The tuples emitted by the threshold bolt are passed to the next corresponding bolt, which is the DBWriterBolt bolt in our case.
DBWriterBolt
The processed tuple has to be persisted for raising a trigger or for further use. DBWriterBolt does the job of persisting the tuples into the database. The creation of a table is done in prepare(), which is the first method invoked by the topology. Code for this method is given in Listing Six.
Listing Six: Code for creation of tables.
public void prepare( Map StormConf, TopologyContext context )
{
try
{
Class.forName(dbClass);
}
catch (ClassNotFoundException e)
{
System.out.println("Driver not found");
e.printStackTrace();
}
try
{
connection driverManager.getConnection(
"jdbc:mysql://"+databaseIP+":"+databasePort+"/"+databaseName, userName, pwd);
connection.prepareStatement("DROP TABLE IF EXISTS "+tableName).execute();
StringBuilder createQuery = new StringBuilder(
"CREATE TABLE IF NOT EXISTS "+tableName+"(");
for(Field fields : tupleInfo.getFieldList())
{
if(fields.getColumnType().equalsIgnoreCase("String"))
createQuery.append(fields.getColumnName()+" VARCHAR(500),");
else
createQuery.append(fields.getColumnName()+" "+fields.getColumnType()+",");
}
createQuery.append("thresholdTimeStamp timestamp)");
connection.prepareStatement(createQuery.toString()).execute();
// Insert Query
StringBuilder insertQuery = new StringBuilder("INSERT INTO "+tableName+"(");
String tempCreateQuery = new String();
for(Field fields : tupleInfo.getFieldList())
{
insertQuery.append(fields.getColumnName()+",");
}
insertQuery.append("thresholdTimeStamp").append(") values (");
for(Field fields : tupleInfo.getFieldList())
{
insertQuery.append("?,");
}
insertQuery.append("?)");
prepStatement = connection.prepareStatement(insertQuery.toString());
}
catch (SQLException e)
{
e.printStackTrace();
}
}
Insertion of data is done in batches. The logic for insertion is provided in execute() as shown in Listing Seven, and consists mostly of parsing the variety of different possible input types.
Listing Seven: Code for insertion of data.
public void execute(Tuple tuple, BasicOutputCollector collector)
{
batchExecuted=false;
if(tuple!=null)
{
List<Object> inputTupleList = (List<Object>) tuple.getValues();
int dbIndex=0;
for(int i=0;i<tupleInfo.getFieldList().size();i++)
{
Field field = tupleInfo.getFieldList().get(i);
try {
dbIndex = i+1;
if(field.getColumnType().equalsIgnoreCase("String"))
prepStatement.setString(dbIndex, inputTupleList.get(i).toString());
else if(field.getColumnType().equalsIgnoreCase("int"))
prepStatement.setInt(dbIndex,
Integer.parseInt(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("long"))
prepStatement.setLong(dbIndex,
Long.parseLong(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("float"))
prepStatement.setFloat(dbIndex,
Float.parseFloat(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("double"))
prepStatement.setDouble(dbIndex,
Double.parseDouble(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("short"))
prepStatement.setShort(dbIndex,
Short.parseShort(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("boolean"))
prepStatement.setBoolean(dbIndex,
Boolean.parseBoolean(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("byte"))
prepStatement.setByte(dbIndex,
Byte.parseByte(inputTupleList.get(i).toString()));
else if(field.getColumnType().equalsIgnoreCase("Date"))
{
Date dateToAdd=null;
if (!(inputTupleList.get(i) instanceof Date))
{
DateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
try
{
dateToAdd = df.parse(inputTupleList.get(i).toString());
}
catch (ParseException e)
{
System.err.println("Data type not valid");
}
}
else
{
dateToAdd = (Date)inputTupleList.get(i);
java.sql.Date sqlDate = new java.sql.Date(dateToAdd.getTime());
prepStatement.setDate(dbIndex, sqlDate);
}
}
catch (SQLException e)
{
e.printStackTrace();
}
}
Date now = new Date();
try
{
prepStatement.setTimestamp(dbIndex+1, new java.sql.Timestamp(now.getTime()));
prepStatement.addBatch();
counter.incrementAndGet();
if (counter.get()== batchSize)
executeBatch();
}
catch (SQLException e1)
{
e1.printStackTrace();
}
}
else
{
long curTime = System.currentTimeMillis();
long diffInSeconds = (curTime-startTime)/(60*1000);
if(counter.get()<batchSize && diffInSeconds>batchTimeWindowInSeconds)
{
try {
executeBatch();
startTime = System.currentTimeMillis();
}
catch (SQLException e) {
e.printStackTrace();
}
}
}
}
public void executeBatch() throws SQLException
{
batchExecuted=true;
prepStatement.executeBatch();
counter = new AtomicInteger(0);
}
Once the spout and bolt are ready to be executed, a topology is built by the topology builder to execute it. The next section explains the execution steps.
Running and Testing the Topology in a Local Cluster
- Define the topology using
TopologyBuilder, which exposes the Java API for specifying a topology for Storm to execute. - Using Storm Submitter, we submit the topology to the cluster. It takes name of the topology, configuration, and topology as input.
- Submit the topology.
Listing Eight: Building and executing a topology.
public class StormMain
{
public static void main(String[] args) throws AlreadyAliveException,
InvalidTopologyException,
InterruptedException
{
ParallelFileSpout parallelFileSpout = new ParallelFileSpout();
ThresholdBolt thresholdBolt = new ThresholdBolt();
DBWriterBolt dbWriterBolt = new DBWriterBolt();
TopologyBuilder builder = new TopologyBuilder();
builder.setSpout("spout", parallelFileSpout, 1);
builder.setBolt("thresholdBolt", thresholdBolt,1).shuffleGrouping("spout");
builder.setBolt("dbWriterBolt",dbWriterBolt,1).shuffleGrouping("thresholdBolt");
if(this.argsMain!=null && this.argsMain.length > 0)
{
conf.setNumWorkers(1);
StormSubmitter.submitTopology(
this.argsMain[0], conf, builder.createTopology());
}
else
{
Config conf = new Config();
conf.setDebug(true);
conf.setMaxTaskParallelism(3);
LocalCluster cluster = new LocalCluster();
cluster.submitTopology(
"Threshold_Test", conf, builder.createTopology());
}
}
}
After building the topology, it is submitted to local cluster. Once the topology is submitted, it runs until it is explicitly killed or the cluster is shut down without requiring any modifications. This is another big advantage of Storm.
This comparatively simple example shows the ease with which it's possible to set up and use Storm once you understand the basic concepts of topology, spout, and bolt. The code is straightforward and both scalability and speed are provided by Storm. So, if you're looking to handle big data and don't want to traverse the Hadoop universe, you might well find that using Storm is a simple and elegant solution.
Shruthi Kumar works as a technology analyst and Siddharth Patankar is a software engineer with the Cloud Center of Excellence at Infosys Labs.
