Spring properties

There are a lot of tutorials and examples on how to use spring properties, be it a .properties or .yaml file. Here, we will take a look at most common scenarios.

Lets see how we can:

• Inject a property value into a field, using @Value annotation
• Use a property value inside annotation
• Have a list of objects created from properties

Example of .properties configuration:

# Simple properties
app.config.message=Hello

app.config.customBeanName=CustomBeanName

# Array of properties
app.config.beans[0].name=customBean0ID
app.config.beans[0].text=customBean0TxtProperty

app.config.beans[1].name=customBean1ID
app.config.beans[1].text=customBean1TxtProperty

app.config.beans[2].name=customBean2ID
app.config.beans[2].text=customBean2TxtProperty

app.config.beans[3].name=customBean3ID
app.config.beans[3].text=customBean4TxtProperty

Reading of a simple value can be done with @Value annotation.

    @Value("${app.config.message}")
    private String message;

Using a value with annotation, lets see two examples.

    @Autowired
    @Qualifier("${app.config.customBeanName}")
    DummyBean dummyBean;


    @Bean(name="${app.config.customBeanName}")
    public DummyBean dummyBean() {
        return DummyBean.builder().text("I am a dummy bean.").build();
    }

Letting Spring map the properties automatically can be done with annotating the class with @ConfigurationProperties annotation.

@Configuration
@EnableConfigurationProperties
@PropertySource("classpath:application.properties")
@ConfigurationProperties(prefix="app.config") // from properties, find all app.config* values
public class AppPropertiesArray {

    private List<Bean> beans = new ArrayList<>();

    public static class Bean {
        private String name;
        private String text;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getText() {
            return text;
        }

        public void setText(String text) {
            this.text = text;
        }

        @Override
        public String toString() {
            return "Bean{" +
                    "name='" + name + '\'' +
                    ", text='" + text + '\'' +
                    '}';
        }
    }

    public List<Bean> getBeans() {
        return beans;
    }

    public void setBeans(List<Bean> beans) {
        this.beans = beans;
    }

    public List<Bean> getBeanList() {
        return beans;
    }
}

Code is available at github.

There are more ways annotations can be used. Check docs and tutorials.

Spring Boot Docs – Externalizing configuration