How to read an environment variable in Quarkus

Question

I'm trying to read an environment variable in my Quarkus application using @ConfigProperty, but didn't manage to do that. I thought that just specifying variable name should be enough, but it isn't working:

@ConfigProperty(name = "MY_ENV_VAR")
String envVar;

I've also tried to specify a property in application.properties

my.var=${MY_ENV_VAR:defaultValue}

and read it like

@ConfigProperty(name = "my.var")
String myVar;

but the variable is always null.

Did I miss something? What is the correct way to read an environment variable in Quarkus?
I'm using Quarkus 1.2.0.Final

What you have is correct. Can you show the full class? It must be a CDI bean, e.g. `@ApplicationScoped`. — Ladicek, Jan 31 '20 at 14:27

score 9 · Accepted Answer · answered Jan 31 '20 at 16:38

Me and my colleagues have found the source of the problem. I was trying to read a field annotated with @ConfigProperty in the constructor, but the properties are being injected only after calling a constructor.

I provide a working example:

package org.acme.config;

import org.eclipse.microprofile.config.inject.ConfigProperty;

import javax.enterprise.context.ApplicationScoped;

@ApplicationScoped
public class EnvGreetingService {

    private final String varA;

    @ConfigProperty(name = "ENV_VAR_B")
    String varB;

    public EnvGreetingService(@ConfigProperty(name = "ENV_VAR_A") String varA) {
        System.out.println("constructor varA=" + varA);
        System.out.println("constructor varB=" + varB);
        this.varA = varA;
    }

    public void greetWithEnvVar() {
        System.out.println("method varA=" + varA);
        System.out.println("method varB=" + varB);
    }
}

Note: it is not required map environment variables in application.properties

And console output would be:

constructor varA=a
constructor varB=null
method varA=a
method varB=b

So, if you want to use application properties or environment variables in the constructor, you should inject it in constructor arguments.

In case of CDI Bean injection. It is preferable to use @Inject on a void & no params method. This method will be called after a bean is active in CDI lifecycle so it can understand and read your annotated field variables. constructors are not recommended in your case. — iabughosh, Jan 31 '20 at 18:06
I like field injection, constructor injections creates a huge mess once you have too many fields — Marian Klühspies, Jan 31 '20 at 23:49

How to read an environment variable in Quarkus

1 Answers1