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Getting Started#

Config Sources#

By default, SmallRye Config reads configuration properties from multiple configuration sources (by descending ordinal):

  1. (400) System properties
  2. (300) Environment variables
  3. (100) MicroProfile Config configuration file META-INF/ in the classpath

A configuration source is handled by a ConfigSource. A ConfigSource provides configuration values from a specific place.

The final configuration is the aggregation of the properties defined by all these sources. A configuration property lookup starts by the highest ordinal configuration source available and works it way down to other sources until a match is found. This means that any configuration property may override a value just by setting a different value in a higher ordinal config source. For example, a property configured using an Environment Variable overrides the value provided using the file.

System Properties#

System properties can be handed to the application through the -D flag during startup. For instance, java -Dmy.prop -jar my.jar.

Environment Variables#

Environment variables are set directly in the host operating system. Environment variables names follow the conversion rules detailed by Environment Variables.

MicroProfile Config configuration file#

The MicroProfile Config configuration file META-INF/ in the classpath. It follows the standard convention for properties files.


Additional Config Sources#

SmallRye Config provides additional extensions which cover other configuration formats and stores:

It is also possible to create a Custom ConfigSource.

Retrieving the Configuration#


The org.eclipse.microprofile.config.ConfigProvider.getConfig() API allows to access the org.eclipse.microprofile.config.Config API programmatically.

Config config = ConfigProvider.getConfig();

String message = config.getValue("greeting.message", String.class);

The Config instance will be created and registered to the current context class loader if no such configuration is already created and registered. This means that subsequent calls to ConfigProvider.getConfig() will return the same Config instance if the context class loader is the same.

To obtain a detached instanced, use the io.smallrye.config.SmallRyeConfigBuilder:

SmallRyeConfig config = new SmallRyeConfigBuilder()

String message = config.getValue("greeting.message", String.class);

With CDI#

In a CDI environment, configuration can be injected in CDI aware beans with @Inject and the org.eclipse.microprofile.config.inject.ConfigProperty qualifier.

@ConfigProperty(name = "greeting.message") 
String message;

@ConfigProperty(name = "greeting.suffix", defaultValue="!") 
String suffix;

@ConfigProperty(name = "")
Optional<String> name; 

SmallRyeConfig config;
  • If a value if not provided for this greeting.message, the application startup fails with a jakarta.enterprise.inject.spi.DeploymentException: No config value of type [class java.lang.String] exists for: greeting.message.
  • The default value ! is injected if the configuration does not provide a value for greeting.suffix.
  • The property is optional - an empty Optional is injected if the configuration does not provide a value for it.

Override Config#

It is possible to override Config default initialization ConfigProvider.getConfig(), by extending io.smallrye.config.SmallRyeConfigFactory and registering the implementation with the ServiceLoader mechanism.

Config vs SmallRyeConfig#

The io.smallrye.config.SmallRyeConfig is an implementation of org.eclipse.microprofile.config.Config and provides additional APIs and helper methods not available in org.eclipse.microprofile.config.Config. To obtain an instance of io.smallrye.config.SmallRyeConfig, the original org.eclipse.microprofile.config.Config can be unwrapped:

Config config = ConfigProvider.getConfig();
SmallRyeConfig smallRyeConfig = config.unwrap(SmallRyeConfig.class);

Or if using the builder it can be obtained directly:

SmallRyeConfig config = new SmallRyeConfigBuilder().build();

A few notable APIs provided by io.smallrye.config.SmallRyeConfig allow to:

  • Retrive multiple values into a specified Collection
  • Retrive Indexed Values
  • Retrive Config Mappings instances
  • Retrieve the raw value of a configuration
  • Check if a property is present
  • Retrieve a Converter
  • Convert values


The ConfigSource retrieves a configuration value as a String. Other data types require a conversion using the org.eclipse.microprofile.config.spi.Converter API.

Most of the common Converter types are provided by default:

  • boolean and java.lang.Boolean; the values “true”, “1”, “YES”, “Y” “ON” represent true. Any other value will be interpreted as false
  • byte and java.lang.Byte
  • short and java.lang.Short
  • int, java.lang.Integer, and java.util.OptionalInt
  • long, java.lang.Long, and java.util.OptionalLong
  • float and java.lang.Float; a dot ‘.’ is used to separate the fractional digits
  • double, java.lang.Double, and java.util.OptionalDouble; a dot ‘.’ is used to separate the fractional digits
  • char and java.lang.Character
  • java.lang.Class based on the result of Class.forName
  • java.util.UUID
  • java.util.Currency
  • java.util.regex.Pattern
  • java.nio.file.Path
  • Any class with declared static methods of, valueOf or parse that take a String or a CharSequence
  • Any class with declared constructors that takes a String or a CharSequence

All default converters have a priority of 1.