Custom configuration properties in Spring Boot - Performance & Optimization

Performance: Custom configuration properties

MEDIUM IMPACT

This affects application startup time and memory usage by how configuration properties are loaded and bound.

Defining and loading custom configuration properties in Spring Boot

Spring Boot

Using a single @ConfigurationProperties class to bind all related properties:

@ConfigurationProperties(prefix = "app")
public class AppProperties {
  private int timeout;
  private String url;
  // getters and setters
}

@Configuration
@EnableConfigurationProperties(AppProperties.class)
public class MyService {
  private final AppProperties props;
  public MyService(AppProperties props) {
    this.props = props;
  }
}

Binds all related properties once in a structured object, reducing repeated lookups and improving startup efficiency.

📈 Performance GainSingle binding operation reduces startup overhead and improves memory locality.

Defining and loading custom configuration properties in Spring Boot

Spring Boot

Using @Value annotations repeatedly for many properties scattered across classes:

@Component
public class MyService {
  @Value("${app.timeout}")
  private int timeout;
  @Value("${app.url}")
  private String url;
  // many more @Value injections
}

Repeated @Value injections cause multiple property lookups and scattered binding, increasing startup time and complexity.

📉 Performance CostTriggers multiple property resolution calls, increasing startup time by tens of milliseconds in large apps.

Performance Comparison

Pattern	Property Lookups	Startup Delay	Memory Usage	Verdict
Multiple @Value annotations	Many repeated lookups	Higher (tens of ms)	Higher due to scattered bindings	[X] Bad
Single @ConfigurationProperties class	Single batch lookup	Lower (few ms)	Lower due to structured binding	[OK] Good

Rendering Pipeline

Spring Boot loads configuration properties during application startup before the main application context is fully initialized.

→Property Binding

→Bean Initialization

⚠️ BottleneckMultiple scattered property lookups increase binding time and bean initialization delay.

Optimization Tips

1Use @ConfigurationProperties to group related config properties for efficient binding.

2Avoid scattering many @Value annotations across classes to reduce repeated lookups.

3Enable debug logging to monitor property binding performance during startup.

Performance Quiz - 3 Questions

What is a performance benefit of using @ConfigurationProperties over multiple @Value annotations?

A It caches properties in the browser for faster access.

B It delays property loading until first use to save memory.

C It batches property binding reducing repeated lookups and startup time.

D It automatically compresses property files to reduce size.

DevTools: Spring Boot Actuator / Logs

How to check: Enable debug logging for property binding by setting logging.level.org.springframework.boot.context.properties=DEBUG and observe startup logs.

What to look for: Look for repeated property resolution messages indicating multiple lookups versus single batch binding.

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