Spring Boot: read list from yaml using @Value or @ConfigurationProperties

Question

I want to read a list of hosts from a yaml file (application.yml), the file looks like this:

cors:     hosts:         allow:              - http://foo1/             - http://foo2/             - http://foo3/ 

(Example 1)

My class used defines the value like this:

@Value("${cors.hosts.allow}")    List<String> allowedHosts; 

But reading fails as Spring complains about this:

java.lang.IllegalArgumentException: Could not resolve placeholder 'cors.hosts.allow' in string value "${cors.hosts.allow}"

When I change the file like this the property can be read but naturally it does not contain the list but only one entry:

cors:     hosts:         allow: http://foo1, http://foo2, http://foo3 

(I know that I could read the values as a single line and split them by "," but I do not want to go for a workaround yet)

This does not work either (although I think this should be valid according to snakeyamls docs):

cors:     hosts:         allow: !!seq [ "http://foo1", "http://foo2" ]  

(Skipping the !!seq and just using the [ / ] is a failure too)

I read the suggestion here which involves using @ConfigurationProperties and transferred the example to Java and used it with the yaml file you see in Example1:

@Configuration @EnableWebMvc @ConfigurationProperties(prefix = "cors.hosts") public class CorsConfiguration extends WebMvcConfigurerAdapter {     @NotNull     public List<String> allow; ... 

When I run this I get this complaint:

org.springframework.validation.BindException: org.springframework.boot.bind.RelaxedDataBinder$RelaxedBeanPropertyBindingResult: 1 errors Field error in object 'cors.hosts' on field 'allow': rejected value [null]; codes [NotNull.cors.hosts.allow,NotNull.allow,NotNull]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [cors.hosts.allow,allow]; argumen ts []; default message [allow]];

I searched for other means to have my CORS hosts configurable and found this Spring Boot issue but as this is not yet finished I can't use it as a solution. All of this is done with Spring Boot 1.3 RC1

Answer 1

It's easy, the answer is in this doc and also in this one

So, you have a yaml like this:

cors:     hosts:         allow:              - http://foo1/             - http://foo2/             - http://foo3/ 

Then you first bind the data

import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.context.annotation.Configuration; import org.springframework.stereotype.Component;  import java.util.List;  @Component @ConfigurationProperties(prefix="cors.hosts") public class AllowedHosts {     private List<String> HostNames; //You can also bind more type-safe objects } 

Then in another component you just do

@Autowired private AllowedHosts allowedHosts; 

And you are done!