juneau-doc/docs/Topics/05.juneau-config/03.Variables.html

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Variables

<p>
	Config files can contain variables that get resolved dynamically using the previously-described {@link oaj.svl.VarResolver} API.
</p>
<h5 class='figure'>Example:</h5>
<p class='bpcode w800'>
	<cc>#--------------------------</cc>
	<cc># My section</cc>
	<cc>#--------------------------</cc>
	<cs>[MySection]</cs>
	
	<cc># A system property</cc>
	<ck>locale</ck> = <cv>$S{java.locale, en_US}</cv>
	
	<cc># An environment variable</cc>
	<ck>path</ck> = <cv>$E{PATH, unknown}</cv>
	
	<cc># Another value in this config file</cc>
	<ck>anotherLocale</ck> = <cv>$C{MySection/locale}</cv>
	
	<cc># Look for system property, or env var if that doesn't exist, or a default value if that doesn't exist.</cc>
	<ck>nested</ck> = <cv>$S{mySystemProperty,$E{MY_ENV_VAR,$C{MySection/anotherLocale}}}</cv>

	<cc># A POJO with embedded variables</cc>
	<ck>aBean</ck> = <cv>{foo:'$S{foo}',baz:$C{MySection/anInt}}</cv>
</p>
<p class='bpcode w800'>
	Config c = Config.<jsf>create</jsf>().build();
	
	Locale locale = cf.getObject(<js>"MySection/locale"</js>, Locale.<jk>class</jk>); 
	String path = cf.getString(<js>"MySection/path"</js>); 
	<jk>int</jk> sameAsAnInt = cf.getInt(<js>"MySection/sameAsAnInt"</js>); 
	ABean bean = cf.getObject(<js>"MySection/aBean"</js>, ABean.<jk>class</jk>); 
</p>
<p>
	By default, <c>Configs</c> use the {@link oaj.svl.VarResolver#DEFAULT} variable resolver
	which provides support for the following variables and constructs:
</p>
<ul class='javatree'>
	<li class='jc'>{@link oaj.svl.vars.SystemPropertiesVar} - <c>$S{key[,default]}</c>
	<li class='jc'>{@link oaj.svl.vars.EnvVariablesVar} - <c>$E{key[,default]}</c>
	<li class='jc'>{@link oaj.config.vars.ConfigVar} - <c>$C{key[,default]}</c>
</ul>
<p>
	The variable resolver is controlled via the following setting:
</p>
<ul class='javatree'>
	<li class='jf'>{@link oaj.config.Config#CONFIG_varResolver}
</ul>
<p>
	Additionally, the following method can be used to retrieve a <c>Config</c> with a different variable resolver:
</p>
<ul class='javatree'>
	<li class='jm'>{@link oaj.config.Config#resolving(VarResolverSession)}
</ul>