INT-2218 - Chain Parser Validation Improvements

Components within Chain: Add parser validation

For reference see: https://jira.springsource.org/browse/INT-2218

INT-2218 - Code review changes

INT-2218 - Fix HttpOutboundGatewayParserTests

INT-2218 - Remove input-channel validation

Was already covered by PR #592

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

@@ -13,10 +13,13 @@
 
 package org.springframework.integration.config.xml;
 
+import java.util.List;
+
 import org.w3c.dom.Element;
 import org.w3c.dom.Node;
 import org.w3c.dom.NodeList;
 
+import org.springframework.beans.BeanMetadataElement;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
@@ -24,6 +27,8 @@ import org.springframework.beans.factory.support.BeanDefinitionReaderUtils;
 import org.springframework.beans.factory.support.ManagedList;
 import org.springframework.beans.factory.xml.ParserContext;
 import org.springframework.integration.handler.MessageHandlerChain;
+import org.springframework.util.StringUtils;
+import org.springframework.util.xml.DomUtils;
 
 /**
  * Parser for the <chain> element.
@@ -32,14 +37,14 @@ import org.springframework.integration.handler.MessageHandlerChain;
  * @author Iwein Fuld
  * @author Oleg Zhurakousky
  * @author Artem Bilan
+ * @author Gunnar Hillert
  */
 public class ChainParser extends AbstractConsumerEndpointParser {
 
 	@Override
-	@SuppressWarnings("unchecked")
 	protected BeanDefinitionBuilder parseHandler(Element element, ParserContext parserContext) {
 		BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MessageHandlerChain.class);
-		ManagedList handlerList = new ManagedList();
+		ManagedList<BeanMetadataElement> handlerList = new ManagedList<BeanMetadataElement>();
 		NodeList children = element.getChildNodes();
 		for (int i = 0; i < children.getLength(); i++) {
 			Node child = children.item(i);
@@ -63,12 +68,38 @@ public class ChainParser extends AbstractConsumerEndpointParser {
 		return builder;
 	}
 
+	private void validateChild(Element element, ParserContext parserContext) {
+
+		final Object source = parserContext.extractSource(element);
+
+		final String order = element.getAttribute(IntegrationNamespaceUtils.ORDER);
+
+		if (StringUtils.hasText(order)) {
+			parserContext.getReaderContext().error(IntegrationNamespaceUtils.createElementDescription(element) + " must not define " +
+				"an 'order' attribute when used within a chain.", source);
+		}
+
+		final List<Element> pollerChildElements = DomUtils
+				.getChildElementsByTagName(element, "poller");
+
+		if (!pollerChildElements.isEmpty()) {
+			parserContext.getReaderContext().error(IntegrationNamespaceUtils.createElementDescription(element) + " must not define " +
+				"a 'poller' sub-element when used within a chain.", source);
+		}
+
+	}
+
 	private BeanDefinitionHolder parseChild(Element element, ParserContext parserContext, BeanDefinition parentDefinition) {
+
 		BeanDefinitionHolder holder = null;
+
 		if ("bean".equals(element.getLocalName())) {
 			holder = parserContext.getDelegate().parseBeanDefinitionElement(element, parentDefinition);
 		}
 		else {
+
+			this.validateChild(element, parserContext);
+
 			BeanDefinition beanDefinition = parserContext.getDelegate().parseCustomElement(element, parentDefinition);
 			if (beanDefinition == null) {
 				parserContext.getReaderContext().error("child BeanDefinition must not be null", element);

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

@@ -20,8 +20,10 @@ import java.util.Properties;
 
 import static org.junit.Assert.fail;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 import org.junit.Test;
 import org.springframework.beans.factory.config.PropertiesFactoryBean;
+import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;
 import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
 import org.springframework.beans.factory.xml.XmlBeanDefinitionStoreException;
 import org.springframework.context.ApplicationContext;
@@ -208,6 +210,23 @@ public class ChainElementsFailureTests {
 		}
 	}
 
