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Config Events#

The Config Events extension allows you to fire change events on Config Sources.

Usage#

To use the Config Events, add the following to your Maven pom.xml:

<dependency>
    <groupId>io.smallrye.config</groupId>
    <artifactId>smallrye-config-events</artifactId>
    <version>3.9.1</version>
</dependency>

Events#

The CDI Event is a ChangeEvent and contains the following fields:

  • String key
  • Optional\ oldValue
  • String newValue
  • Type type
  • String fromSource

The ChangeEvent can be of any of the following types:

  • NEW - When you create a new key and value (i.e. the key does not exist anywhere in any config source)
  • UPDATE - When you update a value of an existing key (i.e. the key and value exist somewhere in a config source)
  • REMOVE - When you remove the value from the source (and that changed the overall config)

Observing Events#

You can listen to all or some of these events, filtering by type and/or key and/or source, example:

// Getting all config event
public void all(@Observes ChangeEvent changeEvent){
    log.log(Level.SEVERE, "ALL: Received a config change event: {0}", changeEvent);
}

// Get only new values
public void newValue(@Observes @TypeFilter(Type.NEW) ChangeEvent changeEvent){
    log.log(Level.SEVERE, "NEW: Received a config change event: {0}", changeEvent);
}

// Get only override values
public void overrideValue(@Observes @TypeFilter(Type.UPDATE) ChangeEvent changeEvent){
    log.log(Level.SEVERE, "UPDATE: Received a config change event: {0}", changeEvent);
}

// Get only revert values
public void revertValue(@Observes @TypeFilter(Type.REMOVE) ChangeEvent changeEvent){
    log.log(Level.SEVERE, "REMOVE: Received a config change event: {0}", changeEvent);
}

// Getting all config event when key is some.key
public void allForKey(@Observes @KeyFilter("some.key") ChangeEvent changeEvent){
    log.log(Level.SEVERE, "ALL for key [some.key]: Received a config change event: {0}", changeEvent);
}

// Getting all config event when key is some.key for new events
public void newForKey(@Observes @TypeFilter(Type.NEW) @KeyFilter("some.key") ChangeEvent changeEvent){
    log.log(Level.SEVERE, "NEW for key [some.key]: Received a config change event: {0}", changeEvent);
}

// Getting all config event when key is some.key for override events
public void overrideForKey(@Observes @TypeFilter(Type.UPDATE) @KeyFilter("some.key") ChangeEvent changeEvent){
    log.log(Level.SEVERE, "UPDATE for key [some.key]: Received a config change event: {0}", changeEvent);
}

// Getting all config event when key is some.key for revert events
public void revertForKey(@Observes @TypeFilter(Type.REMOVE) @KeyFilter("some.key") ChangeEvent changeEvent){
    log.log(Level.SEVERE, "REMOVE for key [some.key]: Received a config change event: {0}", changeEvent);
}

// Getting all config events for a certain source
public void allForSource(@Observes @SourceFilter("MemoryConfigSource") ChangeEvent changeEvent){
    log.log(Level.SEVERE, "ALL for source [MemoryConfigSource]: Received a config change event: {0}", changeEvent);
}

// Getting all config events for a certain source
public void allForSourceAndKey(@Observes @SourceFilter("MemoryConfigSource") @KeyFilter("some.key")  ChangeEvent changeEvent){
    log.log(Level.SEVERE, "ALL for source [MemoryConfigSource] and for key [some.key]: Received a config change event: {0}", changeEvent);
}

// Getting all config events for a certain source
public void overrideForSourceAndKey(@Observes @TypeFilter(Type.UPDATE) @SourceFilter("MemoryConfigSource") @KeyFilter("some.key")  ChangeEvent changeEvent){
    log.log(Level.SEVERE, "UPDATE for source [MemoryConfigSource] and for key [some.key]: Received a config change event: {0}", changeEvent);
}

Note: You can filter by including the @TypeFilter and/or the @KeyFilter and/or the @SourceFilter.

Pattern matching on field.#

You might want to listen for fields that match a certain regex.

Example, listen to all keys that starts with some.:

@RegexFilter("^some\\..+")
public void allForPatternMatchOnKey(@Observes ChangeEvent changeEvent){
    log.log(Level.SEVERE, "Pattern match on key: Received a config change event: {0}", changeEvent);
}

By default, it will match on key, however you also listen on another field, for example, listen to all oldValue that starts with some.:

@RegexFilter(onField = Field.oldValue, value = "^some\\..+")
public void allForPatternMatchOnOldValue(@Observes ChangeEvent changeEvent){
    log.log(Level.SEVERE, "Pattern match on old value: Received a config change event: {0}", changeEvent);
}

You can Match on the following fields of the ChangeEvent object:

  • key
  • oldValue
  • newValue
  • fromSource

Implementing Events in a ConfigSource#

The ChangeEventNotifier allows you to detect changes and fire the appropriate events.

To use it in your own source:

  • Get a snapshot of the properties before the change.
  • Get a snapshot of the properties after the change.
  • Call detectChangesAndFire method:

Example:

Map<String,String> before = new HashMap<>(configSource.getProperties());
memoryConfigSource.getProperties().remove(key);
Map<String,String> after = new HashMap<>(configSource.getProperties());
ChangeEventNotifier.getInstance().detectChangesAndFire(before, after,configSource.getName());

or if you know the change and do not need detection:

configSource.getProperties().remove(key);
ChangeEventNotifier.getInstance().fire(new ChangeEvent(Type.REMOVE,key,getOptionalOldValue(oldValue),null,configSource.getName()));