application.properties structure in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding property key-value pairs in application.properties

Which of the following lines correctly defines a property in application.properties to set the server port to 8080?

A server-port: 8080

B server.port=8080

C server_port=8080

D server.port:8080

💡 Hint

Look for the standard syntax using dot notation and equals sign.

In application.properties, properties are defined as key-value pairs separated by an equals sign. The key uses dot notation for hierarchy. So server.port=8080 is correct.

❓ component_behavior

intermediate

Effect of duplicate keys in application.properties

If application.properties contains these two lines:
spring.datasource.url=jdbc:mysql://localhost:3306/db1
spring.datasource.url=jdbc:mysql://localhost:3306/db2
What will be the effective value of spring.datasource.url when the application runs?

A jdbc:mysql://localhost:3306/db1

B Both values are merged into a list

C An error occurs due to duplicate keys

D jdbc:mysql://localhost:3306/db2

💡 Hint

Think about which value overrides the other in properties files.

When duplicate keys exist, the last occurrence overrides previous ones. So the effective value is the second line's URL.

📝 Syntax

advanced

Correct syntax for multiline values in application.properties

Which option correctly defines a multiline property value in application.properties?

A

my.property=Line1
Line2
Line3

B

my.property=Line1
\Line2
\Line3

C my.property=Line1\nLine2\nLine3

D

my.property=Line1\
Line2\
Line3

💡 Hint

Escape sequences are used for new lines inside values.

To represent new lines inside a property value, use the escape sequence \n. So option C is correct. Actual new lines in the file break the syntax.

🔧 Debug

advanced

Identify the error in this application.properties snippet

Given this snippet:
server.port=8080
spring.datasource.username=root
spring.datasource.password
What error will Spring Boot raise when loading this configuration?

A No error, empty password is allowed

B Missing value for property 'spring.datasource.password'

C Duplicate property key error

D Invalid property key syntax

💡 Hint

In properties files, a line with just a key sets an empty value.

No error occurs; the property spring.datasource.password is loaded with an empty string value since no separator is found.

❓ state_output

expert

Number of properties loaded from this application.properties

Consider this application.properties content:

app.name=TestApp
app.version=1.0
app.description=Sample app
app.name=ProdApp
app.debug=true

How many unique properties will Spring Boot load?

A 4

B 5

C 3

D 2

💡 Hint

Remember that duplicate keys overwrite previous ones.

There are 5 lines but app.name appears twice. The last value overwrites the first, so 4 unique properties are loaded.