Support @Beans for Partitioning Properties

Fixed support for partition properties to be Spring configured

- Fixed support for 'partitionKeyExtractor' and 'partitionSelector' to be Spring configured
- Added new producer properties 'partitionKeyExtractorName' and 'partitionSelectorName'
- Deprecated 'partitionKeyExtractorClass' and 'partitionSelectorClass' properties
- Removed InitilaizingBean from MessageConverterConfigurer
- Updated documentation
- Added additional tests
- Removed PartitionedProducerTest  as redundant
- Fixed unrelated to this effort BinderPropertiesTests due to recent Boot changes

polishing

spring-cloud-stream-core-docs/src/main/asciidoc/spring-cloud-stream-overview.adoc

@@ -2028,7 +2028,8 @@ In a scaled-up scenario, correct configuration of these two properties is import
 
 ==== Configuring Output Bindings for Partitioning
 
-An output binding is configured to send partitioned data by setting one and only one of its `partitionKeyExpression` or `partitionKeyExtractorClass` properties, as well as its `partitionCount` property.
+An output binding is configured to send partitioned data by setting one and only one of its `partitionKeyExpression` or `partitionKeyExtractorName` (see next paragraph) properties, as well as its `partitionCount` property.
+
 For example, the following is a valid and typical configuration:
 
 ----
@@ -2042,37 +2043,35 @@ A partition key's value is calculated for each message sent to a partitioned out
 The `partitionKeyExpression` is a SpEL expression which is evaluated against the outbound message for extracting the partitioning key.
 
 
-If a SpEL expression is not sufficient for your needs, you can instead calculate the partition key value by setting the property `partitionKeyExtractorClass` to a class which implements the `org.springframework.cloud.stream.binder.PartitionKeyExtractorStrategy` interface.
-While the SpEL expression should usually suffice, more complex cases may use the custom implementation strategy.
-In that case, the property 'partitionKeyExtractorClass' can be set as follows:
+If a SpEL expression is not sufficient for your needs, you can instead calculate the partition key value by providing implementation of `org.springframework.cloud.stream.binder.PartitionKeyExtractorStrategy` and configuring it as a bean (i.e., `@Bean`). In the event you have more then one bean of type `org.springframework.cloud.stream.binder.PartitionKeyExtractorStrategy` available in the Application Context you can further filter it by specifying its name via `partitionKeyExtractorName` property:
 
 ----
-spring.cloud.stream.bindings.output.producer.partitionKeyExtractorClass=com.example.MyKeyExtractor
-spring.cloud.stream.bindings.output.producer.partitionCount=5
-----
-
-Once the message key is calculated, the partition selection process will determine the target partition as a value between `0` and `partitionCount - 1`.
-The default calculation, applicable in most scenarios, is based on the formula `key.hashCode() % partitionCount`.
-This can be customized on the binding, either by setting a SpEL expression to be evaluated against the 'key' (via the `partitionSelectorExpression` property) or by setting a `org.springframework.cloud.stream.binder.PartitionSelectorStrategy` implementation (via the `partitionSelectorClass` property).
-
-The binding level properties for 'partitionSelectorExpression' and 'partitionSelectorClass' can be specified similar to the way 'partitionKeyExpression' and 'partitionKeyExtractorClass' properties are specified in the above examples.
-Additional properties can be configured for more advanced scenarios, as described in the following section.
-
-===== Spring-managed custom `PartitionKeyExtractorClass` implementations
-
-In the example above, a custom strategy such as `MyKeyExtractor` is instantiated by the Spring Cloud Stream directly.
-In some cases, it is necessary for such a custom strategy implementation to be created as a Spring bean, for being able to be managed by Spring, so that it can perform dependency injection, property binding, etc.
-This can be done by configuring it as a @Bean in the application context and using the fully qualified class name as the bean's name, as in the following example.
-
-----
-@Bean(name="com.example.MyKeyExtractor")
-public MyKeyExtractor extractor() {
-    return new MyKeyExtractor();
+--spring.cloud.stream.bindings.output.producer.partitionKeyExtractorName=customPartitionKeyExtractor
+--spring.cloud.stream.bindings.output.producer.partitionCount=5
+. . .
+@Bean
+public CustomPartitionKeyExtractorClass customPartitionKeyExtractor() {
+	return new CustomPartitionKeyExtractorClass();
 }
 ----
 
-As a Spring bean, the custom strategy benefits from the full lifecycle of a Spring bean.
-For example, if the implementation need access to the application context directly, it can make implement 'ApplicationContextAware'.
+NOTE: In previous versions of Spring Cloud Stream you could specify the implementation of `org.springframework.cloud.stream.binder.PartitionKeyExtractorStrategy` as `spring.cloud.stream.bindings.output.producer.partitionKeyExtractorClass` property. Since version 2.0 this property is deprecated and support for it will be removed in a future version.
+
+Once the message key is calculated, the partition selection process will determine the target partition as a value between `0` and `partitionCount - 1`.
+The default calculation, applicable in most scenarios, is based on the formula `key.hashCode() % partitionCount`.
+This can be customized on the binding, either by setting a SpEL expression to be evaluated against the 'key' (via the `partitionSelectorExpression` property) or by configuring an implementation of `org.springframework.cloud.stream.binder.PartitionSelectorStrategy` as a bean (i.e., @Bean). And similarly to the `PartitionKeyExtractorStrategy` you can further filter it using `spring.cloud.stream.bindings.output.producer.partitionSelectorName` property in the event there are more then one bean of this type is available in the Application Context.
+
+----
+--spring.cloud.stream.bindings.output.producer.partitionSelectorName=customPartitionSelector
+. . .
+@Bean
+public CustomPartitionSelectorClass customPartitionSelector() {
+	return new CustomPartitionSelectorClass();
+}
+----
+
+NOTE: In previous versions of Spring Cloud Stream you could specify the implementation of `org.springframework.cloud.stream.binder.PartitionSelectorStrategy` as `spring.cloud.stream.bindings.output.producer.partitionSelectorClass` property. Since version 2.0 this property is deprecated and support for it will be removed in a future version.
+
 
 ===== Configuring Input Bindings for Partitioning