Property Placeholders

The values in application.properties and application.yml are filtered through the existing Environment when they are used, so you can refer back to previously defined values (for example, from System properties or environment variables). The standard ${name} property-placeholder syntax can be used anywhere within a value. Property placeholders can also specify a default value using a : to separate the default value from the property name, for example ${name:default}.

The use of placeholders with and without defaults is shown in the following example:

  • Properties

  • YAML

app.name=MyApp
app.description=${app.name} is a Spring Boot application written by ${username:Unknown}
app:
  name: "MyApp"
  description: "${app.name} is a Spring Boot application written by ${username:Unknown}"

Assuming that the username property has not been set elsewhere, app.description will have the value MyApp is a Spring Boot application written by Unknown.

You should always refer to property names in the placeholder using their canonical form (kebab-case using only lowercase letters). This will allow Spring Boot to use the same logic as it does when relaxed binding @ConfigurationProperties.

For example, ${demo.item-price} will pick up demo.item-price and demo.itemPrice forms from the application.properties file, as well as DEMO_ITEMPRICE from the system environment. If you used ${demo.itemPrice} instead, demo.item-price and DEMO_ITEMPRICE would not be considered.
You can also use this technique to create “short” variants of existing Spring Boot properties. See the Use ‘Short’ Command Line Arguments how-to for details.