Web Client 8.0.3

MpnSubscription

MpnSubscription

Class representing a Web Push Notification subscription to be submitted to the MPN Module of a Lightstreamer Server.
It contains subscription details and the listener needed to monitor its status. Real-time data is routed via native push notifications.
In order to successfully subscribe an MPN subscription, first an MpnDevice must be created and registered on the LightstreamerClient with LightstreamerClient#registerForMpn.
After creation, an MpnSubscription object is in the "inactive" state. When an MpnSubscription object is subscribed to on an LightstreamerClient object, through the LightstreamerClient#subscribeMpn method, its state switches to "active". This means that the subscription request is being sent to the Lightstreamer Server. Once the server accepted the request, it begins to send real-time events via native push notifications and the MpnSubscription object switches to the "subscribed" state.
If a trigger expression is set, the MPN subscription does not send any push notifications until the expression evaluates to true. When this happens, the MPN subscription switches to "triggered" state and a single push notification is sent. Once triggered, no other push notifications are sent.
When an MpnSubscription is subscribed on the server, it acquires a permanent subscription ID that the server later uses to identify the same MPN subscription on subsequent sessions.
An MpnSubscription 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. The same rules that apply to Subscription apply to MpnSubscription.
An MpnSubscription object can also be provided by the client to represent a pre-existing MPN subscription on the server. In fact, differently than real-time subscriptions, MPN subscriptions are persisted on the server's MPN Module database and survive the session they were created on.
MPN subscriptions are associated with the MPN device, and after the device has been registered the client retrieves pre-existing MPN subscriptions from the server's database and exposes them with the LightstreamerClient#getMpnSubscriptions method.

Constructor

new MpnSubscription(subscriptionMode, items, fields)

Creates an object to be used to describe an MPN subscription that is going to be subscribed to through the MPN Module of Lightstreamer Server.
The object can be supplied to LightstreamerClient#subscribeMpn in order to bring the MPN subscription to "active" 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.

Alternatively you can create an MpnSubscription object by passing a single argument either of type

  • Subscription: the new object is initialized by copying subscription mode, items, fields and data adapter from the specified real-time subscription; or
  • MpnSubscription: the new object is initialized by copying all properties (including the subscription ID) from the specified MPN subscription. The created MpnSubscription is a copy of the original MpnSubscription object and represents the same MPN subscription, since their subscription ID is the same. When the object is supplied to LightstreamerClient#subscribeMpn in order to bring it to "active" state, the MPN subscription is modified: any property changed in this MpnSubscription replaces the corresponding value of the MPN subscription on the server.
Parameters:
Name Type Description
subscriptionMode String

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

  • MERGE
  • DISTINCT
items Array.<String>

An array of items to be subscribed to through Lightstreamer Server. It is also possible specify the "Item List" or "Item Group" later through MpnSubscription#setItems and MpnSubscription#setItemGroup.

fields Array.<String>

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 MpnSubscription#setFields and MpnSubscription#setFieldSchema.

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 MpnSubscription#setItems and MpnSubscription#setFields for details.

Methods

addListener(listener)

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

Lifecycle: a listener can be added at any time.

Parameters:
Name Type Description
listener MpnSubscriptionListener

An object that will receive the events as shown in the MpnSubscriptionListener interface.
Note that the given instance does not have to implement all of the methods of the MpnSubscriptionListener interface. In fact it may also implement none of the interface methods and still be considered a valid listener. In the latter case it will obviously receive no events.

getDataAdapter() → {String}

Inquiry method that can be used to read the name of the Data Adapter specified for this MpnSubscription through MpnSubscription#setDataAdapter.

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.

Type
String

getFields() → {Array.<String>}

Inquiry method that can be used to read the "Field List" specified for this MpnSubscription.
Note: if the MpnSubscription has been created by the client, such as when obtained through LightstreamerClient#getMpnSubscriptions, fields are always expressed with a "Field Schema"", even if originally the MPN subscription used a "Field List".

Lifecycle: This method can only be called if the MpnSubscription has been initialized using a "Field List".

