How to get keys of a particular type

Question

Following are my objects:
DepartmentKey - primary key is departmentName, a String
Department
EmployeeKey - primary key is employeeId, an integer
Employee
I have 5 DepartmentKey-Department key-value entries in a cache and 2000 EmployeeKey-Employee key-value entries in the same cache.
How do I get all the DepartmentKeys from the cache? In general, how to get keys of a particular type (class name)?
Thanks
Ghanshyam

Answer 1

I guess I am deeply off track regarding the general approach towards storing items in the cache.
Following is my problem domain:
A Merchant is any establishment that accepts credit cards. (It could be the local Subway down the street or Macy's, etc.). A Transaction is a credit card transaction.
public class Merchant implements Serializable{
private String merchantId; // primary key
private double averageTxnAmount;
private double totalTxnAmount;
private long totalTxnCount;
public class Transaction implements Serializable{
private String merchantId; // merchant that originated the txn
private double amount;
private Timestamp txnTime;
private String txnType; // sale, return, etc.
public class MerchantKey implements Serializable, KeyAssociation{
private String merchantId;
public Object getAssociatedKey{
return merchantId;
public class TransactionKey implements Serializable, KeyAssociation{
private String merchantId;
private Timestamp txnTime;
private double amount;
public Object getAssociatedKey{
return merchantId;
I want to update a merchant's average txn amount as transactions come in.
Let's say I have a million merchants in a partitioned cache cluster spread across some machines.
Transactions come into the cluster quite rapidly, say tens in a second. The process that inserts the transaction into the cluster must also update the merchant to which the transaction belongs, as follows:
Transaction t = ...
cache.put(tKey, t); // store the transaction into the cache
MerchantKey mKey = new MerchantKey(txn.getMerchantId());
Merchant m = (Merchant)cache.get(mKey);
// update the merchant's avg txn amt
m.setAverageTxnAmount((txn.getAmount() + m.getTotalTxnAmount())/m.getTotalTxnCount() + 1);
m.setTotalCount(m.getTotalCount() + 1);
// store the updated merchant back into cache
cache.put(mKey, m);
OR
Transaction t = ...
cache.put(tKey, t); // store the transaction into the cache
MerchantKey mKey = new MerchantKey(txn.getMerchantId());
Merchant m = (Merchant)cache.get(mKey);
MerchantUpdater agent = new MerchantUpdater(t);
cache.invoke(mKey, agent);
public class MerchantUpdater implements AbstractProcessor{
public Object process(Entry entry){
Merchant m = (Merchant)entry.getValue();
// update m's avg txn amt, total count using t
entry.setValue(m);
The basic idea is to store all merchants and all transactions (which could be tens of millions in a day) for a day in memory and to update the merchant objects as transactions come in throughout the day. The above example shows updating just the merchant's average txn amount, but in reality, it could be updating a number of things about the merchant.
Am I using the api in the right spirit or is my approach seriously whacked? Can you please comment?
Thanks
Ghanshyam