HBase - Hadoop: The Definitive Guide - page 721

static final byte [] INFO_COLUMNFAMILY = Bytes . toBytes ( "info" );
static final byte [] NAME_QUALIFIER = Bytes . toBytes ( "name" );
static final byte [] LOCATION_QUALIFIER = Bytes . toBytes ( "location" );
static final byte [] DESCRIPTION_QUALIFIER =
Bytes . toBytes ( "description" );
public Map < String , String > getStationInfo ( HTable table , String
stationId )
throws IOException {
Get get = new Get ( Bytes . toBytes ( stationId ));
get . addFamily ( INFO_COLUMNFAMILY );
Result res = table . get ( get );
if ( res == null ) {
return null ;
}
Map < String , String > resultMap = new LinkedHashMap < String ,
String >();
resultMap . put ( "name" , getValue ( res , INFO_COLUMNFAMILY ,
NAME_QUALIFIER ));
resultMap . put ( "location" , getValue ( res , INFO_COLUMNFAMILY ,
LOCATION_QUALIFIER ));
resultMap . put ( "description" , getValue ( res , INFO_COLUMNFAMILY ,
DESCRIPTION_QUALIFIER ));
return resultMap ;
}
private static String getValue ( Result res , byte [] cf , byte []
qualifier ) {
byte [] value = res . getValue ( cf , qualifier );
return value == null ? "" : Bytes . toString ( value );
}
In this example, getStationInfo() takes an HTable instance and a station ID. To
get the station info, we use get() , passing a Get instance configured to retrieve all the
column values for the row identified by the station ID in the defined column family,
INFO_COLUMNFAMILY .
The get() results are returned in a Result . It contains the row, and you can fetch cell
values by stipulating the column cell you want. The getStationInfo() method con-
verts the Result into a more friendly Map of String keys and values.
We can already see how there is a need for utility functions when using HBase. There are
an increasing number of abstractions being built atop HBase to deal with this low-level in-
teraction, but it's important to understand how this works and how storage choices make a
difference.