The RandomValuePropertySource is useful for injecting random values (e.g. into secrets or test cases). It can produce integers, longs or strings, e.g.

my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.number.less.than.ten=${random.int(10)}
my.number.in.range=${random.int[1024,65536]}

The random.int* syntax is OPEN value (,max) CLOSE where the OPEN,CLOSE are any character and value,max are integers. If max is provided then value is the minimum value and max is the maximum (exclusive).

By default SpringApplication will convert any command line option arguments (starting with ‘--’, e.g. --server.port=9000) to a property and add it to the Spring Environment. As mentioned above, command line properties always take precedence over other property sources.

If you don’t want command line properties to be added to the Environment you can disable them using SpringApplication.setAddCommandLineProperties(false).

SpringApplication will load properties from application.properties files in the following locations and add them to the Spring Environment:

The list is ordered by precedence (locations higher in the list override lower items).

	Note
	You can also use YAML ('.yml') files as an alternative to '.properties'.

If you don’t like application.properties as the configuration file name you can switch to another by specifying a spring.config.name environment property. You can also refer to an explicit location using the spring.config.location environment property (comma-separated list of directory locations, or file paths).

$ java -jar myproject.jar --spring.config.name=myproject

or

$ java -jar myproject.jar --spring.config.location=classpath:/default.properties,classpath:/override.properties

If spring.config.location contains directories (as opposed to files) they should end in / (and will be appended with the names generated from spring.config.name before being loaded). The default search path classpath:,classpath:/config,file:,file:config/ is always used, irrespective of the value of spring.config.location. In that way you can set up default values for your application in application.properties (or whatever other basename you choose with spring.config.name) and override it at runtime with a different file, keeping the defaults.

	Note
	If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (e.g. SPRING_CONFIG_NAME instead of spring.config.name).

	Note
	If you are running in a container then JNDI properties (in java:comp/env) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.

In addition to application.properties files, profile-specific properties can also be defined using the naming convention application-{profile}.properties.

Profile specific properties are loaded from the same locations as standard application.properties, with profile-specific files always overriding the default ones irrespective of whether the profile-specific files are inside or outside your packaged jar.

The values in application.properties are filtered through the existing Environment when they are used so you can refer back to previously defined values (e.g. from System properties).

app.name=MyApp
app.description=${app.name} is a Spring Boot application

	Tip
	You can also use this technique to create ‘short’ variants of existing Spring Boot properties. See the Section 63.3, “Use ‘short’ command line arguments” how-to for details.

YAML is a superset of JSON, and as such is a very convenient format for specifying hierarchical configuration data. The SpringApplication class will automatically support YAML as an alternative to properties whenever you have the SnakeYAML library on your classpath.

	Note
	If you use ‘starter POMs’ SnakeYAML will be automatically provided via spring-boot-starter.

environments:
    dev:
        url: http://dev.bar.com
        name: Developer Setup
    prod:
        url: http://foo.bar.com
        name: My Cool App

environments.dev.url=http://dev.bar.com
environments.dev.name=Developer Setup
environments.prod.url=http://foo.bar.com
environments.prod.name=My Cool App

my:
   servers:
       - dev.bar.com
       - foo.bar.com

my.servers[0]=dev.bar.com
my.servers[1]=foo.bar.com

@ConfigurationProperties(prefix="my")
public class Config {

    private List<String> servers = new ArrayList<String>();

    public List<String> getServers() {
        return this.servers;
    }
}

server:
    address: 192.168.1.100
---
spring:
    profiles: development
server:
    address: 127.0.0.1
---
spring:
    profiles: production
server:
    address: 192.168.1.120

Using the @Value("${property}") annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature. Spring Boot provides an alternative method of working with properties that allows strongly typed beans to govern and validate the configuration of your application. For example:

@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {

    private String username;

    private InetAddress remoteAddress;

    // ... getters and setters

}

Note

The getters and setters are advisable, since binding is via standard Java Beans property descriptors, just like in Spring MVC. They are mandatory for immutable types or those that are directly coercible from String. As long as they are initialized, maps, collections, and arrays need a getter but not necessarily a setter since they can be mutated by the binder. If there is a setter, Maps, collections, and arrays can be created. Maps and collections can be expanded with only a getter, whereas arrays require a setter. Nested POJO properties can also be created (so a setter is not mandatory) if they have a default constructor, or a constructor accepting a single value that can be coerced from String. Some people use Project Lombok to add getters and setters automatically.

When the @EnableConfigurationProperties annotation is applied to your @Configuration, any beans annotated with @ConfigurationProperties will be automatically configured from the Environment properties. This style of configuration works particularly well with the SpringApplication external YAML configuration:

# application.yml

connection:
    username: admin
    remoteAddress: 192.168.1.1

# additional configuration as required

To work with @ConfigurationProperties beans you can just inject them in the same way as any other bean.

@Service
public class MyService {

    @Autowired
    private ConnectionSettings connection;

     //...

    @PostConstruct
    public void openConnection() {
        Server server = new Server();
        this.connection.configure(server);
    }

}

It is also possible to shortcut the registration of @ConfigurationProperties bean definitions by simply listing the properties classes directly in the @EnableConfigurationProperties annotation:

@Configuration
@EnableConfigurationProperties(ConnectionSettings.class)
public class MyConfiguration {
}

	Tip
	Using @ConfigurationProperties also allows you to generate meta-data files that can be used by IDEs. See the Appendix B, Configuration meta-data appendix for details.

@ConfigurationProperties(prefix = "foo")
@Bean
public FooComponent fooComponent() {
    ...
}

@Component
@ConfigurationProperties(prefix="person")
public class ConnectionSettings {

    private String firstName;

    public String getFirstName() {
        return this.firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

}

23.7.3 @ConfigurationProperties Validation

Spring Boot will attempt to validate external configuration, by default using JSR-303 (if it is on the classpath). You can simply add JSR-303 javax.validation constraint annotations to your @ConfigurationProperties class:

@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {

    @NotNull
    private InetAddress remoteAddress;

    // ... getters and setters

}

You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator.

	Tip
	The spring-boot-actuator module includes an endpoint that exposes all @ConfigurationProperties beans. Simply point your web browser to /configprops or use the equivalent JMX endpoint. See the Production ready features. section for details.