Custom configuration properties in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a configuration property class with the correct annotation.

Spring Boot

@[1]("app.settings")
public class AppSettings {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Drag options to blanks, or click blank then click option'

AComponent

BConfigurationProperties

CService

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @ConfigurationProperties

Forgetting to specify the prefix in the annotation

The @ConfigurationProperties annotation binds external properties to this class.

2fill in blank

medium

Complete the code to enable configuration properties scanning in the main application class.

Spring Boot

@SpringBootApplication
@[1](AppSettings.class)
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

Drag options to blanks, or click blank then click option'

AEnableAutoConfiguration

BComponentScan

CEnableConfigurationProperties

DConfigurationPropertiesScan

Attempts:

3 left

💡 Hint

Common Mistakes

Using @ComponentScan instead of @EnableConfigurationProperties

Not specifying the class in the annotation

The @EnableConfigurationProperties annotation tells Spring Boot to process the specified configuration properties class.

3fill in blank

hard

Fix the error in the configuration properties class by completing the missing annotation.

Spring Boot

public class DatabaseConfig {
    private String url;

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }
}

@[1]("database")
class DatabaseProperties extends DatabaseConfig {}

Drag options to blanks, or click blank then click option'

AConfigurationProperties

BComponent

CService

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add @ConfigurationProperties

Using incorrect annotation like @Component

The subclass must be annotated with @ConfigurationProperties to bind properties with the prefix 'database'.

4fill in blank

hard

Fill both blanks to create a configuration properties class with a nested property and its getter.

Spring Boot

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

@[1]("server")
public class ServerProperties {
    private Security security = new Security();

    public Security getSecurity() {
        return [2];
    }

    public static class Security {
        private boolean enabled;

        public boolean isEnabled() {
            return enabled;
        }

        public void setEnabled(boolean enabled) {
            this.enabled = enabled;
        }
    }
}

Drag options to blanks, or click blank then click option'

AConfigurationProperties

BComponent

Csecurity

DsecurityProperties

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @ConfigurationProperties

Returning wrong field name in getter

The class must be annotated with @ConfigurationProperties and the getter should return the field named security.

5fill in blank

hard

Fill all three blanks to create a configuration properties class with a list property and its setter.

Spring Boot

import org.springframework.boot.context.properties.ConfigurationProperties;
import java.util.List;

@[1]("app")
public class AppConfig {
    private List<String> [2];

    public void set[3](List<String> values) {
        this.modules = values;
    }
}

Drag options to blanks, or click blank then click option'

AConfigurationProperties

Bmodules

CModules

Dcomponents

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the setter method incorrectly

Using wrong field name for the list

The class uses @ConfigurationProperties with prefix 'app'. The list field is named modules and the setter method is setModules.

Practice

1. What is the main purpose of using @ConfigurationProperties in Spring Boot?

easy

A. To create REST endpoints automatically

B. To enable security features in the application

C. To define database connection pools

D. To bind external configuration properties to a Java class

Solution

1. Step 1: Understand the role of @ConfigurationProperties

   This annotation is used to map external configuration values (from files like application.properties or application.yml) to fields in a Java class.

2. Step 2: Compare with other options

   Options A, C, and D relate to other Spring Boot features but not to property binding.

3. Final Answer:

   To bind external configuration properties to a Java class -> Option D

4. Quick Check:

   Property binding = B [OK]

Hint: Remember: @ConfigurationProperties binds config files to classes [OK]

Common Mistakes:

• Confusing @ConfigurationProperties with @RestController
• Thinking it manages database connections
• Assuming it enables security automatically

2. Which of the following is the correct way to enable @ConfigurationProperties support in a Spring Boot application?

easy

A. Add @SpringBootApplication on the properties class

B. Add @EnableConfigurationProperties on a configuration class or main class

C. Add @RestController on the properties class

D. Add @ComponentScan on the properties class

Solution

1. Step 1: Identify how to activate configuration properties

   Spring Boot requires @EnableConfigurationProperties on a configuration or main class to enable binding of @ConfigurationProperties classes.

2. Step 2: Review other annotations

   @ComponentScan scans components but does not enable properties binding. @RestController is for web controllers. @SpringBootApplication is for main app class but does not alone enable properties binding.

