routing in mule Thanks Karthik and Sateesh for your inputs

1. Understanding Routing in Mule

2. Routing
The Routing module reviews the different types of Routers and how Routers are
used to control how messages are sent and received by components. The message
can be route in different ways. Below are explained in this example.
• Splitters and Aggregators
• Collection splitter and Collection Aggregator
• Message chunk splitter and Message chunk aggregator
• Scatter gather
• For each
• Mule flows, Sub flows and flow reference
• Filters
Splitters
Splitters are used to split the message and process split messages in parallel.
After processing completed, those messages get aggregate by aggregator
components. Below is the splitters main flow diagram.

3. Above flow exposes a HTTP service to implement collection splitter and message
chunk splitter. This flow expects a query parameter ‘splitter’. If ‘splitter’ parameter
value is ‘collection’ then choice router routes the flow to collection splitter or if
the value is ‘chunk’ then it routes to message chunk splitter implementation.

4. Collection splitter and Collection Aggregator
Collection splitter is used to split collection object and process split messages individually.
Collection splitter expects a collection object as a payload. A java component has been used
to create a List object. Each object of List is routed to another flow via VM queue in one-way
mode.
In the below flow after logger component (which logs payload) we have two important
message processors. Resequencer and Collection Aggregator. While elements of List are
processing invidually, the elements may get change their order. Resequencer is used to
reorder the elements of List object. Collection Aggregator is used to aggregate the processed
invidual message payload.
Message chunk splitter and Message chunk Aggregator
We need to provide some message payload to split the message.
Message chunk splitter is used to chunk a message into a number of fixed-length messages
based on the Message Size you configure in the Message Chunk Spliter.

5. This splitter first convert the message into byte array then split this array into chunks. Each
chunked message is routed to another flow via VM queue in one-way mode.
Message Chunk Aggregator is used to aggregate the chunked messages. Byte Array to
String component needs to co
Scatter Gather
Scatter Gather is used to send a message to multiple endpoints concurrently. It collects
the response of all the routes and aggregate into a single message.

7. For Each
The Foreach scope splits a collection into elements and processes them iteratively through
the processors embedded in the scope, then returns the original message to the flow.
As For Each expects a collection object is expected a java component is used to generate a
List OBJECT
Main Flow, Sub Flow and Flow reference.
A mule flow (main flow) which accepts message source and message processor where
sub flow accepts only message processor. Sub flow can be called via flow reference
because it doesn't accept message source.
Sub flow runs completely in the same context of the flow that calls it, inheriting
transaction context, exception handler, all variables and headers, etc.
A Main flow has its own context, transaction context, exception handler, all variables and
headers etc.

8. Filters:
Filters are used to filter the message using mule expressions.
Above flow accepts a HTTP request and filters the message using Expression filter and also
throws an exception if Expression filter is not satisfied using Message Filter. Refer slide 9
Expression Filter allows you to right a Mule Expression. if the expression returns true then
the process continuous to next message processor. or else the flow get discarded without
throwing any exception. Here the condition is checking for payload instance is java.util.List or
not.
If we need to throw an exception when Expression Filter returns false, then Expression filter
needs wrapped up the Message Filter and throwOnUnaccecpted attribute should be true as
shown in below snippet.
<message-filter throwOnUnaccepted="true" doc:name="Message-filter-thow-exception">
<expression-filter expression="#[payload instanceof
com.techm.splitters.SplitterCollections]"/>
</message-filter>