Spring Environment backed by Typesafe Config

Question

I want to use typesafe config (HOCON config files) in my project, which facilitate easy and organized application configuration. Currently I am using normal Java properties file(application.properties) and which is difficult to handle on big project.

My project is a Spring MVC (Not a spring boot project). Is there a way to back my Spring Environment (that I am getting injected to my services) to be backed by typesafe config. Which should not brake my existing Environment usage Like @Value annotation, @Autowired Environment etc.

How can I do this with minimal effort and changes on my code.

This is my current solution: Looking for is there any other better way

@Configuration
public class PropertyLoader{
    private static Logger logger = LoggerFactory.getLogger(PropertyLoader.class);

    @Bean
    @Autowired
    public static PropertySourcesPlaceholderConfigurer properties(Environment env) {
        PropertySourcesPlaceholderConfigurer pspc = new PropertySourcesPlaceholderConfigurer();

        Config conf = ConfigFactory.load();
        conf.resolve();
        TypesafePropertySource propertySource = new TypesafePropertySource("hoconSource", conf);

        ConfigurableEnvironment environment = (StandardEnvironment)env;
        MutablePropertySources propertySources = environment.getPropertySources();
        propertySources.addLast(propertySource);
        pspc.setPropertySources(propertySources);

        return pspc;
    }
}

class TypesafePropertySource extends PropertySource<Config>{
    public TypesafePropertySource(String name, Config source) {
        super(name, source);
    }

    @Override
    public Object getProperty(String name) {
        return this.getSource().getAnyRef(name);
    }
}

Answer 1

I think I came up with a slightly more idiomatic way than manually adding the PropertySource to the property sources. Creating a PropertySourceFactory and referencing that with @PropertySource

First, we have a TypesafeConfigPropertySource almost identical to what you have:

public class TypesafeConfigPropertySource extends PropertySource<Config> {
    public TypesafeConfigPropertySource(String name, Config source) {
        super(name, source);
    }

    @Override
    public Object getProperty(String path) {
        if (source.hasPath(path)) {
            return source.getAnyRef(path);
        }
        return null;
    }
}

Next, we create a PropertySource factory that returns that property source

public class TypesafePropertySourceFactory implements PropertySourceFactory {

    @Override
    public PropertySource<?> createPropertySource(String name, EncodedResource resource) throws IOException {
        Config config = ConfigFactory.load(resource.getResource().getFilename()).resolve();

        String safeName = name == null ? "typeSafe" : name;
        return new TypesafeConfigPropertySource(safeName, config);
    }

}

And finally, in our Configuration file, we can just reference the property source like any other PropertySource instead of having to add the PropertySource ourselves:

@Configuration
@PropertySource(factory=TypesafePropertySourceFactory.class, value="someconfig.conf")
public class PropertyLoader {
    // Nothing needed here
}

Answer 2

You create a PropertySource class as follows, it is similar to yours with the difference that you have to return the value or null and not let the lib throw a missing exception

public class TypesafeConfigPropertySource extends PropertySource<Config> {

    private static final Logger LOG = getLogger(TypesafeConfigPropertySource.class);

    public TypesafeConfigPropertySource(String name, Config source) {
        super(name, source);
    }

    @Override
    public Object getProperty(String name) {
        try {
            return source.getAnyRef(name);
        } catch (ConfigException.Missing missing) {
            LOG.trace("Property requested [{}] is not set", name);
            return null;
        }
    }
}

Second step is to define a bean as follows

    @Bean
    public TypesafeConfigPropertySource provideTypesafeConfigPropertySource(
        ConfigurableEnvironment env) {

        Config conf = ConfigFactory.load().resolve();
        TypesafeConfigPropertySource source = 
                          new TypesafeConfigPropertySource("typeSafe", conf);
        MutablePropertySources sources = env.getPropertySources();
        sources.addFirst(source); // Choose if you want it first or last
        return source;

    }

In cases where you want to autowire properties to other beans you need to use the annotation @DependsOn to the propertysource bean in order to ensure it is first loaded

Hope it helps