[FIXED] Spring MVC: configure properties from before bean creation

Issue

I have a scenario where I want to programmatically inject properties into Spring before any beans are created/initialized:

1. The beans (not modifiable) are configured with ConditionalOnProperty, so properties need to be set before creation.
2. Properties need to be configured dynamically and programmatically, not via property file (we call an API and use the result to set the property value).

I see ApplicationContext has a way to get the current environment's property sources (via ConfigurableEnvironment), but I am not sure how to inject into the Spring lifecycle to configure the ApplicationContext before beans are initialized.

I'm aware of BeanFactoryPostProcessor as a hook which occurs before bean initialization, but I don't see a way to obtain an instance of ApplicationContext in it.

How can it be accomplished?

Note: the application itself is Spring Web/MVC, not Spring Boot. The third party library internally uses Spring Boot classes (ConditionalOnProperty).

Solution

Based on @m-deinum's comment, I was able to get it working with the following:

public class MyPropertyInitializer extends WebMvcConfigurerAdapter implements WebApplicationInitializer, ApplicationContextInitializer<ConfigurableApplicationContext> {
    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        String initializerClasses = servletContext.getInitParameter(ContextLoader.GLOBAL_INITIALIZER_CLASSES_PARAM);
        String initClassName = this.getClass().getName();
        if (StringUtils.isNotBlank(initializerClasses)) {
            initializerClasses += "," + initClassName;
        } else {
            initializerClasses = initClassName;
        }
        servletContext.setInitParameter(ContextLoader.GLOBAL_INITIALIZER_CLASSES_PARAM, initializerClasses);
    }

    @Override
    public void initialize(ConfigurableApplicationContext context) {
        Properties props = getCustomProperties();
        PropertySource<?> propertySource = new PropertiesPropertySource("my-custom-props", props);
        context.getEnvironment().getPropertySources().addLast(propertySource);
    }

    protected Properties getCustomProperties() {
        Properties props = new Properties();
        // do logic to set desired values
        return props;
    }
}

Answered By - trebor
Answer Checked By - David Goodson (JavaFixing Volunteer)