How to override spring boot starter's default properties in application.properties file?

Question

I created a multi module maven project that contains the library module (spring boot starter application) and application module (spring boot application that have included library as a dependency).

This is the structure of my project:

.
├── application
│   ├── pom.xml
│   └── src
│       ├── main
│       │   ├── kotlin
│       │   │   └── com
│       │   │       └── application
│       │   │           ├── ApplicationService.kt
│       │   │           └── Application.kt
│       │   └── resources
│       │       └── application.properties
│       └── test
│           └── kotlin
│               └── com
│                   └── application
│                       └── ApplicationServiceTest.kt
├── library
│   ├── pom.xml
│   └── src
│       └── main
│           ├── kotlin
│           │   └── com
│           │       └── application
│           │           ├── LibraryService.kt
│           │           └── Properties.kt
│           └── resources
│               ├── META-INF
│               │   └── spring.factories
│               └── config
│                   └── application.properties
└── pom.xml

library/.../Properties.kt:

@ConfigurationProperties("properties")
class Properties {
    lateinit var name: String
}

library/.../LibraryService.kt:

@Service
@EnableConfigurationProperties(Properties::class)
class LibraryService(private val properties: Properties) {
    fun name() = properties.name
}

library/.../spring.factories:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.application.LibraryService

library/.../config/application.properties:

properties.name=library

application/.../Application.kt

@SpringBootApplication
class Application

fun main(args: Array<String>) {
    runApplication<Application>(*args)
}

application/.../ApplicationService.kt

@Service
class ApplicationService(private val libraryService: LibraryService) {
    fun call() = libraryService.name()
}

application/.../application.properties

properties.name=application

So, I have the library module where I put application.properties file with default parameter properties.name=library. The library module has Property class injected in LibraryService. LibraryService has the simple method name() that just returns value from property. I also have application module where I use LibraryService in ApplicationService and invoke name() function, but I have application.properties in application module where properties.name=application.

I expect that application's properties.name=application overrides library's properties.name=library and ApplicationService::call must return value application instead of default value library in properties.name in library module. But this does not happen. ApplicationService::call returns value library.

I created simple junit test to reproduce this behaviour (ApplicationServiceTest.kt):

@SpringBootTest
class ApplicationServiceTest {

    @Autowired
    lateinit var applicationService: ApplicationService

    @Test
    fun test() {
        println(applicationService.call())
    }
}

It prints library. I would like to have the following behaviour: library has some several defined default properties, but I want to be able to override some of these properties in application. How to achieve that?

source code: https://github.com/grolegor/maven-multi-module-spring-starter

Answer 1

Form the documentation

4.2.3. Application Property Files SpringApplication loads properties from application.properties files in the following locations and adds them to the Spring Environment:

1. A /config subdirectory of the current directory

2. The current directory

3. A classpath /config package

4. The classpath root

The list is ordered by precedence (properties defined in locations higher in the list override those defined in lower locations).

So in your case [library] config/application.properties will be used, because it is higher-ordered then [application] application.properties.

Also, you cannot use application.properties twice.

Looking in your repository I would suggest that you remove the /config/application.properties from the library-module and provide default values in your Properties-class

package com.application

import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("properties")
class Properties {
    var name: String = "library"
}