class Subscription

package com.lightstreamer.client

Class representing a Subscription to be submitted to a Lightstreamer Server. It contains subscription details and the listeners needed to process the real-time data.
After the creation, a Subscription object is in the "inactive" state. When a Subscription object is subscribed to on a LightstreamerClient object, through the LightstreamerClient.subscribe(Subscription) method, its state becomes "active". This means that the client activates a subscription to the required items through Lightstreamer Server and the Subscription object begins to receive real-time events.
A Subscription can be configured to use either an Item Group or an Item List to specify the items to be subscribed to and using either a Field Schema or Field List to specify the fields.
"Item Group" and "Item List" are defined as follows:

  • "Item Group": an Item Group is a String identifier representing a list of items. Such Item Group has to be expanded into a list of items by the getItems method of the MetadataProvider of the associated Adapter Set. When using an Item Group, items in the subscription are identified by their 1-based index within the group.
    It is possible to configure the Subscription to use an "Item Group" using the this.setItemGroup(String) method.
  • "Item List": an Item List is an array of Strings each one representing an item. For the Item List to be correctly interpreted a LiteralBasedProvider or a MetadataProvider with a compatible implementation of getItems has to be configured in the associated Adapter Set.
    Note that no item in the list can be empty, can contain spaces or can be a number.
    When using an Item List, items in the subscription are identified by their name or by their 1-based index within the list.
    It is possible to configure the Subscription to use an "Item List" using the this.setItems(String[]) method or by specifying it in the constructor.
"Field Schema" and "Field List" are defined as follows:
  • "Field Schema": a Field Schema is a String identifier representing a list of fields. Such Field Schema has to be expanded into a list of fields by the getFields method of the MetadataProvider of the associated Adapter Set. When using a Field Schema, fields in the subscription are identified by their 1-based index within the schema.
    It is possible to configure the Subscription to use a "Field Schema" using the this.setFieldSchema(String) method.
  • "Field List": a Field List is an array of Strings each one representing a field. For the Field List to be correctly interpreted a LiteralBasedProvider or a MetadataProvider with a compatible implementation of getFields has to be configured in the associated Adapter Set.
    Note that no field in the list can be empty or can contain spaces.
    When using a Field List, fields in the subscription are identified by their name or by their 1-based index within the list.
    It is possible to configure the Subscription to use a "Field List" using the this.setFields(String[]) method or by specifying it in the constructor.

Constructor

new(mode:String, items:NativeArray<String>, fields:NativeArray<String>)

Creates an object to be used to describe a Subscription that is going to be subscribed to through Lightstreamer Server. The object can be supplied to LightstreamerClient.subscribe(Subscription) and LightstreamerClient.unsubscribe(Subscription), in order to bring the Subscription to "active" or back to "inactive" state.
Note that all of the methods used to describe the subscription to the server can only be called while the instance is in the "inactive" state; the only exception is this.setRequestedMaxFrequency(String).

Parameters:

subscriptionMode

the subscription mode for the items, required by Lightstreamer Server. Permitted values are:

  • MERGE
  • DISTINCT
  • RAW
  • COMMAND

items

an array of items to be subscribed to through Lightstreamer server.
It is also possible specify the "Item List" or "Item Group" later through this.setItems(String[]) and this.setItemGroup.

fields

an array of fields for the items to be subscribed to through Lightstreamer Server.
It is also possible to specify the "Field List" or "Field Schema" later through this.setFields(String[]) and this.setFieldSchema(String).

Throws:

IllegalArgumentException

If no or invalid subscription mode is passed.

IllegalArgumentException

If either the items or the fields array is left null.

IllegalArgumentException

If the specified "Item List" or "Field List" is not valid; see this.setItems(String[]) and this.setFields(String[]) for details.

Methods

addListener(listener:SubscriptionListener):Void

Adds a listener that will receive events from the Subscription instance.
The same listener can be added to several different Subscription instances.

lifecycle A listener can be added at any time. A call to add a listener already present will be ignored.

Parameters:

listener

An object that will receive the events as documented in the SubscriptionListener interface.

See also:

removeListener(listener:SubscriptionListener):Void

Removes a listener from the Subscription instance so that it will not receive events anymore.

lifecycle a listener can be removed at any time.

Parameters:

listener

The listener to be removed.

See also:

getListeners():NativeList<SubscriptionListener>

Returns a list containing the SubscriptionListener instances that were added to this client.

Returns:

a list containing the listeners that were added to this client.

