Application Configuration with Spring Boot

Jul 05, 2022 - 5 minutes

This guide will introduce you to the various application configuration options that are present in Spring Boot. You will also learn how to create custom configuration for an application.

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You will learn

  • What is application configuration?
  • Why do we need application configuration?
  • What is application.properties?
  • What are some of the important things that can customized in application.properties?
  • How do you externalize configuration using Spring Boot?
  • How can you add custom application properties using Spring Boot?
  • What is @ConfigurationProperties?
  • What are the advantages of using @ConfigurationProperties?

Need for Application Configuration

Configuration for applications vary from one environment to another

  • You would want to connect to a different database or queues
  • You would want to connect with different services
  • You would want to configure less logging in production
  • You might want to have different custom configuration

Application Configuration with Spring Boot application.properties

Spring Boot allows you to configure your application configuration using a file named application.properties

application.properties can reside anywhere in the classpath of the application.

In application.properties, we can use the “logging.level” prefix to set logging levels.

logging.level.some.package.path=DEBUG
logging.level.some.other.package.path=ERROR

You can configure a log file by using logging.file property in application.properties. The logging here would be in addition to the logging in console.

logging.file=\path_to\logfile.log

You can also configure the port to run the server on using server.port

server.port = 9080

For complete list of options refer spring documentation - https://docs.spring.io/spring-boot/docs/current/reference/html/common-application-properties.html

In this guide, we will create three services using proper URIs and HTTP methods:

Project Code Structure

Following screenshot shows the structure of the project we will create.

Image

A few details:

  • SpringBootTutorialBasicsConfigurationApplication.java - The Spring Boot Application class generated with Spring Initializer. This class acts as the launching point for application.
  • pom.xml - Contains all the dependencies needed to build this project.
  • BasicConfiguration.java - We will use this component to define application configuration using @ConfigurationProperties
  • WelcomeResource.java - Example of a resource using @Value
  • application.properties - Configuration for application

Tools you will need

  • Maven 3.0+ is your build tool
  • Your favorite IDE. We use Eclipse.
  • JDK 1.8+

Complete Maven Project With Code Examples

Our Github repository has all the code examples - https://github.com/in28minutes/spring-boot-examples/tree/master/spring-boot-tutorial-basics-configuration

Bootstrapping with Spring Initializr

Spring Initializr http://start.spring.io/ is great tool to bootstrap your Spring Boot projects.

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As shown in the image above, following steps have to be done

  • Launch Spring Initializr and choose the following
    • Choose com.in28minutes.springboot.tutorial.basics.application.configuration as Group
    • Choose spring-boot-tutorial-basics-configuration as Artifact
    • Choose following dependencies
      • Web
      • DevTools
  • Click Generate Project.
  • Import the project into Eclipse. File -> Import -> Existing Maven Project.

Application Configuration using @Value

Let’s create a very simple example.

@RestController
public class WelcomeResource {

	@Value("${welcome.message}")
	private String welcomeMessage;

	@GetMapping("/welcome")
	public String retrieveWelcomeMessage() {
		// Complex Method
		return welcomeMessage;
	}
}

Notes

  • @Value("${welcome.message}") private String welcomeMessage; - Pick up the value for welcome.message from application configuration and assign it to this member variable.
  • @GetMapping("/welcome") public String retrieveWelcomeMessage() - Expose a simple service using the configuration

Let’s configure a value for welcome message in the application.properties.

welcome.message=Welcome message from property file! Welcome to in28Minutes

When you launch http://localhost:8080/welcome, you would see a page with this message

Welcome message from property file! Welcome to in28Minutes

We can make the application.properties more creative by using other properties as variables too.

app.name=in28Minutes
welcome.message=Welcome message from property file! Welcome to ${app.name}

Spring Boot provides different ways of configuring your property values.

  • You can send in a program argument
    • –welcome.message=”SomethingElse”
  • You can use a different file as property file
    • –spring.config.location=classpath:/default.properties
  • You can configure an environment variable

@Value is the basic approach for application configuration using Spring.

Application Configuration using Type-safe Configuration Properties

The problem with @Value is that you would have your configuration values distributed through out your application. A better option would be to have a centralized approach.

You can define a configuration component using @ConfigurationProperties.

@Component
@ConfigurationProperties("basic")
public class BasicConfiguration {
    private boolean value;
    private String message;
    private int number;

    public boolean isValue() {
        return value;
    }

    public void setValue(boolean value) {
        this.value = value;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

}

Notes:

  • @Component @ConfigurationProperties("basic") - Defines that this java bean contains configuration properties. All property names will start with basic..
  • private boolean value - A boolean value. Can be configured as basic.value.
  • private String message - A String value. Can be configured as basic.message.

We would need to use the BasicConfiguration in a service to expose the values

@Autowired
private BasicConfiguration configuration;

@RequestMapping("/dynamic-configuration")
public Map dynamicConfiguration() {
    // Not the best practice to use a map to store differnt types!
    Map map = new HashMap();
    map.put("message", configuration.getMessage());
    map.put("number", configuration.getNumber());
    map.put("key", configuration.isValue());
    return map;
}

Notes

  • @Autowired private BasicConfiguration configuration - Its very easy to use BasicConfiguration. Autowire it in when ever you need the value for a property from it.
  • @RequestMapping("/dynamic-configuration") public Map dynamicConfiguration() { - Define a simple service to expose the configured values.

The values can be configured in application.properties

basic.value: true
basic.message: Dynamic Message
basic.number: 100

When you browse to http://localhost:8080/dynamic-configuration, you see the following response.

{"number":100,"message":"Dynamic Message","key":true}

Understand Type Safety

@ConfigurationProperties is type safe. If you configure any property with a value of an invalid type, the application fails at startup.

Below snippet shows the log when basic.number is assigned a non numberic value.

***************************
APPLICATION FAILED TO START
***************************

Description:

Binding to target [email protected]8545 failed:

    Property: basic.number
    Value: ABC
    Reason: Failed to convert property value of type [java.lang.String] to required type [int] for property 'number'; nested exception is org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.String] to type [int]


Action:

Update your application's configuration

Complete Code Example

Github repository has all the code examples - https://github.com/in28minutes/spring-boot-examples/tree/master/spring-boot-tutorial-basics-configuration

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