CachedMessageQueue

Message queue that caches received messages in memory to allow peek operations that may not be supported by the undelying queue.

Extends: MessageQueue

Implements: ICleanable

Description

The CachedMessageQueue class allows you to create message queues that cache received messages in memory, to allow peek operations that may not be supported by the undelying queue.

Important points

  • This queue is used as a base implementation for other queues.

Constructors

Creates a new instance of the persistence component.

constructor(name?: string, capabilities?: MessagingCapabilities)

  • name: string - (optional) queue name
  • capabilities: MessagingCapabilities - (optional) capabilities of the message queue

Fields

_autoSubscribe

Boolean variable indicating whether a message queue auto-subscribes or not.

protected _autoSubscribe: boolean

_messages

List of messages in a queue.

protected _messages: MessageEnvelope[]

_receiver

Message receiver.

protected _receiver: IMessageReceiver

Abstract methods

subscribe

Subscribes to the message broker.

abstract subscribe(correlationId: string): Promise<void>

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.

unsubscribe

Unsubscribes from the message broker.

abstract unsubscribe(correlationId: string): Promise<void>

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.

Instance methods

clear

Clears component state.

public clear(correlationId: string): Promise<void>

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.

configure

Configures a component by passing its configuration parameters.

public configure(config: ConfigParams): void

  • config: ConfigParams - configuration parameters to be set.

endListen

Ends listening for incoming messages. When this method is called, listen unblocks the thread and execution continues.

public endListen(correlationId: string): void

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.

listen

Listens for incoming messages and blocks the current thread until the queue is closed. See IMessageReceiver, receive

public listen(correlationId: string, receiver: IMessageReceiver): void

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.
  • receiver: IMessageReceiver - receiver used to receive incoming messages.

open

Opens the component.

public open(correlationId: string): Promise<void>

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.

peek

Peeks a single incoming message from the queue without removing it. If there are no messages available in the queue it returns null.

public peek(correlationId: string): Promise<MessageEnvelope>

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.
  • returns: Promise<MessageEnvelope> - peeked message or null.

peekBatch

Peeks multiple incoming messages from the queue without removing them. If there are no messages available in the queue it returns an empty list.

Important: This method is not supported by MQTT.

public peekBatch(correlationId: string, messageCount: number): Promise<MessageEnvelope[]

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.
  • messageCount: number - maximum number of messages to peek.
  • returns: Promise<MessageEnvelope[]] - list with peeked messages.

read_message_count

Reads the current number of messages in the queue to be delivered.

public readMessageCount(): Promise<number>

  • returns: number - number of messages in the queue.

receive

Receives an incoming message and removes it from the queue.

public receive(correlationId: string, waitTimeout: number): MessageEnvelope

  • correlationId: string - (optional) transaction id used to trace execution through the call chain.
  • waitTimeout: number - timeout in milliseconds to wait for a message to come.
  • returns: MessageEnvelope - received message or null.

sendMessageToReceiver

Sends a message to a receiver.

protected sendMessageToReceiver(receiver: IMessageReceiver, message: MessageEnvelope): Promise<void>

See also