Passing parameters to an Aggregator

Question

I'm using an aggregator to processing some data in my cluster, but this process depends on a 'context'. For example, an aggregator needs to know which tenant and which user is running the aggregation.
To pass this context to the aggregator I'm using a serializable class member on the Aggregator class like this:
public class MyAggregator<D , R> extends AbstractAggregator {
         * This is the accumulator / aggregator. It is transient to avoid passing it to another cluster member
     private transient Map<String, List<R>> aggregators;
      * Identifier of tenant. It should be pass it to all the cluster members
     private String tenantId;
      * Username. It should be pass it to all the cluster members
     private String username;
        // Rest of the aggregator
}In my first version, I was setting the 'context' (tenant/username) using the constructor of the aggregator, but when I ran this aggregator I got a NoSuchMethodException because my class did not have a constructor with no parameters. In my second version I've added the no-args constructor but now I'm getting a NullPointerException because my tenant/username are null.
So, here are my questions?
* Why coherence needs a no-args contructor in the aggregator? I was expecting coherence to serialize my Aggregator (with all the serializable class members) and then pass it to another cluser member. So why it needs to construct a new aggregator? NOTE: if you see my example code, you will see that the aggregator is actually transient to avoid passing it to another cluster member (I got this from the book Oracle Coherence 3.5 by Aleksander Seovic).
* If this does not work ... How can I pass parameters to my aggregators? I cannot run the aggregator "anonymously" ... The elements to be aggregated depends on the tenant and the user.
Thanks in advance,

Answer 1

Coherence need the empty constructor for the POF de-serialization.
You can just put both constructor in your class and use the one with two String input parameter when you instantiate the object. However, you will need to implement the readExternal and writeExternal (assume you have POF configured) method to pass the tenantId and username.
Something like this.
public class MyAggregator<D, R> extends AbstractAggregator
     * This is the accumulator / aggregator. It is transient to avoid passing it
     * to another cluster member
    private transient Map<String, List<R>> aggregators;
     * Identifier of tenant. It should be pass it to all the cluster members
    private String tenantId;
     * Username. It should be pass it to all the cluster members
    private String username;
    public MyAggregator(String tenantId, String username)
        this.tenantId = tenantId;
        this.username = username;
    public MyAggregator()
    @Override
    public void readExternal(
        PofReader in)
        throws IOException
        this.tenantId = in.readString(1000);
        this.username = in.readString(1001);
        super.readExternal(in);
    @Override
    public void writeExternal(
        PofWriter out)
        throws IOException
        super.writeExternal(out);
        out.writeString(1000, tenantId);
        out.writeString(1001, username);
    // Rest of the aggregator
}