This document discusses creating a custom aggregation strategy for the Scatter-Gather routing component in Mule. It describes implementing the AggregationStrategy interface and overriding the default CollectAllAggregationStrategy. The snippet provided shows an example aggregation strategy class that collects successful responses even if errors occur, logging any exceptions. To use it, the custom strategy class would be provided in the Scatter-Gather component configuration.

1. Creating Custom Aggregation
Strategy for Scatter-Gather
- By Rahul Kumar

2. Creating Custom
Aggregation Strategy
Create your own Aggregation Strategy by
Implementing org.mule.routing.AggregationStrategy interface
Overriding the standard implementations of org.mule.routing.AggregationStrategy like
org.mule.routing.CollectAllAggregationStrategy (used by default in Scatter-Gather

3. Snippet for Custom
Aggregator
package org.rahul.mule.scattergather;
import java.util.List;
import java.util.Map;
import org.apache.log4j.Logger;
import org.mule.api.MuleContext;
import org.mule.api.MuleEvent;
import org.mule.api.MuleException;
import org.mule.api.context.MuleContextAware;
import org.mule.api.routing.AggregationContext;
import org.mule.api.routing.RouterResultsHandler;
import org.mule.routing.AggregationStrategy;
import org.mule.routing.DefaultRouterResultsHandler;
public class ProcessCollectedAggregationStrategy implements AggregationStrategy, MuleContextAware {
private static final Logger logger = Logger.getLogger(ProcessCollectedAggregationStrategy.class);

4. Snippet for Custom
Aggregator
private RouterResultsHandler resultsHandler = new DefaultRouterResultsHandler();
private MuleContext muleContext;
@Override
public MuleEvent aggregate(AggregationContext context) throws MuleException {
List<MuleEvent> eventsWithExceptions = context.collectEventsWithExceptions();
List<MuleEvent> eventsWithoutExceptions = context.collectEventsWithoutExceptions();
if (!eventsWithExceptions.isEmpty()) {
logger.warn(String.format("Found %d exceptions in total. Continuing with whatever has been
collected so far.", eventsWithExceptions.size()));

5. Snippet for Custom
Aggregator
logger.debug("Logging exceptions for individual paths. Route indexes are zero-based.");
for (Map.Entry<Integer, Throwable> routeException :
context.collectRouteExceptions().entrySet()) {
logger.debug(String.format("An exception was found for route %d: ",
routeException.getKey()), routeException.getValue());
}
}
return resultsHandler.aggregateResults(eventsWithoutExceptions, context.getOriginalEvent(),
muleContext);
}
@Override
public void setMuleContext(MuleContext context) {
this.muleContext = context;
}
}

6. Snippet for Custom
Aggregator
The snippet shown will create a custom Aggregation Strategy for Scatter
Gather component
By default if error occurs in any of parallel branch of Scatter-Gather the error
will be throw. The aggregation strategy shown in the snippet will make it
lenient. Thus all the branches which didn’t throw errors , their responses
will be collected.

7. Configuration
Provide this class in the Scatter Gather component from the palette.

8. Thank You