3. Final Answer:

   Add @EnableConfigurationProperties on a configuration class or main class -> Option B

4. Quick Check:

   Enable config properties = D [OK]

Hint: Use @EnableConfigurationProperties to activate property binding [OK]

Common Mistakes:

• Confusing @ComponentScan with enabling properties
• Adding @RestController on properties class
• Assuming @SpringBootApplication alone enables properties

3. Given the following properties in application.yml and class, what will be the output of System.out.println(appProperties.getTimeout())?

application.yml:
app:
  timeout: 5000

Java class:
@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private int timeout;
    public int getTimeout() { return timeout; }
    public void setTimeout(int timeout) { this.timeout = timeout; }
}

medium

A. null

B. 0

C. 5000

D. Compilation error

Solution

1. Step 1: Understand property binding from YAML to class

   The app.timeout property in YAML is set to 5000. The class with @ConfigurationProperties(prefix = "app") binds this value to the timeout field.

2. Step 2: Check getter method output

   Calling getTimeout() returns the bound value 5000, so the printed output is 5000.

3. Final Answer:

   5000 -> Option C

4. Quick Check:

   Bound value printed = 5000 [OK]

Hint: Property prefix matches class prefix to bind values correctly [OK]

Common Mistakes:

• Forgetting to add setter method causes binding failure
• Using wrong prefix in annotation
• Expecting null or default instead of bound value

4. Identify the error in this custom properties class that prevents property binding:

@ConfigurationProperties(prefix = "server")
public class ServerProperties {
    private String port;
    public String getPort() { return port; }
    // Missing setter method
}

medium

A. Missing setter method for 'port' prevents binding

B. Prefix 'server' is invalid and causes error

C. Class must be annotated with @Component

D. Field 'port' should be public for binding

Solution

1. Step 1: Check property binding requirements

   Spring Boot binds properties using setters. Without a setter for 'port', the value cannot be set.

2. Step 2: Validate other options

   The prefix 'server' is valid. The class does not require @Component if registered via @EnableConfigurationProperties. Fields should be private with getters/setters, not public.

3. Final Answer:

   Missing setter method for 'port' prevents binding -> Option A

4. Quick Check:

   Setter missing = binding fails [OK]

Hint: Always add setters for fields to enable binding [OK]

Common Mistakes:

• Assuming prefix must be custom or different
• Thinking @Component is always required
• Making fields public instead of using setters

5. You want to create a nested configuration property for a mail server with host and port inside application.properties like this:

mail.server.host=smtp.example.com
mail.server.port=587

Which of the following Java classes correctly models this nested property using @ConfigurationProperties?

hard

A. @ConfigurationProperties(prefix = "mail")
public class MailProperties {
private Server server;
public static class Server {
private String host;
private int port;
// getters and setters
}
// getters and setters for server
}

B. @ConfigurationProperties(prefix = "mail.server")
public class MailProperties {
private String host;
private int port;
// getters and setters
}

C. @ConfigurationProperties(prefix = "mail")
public class MailProperties {
private String host;
private int port;
// getters and setters
}

D. @ConfigurationProperties(prefix = "mail.server")
public class MailProperties {
private Server server;
public static class Server {
private String host;
private int port;
// getters and setters
}
// getters and setters for server
}

Solution

1. Step 1: Understand nested property binding

   Properties like mail.server.host require a class with prefix mail and a nested class Server to hold host and port.

2. Step 2: Analyze options

   @ConfigurationProperties(prefix = "mail") public class MailProperties { private Server server; public static class Server { private String host; private int port; // getters and setters } // getters and setters for server } correctly uses @ConfigurationProperties(prefix = "mail") with a nested Server class. @ConfigurationProperties(prefix = "mail.server") public class MailProperties { private String host; private int port; // getters and setters } flattens properties incorrectly. @ConfigurationProperties(prefix = "mail") public class MailProperties { private String host; private int port; // getters and setters } misses nesting. @ConfigurationProperties(prefix = "mail.server") public class MailProperties { private Server server; public static class Server { private String host; private int port; // getters and setters } // getters and setters for server } uses prefix mail.server but still nests, which is inconsistent.

3. Final Answer:

   @ConfigurationProperties(prefix="mail") with nested Server class -> Option A

4. Quick Check:

   Nested class with prefix mail = A [OK]

Hint: Use nested classes for nested property groups [OK]

Common Mistakes:

• Using wrong prefix for nested properties
• Flattening nested properties into one class
• Missing getters/setters in nested class