How to access a value defined in the application.properties file in Spring Boot ( Externalized Conf)

 

  

   

    
24. Externalized Configuration
   
  
 
Spring Boot allows you to externalize your configuration so you can work with the same application code in different environments. You can use properties files, YAML files, environment variables and command-line arguments to externalize configuration. Property values can be injected directly into your beans using the @Valueannotation, accessed via Spring’s Environment abstraction or bound to structured objects via @ConfigurationProperties.
Spring Boot uses a very particular PropertySource order that is designed to allow sensible overriding of values, properties are considered in the following order:
 

  
Command line arguments.
Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property)
JNDI attributes from java:comp/env.
Java System properties (System.getProperties()).
OS environment variables.
A RandomValuePropertySource that only has properties in random.*.
Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants)
Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants)
Application properties outside of your packaged jar (application.properties and YAML variants).
Application properties packaged inside your jar (application.properties and YAML variants).
@PropertySource annotations on your @Configuration classes.
Default properties (specified using SpringApplication.setDefaultProperties).
 
To provide a concrete example, suppose you develop a @Component that uses a name property:
import org.springframework.stereotype.*
import org.springframework.beans.factory.annotation.*

@Component
public class MyBean {

    @Value("${name}")
    private String name;

    // ...

}
On your application classpath (e.g. inside your jar) you can have an application.properties that provides a sensible default property value for name. When running in a new environment, an application.properties can be provided outside of your jar that overrides the name; and for one-off testing, you can launch with a specific command line switch (e.g. java -jar app.jar --name="Spring").
 

  
The SPRING_APPLICATION_JSON properties can be supplied on the command line with an environment variable. For example in a UN*X shell:
$ SPRING_APPLICATION_JSON='{"foo":{"bar":"spam"}}' java -jar myapp.jar
In this example you will end up with foo.bar=spam in the Spring Environment. You can also supply the JSON as spring.application.json in a System variable:
$ java -Dspring.application.json='{"foo":"bar"}' -jar myapp.jar
or command line argument:
$ java -jar myapp.jar --spring.application.json='{"foo":"bar"}'
or as a JNDI variable java:comp/env/spring.application.json.
 
 

  

   

    

     
24.1 Configuring random values
    
   
  
  
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).
 
 

  

   

    

     
24.2 Accessing command line properties
    
   
  
  
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 SpringEnvironment. 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 usingSpringApplication.setAddCommandLineProperties(false).
 
 

  

   

    

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

   
A /config subdirectory of the current directory.
The current directory
A classpath /config package
The classpath root
  
  
The list is ordered by precedence (properties defined in locations higher in the list override those defined in lower locations).
  

   
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
  

   
spring.config.name and spring.config.location are used very early to determine which files have to be loaded so they have to be defined as an environment property (typically OS env, system property or command line argument).
  
  
If spring.config.location contains directories (as opposed to files) they should end in / (and will be appended with the names generated fromspring.config.name before being loaded, including profile-specific file names). Files specified in spring.config.location are used as-is, with no support for profile-specific variants, and will be overridden by any profile-specific properties.
  
The default search path classpath:,classpath:/config,file:,file:config/ is always used, irrespective of the value of spring.config.location. This search path is ordered from lowest to highest precedence (file:config/ wins). If you do specify your own locations, they take precedence over all of the default locations and use the same lowest to highest precedence ordering. 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.
  

   
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).
  
  

   
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.
  
 
 

  

   

    

     
24.4 Profile-specific properties
    
   
  
  
In addition to application.properties files, profile-specific properties can also be defined using the naming convention application-{profile}.properties. TheEnvironment has a set of default profiles (by default [default]) which are used if no active profiles are set (i.e. if no profiles are explicitly activated then properties from application-default.properties are loaded).
  
Profile-specific properties are loaded from the same locations as standard application.properties, with profile-specific files always overriding the non-specific ones irrespective of whether the profile-specific files are inside or outside your packaged jar.
  
If several profiles are specified, a last wins strategy applies. For example, profiles specified by the spring.profiles.active property are added after those configured via the SpringApplication API and therefore take precedence.
  

   
If you have specified any files in spring.config.location, profile-specific variants of those files will not be considered. Use directories in`spring.config.location` if you also want to also use profile-specific properties.
  
 
 

  

   

    

     
24.5 Placeholders in properties
    
   
  
  
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
  

   
You can also use this technique to create ‘short’ variants of existing Spring Boot properties. See the Section 69.3, “Use ‘short’ command line arguments”how-to for details.
  
 
 

  

   

    

     
24.6 Using YAML instead of Properties
    
   
  
  
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.
  

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

   

    

     

      
24.6.1 Loading YAML
     
    
   
   
Spring Framework provides two convenient classes that can be used to load YAML documents. The YamlPropertiesFactoryBean will load YAML as Properties and the YamlMapFactoryBean will load YAML as a Map.
   
