Instaclustr Technology Evangelism Blog - Java client code sample for connecting to trial cluster

CassTest1.java

package test1;

import java.util.Date;

import com.datastax.driver.core.*;
import com.datastax.driver.core.policies.DCAwareRoundRobinPolicy;

/*
 * Simple Java client test to connect to trial cluster, create a time series data table, fill it, query it, and save it as csv for graphing.
 */

public class CassTest1 {
	 // the 3 node trial Cassandra test cluster Public IPs. These are dummy values.
	static String n1PubIP = "01.23.45.678";
	static String n2PubIP = "01.234.56.78";
	static String n3PubIP = "01.23.456.78";
	static String dcName = "hal_sydney"; // this is the DC name you used when created
	static String user = "user";
	static String password = "password";

	public static void main(String[] args) {
		
		long t1 = 0; // time each CQL operation, t1 is start time t2 is end time, time is t2-t1
		long t2 = 0;
		long time = 0; 
		
		Cluster.Builder clusterBuilder = Cluster.builder()
			    .addContactPoints(
			    			n1PubIP, n2PubIP, n3PubIP // provide all 3 public IPs
			    )
			    .withLoadBalancingPolicy(DCAwareRoundRobinPolicy.builder().withLocalDc(dcName).build()) // your local data centre
			    .withPort(9042)
			    .withAuthProvider(new PlainTextAuthProvider(user, password));

		Cluster cluster = null;
		try {
			cluster = clusterBuilder.build();
			
		    Metadata metadata = cluster.getMetadata();
		    System.out.printf("Connected to cluster: %s\n", metadata.getClusterName());
		    
		    for (Host host: metadata.getAllHosts()) {
		        System.out.printf("Datacenter: %s; Host: %s; Rack: %s\n", host.getDatacenter(), host.getAddress(), host.getRack());
		    }
		    
		    Session session = cluster.connect();                                           

		    ResultSet rs;
		    boolean createTable = true;
		    if (createTable) {
		    		rs = session.execute("CREATE KEYSPACE IF NOT EXISTS hals WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3}");
		    		rs = session.execute("DROP TABLE IF EXISTS hals.sensordata");
		    		rs = session.execute("CREATE TABLE hals.sensordata(host text, metric text, time timestamp, value double, PRIMARY KEY ((host, metric), time) ) WITH CLUSTERING ORDER BY (time ASC)");
		    		System.out.println("Table hals.sensordata created!");
		    }
		 
		    // Fill the table with some realistic sensor data. if createTable=false we just ADD data to the table
		    
		    double startValue = 100;	// start value for random walk
		    double nextValue = startValue; // next value in random walk, initially startValue
		    int numHosts = 100;	// how many host names to generate
		    int toCreate = 1000;	// how many times to pick a host name and create all metrics for it
		    
		    boolean usePrepared = false;
		    PreparedStatement prepared = null;
		    // prepare a prepared statement
		    if (usePrepared) 
		    	{
		    		System.out.println("Using PREPARED statements for INSERT");
		    		prepared = session.prepare("insert into hals.sensordata (host, metric, time, value) values (?, ?, ?, ?)");
		    	}
		    
		    t1 = System.currentTimeMillis();
		    System.out.println("Creating data... iterations = " + toCreate);
		    for (int r=1; r <= toCreate; r++) {
		    		long now = System.currentTimeMillis();
		    		Date date = new Date(now);
		    		// generate a random host name
		    		String hostname = "host" + (long)Math.round((Math.random() * numHosts));
		    		// do a random walk to produce realistic data
		    		double rand = Math.random();
		    		if (rand < 0.5)
		    			// 50% chance that value doesn't change
		    			;
		    		else if (rand < 0.75)
		    			// 25% chance that value increases by 1
		    			nextValue++;
		    		else
		    			// 25% chance that value decreases by 1
		    			nextValue--;
		    		// never go negative
		    		if (nextValue < 0)
		    			nextValue = 0;
		    		
		    		// comparison of prepared vs. non-prepared statements
		    		if (usePrepared)  {
	    				session.execute(prepared.bind("'" + hostname + "'", "'m1'", date, nextValue));
	    				session.execute(prepared.bind("'" + hostname + "'", "'m2'", date, nextValue * 10));
	    				session.execute(prepared.bind("'" + hostname + "'", "'m3'", date, nextValue * 100));
		    		}
		    		else {
		    			// fake three metrics (m1, m2, m3) which are somehow related.
		    			rs = session.execute("insert into hals.sensordata (host, metric, time, value) values (" + "'" + hostname + "'" + ", " + "'m1'" + ", " + now + "," + (nextValue) + ");" );
		    			rs = session.execute("insert into hals.sensordata (host, metric, time, value) values (" + "'" + hostname + "'" + ", " + "'m2'" + ", " + now + "," + (nextValue * 10) + ");" );
		    			rs = session.execute("insert into hals.sensordata (host, metric, time, value) values (" + "'" + hostname + "'" + ", " + "'m3'" + ", " + now + "," + (nextValue * 100) + ");" );
		    		}
		    	}
		    
		    t2 = System.currentTimeMillis();
		    System.out.println("Created rows = " + toCreate*3 + " in time = " + (t2-t1));	
		    
		    // find the max value for a sample
		    System.out.println("Getting max value for sample...");
		    t1 = System.currentTimeMillis();
		    rs = session.execute("select max(value) from hals.sensordata where host='host1' and metric='m1'");   
		    t2 = System.currentTimeMillis();
		    time = t2-t1;
		   
		    Row row = rs.one();
		    System.out.println("Max value = " + row.toString() + " in time = " + time);   
		    
		    // get all the values for a sample
		    System.out.println("Getting all rows for sample...");
		    t1 = System.currentTimeMillis();
		    rs = session.execute("select * from hals.sensordata where host='host1' and metric='m1'"); 
		    for (Row rowN : rs) {
		    		System.out.println(rowN.toString());
		    }
		    t2 = System.currentTimeMillis();
		    time = t2-t1;
		    System.out.println("time = " + time);   
		    
		    // get all host/metric permutations
		    System.out.println("Getting all host/metric permutations");
		    t1 = System.currentTimeMillis();
		    rs = session.execute("select distinct host, metric from hals.sensordata"); 
		    for (Row rowN : rs) {
		    		System.out.println(rowN.toString());
		    }
		    t2 = System.currentTimeMillis();
		    time = t2-t1;
		    System.out.println("time = " + time);   
		    
		    // Note that SELECT * will return all results without limit (even though the driver might use multiple queries in the background).
		    // To handle large result sets, you use a LIMIT clause in your CQL query, or use one of the techniques described in the paging documentation.
		    System.out.println("Select ALL...");
		    t1 = System.currentTimeMillis();
		    rs = session.execute("select * from hals.sensordata");   
		    System.out.println("Got rows (without fetching) = " + rs.getAvailableWithoutFetching());
		    int i = 0;
		    long numBytes = 0;
		    // example use of the data: count rows and total bytes returned.
		    for (Row rowN : rs)
		    {
		    		i++;
		    		numBytes += rowN.toString().length();
		    }
		    t2 = System.currentTimeMillis();
		    time = t2-t1;
		    System.out.println("Returned rows = " + i + ", total bytes = " + numBytes + ", in time = " + time);
	
		} finally {
			 if (cluster != null) cluster.close();     
		}
	}
}