Merging Complex Types

When lists are configured in more than one place, overriding works by replacing the entire list.

For example, assume a MyPojo object with name and description attributes that are null by default. The following example exposes a list of MyPojo objects from MyProperties:

  • Java

  • Kotlin

import java.util.ArrayList;
import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("my")
public class MyProperties {

	private final List<MyPojo> list = new ArrayList<>();

	public List<MyPojo> getList() {
		return this.list;
	}

}
import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("my")
class MyProperties {

	val list: List<MyPojo> = ArrayList()

}

Consider the following configuration:

  • Properties

  • YAML

my.list[0].name=my name
my.list[0].description=my description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another name
my:
  list:
  - name: "my name"
    description: "my description"
---
spring:
  config:
    activate:
      on-profile: "dev"
my:
  list:
  - name: "my another name"

If the dev profile is not active, MyProperties.list contains one MyPojo entry, as previously defined. If the dev profile is enabled, however, the list still contains only one entry (with a name of my another name and a description of null). This configuration does not add a second MyPojo instance to the list, and it does not merge the items.

When a List is specified in multiple profiles, the one with the highest priority (and only that one) is used. Consider the following example:

  • Properties

  • YAML

my.list[0].name=my name
my.list[0].description=my description
my.list[1].name=another name
my.list[1].description=another description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another name
my:
  list:
  - name: "my name"
    description: "my description"
  - name: "another name"
    description: "another description"
---
spring:
  config:
    activate:
      on-profile: "dev"
my:
  list:
  - name: "my another name"

In the preceding example, if the dev profile is active, MyProperties.list contains one MyPojo entry (with a name of my another name and a description of null). For YAML, both comma-separated lists and YAML lists can be used for completely overriding the contents of the list.

For Map properties, you can bind with property values drawn from multiple sources. However, for the same property in multiple sources, the one with the highest priority is used. The following example exposes a Map<String, MyPojo> from MyProperties:

  • Java

  • Kotlin

import java.util.LinkedHashMap;
import java.util.Map;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("my")
public class MyProperties {

	private final Map<String, MyPojo> map = new LinkedHashMap<>();

	public Map<String, MyPojo> getMap() {
		return this.map;
	}

}
import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("my")
class MyProperties {

	val map: Map<String, MyPojo> = LinkedHashMap()

}

Consider the following configuration:

  • Properties

  • YAML

my.map.key1.name=my name 1
my.map.key1.description=my description 1
#---
spring.config.activate.on-profile=dev
my.map.key1.name=dev name 1
my.map.key2.name=dev name 2
my.map.key2.description=dev description 2
my:
  map:
    key1:
      name: "my name 1"
      description: "my description 1"
---
spring:
  config:
    activate:
      on-profile: "dev"
my:
  map:
    key1:
      name: "dev name 1"
    key2:
      name: "dev name 2"
      description: "dev description 2"

If the dev profile is not active, MyProperties.map contains one entry with key key1 (with a name of my name 1 and a description of my description 1). If the dev profile is enabled, however, map contains two entries with keys key1 (with a name of dev name 1 and a description of my description 1) and key2 (with a name of dev name 2 and a description of dev description 2).

The preceding merging rules apply to properties from all property sources, and not just files.