#98 - Add support for AbstractRoutingConnectionFactory.

We now provide an abstract base class for ConnectionFactory routing. Routing keys are typically obtained from a subscriber context. AbstractRoutingConnectionFactory is backed by either a map of string identifiers or connection factories. When using string identifiers, these can map agains e.g. Spring bean names that can be resolved using BeanFactoryConnectionFactoryLookup.

class MyRoutingConnectionFactory extends AbstractRoutingConnectionFactory {

		@OverRide
		protected Mono<Object> determineCurrentLookupKey() {
			return Mono.subscriberContext().filter(it -> it.hasKey(ROUTING_KEY)).map(it -> it.get(ROUTING_KEY));
		}
}

@bean
public void routingConnectionFactory() {

		MyRoutingConnectionFactory router = new MyRoutingConnectionFactory();

		Map<String, ConnectionFactory> factories = new HashMap<>();
		ConnectionFactory myDefault = …;
		ConnectionFactory primary = …;
		ConnectionFactory secondary = …;

		factories.put("primary", primary);
		factories.put("secondary", secondary);

		router.setTargetConnectionFactories(factories);
		router.setDefaultTargetConnectionFactory(myDefault);

		return router;
}

Original pull request: #132.

src/main/java/org/springframework/data/r2dbc/connectionfactory/lookup/AbstractRoutingConnectionFactory.java