+	@Test
+	public void chainResequencerPoller() throws Exception {
+
+		try {
+			this.bootStrap("resequencer-poller");
+			fail("Expected a XmlBeanDefinitionStoreException to be thrown.");
+		}
+		catch (BeanDefinitionParsingException e) {
+			final String expectedMessage = "Configuration problem: " +
+					"'int:resequencer' must not define a 'poller' sub-element " +
+					"when used within a chain.";
+			final String actualMessage = e.getMessage();
+			assertTrue("Error message did not start with '" + expectedMessage +
+					"' but instead returned: '" + actualMessage + "'", actualMessage.startsWith(expectedMessage));
+		}
+	}
+
 	private ApplicationContext bootStrap(String configProperty) throws Exception {
 		PropertiesFactoryBean pfb = new PropertiesFactoryBean();
 		pfb.setLocation(new ClassPathResource("org/springframework/integration/config/xml/chain-elements-config.properties"));

spring-integration-core/src/test/java/org/springframework/integration/config/xml/chain-elements-config.properties

@@ -75,3 +75,10 @@ resequencer=\
 	<int:chain input-channel="input"> \
 		<int:resequencer input-channel="fail"/> \
 	</int:chain>
+
+resequencer-poller=\
+	<int:chain input-channel="input"> \
+		<int:resequencer> \
+			<int:poller fixed-rate="5000" max-messages-per-poll="10" />\
+		</int:resequencer> \
+	</int:chain>

spring-integration-file/src/test/java/org/springframework/integration/file/config/ChainElementsTests.java

@@ -0,0 +1,92 @@
+/*
+ * 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.file.config;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import java.io.ByteArrayInputStream;
+import java.util.Properties;
+
+import org.junit.Test;
+import org.springframework.beans.factory.config.PropertiesFactoryBean;
+import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;
+import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
+import org.springframework.beans.factory.xml.XmlBeanDefinitionStoreException;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.InputStreamResource;
+
+
+/**
+ * @author Gunnar Hillert
+ * @since 2.2
+ */
+public class ChainElementsTests {
+
+	@Test
+	public void chainOutboundGateway() throws Exception {
+
+		try {
+			this.bootStrap("file-oubound-gateway");
+			fail("Expected a BeanDefinitionParsingException to be thrown.");
+		}
+		catch (BeanDefinitionParsingException e) {
+			final String expectedMessage = "Configuration problem: The " +
+					"'request-channel' attribute isn't allowed for a nested (e.g. " +
+					"inside a <chain/>) endpoint element: 'int-file:outbound-gateway' " +
+					"with id='myFileOutboundGateway'.";
+			final String actualMessage = e.getMessage();
+			assertTrue("Error message did not start with '" + expectedMessage +
+					"' but instead returned: '" + actualMessage + "'", actualMessage.startsWith(expectedMessage));
+		}
+
+	}
+
+	@Test
+	public void chainOutboundGatewayWithInputChannel() throws Exception {
+
+		try {
+			this.bootStrap("file-oubound-gateway-input-channel");
+			fail("Expected a XmlBeanDefinitionStoreException to be thrown.");
+		}
+		catch (XmlBeanDefinitionStoreException e) {
+			assertEquals("cvc-complex-type.3.2.2: Attribute 'input-channel' is not" +
+					" allowed to appear in element 'int-file:outbound-gateway'.", e.getCause().getMessage());
+		}
+
+	}
+
+	private ApplicationContext bootStrap(String configProperty) throws Exception {
+		PropertiesFactoryBean pfb = new PropertiesFactoryBean();
+		pfb.setLocation(new ClassPathResource("org/springframework/integration/file/config/chain-elements-config.properties"));
+		pfb.afterPropertiesSet();
+		Properties prop = pfb.getObject();
+		StringBuffer buffer = new StringBuffer();
+		buffer.append(prop.getProperty("xmlheaders")).append(prop.getProperty(configProperty)).append(prop.getProperty("xmlfooter"));
+		ByteArrayInputStream stream = new ByteArrayInputStream(buffer.toString().getBytes());
+
+		GenericApplicationContext ac = new GenericApplicationContext();
+		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(ac);
+		reader.setValidationMode(XmlBeanDefinitionReader.VALIDATION_XSD);
+		reader.loadBeanDefinitions(new InputStreamResource(stream));
+		ac.refresh();
+		return ac;
+	}
+
+}

spring-integration-file/src/test/java/org/springframework/integration/file/config/chain-elements-config.properties

