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} catch (InterruptedException e) {
    throw e;
} catch (Exception e) {
    log.error("Error: " + e, e);
    throwUnhandledETLException(e);
}

@Override
protected boolean processWireData(List<ETLStepMetadataFieldBean> fields)
                                  throws ETLException, InterruptedException {
         
    // The options should've been validated by the validate() method,
    // so no need for further checks here
    String appendFieldUUID = this.getStepOption("APPEND_FIELD");
    String newFieldUUID = this.getStepOption("NEW_FIELD");
    String appendValue = this.getStepOption("APPEND_VALUE");
  
    Wire<Object, String> appendFieldWire = this.getWireForField(appendFieldUUID);
    Wire<Object, String> newFieldWire = this.getWireForField(newFieldUUID);
  
    Object data = appendFieldWire.getValue();
    String newFieldData = null;
    if (data == null) {
        newFieldData = appendValue;
    } else {
        newFieldData = data.toString() + appendValue;
    }
     
    newFieldWire.send(newFieldData);
     
    return true;
}

@Override
protected void processEndRows() throws ETLException, InterruptedException {
 
    // Get the first output flow;
    // Useful for most steps which have a single output
    String outFlow = getFirstOutputFlow();
 
    // The step outputs four Generated fields.
    List<String> orderedFieldUUIDs = new ArrayList<>(4);
 
    // The step's implementation of setupGeneratedFields()
    // should set these up. Their UUIDs would've been saved as step options.
    orderedFieldUUIDs.add(getStepOption("FIELD1_UUID"));
    orderedFieldUUIDs.add(getStepOption("FIELD2_UUID"));
    orderedFieldUUIDs.add(getStepOption("FIELD3_UUID"));
    orderedFieldUUIDs.add(getStepOption("FIELD4_UUID"));
 
    // Sample Data
    String[] field1_data = {"Adventure", "Relaxation", "Culture", "Family"};
    int[] field2_data = {30, 32, 11, 44};
    Date[] field3_data = {new Date(103882823L), new Date(10388283323L),
                          new Date(103883232823L), new Date(102323882823L)};
    Timestamp[] field4_data = {new Timestamp(103882823L), new Timestamp(10388283323L),
                              new Timestamp(103883232823L), new Timestamp(102323882823L)};
 
    // Generate as many rows as configured in Step Option ROW_COUNT
    int rowCount = 10;//Integer.parseInt(getStepOption("ROW_COUNT"));
    Random random = new Random();
 
    for (int i = 0 ; i < rowCount ; i++) {
        // Data is emitted in packets.
        // This implementation creates a new packet for every row.
        // Data packets can accumulate rows and emit, say, every 20 rows.
        ETLStepResult dataPacket = getFreshDataPacket(outFlow);
 
        Object[] row = new Object[4];
        row[0] = field1_data[random.nextInt(4)];
        row[1] = field2_data[random.nextInt(4)];
        row[2] = field3_data[random.nextInt(4)];
        row[3] = field4_data[random.nextInt(4)];
 
        // Send the row of data from Default Fields to Output Fields
        beginInternalTransmission(row, orderedFieldUUIDs);
 
        // Accumulate transmitted data in a data packet
        endInternalTransmission(dataPacket);
 
        // Emit the packet of data to the next step.
        // This may be done less frequently, after accumulating rows
        emitData(dataPacket);
    }
}

@Override
protected void processEndRows() throws ETLException, InterruptedException {
    // Get input flows which feed data to this step
    Set<String> inputFlowUuids = this.getInputFlowUuids();
 
    // Get the output flow as there can be only one
    String outFlowUuid = getFirstOutputFlow();
 
    // Get a data packet
    ETLStepResult dataPacket = getFreshDataPacket(outFlowUuid);
 
    for (String inputFlowUuid : inputFlowUuids) {
        // Get data of each input from its cache
        ETLDataCache inputData = getDataCache(inputFlowUuid);
 
        // Use this to get the Default Metadata Field corresponding to an Input Field.
        // Input Metadata Field is the field in the input step.
        // Cached data will be in the order of input fields.
        Map<String, String> inputToDefaultFieldMap = getInputToDefaultFieldMap();
 
        // The data will match the Input Metadata Fields
        List<ETLStepMetadataFieldBean> inputFieldList = inputData.getMetadataFields();
        List<String> unionResultFields = new ArrayList<String>();
 
        for(ETLStepMetadataFieldBean fieldBean : inputFieldList){
            // Get the Default Metadata Field for an Input Metadata Field
            String inputFieldUuid = fieldBean.getEtlStepMetadataFieldUUID();
            String defaultFieldUuid = inputToDefaultFieldMap.get(inputFieldUuid);
 
            // Get the Generated Default Metadata Field holding the result of the Union.
            // getUnionFieldForDefaultField() is a method defined in the Step.
            // The result of the union operation is sent to new generated fields.
            // It figures out how a Default Field is linked to the generated field.
            String unionResultField = getUnionFieldForDefaultField(defaultFieldUuid);
 
            // This holds the Union field corresponding to the Input Field.
            // Fields which are excluded from the union will have a null entry.
            unionResultFields.add(unionResultField);   
        }
 
        // Iterate through the cached data
        Iterator<Object[]> it = inputData.iterator();
 
        while (it.hasNext()) {
            Object[] row = it.next();
 
            // Transmit data from:
            // input fields -> default -> generated default (union fields) -> output
            // Data excluded from the union will have a "null" field,
            // so nothing will be transmitted.
            this.beginInternalTransmission(row, unionResultFields);
            this.endInternalTransmission(dataPacket);
        }
    }
 
    // Accumulate all data before emitting to the next step
    emitData(dataPacket);
}