See also:

isActive():Bool

Inquiry method that checks if the Subscription is currently "active" or not. Most of the Subscription properties cannot be modified if a Subscription is "active".
The status of a Subscription is changed to "active" through the
LightstreamerClient.subscribe(Subscription) method and back to "inactive" through the LightstreamerClient.unsubscribe(Subscription) one.

lifecycle This method can be called at any time.

Returns:

true/false if the Subscription is "active" or not.

See also:

isSubscribed():Bool

Inquiry method that checks if the Subscription is currently subscribed to through the server or not.
This flag is switched to true by server sent Subscription events, and back to false in case of client disconnection, LightstreamerClient.unsubscribe(Subscription) calls and server sent unsubscription events.

lifecycle This method can be called at any time.

Returns:

true/false if the Subscription is subscribed to through the server or not.

getDataAdapter():Null<String>

Inquiry method that can be used to read the name of the Data Adapter specified for this Subscription through this.setDataAdapter(String).

lifecycle This method can be called at any time.

Returns:

the name of the Data Adapter; returns null if no name has been configured, so that the "DEFAULT" Adapter Set is used.

setDataAdapter(dataAdapter:Null<String>):Void

Setter method that sets the name of the Data Adapter (within the Adapter Set used by the current session) that supplies all the items for this Subscription.
The Data Adapter name is configured on the server side through the "name" attribute of the "data_provider" element, in the "adapters.xml" file that defines the Adapter Set (a missing attribute configures the "DEFAULT" name).
Note that if more than one Data Adapter is needed to supply all the items in a set of items, then it is not possible to group all the items of the set in a single Subscription. Multiple Subscriptions have to be defined.

Parameters:

dataAdapter

the name of the Data Adapter. A null value is equivalent to the "DEFAULT" name.

Throws:

IllegalStateException

if the Subscription is currently "active".

See also:

getMode():String

Inquiry method that can be used to read the mode specified for this Subscription.

lifecycle This method can be called at any time.

Returns:

the Subscription mode specified in the constructor.

getItems():Null<NativeArray<String>>

Inquiry method that can be used to read the "Item List" specified for this Subscription. Note that if the single-item-constructor was used, this method will return an array of length 1 containing such item.

Returns:

the "Item List" to be subscribed to through the server or null if the Subscription was initialized with an "Item Group" or was not initialized at all.

setItems(items:Null<NativeArray<String>>):Void

Setter method that sets the "Item List" to be subscribed to through Lightstreamer Server.
Any call to this method will override any "Item List" or "Item Group" previously specified.

lifecycle This method can only be called while the Subscription instance is in its "inactive" state.

Parameters:

items

an array of items to be subscribed to through the server.

Throws:

IllegalArgumentException

if any of the item names in the "Item List" contains a space or is a number or is empty/null.

IllegalStateException

if the Subscription is currently "active".

getItemGroup():Null<String>

Inquiry method that can be used to read the item group specified for this Subscription.

Returns:

the "Item Group" to be subscribed to through the server or null if the Subscription was initialized with an "Item List" or was not initialized at all.

setItemGroup(group:Null<String>):Void

Setter method that sets the "Item Group" to be subscribed to through Lightstreamer Server.
Any call to this method will override any "Item List" or "Item Group" previously specified.

lifecycle This method can only be called while the Subscription instance is in its "inactive" state.

Parameters:

groupName

A String to be expanded into an item list by the Metadata Adapter.

Throws:

IllegalStateException

if the Subscription is currently "active".

getFields():Null<NativeArray<String>>

Inquiry method that can be used to read the "Field List" specified for this Subscription.

Returns:

the "Field List" to be subscribed to through the server or null if the Subscription was initialized with a "Field Schema" or was not initialized at all.

setFields(fields:Null<NativeArray<String>>):Void

Setter method that sets the "Field List" to be subscribed to through Lightstreamer Server.
Any call to this method will override any "Field List" or "Field Schema" previously specified.

lifecycle This method can only be called while the Subscription instance is in its "inactive" state.

Parameters:

fields

an array of fields to be subscribed to through the server.

Throws:

IllegalArgumentException

if any of the field names in the list contains a space or is empty/null.

IllegalStateException

if the Subscription is currently "active".

getFieldSchema():Null<String>

Inquiry method that can be used to read the field schema specified for this Subscription.

Returns:

the "Field Schema" to be subscribed to through the server or null if the Subscription was initialized with a "Field List" or was not initialized at all.

setFieldSchema(schema:Null<String>):Void

Setter method that sets the "Field Schema" to be subscribed to through Lightstreamer Server.
Any call to this method will override any "Field List" or "Field Schema" previously specified.

lifecycle This method can only be called while the Subscription instance is in its "inactive" state.

