ConfiJ maven artifacts are available on Maven Central.

Artifacts with two different classifiers are published. The nodeps ones do not depend on any non-shadowed 3rd party libs and are generally prefered. The default ch.kk7:confij-core:0.6.6 might introduce dependency issues only if an incompatible lib is already on the classpath (for example an old com.fasterxml:classmate).

The corresponding properties file must have the same attributes as in the interface. ConfiJ will make sure no unknown keys are present and bind all configuration strings to their configuration types.

ConfiJ loads sources one after the other. Each consecutive source overrides (merges) attributes of the previous ones. The last source therefore has the highest preference. Typically, this is useful to load a set of default values first, then continue with application specifics and environment specific values getting more and more detailed. Source types can be freely mixed, meaning you can load from classpath, then from a remote file, then from envionment variables and so on.

This will result in the final configuration:

Validation generally only applies to the final configuration. It is allowed to have incomplete configurations while there are still more configuration sources to load. However, it is never allowed to have an unknown configuration value. Confij has a default fail-fast strategy such that you don’t have to worry about legacy configs.

Configuration default can be defined directly in your configuration interface using the @Default annotation. For more complex scenarios where the default value is not easily stingifyable, use a default method.

The default method is called only when no other configuration values is defined. However only @Default values can be used for templating.

The AnySource simply takes a string and determines resource location and type based on it. It is the most compact form to specify a source unless you require special settings.

Variable substitutions are supported anywhere in the template string (see Templating). They take into account the previously loaded configuration keys. Replacement keys are always absolute (relative to the configuration root).

Most commonly the resource location (file, classpath,…​) is detected based on a URI scheme (see Section 6.1, “Resource Providers”). The configuration format (yaml, json,…​) is usually detected based on the ending.

For more complicated scenarios where Chapter 5, The AnySource is not suited, a ConfijSource must be passed explicitly. Confij distinguishes between where something is read from (Resource) and what format it is.

ConfiJ allows utilizing Java’s ServiceLoader mechanism to register additional services like source formats or validators. All you have to do is to add the file with the service-interface name to META-INF/services. In this service file you list the fully qualified classnames of your constraint validator classes (one per line).

To change the priority of a service loader instance implement the ServiceLoaderPriority.

When values are read from a configuration files they are first available as Strings. They are then transparently mapped to Objects or pimitives to match the defined type.

Configurations can themselves contain child configurations recursively. Since every configuration is organized in a tree-structure, we call them branches.

Typical branches contain, but are not limited to:

If the standard Collection interfaces are used ConfiJ will use an immutable representation of it. But any instance can be used as long as it has an empty constructor (but at the loss of immutability). Same holds for Map<String,?> types.

Interface proxies are Java-serializable if all the customized values are serializable, too.

Any property can contain placeholders wrapped in ${ }. These referenced properties can themselves reference other properties.

To disable templating support, see Chapter 11, Custom Templating.

It is possible register a custom templating functionality globally or per property. One use case is to disable templating per property.

A custom templating engine can be registered in the same ways. Every custom resolver must provide an empty constructor.

A recursive non-null validator is part of core. It verifies that the final configuration has all values set. It will not complain about null-values per default. To activate it add any @NotNull or @NonNull annotation to your config definition. Add such an annotation to your configuration root to apply it everywhere as non-null is enforced in all child-configuration values as well. To again allow for null values, use the opposite @Nullable. Any annotation named alike will do as long as it is available at runtime.

Core provides a @NonNullValidator.Nullable annotation but you can also restrict yourself to Hibernate annotations in case you are using the Chapter 13, JSR303 Validator already.

This validator can be disabled for the whole configuration:

Straight forward Hibernate-Validation. Validation is applied to the configuration as a last step after templating.

The JSR303 validator works together with the Chapter 12, Non-Null Validator, however this means that the semantics of @NonNull is applied recursively to all child-nodes, which is usually desirable for configurations.

ConfiJ core relies on java.util.logging (JUL) only due to it’s zero-dependency strategy. If ch.kk7:confij-slf4j is found on the classpath, logging uses the slf4j-framework. To support a custom logging-framework, register a Chapter 7, ConfiJ’s ServiceLoaders for ConfijLogFactory.

ConfiJ treats configurations are immutable objects. Using mutable objects like arrays is generally possible, but not advised. In any case ConfiJ will always create a completely new configuration if one of the values changes.

If a reload strategy is used, the ConfiJBuilder.buildWrapper() must be used, as it allows to register to change notifications.

You chan be notified on a change on any configuration value (it doesn’t have to be the root). If one of the nested configuration values changes, all parent objects will be notified, too. For example if database.active swaps, a change handler on database will trigger too.