INT-2285 Implement max-subscribers on Channels

Add a subscriber limit on both unicast and publish-subscribe
channels. This permits detection of inadvertent channel wiring
during context initialization.

Also add a mechanism to globally set these defaults.

Two properties are added to ChannelInitializer. If the
'channelInitializer' bean is declared before a channel, and
these properties are set, it will globally override the
default (Integer.MAX_VALUE) for these properties.

For example:

    <bean id="channelInitializer" class="org.springframework.integration.config.xml.ChannelInitializer">
        <property name="autoCreate" value="true" />
        <property name="defaultMaxUnicastSubscribers" value="1" />
        <property name="defaultMaxMulticastSubscribers" value="2" />
    </bean>

will make the default max-subscribers 1 and 2 for <channel/> and
<publish-subscribe/> channels respectively.

Also applies to module channels (jms, amqp, redis).

spring-integration-core/src/main/java/org/springframework/integration/channel/AbstractSubscribableChannel.java

@@ -32,15 +32,15 @@ import org.springframework.util.StringUtils;
 /**
  * Base implementation of {@link MessageChannel} that invokes the subscribed
  * {@link MessageHandler handler(s)} by delegating to a {@link MessageDispatcher}.
- * 
+ *
  * @author Mark Fisher
  * @author Oleg Zhurakousky
  * @author Gary Russell
  */
 public abstract class AbstractSubscribableChannel extends AbstractMessageChannel implements SubscribableChannel {
-	
+
 	private final AtomicInteger handlerCounter = new AtomicInteger();
-	
+
 	public boolean subscribe(MessageHandler handler) {
 		MessageDispatcher dispatcher = this.getRequiredDispatcher();
 		boolean added = dispatcher.addHandler(handler);

spring-integration-core/src/main/java/org/springframework/integration/channel/DirectChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -23,11 +23,12 @@ import org.springframework.integration.dispatcher.UnicastingDispatcher;
 /**
  * A channel that invokes a single subscriber for each sent Message.
  * The invocation will occur in the sender's thread.
- * 
+ *
  * @author Dave Syer
  * @author Mark Fisher
  * @author Iwein Fuld
  * @author Oleg Zhurakousky
+ * @author Gary Russell
  */
 public class DirectChannel extends AbstractSubscribableChannel {
 
@@ -57,6 +58,15 @@ public class DirectChannel extends AbstractSubscribableChannel {
 		this.dispatcher.setFailover(failover);
 	}
 
+	/**
+	 * Specify the maximum number of subscribers supported by the
+	 * channel's dispatcher.
+	 * @param maxSubscribers
+	 */
+	public void setMaxSubscribers(int maxSubscribers) {
+		this.dispatcher.setMaxSubscribers(maxSubscribers);
+	}
+
 	@Override
 	protected UnicastingDispatcher getDispatcher() {
 		return this.dispatcher;

spring-integration-core/src/main/java/org/springframework/integration/channel/ExecutorChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -37,9 +37,10 @@ import org.springframework.util.ErrorHandler;
  * {@link Executor} typically does not block the sender's Thread since it
  * uses another Thread for the dispatch.</emphasis> (SyncTaskExecutor is an
  * exception but would provide no value for this channel. If synchronous
- * dispatching is required, a DirectChannel should be used instead). 
- * 
+ * dispatching is required, a DirectChannel should be used instead).
+ *
  * @author Mark Fisher
+ * @author Gary Russell
  * @since 1.0.3
  */
 public class ExecutorChannel extends AbstractSubscribableChannel {
@@ -50,6 +51,8 @@ public class ExecutorChannel extends AbstractSubscribableChannel {
 
 	private volatile boolean failover = true;
 
+	private volatile int maxSubscribers = Integer.MAX_VALUE;
+
 	private volatile LoadBalancingStrategy loadBalancingStrategy;
 