Parameters:

schemaName

A String to be expanded into a field list by the Metadata Adapter.

Throws:

IllegalStateException

if the Subscription is currently "active".

getRequestedBufferSize():Null<String>

Inquiry method that can be used to read the buffer size, configured though this.setRequestedBufferSize, to be requested to the Server for this Subscription.

lifecycle This method can be called at any time.

Returns:

An integer number, representing the buffer size to be requested to the server, or the string "unlimited", or null.

setRequestedBufferSize(size:Null<String>):Void

Setter method that sets the length to be requested to Lightstreamer Server for the internal queuing buffers for the items in the Subscription. A Queuing buffer is used by the Server to accumulate a burst of updates for an item, so that they can all be sent to the client, despite of bandwidth or frequency limits. It can be used only when the subscription mode is MERGE or DISTINCT and unfiltered dispatching has not been requested. Note that the Server may pose an upper limit on the size of its internal buffers.

Parameters:

size

An integer number, representing the length of the internal queuing buffers to be used in the Server. If the string "unlimited" is supplied, then no buffer size limit is requested (the check is case insensitive). It is also possible to supply a null value to stick to the Server default (which currently depends on the subscription mode).

Throws:

IllegalStateException

if the Subscription is currently "active".

IllegalArgumentException

if the specified value is not null nor "unlimited" nor a valid positive integer number.

See also:

getRequestedSnapshot():Null<String>

Inquiry method that can be used to read the snapshot preferences, configured through this.setRequestedSnapshot(String), to be requested to the Server for this Subscription.

lifecycle This method can be called at any time.

Returns:

"yes", "no", null, or an integer number.

setRequestedSnapshot(snapshot:Null<String>):Void

Setter method that enables/disables snapshot delivery request for the items in the Subscription. The snapshot can be requested only if the Subscription mode is MERGE, DISTINCT or COMMAND.

Parameters:

required

"yes"/"no" to request/not request snapshot delivery (the check is case insensitive). If the Subscription mode is DISTINCT, instead of "yes", it is also possible to supply an integer number, to specify the requested length of the snapshot (though the length of the received snapshot may be less than requested, because of insufficient data or server side limits); passing "yes" means that the snapshot length should be determined only by the Server. Null is also a valid value; if specified, no snapshot preference will be sent to the server that will decide itself whether or not to send any snapshot.

Throws:

IllegalStateException

if the Subscription is currently "active".

IllegalArgumentException

if the specified value is not "yes" nor "no" nor null nor a valid integer positive number.

IllegalArgumentException

if the specified value is not compatible with the mode of the Subscription:

  • In case of a RAW Subscription only null is a valid value;
  • In case of a non-DISTINCT Subscription only null "yes" and "no" are valid values.

See also:

getRequestedMaxFrequency():Null<String>

Inquiry method that can be used to read the max frequency, configured through this.setRequestedMaxFrequency(String), to be requested to the Server for this Subscription.

lifecycle This method can be called at any time.

Returns:

A decimal number, representing the max frequency to be requested to the server (expressed in updates per second), or the strings "unlimited" or "unfiltered", or null.

setRequestedMaxFrequency(freq:Null<String>):Void

Setter method that sets the maximum update frequency to be requested to Lightstreamer Server for all the items in the Subscription. It can be used only if the Subscription mode is MERGE, DISTINCT or COMMAND (in the latter case, the frequency limitation applies to the UPDATE events for each single key). For Subscriptions with two-level behavior (see Subscription.setCommandSecondLevelFields(String[]) and Subscription.setCommandSecondLevelFieldSchema(String)) , the specified frequency limit applies to both first-level and second-level items.
Note that frequency limits on the items can also be set on the server side and this request can only be issued in order to furtherly reduce the frequency, not to rise it beyond these limits.
This method can also be used to request unfiltered dispatching for the items in the Subscription. However, unfiltered dispatching requests may be refused if any frequency limit is posed on the server side for some item.

general_edition_note A further global frequency limit could also be imposed by the Server, depending on Edition and License Type; this specific limit also applies to RAW mode and to unfiltered dispatching. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).

Parameters:

freq

A decimal number, representing the maximum update frequency (expressed in updates per second) for each item in the Subscription; for instance, with a setting of 0.5, for each single item, no more than one update every 2 seconds will be received. If the string "unlimited" is supplied, then no frequency limit is requested. It is also possible to supply the string "unfiltered", to ask for unfiltered dispatching, if it is allowed for the items, or a null value to stick to the Server default (which currently corresponds to "unlimited"). The check for the string constants is case insensitive.

