juneau-doc/docs/Topics/05.juneau-config/09.Listeners.html

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Listeners

<p>
	Configuration change events can be listened for using the following methods:
</p>
<ul class='javatree'>
	<li class='jc'>{@link oaj.config.Config}
	<ul>
		<li class='jm'>{@link oaj.config.Config#addListener(ConfigEventListener) addListener(ConfigEventListener)}
		<li class='jm'>{@link oaj.config.Config#removeListener(ConfigEventListener) removeListener(ConfigEventListener)}
	</ul>
</ul>
<p>
	The {@link oaj.config.event.ConfigEventListener} interface consists of the following method:
</p>		
<ul class='javatree'>
	<li class='jic'>{@link oaj.config.event.ConfigEventListener}
	<ul>
		<li class='jm'>{@link oaj.config.event.ConfigEventListener#onConfigChange(ConfigEvents) onConfigChange(ConfigEvents)}
	</ul>
</ul>
<p>
	The {@link oaj.config.event.ConfigEvent} class provides access to all the information about the updated entry:
</p>
<ul class='javatree'>
	<li class='jc'>{@link oaj.config.event.ConfigEvent}
	<ul>
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getType() getType()}
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getSection() getSection()}
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getKey() getKey()}
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getValue() getValue()}
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getModifiers() getModifiers()}
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getComment() getComment()}
		<li class='jm'>{@link oaj.config.event.ConfigEvent#getPreLines() getPreLines}
	</ul>
</ul>
<p>
	The listener method is triggered:
</p>
<ul class='spaced-list'>
	<li>After {@link oaj.config.Config#commit()} is called.
	<li>When the file changes on the file system. 
</ul>
<p>
	In both cases, the listener is triggered after the changes have been committed.
</p>
<p class='bpcode w800'>
	<jk>final</jk> Config c = Config.<jsm>create</jsm>(<js>"MyConfig.cfg"</js>).build();
	
	<jc>// Add a listener for changes to MySection/key1</jc>
	c.addListener(
		<jk>new</jk> ConfigEventListener() {
			<ja>@Override</ja>
			<jk>public void</jk> onConfigChange(ConfigEvents) {
				<jk>for</jk> (ConfigEvent event : events) {
					<jk>if</jk> (event.getType() == <jsf>SET_ENTRY</jsf>) {
						
						String section = event.getSection();
						String key = event.getKey();
					
						<jk>if</jk> (section.equals(<js>"MySection"</js>) &amp;&amp; key.equals(<js>"key1"</js>)) {
		
							<jc>// Get the new value from the event.</jc>
							String newVal = event.getValue();
							
							<jc>// Or get the new value from the config (since the change has already been committed).</jc>
							newVal = c.getString(<js>"MySection/key1"</js>);
						}
					}
				}
			}
		}
	)
</p>