("io.projectreactor:reactor-core")
 	optional("io.vavr:vavr:0.10.0")
 	testCompile("org.aspectj:aspectjweaver:${aspectjVersion}")
 	testCompile("org.codehaus.groovy:groovy:${groovyVersion}")
 	testCompile("org.eclipse.persistence:javax.persistence:2.2.0")
+	testCompile("io.projectreactor:reactor-test")
 }

spring-tx/src/main/java/org/springframework/transaction/ReactiveTransactionManager.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2002-2019 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
+ *
+ *      http://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.transaction;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.lang.Nullable;
+
+/**
+ * This is the central interface in Spring's reactive transaction infrastructure.
+ * Applications can use this directly, but it is not primarily meant as API:
+ * Typically, applications will work with either transactional operators or
+ * declarative transaction demarcation through AOP.
+ *
+ * @author Mark Paluch
+ * @since 5.2
+ * @see org.springframework.transaction.interceptor.TransactionProxyFactoryBean
+ */
+public interface ReactiveTransactionManager {
+
+	/**
+	 * Emit a currently active transaction or create a new one, according to
+	 * the specified propagation behavior.
+	 * <p>Note that parameters like isolation level or timeout will only be applied
+	 * to new transactions, and thus be ignored when participating in active ones.
+	 * <p>Furthermore, not all transaction definition settings will be supported
+	 * by every transaction manager: A proper transaction manager implementation
+	 * should throw an exception when unsupported settings are encountered.
+	 * <p>An exception to the above rule is the read-only flag, which should be
+	 * ignored if no explicit read-only mode is supported. Essentially, the
+	 * read-only flag is just a hint for potential optimization.
+	 * @param definition the TransactionDefinition instance (can be empty for defaults),
+	 * describing propagation behavior, isolation level, timeout etc.
+	 * @return transaction status object representing the new or current transaction
+	 * @throws TransactionException in case of lookup, creation, or system errors
+	 * @throws IllegalTransactionStateException if the given transaction definition
+	 * cannot be executed (for example, if a currently active transaction is in
+	 * conflict with the specified propagation behavior)
+	 * @see TransactionDefinition#getPropagationBehavior
+	 * @see TransactionDefinition#getIsolationLevel
+	 * @see TransactionDefinition#getTimeout
+	 * @see TransactionDefinition#isReadOnly
+	 */
+	Mono<ReactiveTransactionStatus> getTransaction(@Nullable TransactionDefinition definition) throws TransactionException;
+
+	/**
+	 * Commit the given transaction, with regard to its status. If the transaction
+	 * has been marked rollback-only programmatically, perform a rollback.
+	 * <p>If the transaction wasn't a new one, omit the commit for proper
+	 * participation in the surrounding transaction. If a previous transaction
+	 * has been suspended to be able to create a new one, resume the previous
+	 * transaction after committing the new one.
+	 * <p>Note that when the commit call completes, no matter if normally or
+	 * throwing an exception, the transaction must be fully completed and
+	 * cleaned up. No rollback call should be expected in such a case.
+	 * <p>If this method throws an exception other than a TransactionException,
+	 * then some before-commit error caused the commit attempt to fail. For
+	 * example, an O/R Mapping tool might have tried to flush changes to the
+	 * database right before commit, with the resulting DataAccessException
+	 * causing the transaction to fail. The original exception will be
+	 * propagated to the caller of this commit method in such a case.
+	 * @param status object returned by the {@code getTransaction} method
+	 * @throws UnexpectedRollbackException in case of an unexpected rollback
+	 * that the transaction coordinator initiated
+	 * @throws HeuristicCompletionException in case of a transaction failure
+	 * caused by a heuristic decision on the side of the transaction coordinator
+	 * @throws TransactionSystemException in case of commit or system errors
+	 * (typically caused by fundamental resource failures)
+	 * @throws IllegalTransactionStateException if the given transaction
+	 * is already completed (that is, committed or rolled back)
+	 * @see ReactiveTransactionStatus#setRollbackOnly
+	 */
+	Mono<Void> commit(ReactiveTransactionStatus status) throws TransactionException;
+
+	/**
+	 * Perform a rollback of the given transaction.
+	 * <p>If the transaction wasn't a new one, just set it rollback-only for proper
+	 * participation in the surrounding transaction. If a previous transaction
+	 * has been suspended to be able to create a new one, resume the previous
+	 * transaction after rolling back the new one.
+	 * <p><b>Do not call rollback on a transaction if commit threw an exception.</b>
+	 * The transaction will already have been completed and cleaned up when commit
+	 * returns, even in case of a commit exception. Consequently, a rollback call
+	 * after commit failure will lead to an IllegalTransactionStateException.
+	 * @param status object returned by the {@code getTransaction} method
+	 * @throws TransactionSystemException in case of rollback or system errors
+	 * (typically caused by fundamental resource failures)
+	 * @throws IllegalTransactionStateException if the given transaction
+	 * is already completed (that is, committed or rolled back)
+	 */
+	Mono<Void> rollback(ReactiveTransactionStatus status) throws TransactionException;
+
+}

spring-tx/src/main/java/org/springframework/transaction/ReactiveTransactionStatus.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2002-2019 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
+ *
+ *      http://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.transaction;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * Representation of the status of a transaction exposing a reactive
+ * interface.
+ *
+ * <p>Transactional code can use this to retrieve status information,
+ * and to programmatically request a rollback (instead of throwing
+ * an exception that causes an implicit rollback).
+ *
+ * @author Mark Paluch
+ * @since 5.2
+ * @see #setRollbackOnly()
+ * @see ReactiveTransactionManager#getTransaction
+ */
+public interface ReactiveTransactionStatus {
+
+	/**
+	 * Return whether the present transaction is new; otherwise participating
+	 * in an existing transaction, or potentially not running in an actual
+	 * transaction in the first place.
+	 */
+	boolean isNewTransaction();
+
+	/**
+	 * Set the transaction rollback-only. This instructs the transaction manager
+	 * that the only possible outcome of the transaction may be a rollback, as
+	 * alternative to throwing an exception which would in turn trigger a rollback.
+	 * <p>This is mainly intended for transactions managed by
+	 * {@link org.springframework.transaction.reactive.support.TransactionalOperator} or
+	 * {@link org.springframework.transaction.interceptor.ReactiveTransactionInterceptor},
+	 * where the actual commit/rollback decision is made by the container.
+	 * @see org.springframework.transaction.reactive.support.ReactiveTransactionCallback#doInTransaction
+	 * @see org.springframework.transaction.interceptor.TransactionAttribute#rollbackOn
+	 */
+	void setRollbackOnly();
+
+	/**
+	 * Return whether the transaction has been marked as rollback-only
+	 * (either by the application or by the transaction infrastructure).
+	 */
+	boolean isRollbackOnly();
+
+	/**
+	 * Flush the underlying session to the datastore, if applicable.
+	 * <p>This is effectively just a hint and may be a no-op if the underlying
+	 * transaction manager does not have a flush concept. A flush signal may
+	 * get applied to the primary resource or to transaction synchronizations,
+	 * depending on the underlying resource.
+	 */
+	Mono<Void> flush();
+
+	/**
+	 * Return whether this transaction is completed, that is,
+	 * whether it has already been committed or rolled back.
+	 * @see ReactiveTransactionManager#commit
+	 * @see ReactiveTransactionManager#rollback
+	 */
+	boolean isCompleted();
+}