Best Practices

Get the most out of AndHow and your application

Declare properties in the class or interface where they are used. Place related sets of Properties in nested interfaces.

Just like constants, Properties can (and should) be declared where they are be used to create natural scope: If a secret is only needed by one class, don't make it visible to the entire application. Avoid placing Properties in a central 'Config' class.

Nesting related Properties into interfaces creates logical, canonical names for Properties. It also takes advantage of the Java language to save some typing: Variables declared in an interface are implicitly static final. As of Java 11, inner interfaces may be declared private.

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Don't worry about Property names unless you have to

Properties always have a unique canonical name based on their logical path. A Property named MY_PROP declared in the com.bigcorp.MyClass has the canonical name com.bigcorp.MyClass.MY_PROP. The same pattern continues with nested inner classes or interfaces.

Properties may have aliases, but the canonical names are often good enough and will implicitly update when refactoring.

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Use a Property default value when there is a good business-related default that works in all environments

Don't use a default value for local workstation or test environment configuration values.

Its easy for a default value to end up in production. Some Properties have good defaults: report margin, retry counts or log level. Others do not: DB connection string, user name or password. If a Property has no value that is acceptable in all environments, its better to not specify a default and rely on configuration to supply the value.

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Use an AndHowInit class to configure AndHow and include it with your deployable application, not a library or dependency

AndHow allows only a single class implementing the AndHowInit interface on the classpath and will complain (i.e. throw a RuntimeException) at startup if it finds more. Why? AndHowIinit configures how AndHow configures your application - it cannot be ambiguous which AndHowInit is intended to be the effective one. If an AndHowInit instance is included in a library, it prohibits applications using that library from creating their own AndHowInit.

If you have a dual-use library, such as a calculation utility that can be run from command line or bundled into a larger application, use a packaging tool like Maven to create two packaged version: One with an AndHowInit instance for independant usage, and another without an AndHowInit instance for so the library can be included as a dependency in other applications.

Include an andhow.properties file in your deployable artifact, not in library or dependency

Incluing an andhow.properties file in a library is essentially just like setting default values for each Property. Properties already can have their defalaults declared in their construction, so there is no need to do this. Worse, if the deployed application includes its own properties file, it may become ambiguous which one is suppose to be in use (though web containers like Tomcat and SpringBoot generally get this right).

If you want to include a sample configuration file for applications using a library, it might be clearer to call it andhow.properties.sample or similar.

Use an andhow.properties on your test classpath (not your production one)