@@ -0,0 +1,17 @@
+xmlheaders=\
+<?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:int-file="http://www.springframework.org/schema/integration/file" \
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd \
+		http://www.springframework.org/schema/integration/file http://www.springframework.org/schema/integration/file/spring-integration-file.xsd \
+		http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration.xsd">
+xmlfooter= </beans>
+
+file-oubound-gateway=<int:chain input-channel="fileOutboundGatewayInsideChain" output-channel="nullChannel">\
+		<int-file:outbound-gateway id="myFileOutboundGateway" request-channel="request" directory="${java.io.tmpdir}/anyDir" delete-source-files="true"/>\
+	</int:chain>
+file-oubound-gateway-input-channel=<int:chain input-channel="fileOutboundGatewayInsideChain" output-channel="nullChannel">\
+		<int-file:outbound-gateway id="myFileOutboundGateway" input-channel="request" directory="${java.io.tmpdir}/anyDir" delete-source-files="true"/>\
+	</int:chain>

spring-integration-http/src/test/java/org/springframework/integration/http/config/ChainElementsTests.java

@@ -0,0 +1,74 @@
+/*
+ * 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.http.config;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import java.io.ByteArrayInputStream;
+import java.util.Properties;
+
+import org.junit.Test;
+import org.springframework.beans.factory.config.PropertiesFactoryBean;
+import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;
+import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.InputStreamResource;
+
+
+/**
+ * @author Gunnar Hillert
+ * @since 2.2
+ */
+public class ChainElementsTests {
+
+	@Test
+	public void chainOutboundGateway() throws Exception {
+
+		try {
+			this.bootStrap("http-oubound-gateway");
+			fail("Expected a BeanDefinitionParsingException to be thrown.");
+		}
+		catch (BeanDefinitionParsingException e) {
+			final String expectedMessage = "Configuration problem: The " +
+					"'request-channel' attribute isn't allowed for a nested " +
+					"(e.g. inside a <chain/>) endpoint element: 'int-http:outbound-gateway'.";
+			final String actualMessage = e.getMessage();
+			assertTrue("Error message did not start with '" + expectedMessage +
+					"' but instead returned: '" + actualMessage + "'", actualMessage.startsWith(expectedMessage));
+		}
+
+	}
+
+	private ApplicationContext bootStrap(String configProperty) throws Exception {
+		PropertiesFactoryBean pfb = new PropertiesFactoryBean();
+		pfb.setLocation(new ClassPathResource("org/springframework/integration/http/config/chain-elements-config.properties"));
+		pfb.afterPropertiesSet();
+		Properties prop = pfb.getObject();
+		StringBuffer buffer = new StringBuffer();
+		buffer.append(prop.getProperty("xmlheaders")).append(prop.getProperty(configProperty)).append(prop.getProperty("xmlfooter"));
+		ByteArrayInputStream stream = new ByteArrayInputStream(buffer.toString().getBytes());
+		GenericApplicationContext ac = new GenericApplicationContext();
+		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(ac);
+		reader.setValidationMode(XmlBeanDefinitionReader.VALIDATION_XSD);
+		reader.loadBeanDefinitions(new InputStreamResource(stream));
+		ac.refresh();
+		return ac;
+	}
+
+}

spring-integration-http/src/test/java/org/springframework/integration/http/config/chain-elements-config.properties

@@ -0,0 +1,15 @@
+xmlheaders=\
+<?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:int-http="http://www.springframework.org/schema/integration/http" \
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd \
+		http://www.springframework.org/schema/integration/http http://www.springframework.org/schema/integration/http/spring-integration-http.xsd \
+		http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration.xsd">
+xmlfooter= </beans>
+
+http-oubound-gateway=<int:chain id="httpChain" input-channel="httpOutboundGatewayInsideChain" output-channel="nullChannel">\
+		<int-http:outbound-gateway request-channel="requestChannel" url="http://google.com/" http-method="POST"/>\
+	</int:chain>
+

