Access to datastream from BucketSink

[ant burton]

Hello,

Given 

        // Set StreamExecutionEnvironment
        final StreamExecutionEnvironment env = 
StreamExecutionEnvironment.getExecutionEnvironment();

        // Set checkpoints in ms
        env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);

        // Add source (input stream)
        DataStream<String> dataStream = StreamUtil.getDataStream(env, params);

How can I construct the s3_filename from the content of the an event, it seems 
that whenever I attempt this I either have access to an event or access to 
.addSink but not both.

        dataStream.addSink(new BucketingSink<String>("s3a://flink/" + 
s3_filename));


Thanks,