Triple composite key in Hbase - hadoop

Question

I have a use case where I want 3 level composite key.
For eg.
Rollnumber:class:friendsRollNumber
I would want to query "Get all friends for a particular roll number and a class"
I could not find sufficient examples over net to use composite keys and range scans over it together.
Currently, I am doing the following.
byte[]rowkey = Bytes.add(Bytes.tobytes("myrollnumber"),Bytes.tobytes("myClass"),Bytes.tobytes("myFriendsRollNumber"))
This is the way I form row key .
Will it select region server based on myRollNumber and myClass ? If not How can I do that ?
Also , For range scan , what is the correct way to use it. I am doing it in the following way. I am still in process of writing the code , so have not tested it.
Scan s = new Scan();
Filter f = New PrefixFilter(Bytes.tobytes("myrollnumber"),Bytes.tobytes("class"))
s.setFilter(f)
Is the above way correct to scan as per my requirement ?
Also , how to get the individual parts of rowKey from the scanner ?

Answer 1

Try this:
byte[] prefix=Bytes.toBytes("rollnumber" + "class");
Scan scan = new Scan(prefix));
PrefixFilter prefixFilter = new PrefixFilter(prefix);
scan.addFilter(prefixFilter);
ResultScanner resultScanner = table.getScanner(scan);

Answer 2

For your requirement, you can use start stop row feature of Scan. You do not need a filter.
byte[]startRow= Bytes.add(Bytes.tobytes("search_rollnumber"),Bytes.tobytes("myClass"));
byte[]stopRow= Bytes.add(Bytes.tobytes("search_rollnumber"),Bytes.tobytes("myClass"));
stopRow[stopRow.length - 1]++;
Scan s = new Scan(startRow, stopRow);
Using this scan you will get all rows starting with search_rollnumberMyClass.
I am not sure you use : in your rowkey. But i think you should if both rollnumber and class are represented as integer.