Java – Read spring properties from consuming applications

I’m working on a Java library/package designed to be used as a jar by Spring Boot applications.

The main driver class relies on a set of props present in applicaton.properties and defines its own collection in the repository.

However, I expect these properties to be configurable by using the app. What is the correct way to build this?

For example, I have a file in the project

public class Properties {
    private int maxConnectingCount; 
    private int maxIdleCount;
    // .. other properties read from application.properties
}

The main driver class looks like this:

public class LibraryDriver {

@Autowired 
    private Properties props
     do stuff with these props
}

How can I make the consuming app override these properties

This is what I usually do:

public class Properties {
    private int maxConnectingCount; 
    private int maxIdleCount;

public Properties(String maxConnectingCount, String maxIdleCount) {
        this.maxConnectingCount = maxConnectingCount;
        this.maxIdleCount = maxIdleCount;
    }
}

Then create bean:: like this

@Configuration
public class LibraryDriverConfiguration {

@Value("${maxConnectingCount}")
    private int maxConnectingCount;

@Value("${maxIdleCount}")
    private int maxIdleCount;

@Bean
    LibraryDriver libraryDriver() {
        return new LibraryDriver(new Properties(maxConnectingCount, maxIdleCount));
}

I like this approach because it allows your properties to have reasonable default values by defining different constructors.

Another option is to create a Property bean and then Autowire it to the LibraryDriver; Something like this:

@Configuration
public class PropertiesConfiguration {

@Value("${maxConnectingCount}")
    private int maxConnectingCount;

@Value("${maxIdleCount}")
    private int maxIdleCount;

@Bean
    Properties properties() {
        return new Properties(maxConnectingCount, maxIdleCount);
    }
}

And then:

@Component
public class LibraryDriver {

private final Properties properties;

@Autowired
    public LibraryDriver(Properties properties) {
        this.properties = properties;
    }
}