What difference does @EnableConfigurationproperties make if a bean is already annotated with @ConfigurationProperties?

Question

The Spring Boot documentation says that to use the @ConfigurationProperties annotation

You also need to list the properties classes to regis

Answer 1

As M. Deinum referred @EnableConfigurationProperties Is for enabling support of @ConfigurationProperties. If you take a look to the annotation Java Doc you can see:

Enable support for ConfigurationProperties annotated beans. ConfigurationProperties beans can be registered in the standard way (for example using Bean @Bean methods) or, for convenience, can be specified directly on this annotation. [...]

For example, let's say you have a class whose responsibility is to read and store information from your application.yml / application.properties that is required to make a connection to different databases. You annotate it with @ConfigurationProperties.

Then, you typically have a @Configuration annotated class that provides a DataSource @Bean to your application. You can use the @EnableConfigurationProperties to link it to the @ConfigurationProperties class and init your data sources accordingly.

Here is a small example:

application.yml

data-sources:
  db1:
    url: "jdbc:postgresql://localhost:5432}/db1"
    username: test
    password: test
  db2:
    url: "jdbc:postgresql://localhost:5432}/db2"
    username: test
    password: test

DataSourcesConfiguration

@ConfigurationProperties
public class DataSourcesConfiguration {

    private Map dataSources;

    public void setDataSources(Map dataSources) {
        this.dataSources = dataSources;
    }

    Map getDataSources() {
        return dataSources;
    }
}

DataSourceConnectionConfiguration

@Configuration
@EnableConfigurationProperties(DataSourcesConfiguration.class)
public class DatabaseConnectionConfiguration implements Provider {

    private DataSourcesConfiguration dataSourcesConfiguration;

    public DatabaseConnectionConfiguration(DataSourcesConfiguration dataSourcesConfiguration) {
        this.dataSourcesConfiguration = dataSourcesConfiguration;
    }

    @Bean
    public DataSource dataSource() {
        // Use dataSourcesConfiguration to create application data source. E.g., a AbstractRoutingDataSource..
    }

}