Hey there! Let's clear up this confusion for you—this behavior is actually a combination of Spring Boot's core configuration rules and how you've set up your IntelliJ IDEA run configurations. Let's break it down step by step:

Spring Boot uses a priority-based system to load configuration files, and the key here is which "profile" is active:

• By default, Spring Boot will always load application.properties as the base configuration.
• If you activate a specific profile (like dev or uat), it will load the corresponding application-{profile}.properties file in addition to the base one—with the profile-specific file overriding any duplicate settings from the base.

There are several ways to activate a profile, and these are what's driving the inconsistent behavior you're seeing:

• Static config file setting: Add spring.profiles.active=dev to your application.properties—this will hardcode the active profile unless overridden by a higher-priority setting.
• Command line arguments: Pass --spring.profiles.active=dev when starting the app.
• JVM system properties: Use -Dspring.profiles.active=dev as a VM argument.
• Environment variables: Set the SPRING_PROFILES_ACTIVE system environment variable to your desired profile.

IDEA doesn't override Spring's rules—it just gives you a convenient way to set those higher-priority startup parameters without editing config files or typing command lines every time:

• Open your Run/Debug Configurations (click the dropdown next to the run button, then "Edit Configurations").
• For your Spring Boot app, check these areas:
  • VM options: If you've added -Dspring.profiles.active=dev here, this will override any spring.profiles.active setting in your application.properties.
  • Program arguments: If you've added --spring.profiles.active=uat here, this also takes priority over the config file.
  • Active Profiles (some IDEA versions have this in the main Configuration tab): Selecting a profile here is equivalent to setting the JVM property automatically.

The most likely scenarios are:

• You’ve toggled the active profile in IDEA's run configs at some point (maybe for testing different environments) and forgot to set it back.
• Your application.properties has a spring.profiles.active setting that's sometimes being overridden by IDEA's startup parameters.
• You might have environment variables or global JVM settings that are interfering (though this is less common for local development).

To get consistent behavior every time:

1. Check your application.properties for any spring.profiles.active line—remove it if you want IDEA to control the active profile, or set it to your default.
2. Verify your IDEA run configuration: Make sure the VM options, program arguments, and active profiles are set to the profile you want.
3. If you want to confirm which profile is active at startup, add a log statement in your app (like @Value("${spring.profiles.active}") private String activeProfile;) and print it on startup—this will tell you exactly which profile is being used.

内容的提问来源于stack exchange，提问作者Mikayil Abdullayev