Package com.lightstreamer.client

Class Subscription

java.lang.Object
com.lightstreamer.client.Subscription
public class Subscription extends Object
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 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 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 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 setFields(String[]) method or by specifying it in the constructor.

  • Constructor Details

  • Method Details

    • addListener

      public void addListener(@Nonnull SubscriptionListener listener)
      Adds a listener that will receive events from the Subscription instance.
      The same listener can be added to several different Subscription instances.
      Parameters:
      listener - An object that will receive the events as documented in the SubscriptionListener interface.
      See Also:
      Lifecycle:
      A listener can be added at any time. A call to add a listener already present will be ignored.

    • removeListener

      public void removeListener(@Nonnull SubscriptionListener listener)
      Removes a listener from the Subscription instance so that it will not receive events anymore.
      Parameters:
      listener - The listener to be removed.
      See Also:
      Lifecycle:
      a listener can be removed at any time.

    • getListeners

      @Nonnull public List<SubscriptionListener> getListeners()
      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

      public boolean isActive()
      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.
      Returns:
      true/false if the Subscription is "active" or not.
      See Also:
      Lifecycle:
      This method can be called at any time.

    • isSubscribed

      public boolean isSubscribed()
      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.
      Returns:
      true/false if the Subscription is subscribed to through the server or not.
      Lifecycle:
      This method can be called at any time.

    • getDataAdapter

      @Nullable public String getDataAdapter()
      Inquiry method that can be used to read the name of the Data Adapter specified for this Subscription through setDataAdapter(String).
      Returns:
      the name of the Data Adapter; returns null if no name has been configured, so that the "DEFAULT" Adapter Set is used.
      Lifecycle:
      This method can be called at any time.

    • setDataAdapter

      public void setDataAdapter(@Nullable String 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 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:
      Default:
      The default Data Adapter for the Adapter Set, configured as "DEFAULT" on the Server.
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getMode

      @Nonnull public String getMode()
      Inquiry method that can be used to read the mode specified for this Subscription.
      Returns:
      the Subscription mode specified in the constructor.
      Lifecycle:
      This method can be called at any time.

    • getItems

      public String[] getItems()
      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.
      Lifecycle:
      This method can only be called if the Subscription has been initialized with an "Item List".

    • setItems

      public void setItems(@Nullable String[] 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.
      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".
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getItemGroup

      @Nullable public String getItemGroup()
      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.
      Lifecycle:
      This method can only be called if the Subscription has been initialized using an "Item Group"

    • setItemGroup

      public void setItemGroup(@Nullable String 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.
      Parameters:
      groupName - A String to be expanded into an item list by the Metadata Adapter.
      Throws:
      IllegalStateException - if the Subscription is currently "active".
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getFields

      public String[] getFields()
      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.
      Lifecycle:
      This method can only be called if the Subscription has been initialized using a "Field List".

    • setFields

      public void setFields(@Nullable String[] 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.
      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".
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getFieldSchema

      @Nullable public String getFieldSchema()
      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.
      Lifecycle:
      This method can only be called if the Subscription has been initialized using a "Field Schema"

    • setFieldSchema

      public void setFieldSchema(@Nullable String 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.
      Parameters:
      schemaName - A String to be expanded into a field list by the Metadata Adapter.
      Throws:
      IllegalStateException - if the Subscription is currently "active".
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getRequestedBufferSize

      @Nullable public String getRequestedBufferSize()
      Inquiry method that can be used to read the buffer size, configured though setRequestedBufferSize(java.lang.String), to be requested to the Server for this Subscription.
      Returns:
      An integer number, representing the buffer size to be requested to the server, or the string "unlimited", or null.
      Lifecycle:
      This method can be called at any time.

    • setRequestedBufferSize

      public void setRequestedBufferSize(@Nullable String size)
      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:
      Default:
      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 Subscription instance is in its "inactive" state.

