Spring Boot - application.yml, read value from a file

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I have a property present in application.yml but the value of that property is present in another file. Over here username is present in file /etc/app/db_username

database:
   url: localhost:14482
   username: /etc/app/db_username
   password: /etc/app/db_password

Is there a way I can have values of username and password from the file automatically instead of me reading the file.

@Value("${database.username}")
String username; //Will give me /etc/app/db_username

@Value("${database.password}")
String password; //Will give me /etc/app/db_password
application.properties spring-boot spring java
1 Answers

You can use @ConfigurationProperties for this:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.ConstructorBinding;

@ConstructorBinding
@ConfigurationProperties("database")
public class DatabaseConfig {
    private final String username;
    private final String password;

    public DatabaseConfig(Path username,
                          Path password) throws IOException {
        this.username = Files.readString(username);
        this.password = Files.readString(password);
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }
}

You need to place a @EnableConfigurationProperties(DatabaseConfig.class) on one of your configuration classes (or the @SpringBootApplication itself) for this to work.

A complete example on GitHub (with Gradle 7, Java 11 and Spring-Boot 2.5.3): https://github.com/jannis-baratheon/stackoverflow--spring-boot-configurationproperties-file-reading

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