 
@@ -89,6 +92,16 @@ public class ExecutorChannel extends AbstractSubscribableChannel {
 		this.dispatcher.setFailover(failover);
 	}
 
+	/**
+	 * Specify the maximum number of subscribers supported by the
+	 * channel's dispatcher.
+	 * @param maxSubscribers
+	 */
+	public void setMaxSubscribers(int maxSubscribers) {
+		this.maxSubscribers = maxSubscribers;
+		this.dispatcher.setMaxSubscribers(maxSubscribers);
+	}
+
 	@Override
 	protected UnicastingDispatcher getDispatcher() {
 		return this.dispatcher;
@@ -103,6 +116,7 @@ public class ExecutorChannel extends AbstractSubscribableChannel {
 		}
 		this.dispatcher = new UnicastingDispatcher(this.executor);
 		this.dispatcher.setFailover(this.failover);
+		this.dispatcher.setMaxSubscribers(maxSubscribers);
 		if (this.loadBalancingStrategy != null) {
 			this.dispatcher.setLoadBalancingStrategy(this.loadBalancingStrategy);
 		}

spring-integration-core/src/main/java/org/springframework/integration/channel/PublishSubscribeChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -24,10 +24,11 @@ import org.springframework.integration.util.ErrorHandlingTaskExecutor;
 import org.springframework.util.ErrorHandler;
 
 /**
- * A channel that sends Messages to each of its subscribers. 
- * 
+ * A channel that sends Messages to each of its subscribers.
+ *
  * @author Mark Fisher
  * @author Oleg Zhurakousky
+ * @author Gary Russell
  */
 public class PublishSubscribeChannel extends AbstractSubscribableChannel {
 
@@ -41,6 +42,9 @@ public class PublishSubscribeChannel extends AbstractSubscribableChannel {
 
 	private volatile boolean applySequence;
 
+	private volatile int maxSubscribers = Integer.MAX_VALUE;
+
+	@Override
 	public String getComponentType(){
 		return "publish-subscribe-channel";
 	}
@@ -56,7 +60,7 @@ public class PublishSubscribeChannel extends AbstractSubscribableChannel {
 
 	/**
 	 * Create a PublishSubscribeChannel that will invoke the handlers in the
-	 * message sender's thread. 
+	 * message sender's thread.
 	 */
 	public PublishSubscribeChannel() {
 		this(null);
@@ -103,6 +107,15 @@ public class PublishSubscribeChannel extends AbstractSubscribableChannel {
 		this.getDispatcher().setApplySequence(applySequence);
 	}
 
+	/**
+	 * Specify the maximum number of subscribers supported by the
+	 * channel's dispatcher.
+	 * @param maxSubscribers
+	 */
+	public void setMaxSubscribers(int maxSubscribers) {
+		this.maxSubscribers = maxSubscribers;
+		this.getDispatcher().setMaxSubscribers(maxSubscribers);
+	}
 	/**
 	 * Callback method for initialization.
 	 */
@@ -119,6 +132,7 @@ public class PublishSubscribeChannel extends AbstractSubscribableChannel {
 			this.dispatcher = new BroadcastingDispatcher(this.executor);
 			this.dispatcher.setIgnoreFailures(this.ignoreFailures);
 			this.dispatcher.setApplySequence(this.applySequence);
+			this.dispatcher.setMaxSubscribers(this.maxSubscribers);
 		}
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/config/xml/AbstractChannelParser.java

@@ -19,7 +19,11 @@ package org.springframework.integration.config.xml;
 import org.w3c.dom.Element;
 
 import org.springframework.aop.scope.ScopedProxyUtils;
+import org.springframework.beans.PropertyValue;
+import org.springframework.beans.PropertyValues;
+import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
+import org.springframework.beans.factory.config.TypedStringValue;
 import org.springframework.beans.factory.support.AbstractBeanDefinition;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
@@ -85,4 +89,37 @@ public abstract class AbstractChannelParser extends AbstractBeanDefinitionParser
 	 */
 	protected abstract BeanDefinitionBuilder buildBeanDefinition(Element element, ParserContext parserContext);
 
