com.datastax.driver.core.policies

Class HostFilterPolicy

java.lang.Object

com.datastax.driver.core.policies.HostFilterPolicy

All Implemented Interfaces:

ChainableLoadBalancingPolicy, LoadBalancingPolicy

Direct Known Subclasses:

WhiteListPolicy

public class HostFilterPolicy
extends Object
implements ChainableLoadBalancingPolicy

A load balancing policy wrapper that ensures that only hosts matching the predicate 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 matching the predicate provided when constructing this policy will ever be returned. Any host not matching the predicate will be considered IGNORED and thus will not be connected to.

Constructor Summary

Constructors

Constructor and Description
HostFilterPolicy(LoadBalancingPolicy childPolicy, Predicate<Host> predicate) Create a new policy that wraps the provided child policy but only "allows" hosts matching the predicate.

Method Summary

Modifier and Type	Method and Description
void	close() Gets invoked at cluster shutdown.
HostDistance	distance(Host host) Returns the distance assigned by this policy to the provided host.
static HostFilterPolicy	fromDCBlackList(LoadBalancingPolicy childPolicy, Iterable<String> dcs) Create a new policy that wraps the provided child policy but only "forbids" hosts whose DC belongs to the provided list.
static HostFilterPolicy	fromDCWhiteList(LoadBalancingPolicy childPolicy, Iterable<String> dcs) Create a new policy that wraps the provided child policy but only "allows" hosts whose DC belongs to the provided list.
LoadBalancingPolicy	getChildPolicy() Returns the child policy.
void	init(Cluster cluster, Collection<Host> hosts) Initialize this load balancing policy.
Iterator<Host>	newQueryPlan(String loggedKeyspace, Statement statement) 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

HostFilterPolicy

public HostFilterPolicy(LoadBalancingPolicy childPolicy,
                        Predicate<Host> predicate)

Create a new policy that wraps the provided child policy but only "allows" hosts matching the predicate.

Parameters:

childPolicy - the wrapped policy.

predicate - the host predicate. Only hosts matching this predicate may get connected to (whether they will get connected to or not depends on the child policy).

Method Detail

getChildPolicy

public LoadBalancingPolicy getChildPolicy()

Description copied from interface: ChainableLoadBalancingPolicy

Returns the child policy.

Specified by:

getChildPolicy in interface ChainableLoadBalancingPolicy

Returns:

the child policy.

init

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

Initialize this load balancing policy.

Note that the driver guarantees that it will call this method exactly once per policy object and will do so before any call to another of the methods of the 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) matches the predicate.

distance

public HostDistance distance(Host host)

Returns the distance assigned by this policy to the provided host.

The distance of an host influence how much connections are kept to the node (see HostDistance). A policy should assign a LOCAL distance to nodes that are susceptible to be returned first by newQueryPlan and it is useless for newQueryPlan to return hosts to which it assigns an IGNORED distance.

The host distance is primarily used to prevent keeping too many connections to host in remote datacenters when the policy itself always picks host in the local datacenter first.

Specified by:

distance in interface LoadBalancingPolicy

Parameters:

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

Returns:

HostDistance.IGNORED if host is not matching the predicate, the HostDistance as returned by the wrapped policy otherwise.

newQueryPlan

public Iterator<Host> newQueryPlan(String loggedKeyspace,
                                   Statement statement)

Returns the hosts to use for a new query.

Each new query will call this method. The first host in the result will then be used to perform the query. In the event of a connection problem (the queried host is down or appear to be so), the next host will be used. If all hosts of the returned Iterator are down, the query will fail.

It is guaranteed that only hosts matching the predicate will be returned.

Specified by:

newQueryPlan in interface LoadBalancingPolicy

Parameters:

loggedKeyspace - the currently logged keyspace (the one set through either Cluster.connect(String) or by manually doing a USE query) for the session on which this plan need to be built. This can be null if the corresponding session has no keyspace logged in.

statement - the query for which to build a plan.

Returns:

an iterator of Host. The query is tried against the hosts returned by this iterator in order, until the query has been sent successfully to one of the host.

onUp

public void onUp(Host host)

Description copied from interface: LoadBalancingPolicy

Called when a node is determined to be up.

Specified by:

onUp in interface LoadBalancingPolicy

Parameters:

host - the host that has been detected up.

onDown

public void onDown(Host host)

Description copied from interface: LoadBalancingPolicy

Called when a node is determined to be down.

Specified by:

onDown in interface LoadBalancingPolicy

Parameters:

host - the host that has been detected down.

onAdd

public void onAdd(Host host)

Description copied from interface: LoadBalancingPolicy

Called when a new node is added to the cluster.

The newly added node should be considered up.

Specified by:

onAdd in interface LoadBalancingPolicy

Parameters:

host - the host that has been newly added.

onRemove

public void onRemove(Host host)

Description copied from interface: LoadBalancingPolicy

Called when a node is removed from the cluster.

Specified by:

onRemove in interface LoadBalancingPolicy

Parameters:

host - the removed host.

close

public void close()

Description copied from interface: LoadBalancingPolicy

Gets invoked at cluster shutdown.

This gives the policy the opportunity to perform some cleanup, for instance stop threads that it might have started.

Specified by:

close in interface LoadBalancingPolicy

fromDCWhiteList

public static HostFilterPolicy fromDCWhiteList(LoadBalancingPolicy childPolicy,
                                               Iterable<String> dcs)

Create a new policy that wraps the provided child policy but only "allows" hosts whose DC belongs to the provided list.

Parameters:

childPolicy - the wrapped policy.

dcs - the DCs.

Returns:

the policy.

fromDCBlackList

public static HostFilterPolicy fromDCBlackList(LoadBalancingPolicy childPolicy,
                                               Iterable<String> dcs)

Create a new policy that wraps the provided child policy but only "forbids" hosts whose DC belongs to the provided list.

Parameters:

childPolicy - the wrapped policy.

dcs - the DCs.

Returns:

the policy.