Throws:

IllegalStateException

if the Subscription is currently "active" and the current value of this property is "unfiltered".

IllegalStateException

if the Subscription is currently "active" and the given parameter is null or "unfiltered".

IllegalArgumentException

if the specified value is not null nor one of the special "unlimited" and "unfiltered" values nor a valid positive number.

getSelector():Null<String>

Inquiry method that can be used to read the selector name
specified for this Subscription through this.setSelector(String).

lifecycle This method can be called at any time.

Returns:

the name of the selector.

setSelector(selector:Null<String>):Void

Setter method that sets the selector name for all the items in the Subscription. The selector is a filter on the updates received. It is executed on the Server and implemented by the Metadata Adapter.

Parameters:

selector

name of a selector, to be recognized by the Metadata Adapter, or null to unset the selector.

Throws:

IllegalStateException

if the Subscription is currently "active".

getCommandPosition():Null<Int>

Returns the position of the "command" field in a COMMAND Subscription.
This method can only be used if the Subscription mode is COMMAND and the Subscription was initialized using a "Field Schema".

lifecycle This method can be called at any time after the first SubscriptionListener.onSubscription event.

Returns:

the 1-based position of the "command" field within the "Field Schema".

Throws:

IllegalStateException

if the Subscription mode is not COMMAND or if the SubscriptionListener.onSubscription event for this Subscription was not yet fired.

IllegalStateException

if a "Field List" was specified.

getKeyPosition():Null<Int>

Returns the position of the "key" field in a COMMAND Subscription.
This method can only be used if the Subscription mode is COMMAND and the Subscription was initialized using a "Field Schema".

lifecycle This method can be called at any time.

Returns:

the 1-based position of the "key" field within the "Field Schema".

Throws:

IllegalStateException

if the Subscription mode is not COMMAND or if the SubscriptionListener.onSubscription event for this Subscription was not yet fired.

getCommandSecondLevelDataAdapter():Null<String>

Inquiry method that can be used to read the second-level Data Adapter name configured through this.setCommandSecondLevelDataAdapter(String).

lifecycle This method can be called at any time.

Returns:

the name of the second-level Data Adapter.

Throws:

IllegalStateException

if the Subscription mode is not COMMAND

See also:

setCommandSecondLevelDataAdapter(dataAdapter:Null<String>):Void

Setter method that sets the name of the second-level Data Adapter (within the Adapter Set used by the current session) that supplies all the second-level items.
All the possible second-level items should be supplied in "MERGE" mode with snapshot available.
The Data Adapter name is configured on the server side through the "name" attribute of the <data_provider> element, in the "adapters.xml" file that defines the Adapter Set (a missing attribute configures the "DEFAULT" name).

Parameters:

dataAdapter

the name of the Data Adapter. A null value is equivalent to the "DEFAULT" name.

Throws:

IllegalStateException

if the Subscription is currently "active".

IllegalStateException

if the Subscription mode is not "COMMAND".

See also:

getCommandSecondLevelFields():Null<NativeArray<String>>

Inquiry method that can be used to read the "Field List" specified for second-level Subscriptions.

Returns:

the list of fields to be subscribed to through the server or null if the Subscription was initialized with a "Field Schema" or was not initialized at all.

Throws:

IllegalStateException

if the Subscription mode is not COMMAND

See also:

setCommandSecondLevelFields(fields:Null<NativeArray<String>>):Void

Setter method that sets the "Field List" to be subscribed to through Lightstreamer Server for the second-level items. It can only be used on COMMAND Subscriptions.
Any call to this method will override any "Field List" or "Field Schema" previously specified for the second-level.
Calling this method enables the two-level behavior:
in synthesis, each time a new key is received on the COMMAND Subscription, the key value is treated as an Item name and an underlying Subscription for this Item is created and subscribed to automatically, to feed fields specified by this method. This mono-item Subscription is specified through an "Item List" containing only the Item name received. As a consequence, all the conditions provided for subscriptions through Item Lists have to be satisfied. The item is subscribed to in "MERGE" mode, with snapshot request and with the same maximum frequency setting as for the first-level items (including the "unfiltered" case). All other Subscription properties are left as the default. When the key is deleted by a DELETE command on the first-level Subscription, the associated second-level Subscription is also unsubscribed from.
Specifying null as parameter will disable the two-level behavior.

lifecycle This method can only be called while the Subscription instance is in its "inactive" state.