+	protected void setMaxSubscribersProperty(ParserContext parserContext, BeanDefinitionBuilder builder, Element element, String channelInitializerPropertyName) {
+		String maxSubscribers = element.getAttribute("max-subscribers");
+		if (!StringUtils.hasText(maxSubscribers)) {
+			maxSubscribers = getDefaultMaxSubscribers(parserContext, channelInitializerPropertyName);
+		}
+		if (StringUtils.hasText(maxSubscribers)) {
+			builder.addPropertyValue("maxSubscribers", maxSubscribers);
+		}
+	}
+
+	protected String getDefaultMaxSubscribers(ParserContext parserContext, String channelInitializerPropertyName) {
+		String maxSubscribers = null;
+		BeanDefinition channelInitializer = parserContext.getRegistry().getBeanDefinition(
+				AbstractIntegrationNamespaceHandler.CHANNEL_INITIALIZER_BEAN_NAME);
+		if (channelInitializer != null) {
+			PropertyValues propertyValues = channelInitializer.getPropertyValues();
+			if (propertyValues != null) {
+				PropertyValue propertyValue = propertyValues
+						.getPropertyValue(channelInitializerPropertyName);
+				if (propertyValue != null) {
+					Object propertyValueValue = propertyValue.getValue();
+					if (propertyValueValue instanceof TypedStringValue) {
+						maxSubscribers = ((TypedStringValue) propertyValueValue).getValue();
+					}
+					else if (propertyValueValue instanceof String) {
+						maxSubscribers = (String) propertyValueValue;
+					}
+				}
+			}
+		}
+		return maxSubscribers;
+	}
+
 }

spring-integration-core/src/main/java/org/springframework/integration/config/xml/ChannelInitializer.java

@@ -19,7 +19,6 @@ import java.util.Collection;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
@@ -41,11 +40,13 @@ import org.springframework.util.Assert;
  * {@link AbstractIntegrationNamespaceHandler}.
  *
  * @author Oleg Zhurakousky
+ * @author Gary Russell
  * @since 2.1.1
  */
 final class ChannelInitializer implements BeanFactoryAware, InitializingBean {
 
 	public static String AUTO_CREATE_CHANNEL_CANDIDATES_BEAN_NAME = "$autoCreateChannelCandidates";
+
 	public static String CHANNEL_NAMES_ATTR = "channelNames";
 
 	private Log logger = LogFactory.getLog(this.getClass());
@@ -54,6 +55,10 @@ final class ChannelInitializer implements BeanFactoryAware, InitializingBean {
 
 	private volatile boolean autoCreate = true;
 
+	private volatile int defaultMaxUnicastSubscribers = Integer.MAX_VALUE;
+
+	private volatile int defaultMaxBroadcastSubscribers = Integer.MAX_VALUE;
+
 	public void setAutoCreate(boolean autoCreate) {
 		this.autoCreate = autoCreate;
 	}
@@ -62,6 +67,32 @@ final class ChannelInitializer implements BeanFactoryAware, InitializingBean {
 		this.beanFactory = beanFactory;
 	}
 
+	public int getDefaultMaxUnicastSubscribers() {
+		return defaultMaxUnicastSubscribers;
+	}
+
+	/**
+	 * Set the default max-subscribers for all unicasting channels that don't have the
+	 * attribute set on their dispatcher. Default {@link Integer#MAX_VALUE}.
+	 * @param defaultMaxUnicastSubscribers
+	 */
+	public void setDefaultMaxUnicastSubscribers(int defaultMaxUnicastSubscribers) {
+		this.defaultMaxUnicastSubscribers = defaultMaxUnicastSubscribers;
+	}
+
+	public int getDefaultMaxBroadcastSubscribers() {
+		return defaultMaxBroadcastSubscribers;
+	}
+
+	/**
+	 * Set the default max-subscribers for all broadcasting (pub-sub) channels that don't have the
+	 * attribute set. Default {@link Integer#MAX_VALUE}.
+	 * @param defaultMaxBroadcastSubscribers
+	 */
+	public void setDefaultMaxBroadcastSubscribers(int defaultMaxBroadcastSubscribers) {
+		this.defaultMaxBroadcastSubscribers = defaultMaxBroadcastSubscribers;
+	}
+
 	public void afterPropertiesSet() throws Exception {
 		Assert.notNull(this.beanFactory, "'beanFactory' must not be null");
 		if (!autoCreate){