    • getRequestedSnapshot

      @Nullable public String getRequestedSnapshot()
      Inquiry method that can be used to read the snapshot preferences, configured through setRequestedSnapshot(String), to be requested to the Server for this Subscription.
      Returns:
      "yes", "no", null, or an integer number.
      Lifecycle:
      This method can be called at any time.

    • setRequestedSnapshot

      public void setRequestedSnapshot(@Nullable String required)
      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:
      Default:
      "yes" if the Subscription mode is not "RAW", null otherwise.
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getRequestedMaxFrequency

      @Nullable public String getRequestedMaxFrequency()
      Inquiry method that can be used to read the max frequency, configured through setRequestedMaxFrequency(String), to be requested to the Server for this Subscription.
      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.
      Lifecycle:
      This method can be called at any time.

    • setRequestedMaxFrequency

      public void setRequestedMaxFrequency(@Nullable String freq)
      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 setCommandSecondLevelFields(String[]) and 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 further 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.
      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.
      Default:
      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 can be called at any time with some differences based on the Subscription status:
      • If the Subscription instance is in its "inactive" state then this method can be called at will.
      • If the Subscription instance is in its "active" state then the method can still be called unless the current value is "unfiltered" or the supplied value is "unfiltered" or null. If the Subscription instance is in its "active" state and the connection to the server is currently open, then a request to change the frequency of the Subscription on the fly is sent to the server.
      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).

    • getSelector

      @Nullable public String getSelector()
      Inquiry method that can be used to read the selector name specified for this Subscription through setSelector(String).
      Returns:
      the name of the selector.
      Lifecycle:
      This method can be called at any time.

    • setSelector

      public void setSelector(@Nullable String selector)
      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".
      Default:
      null (no selector).
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getCommandPosition

      public int getCommandPosition()
      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".
      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.
      Lifecycle:
      This method can be called at any time after the first SubscriptionListener.onSubscription() event.

    • getKeyPosition

      public int getKeyPosition()
      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".
      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.
      Lifecycle:
      This method can be called at any time.

    • getCommandSecondLevelDataAdapter

      @Nullable public String getCommandSecondLevelDataAdapter()
      Inquiry method that can be used to read the second-level Data Adapter name configured through setCommandSecondLevelDataAdapter(String).
      Returns:
      the name of the second-level Data Adapter.
      Throws:
      IllegalStateException - if the Subscription mode is not COMMAND
      See Also:
      Lifecycle:
      This method can be called at any time.

    • setCommandSecondLevelDataAdapter

      public void setCommandSecondLevelDataAdapter(@Nullable String dataAdapter)
      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:
      Default:
      The default Data Adapter for the Adapter Set, configured as "DEFAULT" on the Server.
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getCommandSecondLevelFields

      @Nullable public String[] getCommandSecondLevelFields()
      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:
      Lifecycle:
      This method can only be called if the second-level of this Subscription has been initialized using a "Field List"

    • setCommandSecondLevelFields

      public void setCommandSecondLevelFields(@Nullable String[] fields)
      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.
      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:
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getCommandSecondLevelFieldSchema

      @Nullable public String getCommandSecondLevelFieldSchema()
      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:
      Lifecycle:
      This method can only be called if the second-level of this Subscription has been initialized using a "Field Schema".

    • setCommandSecondLevelFieldSchema

      public void setCommandSecondLevelFieldSchema(@Nullable String schemaName)
      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.
      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:
      Lifecycle:
      This method can only be called while the Subscription instance is in its "inactive" state.

    • getValue

      @Nullable public String getValue(@Nonnull String itemName, @Nonnull String fieldName)
      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 getCommandValue(java.lang.String, java.lang.String, java.lang.String) instead.
      Note that internal data is cleared when the Subscription is unsubscribed from.
      Parameters:
      itemName - an item in the configured "Item List"
      fieldName - a item in the configured "Field List"
      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.
      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.

