org.axonframework.commandhandling.distributed

Class ConsistentHash

java.lang.Object

org.axonframework.commandhandling.distributed.ConsistentHash

public class ConsistentHash
extends Object

Component used by command routers to find members capable of handling a given command. Members are selected based on their capabilities and a given routing key. If a ConsistentHash is asked to provide a member for a given routing key it will always returning the same Member as long as none of the memberships have changed.

A ConsistentHash is used to route commands targeting the same aggregate to the same member. In that case the aggregate identifier is the routing key.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ConsistentHash.ConsistentHashMember Member implementation used by a ConsistentHash registry.

Constructor Summary

Constructors

Constructor and Description
ConsistentHash() Initializes a new ConsistentHash.
ConsistentHash(Function<String,String> hashFunction) Initializes a new ConsistentHash using the given hashFunction to calculate positions for each member on the ring.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object o)
Collection<ConsistentHash.ConsistentHashMember>	getEligibleMembers(String routingKey) Returns the collection of nodes, represented as ConsistentHash.ConsistentHashMember, in the order they would be considered for the given routing key.
Optional<Member>	getMember(String routingKey, CommandMessage<?> commandMessage) Returns the member instance to which the given message should be routed.
Set<Member>	getMembers() Returns the set of members registered with this consistent hash instance.
protected static String	hash(String routingKey) Returns the hash of the given routingKey.
int	hashCode()
String	toString()
int	version() Returns the version of this consistent hash instance.
ConsistentHash	with(Member member, int loadFactor, CommandMessageFilter commandFilter) Registers the given member with given loadFactor and commandFilter if it is not already contained in the ConsistentHash.
ConsistentHash	without(Member member) Deregisters the given member and returns a new ConsistentHash with updated memberships.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ConsistentHash

public ConsistentHash()

Initializes a new ConsistentHash. To register members use with(Member, int, CommandMessageFilter).

ConsistentHash

public ConsistentHash(Function<String,String> hashFunction)

Initializes a new ConsistentHash using the given hashFunction to calculate positions for each member on the ring. To register members use with(Member, int, CommandMessageFilter).

Parameters:

hashFunction - The hash function to use to calculate each member's positions on the ring

Method Detail

hash

protected static String hash(String routingKey)

Returns the hash of the given routingKey. By default this creates a MD5 hash with hex encoding.

Parameters:

routingKey - the routing key to hash

Returns:

a hash of the input key

getEligibleMembers

public Collection<ConsistentHash.ConsistentHashMember> getEligibleMembers(String routingKey)

Returns the collection of nodes, represented as ConsistentHash.ConsistentHashMember, in the order they would be considered for the given routing key. Whether a CommandMessage would be forwarded to each of the candidates, depends on the Command Filter of each node.

Parameters:

routingKey - The routing key to select ordering

Returns:

A collection containing each of the nodes, in the order they would be considered

getMember

public Optional<Member> getMember(String routingKey,
                                  CommandMessage<?> commandMessage)

Returns the member instance to which the given message should be routed. If no suitable member could be found an empty Optional is returned.

Parameters:

routingKey - the routing that should be used to select a member

commandMessage - the command message to find a member for

Returns:

the member that should handle the message or an empty Optional if no suitable member was found

getMembers

public Set<Member> getMembers()

Returns the set of members registered with this consistent hash instance.

Returns:

the members of this consistent hash

with

public ConsistentHash with(Member member,
                           int loadFactor,
                           CommandMessageFilter commandFilter)

Registers the given member with given loadFactor and commandFilter if it is not already contained in the ConsistentHash. It will return the current ConsistentHash if the addition is a duplicate and returns a new ConsistentHash with updated memberships if it is not.

The relative loadFactor of the member determines the likelihood of being selected as a destination for a command.

Parameters:

member - the member to register

loadFactor - the load factor of the new member

commandFilter - filter describing which commands can be handled by the given member

Returns:

a new ConsistentHash instance with updated memberships

without

public ConsistentHash without(Member member)

Deregisters the given member and returns a new ConsistentHash with updated memberships.

Parameters:

member - the member to remove from the consistent hash

Returns:

a new ConsistentHash instance with updated memberships

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

version

public int version()

Returns the version of this consistent hash instance. The version is increased by one each time a change is made.

Returns:

the version of this consistent hash instance