/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hmsonline.storm.cassandra.bolt.mapper;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Tuple;
import backtype.storm.tuple.Values;
/**
* A mapper implementation that emits tuples based on a combination of cassandra
* rowkey, collumnkey, and delimiter.
* <p/>
* When this bolt receives a tuple, it will attempt the following:
* <ol>
* <li>Look up a value in the tuple using <code>rowKeyField</code></li>
* <li>Fetch the corresponding row from cassandra</li>
* <li>Fetch the column <code>columnKeyField</code> value from the row.</li>
* <li>Split the column value into an array based on <code>delimiter</code></li>
* <li>For each value, emit a tuple with <code>{emitIdFieldName}={value}</code></li>
* </ol>
* For example, given the following cassandra row: <br/>
*
* <pre>
* RowKey: mike
* => (column=followers, value=john:bob, timestamp=1328848653055000)
* </pre>
*
* and the following bolt setup:
*
* <pre>
* rowKeyField = "rowKey"
* columnKeyField = "followers"
* delimiter = ":"
* emitIdFieldName = "rowKey"
* emitValueFieldName = "follower"
* </pre>
*
* if the following tuple were received by the bolt:
*
* <pre>
* {rowKey:mike}
* </pre>
*
* The following tuples would be emitted:
*
* <pre>
* {rowKey:mike, follower:john}
* {rowKey:mike, follower:bob}
* </pre>
*
*/
@SuppressWarnings("serial")
public class ValuelessColumnsMapper implements ColumnMapper<String, String, String>, Serializable {
private String emitFieldForRowKey;
private String emitFieldForColumnName;
private boolean isDrpc;
/**
* Constructs a ValuelessColumnsMapper
*
* @param emitFieldForRowKey
* This is the field name for the rowkey in the outbound tuple(s)
* @param emitFieldForColumnName
* This is the field name for column names in the outbound
* tuple(s)
* @param isDrpc
*/
public ValuelessColumnsMapper(String emitFieldForRowKey, String emitFieldForColumnName, boolean isDrpc) {
this.isDrpc = isDrpc;
this.emitFieldForRowKey = emitFieldForRowKey;
this.emitFieldForColumnName = emitFieldForColumnName;
}
/**
* Declares the fields produced by this bolt.
*
*
* @param declarer
*/
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
if (this.isDrpc) {
declarer.declare(new Fields("id", this.emitFieldForRowKey, this.emitFieldForColumnName));
} else {
declarer.declare(new Fields(this.emitFieldForRowKey, this.emitFieldForColumnName));
}
}
/**
* Given a set of columns, maps to values to emit.
*
* @param columns
* @return
*/
@Override
public List<Values> mapToValues(String rowKey, Map<String, String> columns, Tuple input) {
List<Values> values = new ArrayList<Values>();
Set<String> vals = columns.keySet();
for(String columnName : vals){
if(this.isDrpc){
values.add(new Values(input.getValue(0), rowKey, columnName));
} else {
values.add(new Values(rowKey, columnName));
}
}
return values;
}
}