Spring Boot loading a list from a config file returns empty list

Question

I just created a really basic spring boot application using spring initializer and am trying things out. I want to load a list from a yaml configuration file, but it always returns empty.

I have a custom configuration class

@ConfigurationProperties("example-unit")
@EnableConfigurationProperties
public class ConfigurationUnit {

    public List<String> confiList = new ArrayList<>();

    public List<String> getConfiList() {
        return this.confiList;
    }

}

And my main class looks like this

@SpringBootApplication
public class DemoApplication {

    static ConfigurationUnit configurationUnit = new ConfigurationUnit();


    public static void main(String[] args) {

        SpringApplication.run(DemoApplication.class, args);

        List<String> hello = configurationUnit.getConfiList();

        System.out.print("");
    }

}

I have put the application.yaml into resources folder.

example-unit:
  - string1
  - string2
  - hello22

I searched here and online, but can't figure out what's the issue and nothing I changed helped. I know I must be doing something wrong.

Ryuzaki L · Accepted Answer · 2019-02-04 20:06:24Z

1

This statement is wrong static ConfigurationUnit configurationUnit = new ConfigurationUnit(); you should not create the object

Spring only injects the properties into the beans that are handled by application context, and spring creates beans of classes that are annotated with @ Configuration

ConfigurationUnit

@Configuration
@ConfigurationProperties("example-unit")
public class ConfigurationUnit {

public List<String> confiList;

public List<String> getConfiList() {
    return this.confiList;
    }

 }

DemoApplication In the spring boot main get the bean from applicationcontext and from it get the list object

@SpringBootApplication
public class DemoApplication {

public static void main(String[] args) {

    ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
     ConfigurationUnit unit = context.getBean("configurationUnit"):

    System.out.print(unit. getConfiList());
   }

}

edited Feb 4, 2019 at 20:06

answered Feb 4, 2019 at 19:59

Ryuzaki L

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2 Comments

hc_dev Over a year ago

good point. I oversaw the static ConfigurationUnit declaration in Application class. That of course disturbs the whole bean-injection magic Spring is known for.

thisBean Over a year ago

Thanks, yeah that is the main mistake I made. Not using the bean spring boot creates with @Configuration. And also it seems to be sensitive to naming so I had to add example-unit.confi-list: to the header of yaml file so that it recognizes the list by its name, so it can instantiate it with values from the config.

hc_dev · Accepted Answer · 2019-02-04 19:44:45Z

1

Put your list under prefix.property. In your case example-unit.confi-list:. Usually provide a setter for your property: setConfiList(List<String> strings). But since you already initialized it as empty Array list this setter is obsolete says this. There is also advice to add Enable-annotation to Application class:

Application class should have @EnableConfigurationProperties annotation

edited Feb 4, 2019 at 19:44

answered Feb 4, 2019 at 19:22

hc_dev

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1 Comment

thisBean Over a year ago

Tried this and it still returns an empty list, but thanks for answering.

Oleksii Zghurskyi · Accepted Answer · 2019-02-04 21:46:20Z

Here is the reference on how Spring Bboot Configurtion Binding works.

Specifically for your question, this is an example of app that achives your goal:

application.yml

example-unit:
  confiList:
    - string1
    - string2
    - hello22

sources

@SpringBootApplication
@EnableConfigurationProperties(ConfigurationUnit.class)
public class DemoApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(DemoApplication.class, args);
        ConfigurationUnit configurationUnit = context.getBean(ConfigurationUnit.class);
        System.out.println(configurationUnit.getConfiList());
    }

}

@ConfigurationProperties("example-unit")
public class ConfigurationUnit {

    public List<String> confiList = new ArrayList<>();

    public List<String> getConfiList() {
        return this.confiList;
    }

}

Abder KRIMA · Accepted Answer · 2019-02-04 19:46:43Z

Here is an example :

Application.yml:

example-unit: string1,string2,hello22

ConfigurationUnit.class:

@Component
@PropertySource(value="classpath:application.yml")
public class ConfigurationUnit {

    @Value("#{'${example-unit}'.split(',')}")
    private List<String> confiList;

    public List<String> getConfiList() {
        return confiList;
    }
}

DemoFileLoadApplication.class:

@SpringBootApplication
public class DemoFileLoadApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(DemoFileLoadApplication.class, args);
        ConfigurationUnit configurationUnit = context.getBean(ConfigurationUnit.class);
        System.out.println(configurationUnit.getConfiList());
    }
}

Output:

[string1, string2, hello22]

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