@@ -0,0 +1,244 @@
+/*
+ * Copyright 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
+ *
+ *      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.r2dbc.connectionfactory.lookup;
+
+import io.r2dbc.spi.Connection;
+import io.r2dbc.spi.ConnectionFactory;
+import io.r2dbc.spi.ConnectionFactoryMetadata;
+import reactor.core.publisher.Mono;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * Abstract {@link ConnectionFactory} implementation that routes {@link #create()} calls to one of various target
+ * {@link ConnectionFactory factories} based on a lookup key. The latter is typically (but not necessarily) determined
+ * from some subscriber context.
+ * <p>
+ * Allows to configure a {@link #setDefaultTargetConnectionFactory(Object) default ConnectionFactory} as fallback.
+ * <p>
+ * Calls to {@link #getMetadata()} are routed to the {@link #setDefaultTargetConnectionFactory(Object) default
+ * ConnectionFactory} if configured.
+ *
+ * @author Mark Paluch
+ * @see #setTargetConnectionFactories
+ * @see #setDefaultTargetConnectionFactory
+ * @see #determineCurrentLookupKey()
+ */
+public abstract class AbstractRoutingConnectionFactory implements ConnectionFactory, InitializingBean {
+
+	private static final Object FALLBACK_MARKER = new Object();
+
+	private @Nullable Map<Object, Object> targetConnectionFactories;
+
+	private @Nullable Object defaultTargetConnectionFactory;
+
+	private boolean lenientFallback = true;
+
+	private ConnectionFactoryLookup connectionFactoryLookup = new MapConnectionFactoryLookup();
+
+	private @Nullable Map<Object, ConnectionFactory> resolvedConnectionFactories;
+
+	private @Nullable ConnectionFactory resolvedDefaultConnectionFactory;
+
+	/**
+	 * Specify the map of target {@link ConnectionFactory ConnectionFactories}, with the lookup key as key. The mapped
+	 * value can either be a corresponding {@link ConnectionFactory} instance or a connection factory name String (to be
+	 * resolved via a {@link #setConnectionFactoryLookup ConnectionFactoryLookup}).
+	 * <p>
+	 * The key can be of arbitrary type; this class implements the generic lookup process only. The concrete key
+	 * representation will be handled by {@link #resolveSpecifiedLookupKey(Object)} and
+	 * {@link #determineCurrentLookupKey()}.
+	 */
+	@SuppressWarnings("unchecked")
+	public void setTargetConnectionFactories(Map<?, ?> targetConnectionFactories) {
+		this.targetConnectionFactories = (Map) targetConnectionFactories;
+	}
+
+	/**
+	 * Specify the default target {@link ConnectionFactory}, if any.
+	 * <p>
+	 * The mapped value can either be a corresponding {@link ConnectionFactory} instance or a connection factory name
+	 * {@link String} (to be resolved via a {@link #setConnectionFactoryLookup ConnectionFactoryLookup}).
+	 * <p>
+	 * This {@link ConnectionFactory} will be used as target if none of the keyed {@link #setTargetConnectionFactories
+	 * targetConnectionFactories} match the {@link #determineCurrentLookupKey()} current lookup key.
+	 */
+	public void setDefaultTargetConnectionFactory(Object defaultTargetConnectionFactory) {
+		this.defaultTargetConnectionFactory = defaultTargetConnectionFactory;
+	}
+
+	/**
+	 * Specify whether to apply a lenient fallback to the default {@link ConnectionFactory} if no specific
+	 * {@link ConnectionFactory} could be found for the current lookup key.
+	 * <p>
+	 * Default is {@literal true}, accepting lookup keys without a corresponding entry in the target
+	 * {@link ConnectionFactory} map - simply falling back to the default {@link ConnectionFactory} in that case.
+	 * <p>
+	 * Switch this flag to {@literal false} if you would prefer the fallback to only apply no lookup key was emitted.
+	 * Lookup keys without a {@link ConnectionFactory} entry will then lead to an {@link IllegalStateException}.
+	 *
+	 * @see #setTargetConnectionFactories
+	 * @see #setDefaultTargetConnectionFactory
+	 * @see #determineCurrentLookupKey()
+	 */
+	public void setLenientFallback(boolean lenientFallback) {
+		this.lenientFallback = lenientFallback;
+	}
+
+	/**
+	 * Set the {@link ConnectionFactoryLookup} implementation to use for resolving connection factory name Strings in the
+	 * {@link #setTargetConnectionFactories targetConnectionFactories} map.
+	 */
+	public void setConnectionFactoryLookup(ConnectionFactoryLookup connectionFactoryLookup) {
+
+		Assert.notNull(connectionFactoryLookup, "ConnectionFactoryLookup must not be null!");
+
+		this.connectionFactoryLookup = connectionFactoryLookup;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()
+	 */
+	@Override
+	public void afterPropertiesSet() {
+
+		Assert.notNull(this.targetConnectionFactories, "Property 'targetConnectionFactories' must not be null!");
+
+		this.resolvedConnectionFactories = new HashMap<>(this.targetConnectionFactories.size());
+		this.targetConnectionFactories.forEach((key, value) -> {
+			Object lookupKey = resolveSpecifiedLookupKey(key);
+			ConnectionFactory connectionFactory = resolveSpecifiedConnectionFactory(value);
+			this.resolvedConnectionFactories.put(lookupKey, connectionFactory);
+		});
+
+		if (this.defaultTargetConnectionFactory != null) {
+			this.resolvedDefaultConnectionFactory = resolveSpecifiedConnectionFactory(this.defaultTargetConnectionFactory);
+		}
+	}
+
+	/**
+	 * Resolve the given lookup key object, as specified in the {@link #setTargetConnectionFactories
+	 * targetConnectionFactories} map, into the actual lookup key to be used for matching with the
+	 * {@link #determineCurrentLookupKey() current lookup key}.
+	 * <p>
+	 * The default implementation simply returns the given key as-is.
+	 *
+	 * @param lookupKey the lookup key object as specified by the user.
+	 * @return the lookup key as needed for matching.
+	 */
+	protected Object resolveSpecifiedLookupKey(Object lookupKey) {
+		return lookupKey;
+	}
+
+	/**
+	 * Resolve the specified connection factory object into a {@link ConnectionFactory} instance.
+	 * <p>
+	 * The default implementation handles {@link ConnectionFactory} instances and connection factory names (to be resolved
+	 * via a {@link #setConnectionFactoryLookup ConnectionFactoryLookup}).
+	 *
+	 * @param connectionFactory the connection factory value object as specified in the
+	 *          {@link #setTargetConnectionFactories targetConnectionFactories} map.
+	 * @return the resolved {@link ConnectionFactory} (never {@literal null}).
+	 * @throws IllegalArgumentException in case of an unsupported value type.
+	 */
+	protected ConnectionFactory resolveSpecifiedConnectionFactory(Object connectionFactory)
+			throws IllegalArgumentException {
+
+		if (connectionFactory instanceof ConnectionFactory) {
+			return (ConnectionFactory) connectionFactory;
+		} else if (connectionFactory instanceof String) {
+			return this.connectionFactoryLookup.getConnectionFactory((String) connectionFactory);
+		} else {
+			throw new IllegalArgumentException(
+					"Illegal connection factory value - only 'io.r2dbc.spi.ConnectionFactory' and 'String' supported: "
+							+ connectionFactory);
+		}
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see io.r2dbc.spi.ConnectionFactory#create()
+	 */
+	@Override
+	public Mono<Connection> create() {
+
+		return determineTargetConnectionFactory() //
+				.map(ConnectionFactory::create) //
+				.flatMap(Mono::from);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see io.r2dbc.spi.ConnectionFactory#getMetadata()
+	 */
+	@Override
+	public ConnectionFactoryMetadata getMetadata() {
+
+		if (this.resolvedDefaultConnectionFactory != null) {
+			return this.resolvedDefaultConnectionFactory.getMetadata();
+		}
+
+		throw new UnsupportedOperationException(
+				"No default ConnectionFactory configured to retrieve ConnectionFactoryMetadata");
+	}
+
+	/**
+	 * Retrieve the current target {@link ConnectionFactory}. Determines the {@link #determineCurrentLookupKey() current
+	 * lookup key}, performs a lookup in the {@link #setTargetConnectionFactories targetConnectionFactories} map, falls
+	 * back to the specified {@link #setDefaultTargetConnectionFactory default target ConnectionFactory} if necessary.
+	 *
+	 * @see #determineCurrentLookupKey()
+	 * @return {@link Mono} emitting the current {@link ConnectionFactory} as per {@link #determineCurrentLookupKey()}.
+	 */
+	protected Mono<ConnectionFactory> determineTargetConnectionFactory() {
+
+		Assert.state(this.resolvedConnectionFactories != null, "ConnectionFactory router not initialized");
+
+		Mono<Object> lookupKey = determineCurrentLookupKey().defaultIfEmpty(FALLBACK_MARKER);
+
+		return lookupKey.handle((key, sink) -> {
+
+			ConnectionFactory connectionFactory = this.resolvedConnectionFactories.get(key);
+
+			if (connectionFactory == null && (key == FALLBACK_MARKER || this.lenientFallback)) {
+				connectionFactory = this.resolvedDefaultConnectionFactory;
+			}
+
+			if (connectionFactory == null) {
+				sink.error(new IllegalStateException(String.format(
+						"Cannot determine target ConnectionFactory for lookup key '%s'", key == FALLBACK_MARKER ? null : key)));
+				return;
+			}
+
+			sink.next(connectionFactory);
+		});
+	}
+
+	/**
+	 * Determine the current lookup key. This will typically be implemented to check a subscriber context. Allows for
+	 * arbitrary keys. The returned key needs to match the stored lookup key type, as resolved by the
+	 * {@link #resolveSpecifiedLookupKey} method.
+	 *
+	 * @return {@link Mono} emitting the lookup key. May complete without emitting a value if no lookup key available.
+	 */
+	protected abstract Mono<Object> determineCurrentLookupKey();
+}