spring-integration-core/src/main/java/org/springframework/integration/config/xml/IntegrationNamespaceUtils.java

@@ -55,6 +55,20 @@ public abstract class IntegrationNamespaceUtils {
 	static final String EXPRESSION_ATTRIBUTE = "expression";
 	public static final String HANDLER_ALIAS_SUFFIX = ".handler";
 
+	/**
+	 * Property name on ChannelInitializer used to configure the default max subscribers for
+	 * unicast channels.
+	 */
+	public static String DEFAULT_MAX_UNICAST_SUBSCRIBERS_PROPERTY_NAME = "defaultMaxUnicastSubscribers";
+
+	/**
+	 * Property name on ChannelInitializer used to configure the default max subscribers for
+	 * broadcast channels.
+	 */
+	public static String DEFAULT_MAX_BROADCAST_SUBSCRIBERS_PROPERTY_NAME = "defaultMaxBroadcastSubscribers";
+
+
+
 
 	/**
 	 * Configures the provided bean definition builder with a property value corresponding to the attribute whose name

spring-integration-core/src/main/java/org/springframework/integration/config/xml/PointToPointChannelParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -18,8 +18,6 @@ package org.springframework.integration.config.xml;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-import org.w3c.dom.Element;
-
 import org.springframework.beans.factory.config.TypedStringValue;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.xml.ParserContext;
@@ -31,13 +29,15 @@ import org.springframework.integration.channel.RendezvousChannel;
 import org.springframework.integration.store.MessageGroupQueue;
 import org.springframework.util.StringUtils;
 import org.springframework.util.xml.DomUtils;
+import org.w3c.dom.Element;
 
 /**
  * Parser for the <channel> element.
- * 
+ *
  * @author Mark Fisher
  * @author Iwein Fuld
  * @author Oleg Zhurakousky
+ * @author Gary Russell
  */
 public class PointToPointChannelParser extends AbstractChannelParser {
 
@@ -116,11 +116,16 @@ public class PointToPointChannelParser extends AbstractChannelParser {
 			if ("failover".equals(dispatcherAttribute)) {
 				// round-robin dispatcher is used by default, the "failover" value simply disables it
 				builder.addConstructorArgValue(null);
-			} 
+			}
 		}
 		else if (dispatcherElement == null) {
 			// configure the default DirectChannel with a RoundRobinLoadBalancingStrategy
 			builder = BeanDefinitionBuilder.genericBeanDefinition(DirectChannel.class);
+			String maxSubscribers = this.getDefaultMaxSubscribers(parserContext,
+					IntegrationNamespaceUtils.DEFAULT_MAX_UNICAST_SUBSCRIBERS_PROPERTY_NAME);
+			if (maxSubscribers != null) {
+				builder.addPropertyValue("maxSubscribers", maxSubscribers);
+			}
 		}
 		else {
 			// configure either an ExecutorChannel or DirectChannel based on existence of 'task-executor'
@@ -137,8 +142,10 @@ public class PointToPointChannelParser extends AbstractChannelParser {
 			String loadBalancer = dispatcherElement.getAttribute("load-balancer");
 			if ("none".equals(loadBalancer)) {
 				builder.addConstructorArgValue(null);
-			} 
+			}
 			IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, dispatcherElement, "failover");
+			this.setMaxSubscribersProperty(parserContext, builder, dispatcherElement,
+					IntegrationNamespaceUtils.DEFAULT_MAX_UNICAST_SUBSCRIBERS_PROPERTY_NAME);
 		}
 		return builder;
 	}

spring-integration-core/src/main/java/org/springframework/integration/config/xml/PublishSubscribeChannelParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2009 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -16,23 +16,24 @@
 
 package org.springframework.integration.config.xml;
 
