MessageQuery (ActiveMQ :: Broker 5.17.3 API)

```
public interface MessageQuery
```
Represents some kind of query which will load initial messages from some source for a new topic subscriber.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`execute(org.apache.activemq.command.ActiveMQDestination destination, MessageListener listener)`	Executes the query for messages; each message is passed into the listener
`boolean`	`validateUpdate(org.apache.activemq.command.Message message)`	Returns true if the given update is valid and does not overlap with the initial message query.

- Method Detail
  - execute
```
void execute(org.apache.activemq.command.ActiveMQDestination destination,
             MessageListener listener)
      throws Exception
```
    Executes the query for messages; each message is passed into the listener
    
    Parameters:
    
    destination - the destination on which the query is to be performed
    
    listener - is the listener to notify as each message is created or loaded
    
    Throws:
    
    Exception
  - validateUpdate
```
boolean validateUpdate(org.apache.activemq.command.Message message)
```
    Returns true if the given update is valid and does not overlap with the initial message query. When performing an initial load from some source, there is a chance that an update may occur which is logically before the message sent on the initial load - so this method provides a hook where the query instance can keep track of the version IDs of the messages sent so that if an older version is sent as an update it can be excluded to avoid going backwards in time. e.g. if the execute() method creates version 2 of an object and then an update message is sent for version 1, this method should return false to hide the old update message.
    
    Parameters:
    
    message - the update message which may have been sent before the query actually completed
    
    Returns:
    
    true if the update message is valid otherwise false in which case the update message will be discarded.