Throws:

IllegalStateException if the MpnSubscription was not initialized.

Returns:

the "Field List" to be subscribed to through the server.

Type
Array.<String>

getFieldSchema() → {String}

Inquiry method that can be used to read the field schema specified for this MpnSubscription.
Note: if the MpnSubscription has been created by the client, such as when obtained through LightstreamerClient#getMpnSubscriptions, fields are always expressed with a "Field Schema"", even if originally the MPN subscription used a "Field List".

Lifecycle: This method can only be called if the MpnSubscription has been initialized using a "Field Schema"

Throws:

IllegalStateException if the MpnSubscription was not initialized.

Returns:

the "Field Schema" to be subscribed to through the server.

Type
String

getItemGroup() → {String}

Inquiry method that can be used to read the item group specified for this MpnSubscription.
Note: if the MpnSubscription has been created by the client, such as when obtained through LightstreamerClient#getMpnSubscriptions, items are always expressed with an "Item Group"", even if originally the MPN subscription used an "Item List".

Lifecycle: This method can only be called if the MpnSubscription has been initialized using an "Item Group"

Throws:

IllegalStateException if the MpnSubscription was not initialized.

Returns:

the "Item Group" to be subscribed to through the server.

Type
String

getItems() → {Array.<String>}

Inquiry method that can be used to read the "Item List" specified for this MpnSubscription.
Note that if the single-item-constructor was used, this method will return an array of length 1 containing such item.
Note: if the MpnSubscription has been created by the client, such as when obtained through LightstreamerClient#getMpnSubscriptions, items are always expressed with an "Item Group"", even if originally the MPN subscription used an "Item List".

Lifecycle: This method can only be called if the MpnSubscription has been initialized with an "Item List".

Throws:

IllegalStateException if the MpnSubscription was not initialized.

Returns:

the "Item List" to be subscribed to through the server.

Type
Array.<String>

getListeners() → {Array.<MpnSubscriptionListener>}

Returns an array containing the MpnSubscriptionListener instances that were added to this client.

Returns:

an Array containing the listeners that were added to this client. Listeners added multiple times are included multiple times in the array.

Type
Array.<MpnSubscriptionListener>

getMode() → {String}

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

Lifecycle: This method can be called at any time.

Returns:

the MpnSubscription mode specified in the constructor.

Type
String

getNotificationFormat() → {String}

Returns the JSON structure to be used as the format of push notifications.
This JSON structure is sent by the server to the push notification service provider (FCM or APNs), hence it must follow its specifications.

See:
Returns:

the JSON structure to be used as the format of push notifications.

Type
String

getRequestedBufferSize() → {Number|String}

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

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.

Type
Number | String

getRequestedMaxFrequency() → {Number|String}

Inquiry method that can be used to read the max frequency, configured through MpnSubscription#setRequestedMaxFrequency, to be requested to the Server for this MpnSubscription.

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 string "unlimited", or null.

Type
Number | String

getStatus() → {String}

The status of the subscription.
The status can be:

Lifecycle: This method can be called at any time.

See:
Returns:

the status of the subscription.

Type
String

getStatusTimestamp() → {Number}

The server-side timestamp of the subscription status.

Lifecycle: This method can be called at any time.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument status_timestamp on any MpnSubscriptionListener listening to the related MpnSubscription.

See:
Returns:

The server-side timestamp of the subscription status, expressed as a Java time.

Type
Number

getSubscriptionId() → {String}

The server-side unique persistent ID of the MPN subscription.
The ID is available only after the MPN subscription has been successfully subscribed on the server. I.e. when its status is SUBSCRIBED or TRIGGERED.
Note: more than one MpnSubscription may exists at any given time referring to the same MPN subscription, and thus with the same subscription ID. For instace, copying an MpnSubscription with the copy initializer creates a second MpnSubscription instance with the same subscription ID. Also, the coalescing flag of LightstreamerClient#subscribeMpn may cause the assignment of a pre-existing MPN subscription ID to the new subscription.
Two MpnSubscription objects with the same subscription ID always represent the same server-side MPN subscription. It is the client's duty to keep the status and properties of these objects up to date and aligned.