Parameters:

fields

An array of Strings containing a list of fields to be subscribed to through the server.
Ensure that no name conflict is generated between first-level and second-level fields. In case of conflict, the second-level field will not be accessible by name, but only by position.

Throws:

IllegalArgumentException

if any of the field names in the "Field List" contains a space or is empty/null.

IllegalStateException

if the Subscription is currently "active".

IllegalStateException

if the Subscription mode is not "COMMAND".

See also:

getCommandSecondLevelFieldSchema():Null<String>

Inquiry method that can be used to read the "Field Schema" specified for second-level Subscriptions.

Returns:

the "Field Schema" to be subscribed to through the server or null if the Subscription was initialized with a "Field List" or was not initialized at all.

Throws:

IllegalStateException

if the Subscription mode is not COMMAND

See also:

setCommandSecondLevelFieldSchema(schema:String):Void

Setter method that sets the "Field Schema" to be subscribed to through Lightstreamer Server for the second-level items. It can only be used on COMMAND Subscriptions.
Any call to this method will override any "Field List" or "Field Schema" previously specified for the second-level.
Calling this method enables the two-level behavior:
in synthesis, each time a new key is received on the COMMAND Subscription, the key value is treated as an Item name and an underlying Subscription for this Item is created and subscribed to automatically, to feed fields specified by this method. This mono-item Subscription is specified through an "Item List" containing only the Item name received. As a consequence, all the conditions provided for subscriptions through Item Lists have to be satisfied. The item is subscribed to in "MERGE" mode, with snapshot request and with the same maximum frequency setting as for the first-level items (including the "unfiltered" case). All other Subscription properties are left as the default. When the key is deleted by a DELETE command on the first-level Subscription, the associated second-level Subscription is also unsubscribed from.
Specify null as parameter will disable the two-level behavior.

lifecycle This method can only be called while the Subscription instance is in its "inactive" state.

Parameters:

schemaName

A String to be expanded into a field list by the Metadata Adapter.

Throws:

IllegalStateException

if the Subscription is currently "active".

IllegalStateException

if the Subscription mode is not "COMMAND".

See also:

getValue(itemNameOrPos:EitherType<Int, String>, fieldNameOrPos:EitherType<Int, String>):Null<String>

Returns the latest value received for the specified item/field pair.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method. In case of COMMAND Subscriptions, the value returned by this method may be misleading, as in COMMAND mode all the keys received, being part of the same item, will overwrite each other; for COMMAND Subscriptions, use Subscription.getCommandValue instead.
Note that internal data is cleared when the Subscription is unsubscribed from.

lifecycle This method can be called at any time; if called to retrieve a value that has not been received yet, then it will return null.

Parameters:

itemIdentifier

a String representing an item in the configured item list or a Number representing the 1-based position of the item in the specified item group. (In case an item list was specified, passing the item position is also possible).

fieldIdentifier

a String representing a field in the configured field list or a Number representing the 1-based position of the field in the specified field schema. (In case a field list was specified, passing the field position is also possible).

Returns:

the current value for the specified field of the specified item (possibly null), or null if no value has been received yet.

Throws:

IllegalArgumentException

if an invalid item name or field name is specified or if the specified item position or field position is out of bounds.

getCommandValue(itemNameOrPos:EitherType<Int, String>, keyValue:String, fieldNameOrPos:EitherType<Int, String>):Null<String>

Returns the latest value received for the specified item/key/field combination. This method can only be used if the Subscription mode is COMMAND. Subscriptions with two-level behavior are also supported, hence the specified field can be either a first-level or a second-level one.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
Note that internal data is cleared when the Subscription is unsubscribed from.

lifecycle This method can be called at any time; if called to retrieve a value that has not been received yet, then it will return null.

Parameters:

itemIdentifier

a String representing an item in the configured item list or a Number representing the 1-based position of the item in the specified item group. (In case an item list was specified, passing the item position is also possible).

keyValue

a String containing the value of a key received on the COMMAND subscription.

fieldIdentifier

a String representing a field in the configured field list or a Number representing the 1-based position of the field in the specified field schema. (In case a field list was specified, passing the field position is also possible).

Returns:

the current value for the specified field of the specified key within the specified item (possibly null), or null if the specified key has not been added yet (note that it might have been added and eventually deleted).

Throws:

IllegalArgumentException

if an invalid item name or field name is specified or if the specified item position or field position is out of bounds.

IllegalStateException

if the Subscription mode is not COMMAND.