Application Properties and Common Settings

Spring Boot has thousands of configuration properties, but a handful appear in nearly every project: the server port, context path, application name, logging levels, database connection, JSON settings, file upload limits, and error handling. Knowing these — and knowing the order in which Spring Boot reads configuration — lets you change behaviour without touching code.

This lesson is a practical tour of the most common application.properties/application.yml settings, the property source order (command line, environment variables, profile files), relaxed binding, placeholders and random values, and how to find any property you need.

Where Properties Come From (Order of Precedence)

Spring Boot merges many property sources; a higher source overrides a lower one. From highest to lowest, the ones you use most are:

• Command-line arguments: java -jar app.jar --server.port=9090.
• SPRING_APPLICATION_JSON (inline JSON in an environment variable).
• OS environment variables: SERVER_PORT=9090.
• Java system properties: -Dserver.port=9090 (placed above environment variables in the order).
• Profile-specific files outside the jar, then inside the jar: application-prod.yml.
• Application files outside the jar (./config/, current directory), then inside the jar (classpath:application.yml).
• @PropertySource files and default properties set in code.

Relaxed Binding and Environment Variables

Property names are matched flexibly. spring.datasource.url, SPRING_DATASOURCE_URL and spring.datasource.URL all bind to the same property. The environment-variable form — uppercase, dots replaced by underscores, dashes removed — is how containers and cloud platforms configure Spring Boot apps.

Commonly Used Properties

The settings you will change most often:

• server.port (default 8080; 0 picks a random free port) and server.servlet.context-path.
• spring.application.name — used in logs, metrics and service discovery.
• logging.level.<package>, logging.file.name.
• spring.datasource.*, spring.jpa.* — database and JPA.
• spring.jackson.* — JSON formatting.
• spring.servlet.multipart.max-file-size — upload limits.
• server.error.include-message, include-stacktrace — error detail.
• server.compression.enabled, server.ssl.*, server.shutdown.
• spring.profiles.active, spring.config.import.
• management.endpoints.web.exposure.include — Actuator.

Placeholders, Defaults and Random Values

Properties can reference other properties and environment variables with ${...}, including a default after a colon: ${DB_HOST:localhost}. ${random.uuid}, ${random.int(1000,9999)} generate values at startup. Keep secrets as references to environment variables, never as literal values in the file.

Finding Properties

The complete list lives in the Spring Boot reference appendix "Common Application Properties". IDEs (IntelliJ, VS Code with Spring tools) auto-complete property names and show documentation. At runtime, the /actuator/env and /actuator/configprops endpoints show effective values and where each came from (expose them only in secure, non-public environments).

Examples

spring:
  application:
    name: webnest-shop
  profiles:
    active: ${SPRING_PROFILES_ACTIVE:dev}
  datasource:
    url: jdbc:postgresql://${DB_HOST:localhost}:5432/webnest
    username: ${DB_USER:webnest}
    password: ${DB_PASSWORD}
  jpa:
    open-in-view: false
  servlet:
    multipart:
      max-file-size: 5MB

server:
  port: 8081
  servlet:
    context-path: /shop
  compression:
    enabled: true
  error:
    include-message: always
    include-stacktrace: never

logging:
  level:
    root: INFO
    com.webnest: DEBUG
    org.hibernate.SQL: DEBUG
  file:
    name: logs/webnest-shop.log

app:
  instance-id: ${random.uuid}

Tomcat started on port 8081 (http) with context path '/shop'
curl http://localhost:8081/shop/api/products -> 200

# 1. application.properties
server.port=9090

# 2. Command-line argument (highest precedence of these)
java -jar shop.jar --server.port=9091

# 3. Environment variable (containers, CI, cloud)
SERVER_PORT=9092 java -jar shop.jar          # PowerShell: $env:SERVER_PORT=9092; java -jar shop.jar

# 4. Java system property
java -Dserver.port=9093 -jar shop.jar

# 5. Programmatically
@Bean
WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> portCustomizer() {
    return factory -> factory.setPort(9094);
}

# Random free port (useful for running several instances locally)
server.port=0

java -jar shop.jar --server.port=9091
... Tomcat started on port 9091 (http)

# Packaged jar contains application.yml with server.port=8080

# ./config/application.yml next to the jar (overrides the packaged file)
server:
  port: 8181

# Profile file for production
# application-prod.yml
logging:
  level:
    com.webnest: INFO

# Run
java -jar shop.jar --spring.profiles.active=prod

# Inspect where a value came from (Actuator, secured environments only)
curl localhost:8181/actuator/env/server.port

{"property":{"source":"Config resource 'file [config/application.yml]' via location 'optional:file:./config/'","value":"8181"}}