java - Using ConfigurationProperties to fill Map in generic way

Question

I'm wondering, if there is a generic way to fill a map with properties you just know the prefix.

Assuming there are a bunch of properties like

namespace.prop1=value1
namespace.prop2=value2
namespace.iDontKnowThisNameAtCompileTime=anothervalue

I'd like to have a generic way to fill this property inside a map, something like

@Component
@ConfigurationProperties("namespace")
public class MyGenericProps {
    private Map<String, String> propmap = new HashMap<String, String>();

    // setter and getter for propmap omitted

    public Set<String> returnAllKeys() {
        return propmap.keySet();
    }
}

Or is there another convenient way to collect all properties with a certain prefix, instead of iterating over all PropertySources in the environment?

Thanks Hansjoerg

Answer 1

As long as you're happy having every property added into the map, rather than just those that you don't know in advance, you can do this with @ConfigurationProperties. If you want to grab everything that's beneath namespace then you need to use an empty prefix and provide a getter for a map named namespace:

@ConfigurationProperties("")
public class CustomProperties {

    private final Map<String, String> namespace = new HashMap<>();

    public Map<String, String> getNamespace() {
        return namespace;
    }

}

Spring Boot uses the getNamespace method to retrieve the map so that it can add the properties to it. With these properties:

namespace.a=alpha
namespace.b=bravo
namespace.c=charlie

The namespace map will contain three entries:

{a=alpha, b=bravo, c=charlie}

If the properties were nested more deeply, for example:

namespace.foo.bar.a=alpha
namespace.foo.bar.b=bravo
namespace.foo.bar.c=charlie

Then you'd use namespace.foo as the prefix and rename namespace and getNamespace on CustomProperties to bar and getBar respectively.

Note that you should apply @EnableConfigurationProperties to your configuration to enable support for @ConfigurationProperties. You can then reference any beans that you want to be processed using that annotation, rather than providing an @Bean method for them, or using @Component to have them discovered by component scanning:

@SpringBootApplication
@EnableConfigurationProperties(CustomProperties.class)
public class YourApplication {
    // …
}