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 @Value annotation, accessed via Spring’s Environment abstraction or bound to structured objects.

Spring Boot uses a very particular PropertySource order that is designed to allow sensible overriding of values, properties are considered in the following order:

  1. Command line arguments.
  2. JNDI attributes from java:comp/env.
  3. Java System properties (System.getProperties()).
  4. OS environment variables.
  5. A RandomValuePropertySource that only has properties in random.*.
  6. Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants)
  7. Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants)
  8. Application properties outside of your packaged jar (application.properties and YAML variants).
  9. Application properties packaged inside your jar (application.properties and YAML variants).
  10. @PropertySource annotations on your @Configuration classes.
  11. 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.*

public class MyBean {

    private String name;

    // ...


You can bundle an application.properties inside your jar that provides a sensible default name. When running in production, an application.properties can be provided outside of your jar that overrides name; and for one-off testing, you can launch with a specific command line switch (e.g. java -jar app.jar --name="Spring").

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.


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 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).

24.3 Application property files

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

  1. A /config subdir of the current directory.
  2. The current directory
  3. A classpath /config package
  4. The classpath root

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


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


$ 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.


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. The Environment 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.

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.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 67.3, “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:

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

Would be transformed into these properties:

environments.dev.name=Developer Setup
environments.prod.name=My Cool App

YAML lists are represented as property keys with [index] dereferencers, for example this YAML:

       - dev.bar.com
       - foo.bar.com

Would be transformed into these properties:


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

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 @Value annotation 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:

    profiles: development
    profiles: production

In the example above, the server.address property will be if the development profile is active. If the development and production profiles are not enabled, then the value for the property will be

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 is only available in the "default" profile:

  port: 80000
  profiles: default
    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:

  port: 80000
    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 Typesafe 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:

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.

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

    username: admin

# additional configuration as required

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

public class MyService {

    private ConnectionSettings connection;


    public void openConnection() {
        Server server = new Server();


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

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-data appendix 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")
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 to contextPath), and capitalized (e.g. PORT binds to port) environment properties.

For example, given the following @ConfigurationProperties class:

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



Standard camel case syntax.


Dashed notation, recommended for use in .properties and .yml files.


Upper case format. Recommended when using a system environment variables.

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).

24.7.3 @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:

public class ConnectionSettings {

    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 above ConnectionSettings example:

public class ConnectionSettings {

    private RemoteAddress remoteAddress;

    // ... getters and setters

    private static class RemoteAddress {

        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.