Lifecycle: This method can be called at any time.

Returns:

the MPN subscription ID.

Type
String

getTriggerExpression() → {boolean}

Returns the boolean expression that is evaluated against each update and acts as a trigger to deliver the push notification.

See:
Returns:

the boolean expression that acts as a trigger to deliver the push notification.

Type
boolean

isActive() → {boolean}

Checks if the MpnSubscription is currently "active" or not.
Most of the MpnSubscription properties cannot be modified if an MpnSubscription is "active".
The status of an MpnSubscription is changed to "active" through the LightstreamerClient#subscribeMpn method and back to "inactive" through the LightstreamerClient#unsubscribeMpn and LightstreamerClient#unsubscribeMpnSubscriptions ones.

Lifecycle: This method can be called at any time.

See:
Returns:

true if the MpnSubscription is currently "active", false otherwise.

Type
boolean

isSubscribed() → {boolean}

Checks if the MpnSubscription 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#unsubscribeMpn or LightstreamerClient#unsubscribeMpnSubscriptions calls, and server sent unsubscription events.

Lifecycle: This method can be called at any time.

See:
Returns:

true if the MpnSubscription has been successfully subscribed on the server, false otherwise.

Type
boolean

isTriggered() → {boolean}

Checks if the MpnSubscription is currently triggered or not.
This flag is switched to true when a trigger expression has been set and it evaluated to true at least once. For this to happen, the subscription must already be in "active" and "subscribed" states. It is switched back to false if the subscription is modified with a LightstreamerClient#subscribeMpn call on a copy of it, deleted with LightstreamerClient#unsubscribeMpn or LightstreamerClient#unsubscribeMpnSubscriptions calls, and server sent subscription events.

Lifecycle: This method can be called at any time.

See:
Returns:

true if the MpnSubscription's trigger expression has been evaluated to true at least once, false otherwise.

Type
boolean

removeListener(listener)

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

Lifecycle: a listener can be removed at any time.

Parameters:
Name Type Description
listener MpnSubscriptionListener

The listener to be removed.

setDataAdapter(dataAdapter)

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 MpnSubscription.
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 MpnSubscription. Multiple MpnSubscriptions have to be defined.

Default value: The default Data Adapter for the Adapter Set, configured as "DEFAULT" on the Server.

Lifecycle: This method can only be called while the MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument adapter on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
dataAdapter String

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

See:
Throws:

IllegalStateException if the Subscription is currently "active".

setFields(fields)

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 MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument schema on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
fields Array.<String>

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 MpnSubscription is currently "active".

setFieldSchema(schemaName)

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 MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument schema on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
schemaName String

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

Throws:

IllegalStateException if the MpnSubscription is currently "active".

setItemGroup(groupName)

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 MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument group on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
groupName String

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

Throws:

IllegalStateException if the MpnSubscription is currently "active".

setItems(items)

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 MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument group on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
items Array.<String>

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 MpnSubscription is currently "active".

setNotificationFormat(format)

Sets the JSON structure to be used as the format of push notifications.
This JSON structure is sent by the server to the push notification service provider (FCM or APNs), hence it must follow its specifications.
The JSON structure may contain named arguments with the format ${field}, or indexed arguments with the format $[1]. These arguments are replaced by the server with the value of corresponding subscription fields before the push notification is sent.
For instance, if the subscription contains fields "stock_name" and "last_price", the notification format could be something like this:

  • { "notification" : { "body" : "Stock ${stock_name} is now valued ${last_price}" } }
Named arguments are available if the Metadata Adapter is a subclass of LiteralBasedProvider or provides equivalent functionality, otherwise only indexed arguments may be used. In both cases common metadata rules apply: field names and indexes are checked against the Metadata Adapter, hence they must be consistent with the schema and group specified.
A special server-managed argument may also be used:
  • ${LS_MPN_subscription_ID}: the ID of the MPN subscription generating the push notification.
The MpnBuilder object provides methods to build an appropriate JSON structure from its defining fields.
Note: if the MpnSubscription has been created by the client, such as when obtained through LightstreamerClient#getMpnSubscriptions, named arguments are always mapped to its corresponding indexed argument, even if originally the notification format used a named argument.
Note: the content of this property may be subject to length restrictions (See the "General Concepts" document for more information).