-import org.w3c.dom.Element;
-
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.xml.ParserContext;
+import org.springframework.integration.channel.PublishSubscribeChannel;
 import org.springframework.util.StringUtils;
+import org.w3c.dom.Element;
 
 /**
  * Parser for the <publish-subscribe-channel> element.
- * 
+ *
  * @author Mark Fisher
+ * @author Gary Russell
  */
 public class PublishSubscribeChannelParser extends AbstractChannelParser {
 
 	@Override
 	protected BeanDefinitionBuilder buildBeanDefinition(Element element, ParserContext parserContext) {
 		BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(
-				IntegrationNamespaceUtils.BASE_PACKAGE + ".channel.PublishSubscribeChannel");
+				PublishSubscribeChannel.class);
 		String taskExecutorRef = element.getAttribute("task-executor");
 		if (StringUtils.hasText(taskExecutorRef)) {
 			builder.addConstructorArgReference(taskExecutorRef);
@@ -40,6 +41,8 @@ public class PublishSubscribeChannelParser extends AbstractChannelParser {
 		IntegrationNamespaceUtils.setReferenceIfAttributeDefined(builder, element, "error-handler");
 		IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "ignore-failures");
 		IntegrationNamespaceUtils.setValueIfAttributeDefined(builder, element, "apply-sequence");
+		this.setMaxSubscribersProperty(parserContext, builder, element,
+				IntegrationNamespaceUtils.DEFAULT_MAX_BROADCAST_SUBSCRIBERS_PROPERTY_NAME);
 		return builder;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/dispatcher/AbstractDispatcher.java

@@ -20,7 +20,6 @@ import java.util.Set;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-
 import org.springframework.integration.core.MessageHandler;
 import org.springframework.util.Assert;
 
@@ -43,9 +42,18 @@ public abstract class AbstractDispatcher implements MessageDispatcher {
 
 	protected final Log logger = LogFactory.getLog(this.getClass());
 
+	private volatile int maxSubscribers = Integer.MAX_VALUE;
+
 	private final OrderedAwareCopyOnWriteArraySet<MessageHandler> handlers =
 			new OrderedAwareCopyOnWriteArraySet<MessageHandler>();
 
+	/**
+	 * Set the maximum subscribers allowed by this dispatcher.
+	 * @param maxSubscribers
+	 */
+	public void setMaxSubscribers(int maxSubscribers) {
+		this.maxSubscribers = maxSubscribers;
+	}
 
 	/**
 	 * Returns an unmodifiable {@link Set} of this dispatcher's handlers. This
@@ -62,6 +70,7 @@ public abstract class AbstractDispatcher implements MessageDispatcher {
 	 */
 	public boolean addHandler(MessageHandler handler) {
 		Assert.notNull(handler, "handler must not be null");
+		Assert.isTrue(this.handlers.size() < this.maxSubscribers, "Maximum subscribers exceeded");
 		return this.handlers.add(handler);
 	}
 

spring-integration-core/src/main/resources/org/springframework/integration/config/xml/spring-integration-2.2.xsd

@@ -302,6 +302,7 @@
 				</xsd:appinfo>
 			</xsd:annotation>
 		</xsd:attribute>
+		<xsd:attributeGroup ref="subscribersAttributeGroup" />
 	</xsd:complexType>
 
