Listing columns from Apache Cassandra using Java

We already discussed the fundamentals of Apache Cassandra. We discussed about configuring Apache Cassandra in local machine and to start/stop Cassandra database . In the previous coding example we learned to insert data into Apache Cassandra and read data from Cassandra. In this chapter we are discussing how the list of columns from a column family is fetching from Cassandra and how those are iterating .

Listing columns from Apache Cassandra using Java

We already created a key space ‘USERKEYSPACE‘ using the command line client as explained earlier.We already created a column family ‘userColumnFamily‘ in the key space. In the data inserting sample we discussed earlier , we inserted 3 columns . In this chapter we are retrieving the same set of columns using a ‘SliceQuery‘ object.After inserting data , the column family data arrangement will be like this:

Now lets see the java code to retrieve the existing data.

FetchListSample.java

import me.prettyprint.cassandra.model.HColumnImpl; import me.prettyprint.cassandra.serializers.StringSerializer; import me.prettyprint.cassandra.service.ColumnSliceIterator; import me.prettyprint.hector.api.Cluster; import me.prettyprint.hector.api.Keyspace; import me.prettyprint.hector.api.factory.HFactory; import me.prettyprint.hector.api.query.SliceQuery;


public class FetchListSample {

    Cluster cluster = null;

    Keyspace keySpace = null;
    public FetchListSample() {
    }
    public void getList() {

        cluster = HFactory.getOrCreateCluster("Test Cluster", "localHost:9160");

        keySpace = HFactory.createKeyspace("USERKEYSPACE", cluster);

        SliceQuery query = HFactory

                .createSliceQuery(keySpace, StringSerializer.get(),

                        StringSerializer.get(), StringSerializer.get())

                .setKey("names").setColumnFamily("userColumnFamily");

        ColumnSliceIterator iterator = new ColumnSliceIterator(

                query, null, "\u00FFF", false);

        while (iterator.hasNext()) {

            HColumnImpl column = (HColumnImpl) iterator

                    .next();

            System.out.println("Column name = " + column.getName()

                    + "; Column value = " + column.getValue());

        }
    }
    public static void main(String[] args) {

        FetchListSample sample = new FetchListSample();

        sample.getList();

    }

}

Output

To run this application Apache Cassandra should be configured and started in local machine as discussed in: Configuring Apache Cassandra. Also the libraries listed there should be added to the workspace . The output will be:

Column name = 1; Column value = Bijoy

Column name = 2; Column value = Karthik

Column name = 3; Column value = JayaKrishnan