Lifecycle: This method can only be called while the MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument notification_format on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
format String

the JSON structure to be used as the format of push notifications.

See:
Throws:

IllegalStateException if the MpnSubscription is currently "active".

setRequestedBufferSize(size)

Setter method that sets the length to be requested to Lightstreamer Server for the internal queuing buffers for the items in the MpnSubscription.
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.
Note that the Server may pose an upper limit on the size of its internal buffers.

Default value: null, meaning to lean on the Server default based on the subscription mode. This means that the buffer size will be 1 for MERGE subscriptions and "unlimited" for DISTINCT subscriptions. See the "General Concepts" document for further details.

Lifecycle: This method can only be called while the MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument requested_buffer_size on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
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).

See:
Throws:
  • IllegalStateException if the MpnSubscription is currently "active".

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

setRequestedMaxFrequency(freq)

Setter method that sets the maximum update frequency to be requested to Lightstreamer Server for all the items in the MpnSubscription.
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 further reduce the frequency, not to rise it beyond these limits.

Edition Note: A further global frequency limit could also be imposed by the Server, depending on Edition and License Type. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).

Default value: null, meaning to lean on the Server default based on the subscription mode. This consists, for all modes, in not applying any frequency limit to the subscription (the same as "unlimited"); see the "General Concepts" document for further details.

Lifecycle: This method can only be called while the MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument requested_max_frequency on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
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 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 MpnSubscription is currently "active".

  • IllegalArgumentException if the specified value is not null nor the special "unlimited" value nor a valid positive number.

setTriggerExpression(expr)

Sets the boolean expression that will be evaluated against each update and will act as a trigger to deliver the push notification.
If a trigger expression is set, the MPN subscription does not send any push notifications until the expression evaluates to true. When this happens, the MPN subscription "triggers" and a single push notification is sent. Once triggered, no other push notifications are sent. In other words, with a trigger expression set, the MPN subscription sends at most one push notification.
The expression must be in Java syntax and can contain named arguments with the format ${field}, or indexed arguments with the format $[1]. The same rules that apply to MpnSubscription#setNotificationFormat apply also to the trigger expression. The expression is verified and evaluated on the server.
Named and indexed arguments are replaced by the server with the value of corresponding subscription fields before the expression is evaluated. They are represented as String variables, and as such appropriate type conversion must be considered. E.g.

  • Double.parseDouble(${last_price}) > 500.0
Argument variables are named with the prefix LS_MPN_field followed by an index. Thus, variable names like LS_MPN_field1 should be considered reserved and their use avoided in the expression.
Consider potential impact on server performance when writing trigger expressions. Since Java code may use classes and methods of the JDK, a badly written trigger may cause CPU hogging or memory exhaustion. For this reason, a server-side filter may be applied to refuse poorly written (or even maliciously crafted) trigger expressions. See the "General Concepts" document for more information.
Note: if the MpnSubscription has been created by the client, such as when obtained through LightstreamerClient#getMpnSubscriptions, named arguments are always mapped to its corresponding indexed argument, even if originally the trigger expression used a named argument.
Note: the content of this property may be subject to length restrictions (See the "General Concepts" document for more information).

Lifecycle: This method can only be called while the MpnSubscription instance is in its "inactive" state.

Notification: A change to this setting will be notified through a call to MpnSubscriptionListener#onPropertyChanged with argument trigger on any MpnSubscriptionListener listening to the related MpnSubscription.

Parameters:
Name Type Description
expr boolean

the boolean expression that acts as a trigger to deliver the push notification.

See:
Throws:

IllegalStateException if the MpnSubscription is currently "active".