Migrating the Scatter-Gather Router
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Standard Support for Mule 4.1 ended on November 2, 2020, and this version of Mule reached its End of Life on November 2, 2022, when Extended Support ended. Deployments of new applications to CloudHub that use this version of Mule are no longer allowed. Only in-place updates to applications are permitted. MuleSoft recommends that you upgrade to the latest version of Mule 4 that is in Standard Support so that your applications run with the latest fixes and security enhancements. |
The most important change in Scatter-Gather router between Mule 3 and Mule 4
is in the AggregationStrategy used to consolidate the results of the
different routes. Instead of providing a Java class with the aggregation
logic, you can perform the aggregation with a DataWeave transformation.
The payload Scatter-Gather returns is a collection of messages, where each the result of each route. Those messages are accessible with DataWeave.
Example
This is a Mule 3 Scatter-Gather with a custom-aggregation-strategy
element referencing the Java class with the aggregation strategy:
<scatter-gather doc:name="Scatter-Gather">
<custom-aggregation-strategy class="com.example.poc.CustomSGAggregationStrategy"/>
<processor-chain>
...
</processor-chain>
<processor-chain>
...
</processor-chain>
</scatter-gather>
<logger message="#[payload]" level="INFO" doc:name="Logger"/>
And the aggregation strategy implementation is:
package com.example.poc;
import ...
public class CustomSGAggregationStrategy implements AggregationStrategy {
@Override
public MuleEvent aggregate(AggregationContext context) throws MuleException {
StringBuilder responseBuilder = new StringBuilder();
MuleEvent result = null;
ArrayList < MarketRate > marketRates = new ArrayList < > ();
for (MuleEvent event: context.collectEventsWithoutExceptions()) {
String response = (String) event.getMessage().getPayload();
String[] spiltResponse = StringUtils.split(response, ",");
MarketRate marketRate = new MarketRate();
marketRate.setEvent(event);
marketRate.setMarketName(spiltResponse[0]);
marketRate.setMarketRate(new Integer(spiltResponse[1]));
marketRates.add(marketRate);
System.out.println(marketRate);
}
Collections.sort(marketRates);
result = DefaultMuleEvent.copy(marketRates.get(0).getEvent());
result.getMessage().setPayload(marketRates.get(0).toString());
return result;
}
}
For Mule 4, the Java class is removed, and the flow elements become:
<scatter-gather doc:name="Scatter-Gather">
<route>
...
</route>
<route>
...
</route>
</scatter-gather>
<ee:transform>
<ee:message >
<ee:set-payload ><![CDATA[%dw 2.0
output text/plain
---
(payload map ((response, index) -> (response.payload splitBy(','))[1]) orderBy ((rate, index) -> rate))[0]
]]]></ee:set-payload>
</ee:message>
</ee:transform>
<logger message="#[payload]" level="INFO" doc:name="Logger"/>
Notice the ee:transform element that replicates the logic of the
CustomSGAggregationStrategy, in DataWeave rather than Java.