com.dxfeed.api.osub

Class WildcardSymbol

java.lang.Object

com.dxfeed.api.osub.WildcardSymbol

All Implemented Interfaces:

Serializable

public class WildcardSymbol
extends Object
implements Serializable

Represents [wildcard] subscription to all events of the specific event type. The WildcardSymbol.ALL constant can be added to any DXFeedSubscription instance with addSymbols method to the effect of subscribing to all possible event symbols. The corresponding subscription will start receiving all published events of the corresponding types.

NOTE: Wildcard subscription can create extremely high network and CPU load for certain kinds of high-frequency events like quotes. It requires a special arrangement on the side of upstream data provider and is disabled by default in upstream feed configuration. Make that sure you have adequate resources and understand the impact before using it. It can be used for low-frequency events only (like Forex quotes), because each instance of DXFeedSubscription processes events in a single thread and there is no provision to load-balance wildcard subscription amongst multiple threads. Contact your data provider for the corresponding configuration arrangement if needed.

You need to create DXEndpoint with DXFEED_WILDCARD_ENABLE_PROPERTY property in order to support subscription to this wildcard symbols via DXFeed and to observe wildcard subscription via DXPublisher.

Sample usage

See DXFeed on how to create connection to the feed. The following code creates listener that prints all TimeAndSale events that are coming from the feed using wildcard subscription symbol:

 DXFeedSubscription<TimeAndSale> sub = feed.createSubscription(TimeAndSale.class);
 sub.addEventListener(new DXFeedEventListener<TimeAndSale>() {
     public void eventsReceived(List<TimeAndSale> events) {
         for (TimeAndSale event : events)
             System.out.println(event);
     }
 });
 sub.addSymbols(WildcardSymbol.ALL);

Observing wildcard subscription

Any instance of ObservableSubscription that is retrieved via DXPublisher.getSubscription method can observe WildcardSymbol.ALL object in its set of symbols if any feed consumer subscribes to wildcard symbol. The recommended approach is to use instanceof WildcardSymbol check if support of wildcard subscription is required.

Limitations

Do not mix WildcardSymbol subscription and subscription to other symbols in a single instance of DXFeedSubscription. Doing so may result in a duplication of events and/or other implementation-specific adverse effects.

Subscription via wildcard symbol for LastingEvent types does not count for the purpose of DXFeed.getLastEvent and DXFeed.getLastEvents methods. Lasting events that are received via wildcard subscription are not conflated in the usual way. They may incur significantly higher resource requirements to process them and may get queued when network and CPU resources are inadequate.

Future compatibility

In the future this class may be extended with support for more specific wildcards in addition to ALL. Data provides that publish events via DXPublisher, track subscription via DXPublisher.getSubscription method, and plan to detect wildcard subscription in order to start publishing all possible events, should use symbol instanceof WildcardSymbol code to detect wildcard symbols to be future-proof.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static WildcardSymbol	ALL Represents [wildcard] subscription to all events of the specific event type.
static String	RESERVED_PREFIX Symbol prefix that is reserved for wildcard subscriptions.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object o)
int	hashCode()
String	toString() Returns "*".

Methods inherited from class java.lang.Object

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

Field Detail

RESERVED_PREFIX

public static final String RESERVED_PREFIX

Symbol prefix that is reserved for wildcard subscriptions. Any subscription starting with "*" is ignored with the exception of WildcardSymbol subscription.

See Also:

Constant Field Values

ALL

public static final WildcardSymbol ALL

Represents [wildcard] subscription to all events of the specific event type.

NOTE: Wildcard subscription can create extremely high network and CPU load for certain kinds of high-frequency events like quotes. It requires a special arrangement on the side of upstream data provider and is disabled by default in upstream feed configuration. Make that sure you have adequate resources and understand the impact before using it. It can be used for low-frequency events only (like Forex quotes), because each instance of DXFeedSubscription processes events in a single thread and there is no provision to load-balance wildcard subscription amongst multiple threads. Contact your data provider for the corresponding configuration arrangement if needed.

See Also:

WildcardSymbol

Method Detail

toString

public String toString()

Returns "*".

Overrides:

toString in class Object

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object