Spring Property Injection Concepts
Internal
Overview
Spring has two different, but related kinds of configurations: bean wiring, which refers to declaring application components and their dependencies, and how those dependencies should be injected into each other, as described in the Dependency Injection and Inversion of Control Container section, and property injection, which is the process that allows external pieces of data, known as configuration properties, to be provided to the application runtime at startup or while it is running, in form of Java system properties, environment variables and by other means. This section addresses property injection concepts.
Configuration Properties
Configuration properties are pieces of data coded into Spring components using the JavaBeans property conventions. They usually have a corresponding member variable, a getter and a setter. The Spring Framework provides conventions and mechanisms to automatically inject values into configuration properties, while those values come from several different property sources.
The Environment Abstraction
The Spring environment is the only source of configuration properties for components needing them. The environment abstracts the origins of properties and applies precedence rules when the same property is specified in more than one source. It pulls property values from several sources: Java system properties, command-line arguments, environment variables, configuration files, etc. The property sources are described in detail in their corresponding sections, below.
Injecting Properties into Beans
Individual properties can also be injected directly into established components, by .... However, if you have the option, bundling configuration properties into a ... as described above, is probably a better approach.
Property Injection and Auto-Configuration
The beans that are automatically configured by the Spring Boot autoconfiguration. process are all configurable by properties drawn from the Spring environment.
Property Sources
Java System Properties
Command-Line Arguments
java -jar ... --<property.name>=<value>
Example:
java -jar ... --server.port=9999
Environment Variables
The naming style should accommodate restrictions placed on environment variable names by the operating system.
export SERVER_PORT=9999
Property Configuration Files
application.properties
Configuration Service
The configuration service is also referred to as configuration server.
Precedence
Profiles
TODO
- Diagram with property sources and their relative priority, including the configuration service (chapter 14).
- Augment https://kb.novaordis.com/index.php/Spring_Boot_Concepts#Autoconfiguration with specialized sections on property injection for DataSources, etc.
- How do I read the effective values of all configuration properties during testing and at runtime?
- You can figure out the active profile from within a Spring application by @Autowire-ing org.springframework.core.env.Environment and inspecting it.
- https://docs.spring.io/spring-boot/docs/2.1.0.RELEASE/reference/htmlsingle/#configuration-metadata-annotation-processor