Chapter 6. Working with configuration properties

This chapter covers

• Fine-tuning autoconfigured beans
• Applying configuration properties to application components
• Working with Spring profiles

Do you remember when the iPhone first came out? A small slab of metal and glass hardly fit the description of what the world had come to recognize as a phone. And yet, it pioneered the modern smartphone era, changing everything about how we communicate. Although touch phones are in many ways easier and more powerful than their predecessor, the flip phone, when the iPhone was first announced, it was hard to imagine how a device with a single button could be used to place calls.

In some ways, Spring Boot autoconfiguration is like this. Autoconfiguration greatly simplifies Spring application development. But after a decade of setting property values in Spring XML configuration and calling setter methods on bean instances, it’s not immediately apparent how to set properties on beans for which there’s no explicit configuration.

Fortunately, Spring Boot provides a way to set property values on application components with configuration properties. Configuration properties are nothing more than properties on @ConfigurationProperties-annotated beans in the Spring application context. Spring will inject values from one of several property sources—including JVM system properties, command-line arguments, and environment variables—into the bean properties. We’ll see how to use @ConfigurationProperties on our own beans in section 6.2. But Spring Boot itself provides several @ConfigurationProperties-annotated beans that we’ll configure first.

In this chapter, you’re going to take a step back from implementing new features in the Taco Cloud application to explore configuration properties. What you take away will no doubt prove useful as you move forward in the chapters that follow. We’ll start by seeing how to employ configuration properties to fine-tune what Spring Boot automatically configures.