spring application.yml reference list from another property

Question

I have property file application-dev.yml with content:

spring.profiles: dev
config.some.value:
- ELEMENT1
- ELEMENT2

and another application-staging.yml with content:

spring.profiles: staging
config.some.value:
- ELEMENT1
- ELEMENT2
- ELEMENT3

so I basically do not know size of list. When I reference this list in main application.yml like this:

some.value: ${config.some.value}

I get Failed to convert property value of type 'java.lang.String' to required type 'java.util.List' for property 'value' . How to reference it correctly?

Answer 1

Solution

One way would be to use comma-separated lists in your profiles:

• application-dev.yml

spring.profiles: dev
config.some.value: ELEMENT1,ELEMENT2

• application-staging.yml

spring.profiles: staging
config.some.value: ELEMENT1,ELEMENT2,ELEMENT3

Then you should be able to access it in application.yml

some.value: ${config.some.value}

This solution doesn't require knowing list size upfront.

Explanation

The reason why this is working is described here . Specifically:

YAML lists are represented as comma-separated values (useful for simple String values) and also as property keys with [index] dereferencers, for example this YAML:
servers:
    - dev.bar.com
    - foo.bar.com
Would be transformed into these properties:
servers=dev.bar.com,foo.bar.com
servers[0]=dev.bar.com
servers[1]=foo.bar.com

In particular this means, that if you specify comma-separated list of strings in application.yml and define List<String> as value in @ConfigurationProperties , spring configuration properties binder will convert that comma-separated list of string to List<Strings> .

Answer 2

MyProfile:
SomeValues: 
    - ELEMENT1
    - ELEMENT2
     -ELEMENT3
    - ELEMENT4

---
MyProfile:   
someValues: 
    - ELEMENT1
    - ELEMENT2



@Configuration
@EnableConfigurationProperties
@ConfigurationProperties
public class YAMLConfig {


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

    // standard getters and setters

}

To Access properties

  @Autowired
   private YAMLConfig myConfig;


 private List<String> SomeValues= myConfig.SomeValues();

This worked for me

Answer 3

You can make your own configuration class which sets the value to that property as you want.

Please, take a look a this example:

@ConfigurationProperties in Spring Boot

Answer 4

When using String arrays the first and only element CAN be joined by commas - the final result is the same as a list. Meaning that you can set your variable like this:

config.some.value: ELEMENT1, ELEMENT2, ELEMENT3

then, at your profile section, you can reference the configuration value as it were a normal string:

someValues: ${config.some.value}

Answer 5

(I fear,) You'd have to reference it like that:

application.yaml:

some.value:
  -${config.some.value[0]}
  -${config.some.value[1]}
  -${config.some.value[2]}

...and I foresee problems, when there's no ${config.some.value[2]} (list sizes are inconsistent .. -> solution approach: try to "dummy"/"noop").

Refs:

• https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html#boot-features-external-config-yaml
• https://docs.ansible.com/ansible/latest/reference_appendices/YAMLSyntax.html

Answer 6

This is the best way to create .yml file with multiple values:

spring:
  profiles: dev
  config:
    some:
      values: ELEMENT1,ELEMENT2

When we are using .yml files, we recommend pulling apart each word. To read values use:

@Value("${spring.config.some.values}")    
private String[] values;

I hope it helps you.