QuerySystem.java

package org.prevayler.demos.scalability.prevayler;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.prevayler.demos.scalability.Record;
import org.prevayler.demos.scalability.RecordIterator;

class QuerySystem implements ScalabilitySystem {

	private static final long serialVersionUID = -8181198939095700706L;
	private Map recordsByName = new HashMap();


	public List queryByName(String name) {
		return (List)recordsByName.get(name);
	}


	public void replaceAllRecords(RecordIterator newRecords) {
		recordsByName.clear();

		while (newRecords.hasNext()) {
			put(newRecords.next());
		}

		makeReadOnly();
	}


	private void put(Record newRecord) {
		List records = queryByName(newRecord.getName());
		if (records == null) {
			records = new ArrayList();
			recordsByName.put(newRecord.getName(), records);
		}
		
		records.add(newRecord);
	}


	/** This is necessary so that the clients cannot alter the Lists they receive as query results.
	*/
	private void makeReadOnly() {
		Iterator entries = recordsByName.entrySet().iterator();
		while (entries.hasNext()) {
			Map.Entry entry = (Map.Entry)entries.next();
			entry.setValue(Collections.unmodifiableList((List)entry.getValue()));
		}
	}
}