INT-3337: MongoDbMessageStore Refactoring

JIRA: https://jira.spring.io/browse/INT-3337

INT-3337: Addressing PR comments

INT-3337: Add support to store/read Messages

* Add support to store/read `ErrorMessage`. As a trick for `Throwable` is selected (de)serializing converter

INT-3337: Add converters for `Message<?>` impls

INT-3337: Make `MDbMS.MessageWrapper` AuditAware

Add `_id` persistence field

Addressing PR comments

Polishing

- Docs
- Check for null ApplicationContext
- Add afterPropertiesSet() to tests

src/reference/docbook/mongodb.xml

@@ -88,8 +88,8 @@
 
     <para>
     Spring Integration's MongoDB module provides the <classname>MongoDbMessageStore</classname> which is an implementation of both
-    the <classname>MessageStore</classname> strategy (mainly used by the <emphasis>QueueChannel</emphasis> and <emphasis>ClaimCheck</emphasis>
-    patterns) and the <classname>MessageGroupStore</classname> strategy (mainly used by the <emphasis>Aggregator</emphasis> and
+    the <classname>MessageStore</classname> strategy (mainly used by the <emphasis>ClaimCheck</emphasis>pattern)
+	and the <classname>MessageGroupStore</classname> strategy (mainly used by the <emphasis>Aggregator</emphasis> and
     <emphasis>Resequencer</emphasis> patterns).
 	</para>
 
@@ -111,15 +111,18 @@
     and an <emphasis>Aggregator</emphasis>. As you can see it is a simple bean configuration, and it expects a
     <classname>MongoDbFactory</classname> as a constructor argument.
     </para>
+	<para>
+	  The <classname>MongoDbMessageStore</classname> expands the <interfacename>Message</interfacename> as a Mongo document
+	  with all nested properties using the Spring Data Mongo Mapping mechanism. It is useful when you need to have access to
+	  the <code>payload</code> or <code>headers</code> for auditing or analytics, for example, against stored messages.
+	</para>
 	<important>
 		<para>
 			The <classname>MongoDbMessageStore</classname> uses a custom <classname>MappingMongoConverter</classname> implementation
 			to store <interfacename>Message</interfacename>s as MongoDB documents and there are some limitations
 			for the properties (<code>payload</code> and <code>header</code> values) of the <interfacename>Message</interfacename>.
-			For example an <classname>ErrorMessage</classname> can't be converted to the MongoDB document, because it has an
-			<classname>Exception</classname> property, where the cause property is infintely recursed. Also, there is no ability to
-			configure
-			custom converters for complex domain <code>payload</code>s or <code>header</code> values.
+			For example, there is no ability to configure custom converters for complex domain <code>payload</code>s or <code>header</code> values.
+			Or to provide a custom <classname>MongoTemplate</classname> (or <classname>MappingMongoConverter</classname>).
 			To achieve these capabilities, an alternative MongoDB <interfacename>MessageStore</interfacename> implementation has been
 			introduced; see next paragraph.
 		</para>
@@ -128,8 +131,7 @@
 		 <emphasis>Spring Integration 3.0</emphasis> introduced the <classname>ConfigurableMongoDbMessageStore</classname> -
 		 <interfacename>MessageStore</interfacename> and <interfacename>MessageGroupStore</interfacename> implementation.
 		 This class can receive, as a constructor argument, a <classname>MongoTemplate</classname>, with which you can
-		 configure with a
-		 custom <classname>WriteConcern</classname>, for example. Another constructor requires a
+		 configure with a custom <classname>WriteConcern</classname>, for example. Another constructor requires a
 		 <classname>MappingMongoConverter</classname>, and a <interfacename>MongoDbFactory</interfacename>,
 		 which allows you to provide some custom conversions for <interfacename>Message</interfacename>s and their properties.
 		 Note, by default, the <classname>ConfigurableMongoDbMessageStore</classname> uses standard Java serialization
@@ -137,8 +139,8 @@
 		 properties from <classname>MongoTemplate</classname>, which is built from the provided
 		 <interfacename>MongoDbFactory</interfacename> and <classname>MappingMongoConverter</classname>.
 		 The default name for the collection stored by the <classname>ConfigurableMongoDbMessageStore</classname> is
-		 <code>configurableStoreMessages</code>. It is recommended to use this implementation for robust and flexible solutions.
-		 The <classname>MongoDbMessageStore</classname> remains for backward compatibility and may be removed in future releases.
+		 <code>configurableStoreMessages</code>. It is recommended to use this implementation for robust and flexible solutions
+		 when messages contain complex data types.
 	 </para>
   </section>