Canonical properties

Spring Boot 2.0 Canonical Properties

Overview

Canonical properties allow spring boot applications to access properties from underlying sources in a uniform manner. No matter what format is used by the underlying source, Spring Boot application can always use a canonical name to obtain it.

A canonical name is composed of elements separated in dots. The last dot separates the prefix from the property name. Names are alpha-numeric (a-z 0-9) and must be lowercase, the only other characters permitted are [ and ] which are used to indicate indexes. A property name cannot start with a number.

A typical Spring Boot canonical property would be something like spring.jpa.databaseplatform=mysql. An indexed property would be spring.myexample.url[0]=https://example.com.

Input Sources

Properties Files

Simple Types

Simple properties are converted into the canonical by removing any special characters and converting to lowercase. For example, the following YAML properties all result in the mapping spring.jpa.databaseplatform=mysql:

spring.jpa.database-platform=mysql spring.jpa.databasePlatform=mysql spring.JPA.database_platform=mysql

Note	We recommend that properties are stored in lowercase kabab format. i.e. `my.property-name=foo`.

List Types

List types in properties files should be referenced using [ ] notation:

spring.my-example.url[0]=https://example.com spring.my-example.url[1]=https://spring.io

An abbreviated form is also supported:

spring.my-example.url[]=https://example.com,https://spring.io

Note	The `[]` indicator is required for list types. For example, spring.example.foo=`bar,baz is a property containing the String "bar,baz" , and not a list of two elements.

Both of the mappings above result in the following properties:

spring.myexample.url[0]=https://example.com spring.myexample.url[1]=https://spring.io

YAML Files

Simple Types

Simple YAML properties are converted into the canonical by removing any special characters and converting to lowercase. For example, the following YAML properties all result in the mapping spring.jpa.databaseplatform=mysql:

spring: jpa: database-platform: mysql databasePlatform: mysql database_platform: mysql

Note	We recommend that properties are stored in yaml in lowercase kabab format. i.e. `my.property-name=foo`.

Lists

YAML list type may be specified in the standard or abbreviated form:

spring: my-example: url: - https://example.com - https://spring.io

spring: my-example: url: [https://example.com, http:s//spring.io]

Both are mapped as follows:

spring.myexample.url[0]=https://example.com spring.myexample.url[1]=https://spring.io

Note	Simple comma-separated types should not be used to represent lists. For example, spring.example.foo=`bar,baz is a property containing the String "bar,baz" , and not a list of two elements.

Environment Variables

Simple Types

Environment variables are converted into the canonical form by lowercasing and replacing _ with ..

For example: SPRING_JPA_DATABASEPLATFORM=mysql results in the property spring.jpa.databaseplatform=mysql.

Note	The `_` delimiter must not be used within a property name. i.e. `database-platform` must be written as `DATABASEPLATFORM` and not `DATABASE_PLATFORM`.

Lists

The [ and ] characters cannot be used in environment variable names so instead a special form of _ is used. Any numeric value surrounded by underscores is converted to the [,] form. For example:

MY_FOO_1_ = my.foo[1]
MY_FOO_1_BAR = my.foo[1].bar
MY_FOO_1_2_ = my.foo[1][2]`

In addition, if an environment variable ends in a number the trailing _ may be omitted:

MY_FOO_1 = my.foo[1]
MY_FOO_1_2 = my.foo[1][2]`

System properties

Simple Types

System properties are converted into canonical form by lowercasing and removing any special characters. For example, the following command line parameters will all result in spring.jpa.databaseplatform=mysql :

-Dspring.jpa.database-platform=mysql -Dspring.jpa.databasePlatform=mysql -Dspring.JPA.database_platform=mysql

List Types

List types in system properties should be referenced using [ ] notation:

-D"spring.my-example.url[0]=https://example.com" -D"spring.my-example.url[1]=https://spring.io"

An abbreviated form is also supported:

-Dspring.my-example.url[]=https://example.com,https://spring.io

Both of the mappings above result in the following properties:

spring.myexample.url[0]=https://example.com spring.myexample.url[1]=https://spring.io

Note	The `[]` indicator is required for list types. For example, `spring.example.foo=bar,baz` is a property containing the String "bar,baz" , and not a list of two elements.