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.

public CachedMessageQueue(String name, MessagingCapabilities capabilities)

  • 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 boolean _autoSubscribe;

_messages

List of messages in a queue.

protected _messages: MessageEnvelope[]

_receiver

Message receiver.

protected List<IMessageReceiver> _messages;

Abstract methods

subscribe

Subscribes to the message broker.

public abstract void subscribe(IContext context)

  • context: IContext - (optional) a context to trace execution through a call chain.

unsubscribe

Unsubscribes from the message broker.

public abstract void unsubscribe(IContext context)

  • context: IContext - (optional) a context to trace execution through a call chain.

Instance methods

clear

Clears component state.

public void clear(IContext context)

  • context: IContext - (optional) a context to trace execution through a call chain.

configure

Configures a component by passing its configuration parameters.

public void configure(ConfigParams config)

  • 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 void endListen(IContext context)

  • context: IContext - (optional) a context to trace execution through a call chain.

listen

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

public void listen(IContext context, IMessageReceiver receiver)

  • context: IContext - (optional) a context to trace execution through a call chain.
  • receiver: IMessageReceiver - receiver used to receive incoming messages.

open

Opens the component.

public void open(IContext context)

  • context: IContext - (optional) a context to trace execution through a 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 MessageEnvelope peek(IContext context) throws InvalidStateException

  • context: IContext - (optional) a context to trace execution through a 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 List<MessageEnvelope> peekBatch(IContext context, int messageCount) throws InvalidStateException

  • context: IContext - (optional) a context to trace execution through a call chain.
  • messageCount: int - maximum number of messages to peek.
  • returns: List<MessageEnvelope> - list with peeked messages.

readMessageCount

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

public int readMessageCount()

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

receive

Receives an incoming message and removes it from the queue.

public MessageEnvelope receive(IContext context, long waitTimeout) throws InvalidStateException

  • context: IContext - (optional) a context to trace execution through a call chain.
  • waitTimeout: long - timeout in milliseconds to wait for a message to come.
  • returns: MessageEnvelope - received message or null.

sendMessageToReceiver

Sends a message to a receiver.

protected void sendMessageToReceiver(IMessageReceiver receiver, MessageEnvelope message)

See also