Round-Robin

"Round-robin" describes a method of choosing a resource for a task from a list of available ones, usually for the purposes of load balancing. Such may be distribution of incoming requests to a number of processors, worker threads or servers. As the basic algorithm, the scheduler selects a resource pointed to by a counter from a list, after which the counter is incremented and if the end is reached, returned to the beginning of the list. Round-robin selection has a positive characteristic of preventing starvation, as every resource will be eventually chosen by the scheduler, but may be unsuitable for some applications where affinity is desirable, for example when assigning a process to a CPU or in link aggregation.

I had to implement the same thing for an external call, we need to balance the load to a set of servers equally, so I had to create a CircularQueue (It's just a wrapper for a List)
package com.vzw.common.globalrouter.util; import java.util.List; import java.util.ArrayList; public class CircularQueue { private ArrayList list; private int index; private CircularQueue(){} public CircularQueue(List list){ this.list=new ArrayList(); this.list.addAll(list); index=0; } public int size(){ return list.size(); } public Object first(){ return list.get(0); } public Object last(){ return list.get(list.size()-1); } synchronized public Object current(){ return list.get(index); } public Object get(int index){ return list.get(index); } synchronized public Object next(){ index = (index==list.size())?0:index;//starts again when end is reached return list.get( index++ ); } public List getQContents(){ return new ArrayList(this.list); } } All my items are located in an XML, and I just load them in an existing method, I only added a new block of code <posHost billSys = "POS-LOCAL" posURL = "http://127.0.0.1:8888/sqa3/POSWSAdapter"/> <posHost billSys = "POS-QA3" posURL = "http://pos-qa3-new.odc.vzwcorp.com:8888/sqa3/POSWSAdapter"/> <posHost billSys = "POS-QA4" posURL = "http://pos-qa4-new.odc.vzwcorp.com:8888/sqa3/POSWSAdapter"/> private static CircularQueue posHostQueue; public static DVSHostVO getNextPOSHost(){ return (DVSHostVO)posHostQueue.next(); } .... public static void loadHosts (){ List<Element> elemPosHostList = rootElem.getChildren("posHost"); for (Element posHostElem: elemPosHostList){ String billSys = posHostElem.getAttributeValue("billSys"); String posUrl = posHostElem.getAttributeValue("posURL"); DVSHostVO dvsHostVO = new DVSHostVO(billSys, posUrl); tempPosHostList.add(dvsHostVO); } //synchronized multiple write threads only. synchronized(ServiceRegistry.class){ posHostQueue = new CircularQueue(tempPosHostList); } }