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Use the filesystem-based configuration

So far we have not had any way to configure our system other than directly modifying code, which generally is not an elegant way.

The Eclipse Dataspace Connector exposes configuration through its ConfigurationExtension interface. That is a " special" extension in that sense that it gets loaded at a very early stage. There is also a default implementation named FsConfigurationExtension.java which uses a standard Java properties file to store configuration entries.

In the previous steps we had not included that in the JAR file, so we need to add the configuration-filesystem module to the dependency list:

dependencies {
    // ...
    implementation(libs.edc.configuration.filesystem)
    // ...
}

We compile and run the application with:

./gradlew clean basic:basic-03-configuration:build
java -jar basic/basic-03-configuration/build/libs/filesystem-config-connector.jar

you will notice an additional log line stating that the "configuration file does not exist":

INFO 2021-09-07T08:26:08.282159 Configuration file does not exist: dataspaceconnector-configuration.properties. Ignoring.

Set up the configuration extension

By default, the FsConfigurationExtension expects there to be a properties file named dataspaceconnector-configuration.properties located in the current directory. The name (and path) of the config file is configurable using the edc.fs.config property, so we can customize this to our liking.

First, create a properties file in a location of your convenience, e.g. /etc/eclipse/dataspaceconnector/config.properties.

mkdir -p /etc/eclipse/dataspaceconnector
touch /etc/eclipse/dataspaceconnector/config.properties

Second, lets reconfigure the Jetty Web Server to listen to port 9191 instead of the default 8181. Open the config.properties with a text editor of your choice and add the following line:

web.http.port=9191

An example file can be found here. Clean, rebuild and run the connector again, but this time passing the path to the config file:

java -Dedc.fs.config=/etc/eclipse/dataspaceconnector/config.properties -jar basic/basic-03-configuration/build/libs/filesystem-config-connector.jar

Observing the log output we now see that the connector's REST API is exposed on port 9191 instead:

INFO 2022-04-27T14:09:10.547662345 HTTP context 'default' listening on port 9191      <-- this is the relevant line
DEBUG 2022-04-27T14:09:10.589738491 Port mappings: {alias='default', port=9191, path='/api'}   
INFO 2022-04-27T14:09:10.589846121 Started Jetty Service

Add your own configuration value

Let's say we want to have a configurable log prefix in our health REST endpoint. The way to do this involves two steps:

  1. add the config value to the config.properties file
  2. access and read the config value from code

1. Add the config value

Simply add a new line with an arbitrary key to your config.properties:

edc.samples.basic.03.logprefix=MyLogPrefix

2. Access the config value

The ServiceExtensionContext exposes a method getSettings(String, String) to read settings (i.e. config values)'. Modify the code from the HealthEndpointExtension.java as shown below (use the one from the 03-configuration of course):

public class HealthEndpointExtension implements ServiceExtension {

    @Inject
    WebService webService;

    private static final String LOG_PREFIX_SETTING = "edc.samples.basic.03.logprefix"; // this constant is new

    @Override
    public void initialize(ServiceExtensionContext context) {
        var logPrefix = context.getSetting(LOG_PREFIX_SETTING, "health"); //this line is new
        webService.registerResource(new HealthApiController(context.getMonitor(), logPrefix));
    }
}

Next, we must modify the constructor signature of the HealthApiController class and store the logPrefix as variable:

@Consumes({ MediaType.APPLICATION_JSON })
@Produces({ MediaType.APPLICATION_JSON })
@Path("/")
public class HealthApiController {

    private final Monitor monitor;
    private final String logPrefix;

    public HealthApiController(Monitor monitor, String logPrefix) {
        this.monitor = monitor;
        this.logPrefix = logPrefix;
    }

    @GET
    @Path("health")
    public String checkHealth() {
        monitor.info(String.format("%s :: Received a health request", logPrefix));
        return "{\"response\":\"I'm alive!\"}";
    }
}

There are a few things worth mentioning here:

  • things like configuration value names should be implemented as constants, e.g. LOG_PREFIX_SETTING and should have a consistent and hierarchical naming scheme
  • if a config value is not present, we should either specify a default value (i.e. "health") or throw an EdcException
  • configuration values should be handled in the *Extension class, as it's job is to set up the extension and its required business logic (e.g. the controller). The extension itself should not contain any business logic
  • it's better to pass the config value directly into the business logic than passing the entire ServiceExtensionContext, using configuration objects when there are more than one

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