 	<xsd:element name="publish-subscribe-channel">
@@ -388,6 +389,7 @@
 							</xsd:documentation>
 						</xsd:annotation>
 					</xsd:attribute>
+					<xsd:attributeGroup ref="subscribersAttributeGroup" />
 				</xsd:extension>
 			</xsd:complexContent>
 		</xsd:complexType>
@@ -3729,4 +3731,15 @@ endpoint itself is a Polling Consumer for a channel with a queue.
 		<xsd:attributeGroup ref="inputOutputChannelGroup"/>
 	</xsd:attributeGroup>
 
+	<xsd:attributeGroup name="subscribersAttributeGroup">
+		<xsd:attribute name="max-subscribers" type="xsd:string">
+			<xsd:annotation>
+				<xsd:documentation><![CDATA[
+					Specifies the maximum subscribers allowed on this channel; defaults to
+					Integer.MAX_VALUE, unless a 'channelInitializer' bean has previously been
+					declared, with a different default.
+				]]></xsd:documentation>
+			</xsd:annotation>
+		</xsd:attribute>
+	</xsd:attributeGroup>
 </xsd:schema>

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersDefaultConfigurationTests-context.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xmlns:int="http://www.springframework.org/schema/integration"
+	xmlns:task="http://www.springframework.org/schema/task"
+	xsi:schemaLocation="http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration-2.2.xsd
+		http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.1.xsd
+		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+	<int:channel id="defaultChannel" />
+
+	<int:channel id="defaultChannel2">
+		<int:dispatcher />
+	</int:channel>
+
+	<int:channel id="explicitChannel">
+		<int:dispatcher max-subscribers="123" />
+	</int:channel>
+
+	<int:channel id="executorChannel">
+		<int:dispatcher task-executor="taskExecutor" />
+	</int:channel>
+
+	<int:channel id="explicitExecutorChannel">
+		<int:dispatcher task-executor="taskExecutor" max-subscribers="234" />
+	</int:channel>
+
+	<task:executor id="taskExecutor"/>
+
+	<int:publish-subscribe-channel id="pubSubDefaultChannel" />
+
+	<int:publish-subscribe-channel id="pubSubExplicitChannel" max-subscribers="2 "/>
+
+</beans>

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersDefaultConfigurationTests.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2002-2012 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.integration.config.xml;
+
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+/**
+ * @author Gary Russell
+ * @since 2.2
+ *
+ */
+@ContextConfiguration
+@RunWith(SpringJUnit4ClassRunner.class)
+public class DispatcherMaxSubscribersDefaultConfigurationTests extends DispatcherMaxSubscribersTests {
+
+	@Test
+	public void test() {
+		doTestUnicast(Integer.MAX_VALUE, Integer.MAX_VALUE, 123, Integer.MAX_VALUE, 234);
+		doTestMulticast(Integer.MAX_VALUE, 2);
+	}
+}

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersDontOverrideDefaultTests-context.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+	<!-- Explicit channel initializer, but no specification of the default max subscribers properties -->
+
+	<bean id="channelInitializer" class="org.springframework.integration.config.xml.ChannelInitializer">
+		<property name="autoCreate" value="true" />
+	</bean>
+
+	<import resource="DispatcherMaxSubscribersDefaultConfigurationTests-context.xml" />
+
+</beans>

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersDontOverrideDefaultTests.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2002-2012 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.integration.config.xml;
+
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+/**
+ * @author Gary Russell
+ * @since 2.2
+ *
+ */
+@ContextConfiguration
+@RunWith(SpringJUnit4ClassRunner.class)
+public class DispatcherMaxSubscribersDontOverrideDefaultTests extends DispatcherMaxSubscribersTests {
+
+	@Test
+	public void test() {
+		doTestUnicast(Integer.MAX_VALUE, Integer.MAX_VALUE, 123, Integer.MAX_VALUE, 234);
+		doTestMulticast(Integer.MAX_VALUE, 2);
+	}
+}

