We already explained the fundamentals of Apache Cassandra . We also discussed the configuration of Apache Cassandra . In this chapter we are looking into how data is retrieving from Apache Cassandra using java. In the just previous chapter we discussed about inserting data into Apache Cassandra.In this chapter we are reading the same piece of data inserted there .
Reading Data from Apache Cassandra using Java
Apache Cassandra should be installed and configured in local machine to go further in this chapter .These things were explained in the article about configuration of Apache Cassandra. The libraries listed there should be added to the project as dependencies.Also we need to insert the data to Cassandra by running the code explained in the previous article(Because we are trying to retrieve the same data inserted there). Now the keyspace ‘USERKEYSPACE‘ contains column family ‘userColumnFamily‘ . And the column family contains data as shown in the schematic.
Where names is the row key and 1 , 2 and 3 are column names. Values are there against column names as shown above.
ReadSample.java
import me.prettyprint.hector.api.Cluster;
import me.prettyprint.hector.api.Keyspace;
import me.prettyprint.hector.api.beans.HColumn;
import me.prettyprint.hector.api.factory.HFactory;
import me.prettyprint.hector.api.query.ColumnQuery;
import me.prettyprint.hector.api.query.QueryResult;
public class ReadSample {
Cluster cluster = null;
Keyspace keySpace = null;
ColumnQuery
QueryResult
public ReadSample() {
}
public void readDetails() {
cluster = HFactory.getOrCreateCluster("Test Cluster", "localHost:9160");
keySpace = HFactory.createKeyspace("USERKEYSPACE", cluster);
columnQuery = HFactory.createStringColumnQuery(keySpace);
columnQuery.setColumnFamily("userColumnFamily").setKey("names")
.setName("1");
result = columnQuery.execute();
System.out.println("Key = " + result.get().getName() + " ; Value = "
+ result.get().getValue());
columnQuery.setColumnFamily("userColumnFamily").setKey("names")
.setName("2");
result = columnQuery.execute();
System.out.println("Key = " + result.get().getName() + " ; Value = "
+ result.get().getValue());
columnQuery.setColumnFamily("userColumnFamily").setKey("names")
.setName("3");
result = columnQuery.execute();
System.out.println("Key = " + result.get().getName() + " ; Value = "
+ result.get().getValue());
System.out.println("Finished...");
}
public static void main(String[] args) {
ReadSample sample = new ReadSample();
sample.readDetails();
}
}
Output
Compile and run the code . The output will be :
Key = 1 ; Value = Bijoy
Key = 2 ; Value = Karthik
Key = 3 ; Value = JayaKrishnan
Finished…
See Related:
Configuring Apache Cassandra in local machine
Inserting data in to Apache Cassandra database
Listing columns of a column family using java
Deleting column from Apache Cassandra using Java