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

@@ -0,0 +1,122 @@
+/*
+ * 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.xml.config;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import java.io.ByteArrayInputStream;
+import java.util.Properties;
+
+import org.junit.Test;
+import org.springframework.beans.factory.config.PropertiesFactoryBean;
+import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;
+import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.InputStreamResource;
+
+
+/**
+ * @author Gunnar Hillert
+ * @since 2.2
+ */
+public class ChainElementsTests {
+
+	@Test
+	public void chainXPathTransformer() throws Exception {
+
+		try {
+			this.bootStrap("xpath-transformer");
+			fail("Expected a BeanDefinitionParsingException to be thrown.");
+		}
+		catch (BeanDefinitionParsingException e) {
+			final String expectedMessage = "Configuration problem: " +
+					"The 'input-channel' attribute isn't allowed for a nested " +
+					"(e.g. inside a <chain/>) endpoint element: 'int-xml:xpath-transformer'.";
+			final String actualMessage = e.getMessage();
+			assertTrue("Error message did not start with '" + expectedMessage +
+					"' but instead returned: '" + actualMessage + "'", actualMessage.startsWith(expectedMessage));
+		}
+
+	}
+
+	@Test
+	public void chainXPathTransformerId() throws Exception {
+
+		this.bootStrap("xpath-transformer-id");
+
+	}
+
+	@Test
+	public void chainXPathRouterOrder() throws Exception {
+
+		try {
+			this.bootStrap("xpath-router-order");
+			fail("Expected a BeanDefinitionParsingException to be thrown.");
+		}
+		catch (BeanDefinitionParsingException e) {
+			final String expectedMessage = "Configuration problem: " +
+					"'int-xml:xpath-router' must not define an 'order' attribute " +
+					"when used within a chain.";
+			final String actualMessage = e.getMessage();
+			assertTrue("Error message did not start with '" + expectedMessage +
+					"' but instead returned: '" + actualMessage + "'", actualMessage.startsWith(expectedMessage));
+		}
+
+	}
+
+	@Test
+	public void chainXPathTransformerPoller() throws Exception {
+
+		try {
+			this.bootStrap("xpath-transformer-poller");
+			fail("Expected a BeanDefinitionParsingException to be thrown.");
+		}
+		catch (BeanDefinitionParsingException e) {
+			final String expectedMessage = "Configuration problem: " +
+					"'int-xml:xpath-transformer' must not define a 'poller' " +
+					"sub-element when used within a chain.";
+			final String actualMessage = e.getMessage();
+			assertTrue("Error message did not start with '" + expectedMessage +
+					"' but instead returned: '" + actualMessage + "'", actualMessage.startsWith(expectedMessage));
+		}
+	}
+
+	@Test
+	public void chainXPathTransformerSuccess() throws Exception {
+		this.bootStrap("xpath-transformer-success");
+	}
+
+	private ApplicationContext bootStrap(String configProperty) throws Exception {
+		PropertiesFactoryBean pfb = new PropertiesFactoryBean();
+		pfb.setLocation(new ClassPathResource("org/springframework/integration/xml/config/chain-elements-config.properties"));
+		pfb.afterPropertiesSet();
+		Properties prop = pfb.getObject();
+		StringBuffer buffer = new StringBuffer();
+		buffer.append(prop.getProperty("xmlheaders")).append(prop.getProperty(configProperty)).append(prop.getProperty("xmlfooter"));
+		ByteArrayInputStream stream = new ByteArrayInputStream(buffer.toString().getBytes());
+
+		GenericApplicationContext ac = new GenericApplicationContext();
+		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(ac);
+		reader.setValidationMode(XmlBeanDefinitionReader.VALIDATION_XSD);
+		reader.loadBeanDefinitions(new InputStreamResource(stream));
+		ac.refresh();
+		return ac;
+	}
+
+}

spring-integration-xml/src/test/java/org/springframework/integration/xml/config/chain-elements-config.properties

@@ -0,0 +1,30 @@
+xmlheaders=\
+<?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:int-xml="http://www.springframework.org/schema/integration/xml" \
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd \
+		http://www.springframework.org/schema/integration/xml http://www.springframework.org/schema/integration/xml/spring-integration-xml.xsd \
+		http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration.xsd">
+xmlfooter= </beans>
+
+xpath-transformer=<int:chain input-channel="input">\
+	<int-xml:xpath-transformer input-channel="fail" xpath-expression="/person/@name" />\
+</int:chain>
+xpath-transformer-id=<int:chain input-channel="input">\
+	<int-xml:xpath-transformer id="fail" xpath-expression="/person/@name" />\
+</int:chain>
+xpath-router-order=<int:chain input-channel="input">\
+	<int-xml:xpath-router order="1">\
+		<int-xml:xpath-expression expression="/name"/>\
+	</int-xml:xpath-router>\
+</int:chain>
+xpath-transformer-success=<int:chain input-channel="input">\
+	<int-xml:xpath-transformer xpath-expression="/person/@name" />\
+</int:chain>
+xpath-transformer-poller=<int:chain input-channel="input">\
+	<int-xml:xpath-transformer xpath-expression="/person/@name">\
+		<int:poller id="poller" fixed-rate="5000" max-messages-per-poll="10" />\
+	</int-xml:xpath-transformer>\
+</int:chain>

