Application.properties basics in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the effect of this application.properties setting?

Given the following line in application.properties:

server.port=8081

What will be the port number your Spring Boot application listens on?

A The application listens on port 8080 (default).

B The application listens on port 8081.

C The application listens on port 80.

D The application will fail to start due to invalid port.

💡 Hint

The server.port property controls the HTTP port.

Setting server.port=8081 changes the default port from 8080 to 8081.

📝 Syntax

intermediate

Which line correctly sets a custom application name in application.properties?

You want to set the application name to "MyApp" using application.properties. Which option is correct?

A spring.application.name=MyApp

B spring.application.name: MyApp

C spring.application.name = "MyApp"

D spring.application.name => MyApp

💡 Hint

Properties files use key=value format without quotes.

The correct syntax is key=value without quotes or other symbols.

🔧 Debug

advanced

What error occurs with this application.properties line?

Consider this line in application.properties:

spring.datasource.url jdbc:mysql://localhost:3306/db

What happens when Spring Boot tries to start?

A Spring Boot throws a <code>java.lang.IllegalArgumentException</code> due to invalid property syntax.

B Spring Boot starts normally and connects to the database.

C Spring Boot throws a <code>BeanCreationException</code> due to missing URL.

D Spring Boot ignores the line and uses default datasource URL.

💡 Hint

Check the syntax for key-value pairs in properties files.

Missing '=' between key and value leaves spring.datasource.url unset, leading to BeanCreationException due to missing URL.

❓ state_output

advanced

What is the value of logging.level.root after loading this application.properties?

Given these lines in application.properties:

logging.level.root=INFO
logging.level.org.springframework=DEBUG

What is the effective logging level for the root logger?

A INFO

B DEBUG

C WARN

D ERROR

💡 Hint

Specific package levels override root, but root applies globally.

The root logger level is set to INFO explicitly; package-specific DEBUG does not change root.

🧠 Conceptual

expert

Which statement about application.properties loading order is true?

In Spring Boot, which of these statements about application.properties loading order is correct?

A Properties in <code>src/main/resources/application.properties</code> override those in external config files.

B The order of properties loading is random and unpredictable.

C Properties defined in <code>application.properties</code> are always overridden by environment variables.

D External configuration files have higher priority than packaged <code>application.properties</code>.

💡 Hint

Think about how Spring Boot prioritizes external vs internal config.

Spring Boot loads external config files last, which override packaged defaults.