src/main/java/org/springframework/data/r2dbc/connectionfactory/lookup/BeanFactoryConnectionFactoryLookup.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 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
+ *
+ *      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.r2dbc.connectionfactory.lookup;
+
+import io.r2dbc.spi.ConnectionFactory;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * {@link ConnectionFactoryLookup} implementation based on a Spring {@link BeanFactory}.
+ * <p>
+ * Will lookup Spring managed beans identified by bean name, expecting them to be of type {@link ConnectionFactory}.
+ *
+ * @author Mark Paluch
+ * @see BeanFactory
+ */
+public class BeanFactoryConnectionFactoryLookup implements ConnectionFactoryLookup, BeanFactoryAware {
+
+	@Nullable private BeanFactory beanFactory;
+
+	/**
+	 * Creates a new {@link BeanFactoryConnectionFactoryLookup} instance.
+	 * <p>
+	 * The {@link BeanFactory} to access must be set via {@code setBeanFactory}.
+	 *
+	 * @see #setBeanFactory
+	 */
+	public BeanFactoryConnectionFactoryLookup() {}
+
+	/**
+	 * Create a new instance of the {@link BeanFactoryConnectionFactoryLookup} class.
+	 * <p>
+	 * Use of this constructor is redundant if this object is being created by a Spring IoC container, as the supplied
+	 * {@link BeanFactory} will be replaced by the {@link BeanFactory} that creates it (see the {@link BeanFactoryAware}
+	 * contract). So only use this constructor if you are using this class outside the context of a Spring IoC container.
+	 *
+	 * @param beanFactory the bean factory to be used to lookup {@link ConnectionFactory ConnectionFactories}.
+	 */
+	public BeanFactoryConnectionFactoryLookup(BeanFactory beanFactory) {
+
+		Assert.notNull(beanFactory, "BeanFactory must not be null!");
+
+		this.beanFactory = beanFactory;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.beans.factory.BeanFactoryAware#setBeanFactory(org.springframework.beans.factory.BeanFactory)
+	 */
+	@Override
+	public void setBeanFactory(BeanFactory beanFactory) {
+		this.beanFactory = beanFactory;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.r2dbc.connectionfactory.lookup.ConnectionFactoryLookup#getConnectionFactory(java.lang.String)
+	 */
+	@Override
+	public ConnectionFactory getConnectionFactory(String connectionFactoryName)
+			throws ConnectionFactoryLookupFailureException {
+
+		Assert.state(this.beanFactory != null, "BeanFactory must not be null!");
+
+		try {
+			return this.beanFactory.getBean(connectionFactoryName, ConnectionFactory.class);
+		} catch (BeansException ex) {
+			throw new ConnectionFactoryLookupFailureException(
+					String.format("Failed to look up ConnectionFactory bean with name '%s'", connectionFactoryName), ex);
+		}
+	}
+
+}

src/main/java/org/springframework/data/r2dbc/connectionfactory/lookup/ConnectionFactoryLookup.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 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
+ *
+ *      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.r2dbc.connectionfactory.lookup;
+
+import io.r2dbc.spi.ConnectionFactory;
+
+/**
+ * Strategy interface for looking up {@link ConnectionFactory} by name.
+ *
+ * @author Mark Paluch
+ */
+@FunctionalInterface
+public interface ConnectionFactoryLookup {
+
+	/**
+	 * Retrieve the {@link ConnectionFactory} identified by the given name.
+	 *
+	 * @param connectionFactoryName the name of the {@link ConnectionFactory}.
+	 * @return the {@link ConnectionFactory} (never {@literal null}).
+	 * @throws ConnectionFactoryLookupFailureException if the lookup failed.
+	 */
+	ConnectionFactory getConnectionFactory(String connectionFactoryName) throws ConnectionFactoryLookupFailureException;
+}