add_config.md

◀︎ Airlift • ◀︎ Getting Started • ◀︎ Next Steps

Add Configuration

Airlift's Configuration support is simple and straightforward. Let's add configuration to our example project.

Currently, the message returned by the hello() method is hard coded. Let's make it configurable:

Step 1 - Add Needed Dependencies

We need a few additional dependencies. Add the following to the dependencies section of your pom.xml file:

<dependency>
    <groupId>javax.validation</groupId>
    <artifactId>validation-api</artifactId>
</dependency>

<dependency>
    <groupId>io.airlift</groupId>
    <artifactId>configuration</artifactId>
</dependency>

<dependency>
    <groupId>javax.inject</groupId>
    <artifactId>javax.inject</artifactId>
</dependency>        

Step 2 - Create the Config Class

Create src/main/java/example/ServiceConfig.java with the following content:

package example;

import io.airlift.configuration.Config;

import javax.validation.constraints.NotBlank;

public class ServiceConfig
{
    private String helloMessage = "Hello Airlift!";

    @NotBlank
    public String getHelloMessage()
    {
        return helloMessage;
    }

    @Config("hello.message")
    public ServiceConfig setHelloMessage(String helloMessage)
    {
        this.helloMessage = helloMessage;
        return this;
    }
}

Step 3 - Bind the Config Class

We need to bind the Config class in our Guice module. Airlift's configBinder is used for this. Edit your ServiceModule.java file so that it looks like this (add the new import and new binding):

package example;

import com.google.inject.Binder;
import com.google.inject.Module;

import static io.airlift.configuration.ConfigBinder.configBinder;   // NEW LINE
import static io.airlift.jaxrs.JaxrsBinder.jaxrsBinder;

public class ServiceModule
        implements Module
{
    @Override
    public void configure(Binder binder)
    {
        jaxrsBinder(binder).bind(ServiceResource.class);
        configBinder(binder).bindConfig(ServiceConfig.class);   // NEW LINE
    }
}

Step 4 - Use the Config Object

Modify the Service resource to use the config object. Edit ServiceResource.java to look like this:

package example;

import javax.inject.Inject; // NEW
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

@Path("/v1/service")
public class ServiceResource
{
    private final ServiceConfig config; // NEW

    @Inject                                         // NEW
    public ServiceResource(ServiceConfig config)    // NEW
    {                                               // NEW
        this.config = config;                       // NEW
    }                                               // NEW

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public String hello()
    {
        return config.getHelloMessage();            // CHANGED
    }
}

Step 5 - Test The Change

Build, run, test:

mvn clean verify
mvn exec:java -Dexec.mainClass=example.Service -Dnode.environment=test

In a different terminal : curl http://localhost:8080/v1/service

Then CTRL+C the service.

---

We assign a default value to helloMessage in ServiceConfig so Airlift uses that by default. Now let's run specifying a different value on the command line.

mvn exec:java -Dexec.mainClass=example.Service -Dnode.environment=test -Dhello.message=Changed

In a different terminal : curl http://localhost:8080/v1/service

Then CTRL+C the service.

Step 6 - Config File

While it's simple to pass configuration on the command line, for production you will use a configuration properties file. Airlift configuration supports standard field=value property files.

Create config.properties in the root of your project with the following content:

node.environment=test
hello.message=Hello from a config file!

Now run and tell Airlift where to find the configuration file:

mvn exec:java -Dexec.mainClass=example.Service -Dconfig=config.properties

In a different terminal : curl http://localhost:8080/v1/service

Then CTRL+C the service.

Next Steps

Return to Next Steps to learn about other Airlift features.