src/reference/docbook/chain.xml

@@ -13,10 +13,10 @@
       progression. For example, it is fairly common to provide a Transformer before other components. Similarly, when
       providing a <emphasis>Filter</emphasis> before some other component in a chain, you are essentially creating a
       <ulink url="http://www.eaipatterns.com/MessageSelector.html">Selective Consumer</ulink>. In either case, the
-      chain only requires a single <code>input-channel</code> and a single <code>output-channel</code> eliminating 
+      chain only requires a single <code>input-channel</code> and a single <code>output-channel</code> eliminating
       the need to define channels for each individual component.
       <tip>
-        Spring Integration's <interfacename>Filter</interfacename> provides a boolean property <methodname>throwExceptionOnRejection</methodname>. 
+        Spring Integration's <interfacename>Filter</interfacename> provides a boolean property <methodname>throwExceptionOnRejection</methodname>.
         When providing multiple Selective Consumers on the same point-to-point channel with different acceptance criteria,
         this value should be set to 'true' (the default is false) so that the dispatcher will know that the Message was
         rejected and as a result will attempt to pass the Message on to other subscribers. If the Exception were not
@@ -68,7 +68,7 @@
     </para>
   <para>
     The &lt;header-enricher&gt; element used in the above example will set a message header named "foo" with a value
-    of "bar" on the message. A header enricher is a specialization of <interfacename>Transformer</interfacename> 
+    of "bar" on the message. A header enricher is a specialization of <interfacename>Transformer</interfacename>
     that touches only header values. You could obtain the same result by implementing a MessageHandler that did the
     header modifications and wiring that as a bean, but the header-enricher is obviously a simpler option.
   </para>
@@ -84,11 +84,52 @@
      <int:logging-channel-adapter level="INFO" log-full-message="true"/>
  </int:chain>]]></programlisting>
   </para>
-  <para>
+	<para><emphasis>Disallowed Attributes and Elements</emphasis></para>
+	<para>
+		It is important to note that certain attributes, such as
+		<emphasis role="bold">order</emphasis> and <emphasis role="bold">input-channel</emphasis>
+		are not allowed to be specified on components used within a
+		<emphasis>chain</emphasis>. The same is true for the <emphasis role="bold">poller</emphasis>
+		sub-element.
+	</para>
+	<important>
+		<para>
+			For the <emphasis>Spring Integration</emphasis> core components, the
+			XML Schema itself will enforce some of these constraints. However, for non-core
+			components or your own custom components, these constraints are enforced
+			by the XML namespace parser, not by the XML Schema.
+		</para>
+		<para>
+			These XML namespace parser constraints were added with
+			<emphasis>Spring Integration 2.2</emphasis>. The XML namespace parser
+			will throw an <classname>BeanDefinitionParsingException</classname> if you try to use disallowed
+			attributes and elements.
+		</para>
+	</important>
+	<para>
+		The <emphasis>id</emphasis> attribute, however, is allowed to be specified.
+		In fact, the <link linkend='delayer'><emphasis>Delayer</emphasis></link>
+		component actually requires the <emphasis>id</emphasis> attribute to be present.
+	</para>
+	<para>
+		In most other cases, the <emphasis>id</emphasis> will generally be
+		ignored but may still add value for documentation purposes, and may also
+		be  used for providing more meaningful log messages.
+	</para>
+	<note>
+		Currently, the XML Schema of the <emphasis>Spring Integration</emphasis> Core module
+		prevents you from setting the <emphasis>id</emphasis> attribute for
+		Core components within a Message Handler Chain. This may be relaxed in future,
+		to provide the benefits described above.
+	</note>
+	<para><emphasis>Calling a Chain from within a Chain</emphasis></para>
+
+	<para>
   Sometimes you need to make a nested call to another chain from within a chain and then come
   back and continue execution within the original chain.
     To accomplish this you can utilize a Messaging Gateway by including a &lt;gateway&gt; element.
     For example:
+	</para>
     <programlisting language="xml"><![CDATA[  <int:chain id="main-chain" input-channel="in" output-channel="out">
     <int:header-enricher>
       <int:header name="name" value="Many" />
@@ -117,7 +158,7 @@
       <bean class="org.foo.SampleService" />
     </int:service-activator>
   </int:chain>]]></programlisting>
-
+	<para>
     In the above example the <emphasis>nested-chain-a</emphasis> will be called at the end of
     <emphasis>main-chain</emphasis> processing by the 'gateway' element configured there. While in
     <emphasis>nested-chain-a</emphasis> a call to a <emphasis>nested-chain-b</emphasis> will be made