Spring Boot - Using ${} placeholders in Property Files

In the last example, we saw maven resource filtering in boot application. Spring also provides it's own variable substitution in property files. We just need to use ${someProp} in property file and start the application having 'someProp' in system properties or as main class (or jar) argument '--someProp=theValue'.

This feature allows us to use 'short' command line arguments.

Example

src/main/resources/application.properties

app.title=Boot ${app} @project.artifactId@

Note that, in above example, we are also using maven variables @..@ (last tutorial).

@SpringBootConfiguration
public class ExampleMain {
    @Bean
    MyBean myBean() {
        return new MyBean();
    }

    public static void main(String[] args) throws InterruptedException {
        SpringApplication bootApp = new SpringApplication(ExampleMain.class);
        bootApp.setBannerMode(Banner.Mode.OFF);
        bootApp.setLogStartupInfo(false);
        ConfigurableApplicationContext context = bootApp.run(args);
        MyBean myBean = context.getBean(MyBean.class);
        myBean.doSomething();
    }

    private static class MyBean {

        @Value("${app.title}")
        private String appTitle;

        public void doSomething() {
            System.out.printf("App title : %s%n", appTitle);
        }
    }
}

mvn spring-boot:run -Dapp=Example

Output

d:\example-projects\spring-boot\place-holders-in-properties>mvn spring-boot:run -Dapp=Example
App title : Boot Example place-holders-in-properties

Example Project

Dependencies and Technologies Used:

• Spring Boot 1.5.4.RELEASE
  Corresponding Spring Version 4.3.9.RELEASE
• spring-boot-starter : Core starter, including auto-configuration support, logging and YAML.
• JDK 1.8
• Maven 3.3.9