Spring Boot YAML configuration for a list of strings

Use comma-separated values in application.yml

ignoreFilenames: .DS_Store, .hg

Java code for access:

@Value("${ignoreFilenames}")    
String[] ignoreFilenames

From the Spring Boot docs:

• https://docs.spring.io/spring-boot/docs/3.0.x/reference/html/features.html#features.external-config (3.0.x)
• https://docs.spring.io/spring-boot/docs/2.7.x/reference/html/features.html#features.external-config (2.7.x)

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

my:
   servers:
       - dev.bar.com
       - foo.bar.com

Would be transformed into these properties:

my.servers[0]=dev.bar.com
my.servers[1]=foo.bar.com

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 and you either need to provide a setter, or initialize it with a mutable value, e.g. this will bind to the properties above. Here is what the question's code would look like.

(Note: The example below only works on Spring Boot 3.0 and greater. Previous versions require the @ConstructorBinding annotation to be present to not throw exceptions when this object is being constructed.)

@ConfigurationProperties(prefix="ignore")
//@ConstructorBinding // uncomment if using Spring Boot 2.x.
public class Filenames {

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

    public List<String> getFilenames() {
        return this.ignoredFilenames;
    }
}

In addition to Ahmet's answer you can add line breaks to the coma separated string using > symbol.

application.yml:

ignoreFilenames: >
  .DS_Store, 
  .hg

Java code:

@Value("${ignoreFilenames}")    
String[] ignoreFilenames;

In my case, this was a syntax issue in the .yml file. I had:

@Value("${spring.kafka.bootstrap-servers}")
public List<String> BOOTSTRAP_SERVERS_LIST;

and the list in my .yml file:

bootstrap-servers:
    - s1.company.com:9092
    - s2.company.com:9092
    - s3.company.com:9092

was not reading into the @Value-annotated field. When I changed the syntax in the .yml file to:

bootstrap-servers: >
    s1.company.com:9092,
    s2.company.com:9092,
    s3.company.com:9092

it worked fine.

Well, the only thing I can make it work is like so:

servers: >
    dev.example.com,
    another.example.com

@Value("${servers}")
private String[] array;

And dont forget the @Configuration above your class....

Without the "," separation, no such luck...

Works too (boot 1.5.8 versie)

servers: 
       dev.example.com,
       another.example.com

@Value("#{'${your.elements}'.split(',')}")  
private Set<String> stringSet;

yml file:

your:
  elements: element1, element2, element3

There is lot more you can play with spring spEL.

Ahmet's answer provides on how to assign the comma separated values to String array.

To use the above configuration in different classes you might need to create getters/setters for this.. But if you would like to load this configuration once and keep using this as a bean with Autowired annotation, here is the how I accomplished:

In ConfigProvider.java

@Bean (name = "ignoreFileNames")
@ConfigurationProperties ( prefix = "ignore.filenames" )
public List<String> ignoreFileNames(){
    return new ArrayList<String>();
}

In outside classes:

@Autowired
@Qualifier("ignoreFileNames")
private List<String> ignoreFileNames;

you can use the same list everywhere else by autowiring.

Configuration in yaml file:

ignore:
    filenames: >
        .DS_Store
        .hg

In spring component:

@Value("#{'${gnore.filenames}'.split(' ')}")
private List<String> igonoredFileNames;

This worked fine for me.

@Value("${coupon.update.fieldsToIgnore}") private List fieldsToIgnore;

coupon:
  update:
    fieldsToIgnore: dbVersion, createdAt, updatedAt

simply use this

I don't know from which version comme this feature, but I am using currently spring-boot 3.3.4 and it works yet simple with List and comma separated value:

ignore.filenames: name1, name2

    @Value("${ignore.filenames}")
    private List<String> sampleListValues;

This one works for me.

servers:
  server1,
  server2,
  server3