For example, the following YAML document:
   
environments:
    dev:
        url: http://dev.bar.com
        name: Developer Setup
    prod:
        url: http://foo.bar.com
        name: My Cool App
   
Would be transformed into these properties:
   
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
   
YAML lists are represented as property keys with [index] dereferencers, for example this YAML:
   
my:
   servers:
       - dev.bar.com
       - foo.bar.com
   
Would be transformed into these properties:
   
my.servers[0]=dev.bar.com
my.servers[1]=foo.bar.com
   
To bind to properties like that using the Spring DataBinder utilities (which is what @ConfigurationProperties does) you need to have a property in the target bean of type java.util.List (or Set) and you either need to provide a setter, or initialize it with a mutable value, e.g. this will bind to the properties above
   
@ConfigurationProperties(prefix="my")
public class Config {

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

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

   

    

     

      
24.6.2 Exposing YAML as properties in the Spring Environment
     
    
   
   
The YamlPropertySourceLoader class can be used to expose YAML as a PropertySource in the Spring Environment. This allows you to use the familiar @Valueannotation with placeholders syntax to access YAML properties.
  
  

   

    

     

      
24.6.3 Multi-profile YAML documents
     
    
   
   
You can specify multiple profile-specific YAML documents in a single file by using a spring.profiles key to indicate when the document applies. For example:
   
server:
    address: 192.168.1.100
---
spring:
    profiles: development
server:
    address: 127.0.0.1
---
spring:
    profiles: production
server:
    address: 192.168.1.120
   
In the example above, the server.address property will be 127.0.0.1 if the development profile is active. If the development and production profiles are notenabled, then the value for the property will be 192.168.1.100.
   
The default profiles are activated if none are explicitly active when the application context starts. So in this YAML we set a value for security.user.password that isonly available in the "default" profile:
   
server:
  port: 8000
---
spring:
  profiles: default
security:
  user:
    password: weak
   
whereas in this example, the password is always set because it isn’t attached to any profile, and it would have to be explicitly reset in all other profiles as necessary:
   
server:
  port: 8000
security:
  user:
    password: weak
  
  

   

    

     

      
24.6.4 YAML shortcomings
     
    
   
   
YAML files can’t be loaded via the @PropertySource annotation. So in the case that you need to load values that way, you need to use a properties file.
  
 
 

  

   

    

     
24.7 Type-safe Configuration Properties
    
   
  
  
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

}
  

   
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.
  
  

   
Contrary to @Value, SpEL expressions are not evaluated prior to injecting a value in the relevant @ConfigurationProperties bean.
  
  
The @EnableConfigurationProperties annotation is automatically applied to your project so that any beans annotated with @ConfigurationProperties will be 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 {
}
  

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

   

    

     

      
24.7.1 Third-party configuration
     
    
   
   
As well as using @ConfigurationProperties to annotate a class, you can also use it on @Bean methods. This can be particularly useful when you want to bind properties to third-party components that are outside of your control.
   
To configure a bean from the Environment properties, add @ConfigurationProperties to its bean registration:
   
@ConfigurationProperties(prefix = "foo")
@Bean
public FooComponent fooComponent() {
    ...
}
   
Any property defined with the foo prefix will be mapped onto that FooComponent bean in a similar manner as the ConnectionSettings example above.
  
  

   

    

     

      
24.7.2 Relaxed binding
     
    
   
   
Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so there doesn’t need to be an exact match between the Environment property name and the bean property name. Common examples where this is useful include dashed separated (e.g. context-path binds tocontextPath), and capitalized (e.g. PORT binds to port) environment properties.
   
For example, given the following @ConfigurationProperties class:
   
@Component
@ConfigurationProperties(prefix="person")
public class ConnectionSettings {

    private String firstName;

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

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

}
   
The following properties names can all be used:
   

    
    
Table 24.1. relaxed binding
    

     
Property
Note
person.firstName
Standard camel case syntax.
person.first-name
Dashed notation, recommended for use in .properties and .yml files.
PERSON_FIRST_NAME
Upper case format. Recommended when using a system environment variables.
    
   
   

  
  

   

    

     

      
24.7.3 Properties conversion
     
    
   
   
Spring will attempt to coerce the external application properties to the right type when it binds to the @ConfigurationProperties beans. If you need custom type conversion you can provide a ConversionService bean (with bean id conversionService) or custom property editors (via a CustomEditorConfigurer bean) or custom Converters (with bean definitions annotated as @ConfigurationPropertiesBinding).
   

    
As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your ConversionService is using. Typically, any dependency that you require may not be fully initialized at creation time. You may want to rename your custom ConversionService if it’s not required for configuration keys coercion and only rely on custom converters qualified with @ConfigurationPropertiesBinding.
   
  
  

   

    

     

      
24.7.4 @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.validationconstraint annotations to your @ConfigurationProperties class:
   
@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {

    @NotNull
    private InetAddress remoteAddress;

    // ... getters and setters

}
   
In order to validate values of nested properties, you must annotate the associated field as @Valid to trigger its validation. For example, building upon the aboveConnectionSettings example:
   
@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {

    @NotNull
    @Valid
    private RemoteAddress remoteAddress;

    // ... getters and setters

    public static class RemoteAddress {

        @NotEmpty
        public String hostname;

        // ... getters and setters

    }

}
   
You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator. There is a Validation sample so you can see how to set things up.
   

    
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.