Spring Boot Configuration Properties

A Quick Setup

add spring-boot-starter-parent as the parent in our pom.xml

	<parent>
    	<groupId> org.springframework.boot	</groupId>
    	<artifactId> spring-boot-starter-parent	</artifactId>
    	<version> 2.1.3.RELEASE	</version>
    	<relativePath/>; 	<!-- lookup parent from repository -->;
	</parent>

Properties

We configure properties using POJOs

    
@Configuration
@ConfigurationProperties(prefix = "mail")
public class ConfigProperties {

    private String hostName;
    private int port;
    private String from;

    // getters and setters
}

@Configuration is used so that Spring creates a Spring bean in the application context.
@ConfigurationProperties works best with properties that all have the same prefix

If we don’t use @Configuration in the POJO, then we need to add @EnableConfigurationProperties(ConfigProperties.class) in the main Spring application class to bind the properties into the POJO:

   
@SpringBootApplication
@EnableConfigurationProperties(ConfigProperties.class)
public class SpringDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringDemoApplication.class, args);
    }
}

Spring will automatically bind any property defined in our property file that has the prefix mail and the same name as in the fields in the ConfigProperties class

   
mail.hostname=host@mail.com
mail.port=900
mail.from=mailer@mail.com

Nested Properties

We can have nested properties in Lists, Maps, and Classes

    
public class Credentials {
    private String authMethod;
    private String username;
    private String password;

    // getters and setters
}

   
public class ConfigProperties {

    private String host;
    private int port;
    private String from;
    private List defaultRecipients;
    private Map<String, String> additionalHeaders;
    private Credentials credentials;
    // getters and setters
}

  
#Simple properties
mail.hostname=support@mail.com
mail.port=9000
mail.from=support@mail.com

#List properties
mail.defaultRecipients[0]=admin@mail.com
mail.defaultRecipients[1]=owner@mail.com

#Map Properties
mail.additionalHeaders.redelivery=true
mail.additionalHeaders.secure=true

#Object properties
mail.credentials.username=ram
mail.credentials.password=password
mail.credentials.authMethod=SHA1

Property Validation

    
@NotBlank
private String hostName;

    
@NotBlank
private String hostName;

   
@Length(max = 4, min = 1)
private String authMethod;

 
@Min(1025)
@Max(65536)
private int port;

@Pattern(regexp = "^[a-z0-9._%+-]+@[a-z0-9.-]+\\.[a-z]{2,6}$")
private String from;

Immutable @ConfigurationProperties binding

    
@ConfigurationProperties(prefix = "mail.credentials")
@ConstructorBinding
public class ImmutableCredentials {

    private final String authMethod;
    private final String username;
    private final String password;

    public ImmutableCredentials(String authMethod, String username, String password) {
        this.authMethod = authMethod;
        this.username = username;
        this.password = password;
    }

    public String getAuthMethod() {
        return authMethod;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }
}

How can Spring Boot help a developer?

• Integration with several frameworks
• Configuration management
• Logging
• Transaction management
• Error/Exception handling
• Monitoring and health checks
• Integrating unit testing and mocking frameworks

Conclusion

We have explored the @ConfigurationProperties annotation and some of the features it provides like data binding and Bean Validation. Spring Boot makes the life of a developer a lot easier by providing important debug and deployment tools. Spring Boot adds some intelligence with autoconfiguration. All we need to do is provide the frameworks that are needed by the application, and Spring Boot magically auto-configures them!

It reduces project startup time to a large extent and provides an easy mechanism termed as starter projects for the development of different applications.