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersOverrideDefaultTests-context.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xmlns:int="http://www.springframework.org/schema/integration"
+	xsi:schemaLocation="http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration-2.2.xsd
+		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+	<bean id="channelInitializer" class="org.springframework.integration.config.xml.ChannelInitializer">
+		<property name="autoCreate" value="true" />
+		<property name="defaultMaxUnicastSubscribers" value="456" />
+		<property name="defaultMaxBroadcastSubscribers" value="789" />
+	</bean>
+
+	<import resource="DispatcherMaxSubscribersDefaultConfigurationTests-context.xml" />
+
+	<int:channel id="oneSub">
+		<int:dispatcher max-subscribers="1" />
+	</int:channel>
+
+</beans>

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersOverrideDefaultTests.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2002-2012 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.integration.config.xml;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.integration.Message;
+import org.springframework.integration.MessagingException;
+import org.springframework.integration.core.MessageHandler;
+import org.springframework.integration.core.SubscribableChannel;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+/**
+ * @author Gary Russell
+ * @since 2.2
+ *
+ */
+@ContextConfiguration
+@RunWith(SpringJUnit4ClassRunner.class)
+public class DispatcherMaxSubscribersOverrideDefaultTests extends DispatcherMaxSubscribersTests {
+
+	@Autowired
+	private SubscribableChannel oneSub;
+
+	@Test
+	public void test() {
+		this.doTestUnicast(456, 456, 123, 456, 234);
+		doTestMulticast(789, 2);
+	}
+
+	@Test
+	public void testExceed() {
+		oneSub.subscribe(new MessageHandler() {
+			public void handleMessage(Message<?> message) throws MessagingException {
+			}
+		});
+		try {
+			oneSub.subscribe(new MessageHandler() {
+				public void handleMessage(Message<?> message) throws MessagingException {
+				}
+			});
+			fail("Expected Exception");
+		}
+		catch (IllegalArgumentException e) {
+			assertEquals("Maximum subscribers exceeded", e.getMessage());
+		}
+	}
+}

spring-integration-core/src/test/java/org/springframework/integration/config/xml/DispatcherMaxSubscribersTests.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2002-2012 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.integration.config.xml;
+
+import static org.junit.Assert.assertEquals;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.integration.MessageChannel;
+import org.springframework.integration.test.util.TestUtils;
+
+/**
+ * @author Gary Russell
+ * @since 2.2
+ *
+ */
+public abstract class DispatcherMaxSubscribersTests {
+
+	@Autowired
+	private MessageChannel defaultChannel;
+
+	@Autowired
+	private MessageChannel defaultChannel2;
+
+	@Autowired
+	private MessageChannel explicitChannel;
+
+	@Autowired
+	private MessageChannel executorChannel;
+
+	@Autowired
+	private MessageChannel explicitExecutorChannel;
+
+	@Autowired
+	private MessageChannel pubSubDefaultChannel;
+
+	@Autowired
+	private MessageChannel pubSubExplicitChannel;
+
+	public DispatcherMaxSubscribersTests() {
+		super();
+	}
+
+	protected void doTestUnicast(int val1, int val2, int val3, int val4, int val5) {
+		Integer defaultMax = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(defaultChannel, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val1, defaultMax.intValue());
+		Integer defaultMax2 = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(defaultChannel2, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val2, defaultMax2.intValue());
+		Integer explicitMax = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(explicitChannel, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val3, explicitMax.intValue());
+		Integer execMax = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(executorChannel, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val4, execMax.intValue());
+		Integer explicitExecMax = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(explicitExecutorChannel, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val5, explicitExecMax.intValue());
+	}
+
+	protected void doTestMulticast(int val1, int val2) {
+		Integer defaultMax = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(pubSubDefaultChannel, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val1, defaultMax.intValue());
+		Integer explicitMax = TestUtils.getPropertyValue(
+				TestUtils.getPropertyValue(pubSubExplicitChannel, "dispatcher"), "maxSubscribers", Integer.class);
+		assertEquals(val2, explicitMax.intValue());
+	}
+}