com.datastax.driver.core.policies

Class WhiteListPolicy

java.lang.Object

com.datastax.driver.core.policies.WhiteListPolicy

All Implemented Interfaces:

Host.StateListener, LoadBalancingPolicy

public class WhiteListPolicy
extends Object
implements LoadBalancingPolicy

A load balancing policy wrapper that ensure that only hosts from a provided white list will ever be returned.

This policy wraps another load balancing policy and will delegate the choice of hosts to the wrapped policy with the exception that only hosts contained in the white list provided when constructing this policy will ever be returned. Any host not in the while list will be considered IGNORED and thus will not be connected to.

This policy can be useful to ensure that the driver only connects to a predefined set of hosts. Keep in mind however that this policy defeats somewhat the host auto-detection of the driver. As such, this policy is only useful in a few special cases or for testing, but is not optimal in general. If all you want to do is limiting connections to hosts of the local data-center then you should use DCAwareRoundRobinPolicy and *not* this policy in particular.

Constructor Summary

Constructors

Constructor and Description
WhiteListPolicy(LoadBalancingPolicy childPolicy, Collection<InetAddress> whiteList) Create a new policy that wraps the provided child policy but only "allow" hosts from the provided while list.

Method Summary

Methods

Modifier and Type	Method and Description
HostDistance	distance(Host host) Return the HostDistance for the provided host.
void	init(Cluster cluster, Collection<Host> hosts) Initialize this load balancing policy.
Iterator<Host>	newQueryPlan(Query query) Returns the hosts to use for a new query.
void	onAdd(Host host) Called when a new node is added to the cluster.
void	onDown(Host host) Called when a node is determined to be down.
void	onRemove(Host host) Called when a node is removed from the cluster.
void	onUp(Host host) Called when a node is determined to be up.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WhiteListPolicy

public WhiteListPolicy(LoadBalancingPolicy childPolicy,
               Collection<InetAddress> whiteList)

Create a new policy that wraps the provided child policy but only "allow" hosts from the provided while list.

Parameters:

childPolicy - the wrapped policy.

whiteList - the white listed hosts. Only hosts from this list may get connected to (whether they will get connected to or not depends on the child policy).

Method Detail

init

public void init(Cluster cluster,
        Collection<Host> hosts)

Initialize this load balancing policy.

Specified by:

init in interface LoadBalancingPolicy

Parameters:

cluster - the Cluster instance for which the policy is created.

hosts - the initial hosts to use.

Throws:

IllegalArgumentException - if none of the host in hosts (which will correspond to the contact points) are part of the white list.

distance

public HostDistance distance(Host host)

Return the HostDistance for the provided host.

Specified by:

distance in interface LoadBalancingPolicy

Parameters:

host - the host of which to return the distance of.

Returns:

HostDistance.IGNORED if host is not part of the white list, the HostDistance as returned by the wrapped policy otherwise.

newQueryPlan

public Iterator<Host> newQueryPlan(Query query)

Returns the hosts to use for a new query.

It is guaranteed that only hosts from the white list will be returned.

Specified by:

newQueryPlan in interface LoadBalancingPolicy

Parameters:

query - the query for which to build the plan.

Returns:

the new query plan.

onUp

public void onUp(Host host)

Description copied from interface: Host.StateListener

Called when a node is determined to be up.

Specified by:

onUp in interface Host.StateListener

Parameters:

host - the host that has been detected up.

onDown

public void onDown(Host host)

Description copied from interface: Host.StateListener

Called when a node is determined to be down.

Specified by:

onDown in interface Host.StateListener

Parameters:

host - the host that has been detected down.

onAdd

public void onAdd(Host host)

Description copied from interface: Host.StateListener

Called when a new node is added to the cluster.

The newly added node should be considered up.

Specified by:

onAdd in interface Host.StateListener

Parameters:

host - the host that has been newly added.

onRemove

public void onRemove(Host host)

Description copied from interface: Host.StateListener

Called when a node is removed from the cluster.

Specified by:

onRemove in interface Host.StateListener

Parameters:

host - the removed host.