    • getValue

      @Nullable public String getValue(int itemPos, int fieldPos)
      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 getCommandValue(java.lang.String, java.lang.String, java.lang.String) instead.
      Note that internal data is cleared when the Subscription is unsubscribed from.
      Parameters:
      itemPos - the 1-based position of an item within the configured "Item Group" or "Item List"
      fieldPos - the 1-based position of a field within the configured "Field Schema" or "Field List"
      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 the specified item position or field position is out of bounds.
      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.

    • getValue

      @Nullable public String getValue(@Nonnull String itemName, int fieldPos)
      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 getCommandValue(java.lang.String, java.lang.String, java.lang.String) instead.
      Note that internal data is cleared when the Subscription is unsubscribed from.
      Parameters:
      itemName - an item in the configured "Item List"
      fieldPos - the 1-based position of a field within the configured "Field Schema" or "Field List"
      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 is specified.
      IllegalArgumentException - if the specified field position is out of bounds.
      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.

    • getValue

      @Nullable public String getValue(int itemPos, @Nonnull String fieldName)
      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 getCommandValue(java.lang.String, java.lang.String, java.lang.String) instead.
      Note that internal data is cleared when the Subscription is unsubscribed from.
      Parameters:
      itemPos - the 1-based position of an item within the configured "Item Group" or "Item List"
      fieldName - a item in the configured "Field List"
      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 field name is specified.
      IllegalArgumentException - if the specified item position is out of bounds.
      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.

    • getCommandValue

      @Nullable public String getCommandValue(@Nonnull String itemName, @Nonnull String keyValue, @Nonnull String fieldName)
      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 (see setCommandSecondLevelFields(String[]) and setCommandSecondLevelFieldSchema(String)) 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.
      Parameters:
      itemName - an item in the configured "Item List"
      keyValue - the value of a key received on the COMMAND subscription.
      fieldName - a item in the configured "Field List"
      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 then deleted).
      Throws:
      IllegalArgumentException - if an invalid item name or field name is specified.
      IllegalStateException - if the Subscription mode is not COMMAND.

    • getCommandValue

      @Nullable public String getCommandValue(int itemPos, @Nonnull String keyValue, int fieldPos)
      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 (see setCommandSecondLevelFields(String[]) and setCommandSecondLevelFieldSchema(String)) 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.
      Parameters:
      itemPos - the 1-based position of an item within the configured "Item Group" or "Item List"
      keyValue - the value of a key received on the COMMAND subscription.
      fieldPos - the 1-based position of a field within the configured "Field Schema" or "Field List"
      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 then deleted).
      Throws:
      IllegalArgumentException - if the specified item position or field position is out of bounds.
      IllegalStateException - if the Subscription mode is not COMMAND.

    • getCommandValue

      @Nullable public String getCommandValue(int itemPos, @Nonnull String keyValue, @Nonnull String fieldName)
      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 (see setCommandSecondLevelFields(String[]) and setCommandSecondLevelFieldSchema(String)) 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.
      Parameters:
      itemPos - the 1-based position of an item within the configured "Item Group" or "Item List"
      keyValue - the value of a key received on the COMMAND subscription.
      fieldName - a item in the configured "Field List"
      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 then deleted).
      Throws:
      IllegalArgumentException - if an invalid field name is specified.
      IllegalArgumentException - if the specified item position is out of bounds.
      IllegalStateException - if the Subscription mode is not COMMAND.

    • getCommandValue

      @Nullable public String getCommandValue(@Nonnull String itemName, @Nonnull String keyValue, int fieldPos)
      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 (see setCommandSecondLevelFields(String[]) and setCommandSecondLevelFieldSchema(String)) 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.
      Parameters:
      itemName - an item in the configured "Item List"
      keyValue - the value of a key received on the COMMAND subscription.
      fieldPos - the 1-based position of a field within the configured "Field Schema" or "Field List"
      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 then deleted).
      Throws:
      IllegalArgumentException - if an invalid item name is specified.
      IllegalArgumentException - if the specified field position is out of bounds.