How to access a value defined in the application.properties file in Spring Boot

Breaking Down Property Access

Direct Property Access Using @Value

The core way to access properties is to use the @Value annotation. It's straightforward, easy, and just works:

// It's like getting that first cup of coffee in the morning - smooth and aromatic!
@Value("${property.name}")
private String propertyName;


Using Environment for Property Retrieval

When @Value doesn't quite fit—perhaps you need dynamic keys or are operating outside the lifecycle of a bean—Environment becomes your lifeline:

@Autowired
private Environment env;

public String getDynamicProperty(String key) {
    return env.getProperty(key);
}
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The Environment class serves as your swiss army knife for accessing the property landscape of your application.

Binding Properties to Structured Objects

For reducing potential errors and when dealing with a group of related properties, @ConfigurationProperties enables you to relate .properties or .yml files to corresponding POJO fields making it less prone to error:

@ConfigurationProperties(prefix="service.details")
public class ServiceDetails {
    private String url;
    private int timeout;
    // don't forget those getters and setters
}
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Don't forget to create getters and setters for each field to ensure they are properly bound.

Custom Property Sources

Need to externalize configuration or pick a different .properties file? @PropertySource along with @ConfigurationProperties is the way:

@Configuration
@PropertySource("classpath:custom.properties")
@ConfigurationProperties(prefix="custom")
public class CustomConfig {
    // ...
}
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Here you're saying "Hey Spring, treat this as a bean factory and do your magic!"

Lifecycle-aware Property Injection

Be aware of @Value in certain phases such as @PostConstruct because it might not work properly. Do resort to constructor injection or rely on Environment for a safer access.

YML and Properties Harmony

@ConfigurationProperties is your easy-going friend—it appreciates both .properties and .yml, allowing you to pick your preferred format.

Direct vs Managed Property Access

When you need direct and immediate property access, Autowired Environment provides a straight road. For managed and type-safe access, inject your ConfigProperties.

Advanced Tips and Tricks

Injecting Values Conditionally

For conditional properties that may be absent, use the : operator with @Value for a default value fallback:

@Value("${optional.property:default}")
private String optionalProperty;
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Safe Practice with @Value

Be very precise while specifying the property name in @Value; a typo can result in a late runtime error—Spring cannot resolve the placeholder if no match is found.

Clean Code with @Configuration

Annotating your POJO with @Configuration signifies cleaner, class-level standardization. This informs Spring that the class acts as a source of bean definitions.