Scheduled tasks with @Scheduled in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to schedule a method to run every 5 seconds.

Spring Boot

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class TaskScheduler {

    @Scheduled(fixedRate = [1])
    public void runTask() {
        System.out.println("Task executed");
    }
}

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

A"5s"

B5

C5000

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Using seconds instead of milliseconds

Using string values instead of numbers

The fixedRate attribute expects milliseconds. To run every 5 seconds, use 5000.

2fill in blank

medium

Complete the code to schedule a method to run every day at 2:30 AM.

Spring Boot

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class DailyTask {

    @Scheduled(cron = [1])
    public void runDaily() {
        System.out.println("Daily task executed");
    }
}

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

A"0 30 2 * * ?"

B"0 2 30 * * ?"

C"30 2 * * *"

D"0 0 2 * * ?"

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up minute and hour positions

Omitting seconds field

The cron expression "0 30 2 * * ?" means at second 0, minute 30, hour 2 every day.

3fill in blank

hard

Fix the error in the code to enable scheduling in the Spring Boot application.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

@SpringBootApplication
[1]
public class MyApp {

    public static void main(String[] args) {
        SpringApplication.run(MyApp.class, args);
    }
}

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

A@EnableScheduling

B@Scheduled

C@Component

D@Configuration

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Scheduled on the main class

Forgetting to enable scheduling

The @EnableScheduling annotation enables Spring's scheduled task execution capability.

4fill in blank

hard

Fill both blanks to create a scheduled method that runs every minute and logs the current time.

Spring Boot

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
import java.time.LocalTime;

@Component
public class ClockTask {

    @Scheduled(cron = [1])
    public void logTime() {
        System.out.println("Current time: " + LocalTime.[2]());
    }
}

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

A"0 * * * * ?"

B"fixedRate = 60000"

Cnow

Attempts:

3 left

💡 Hint

Common Mistakes

Using fixedRate with wrong value

Using incorrect LocalTime method

The cron expression '0 * * * * ?' runs the method every minute at second 0. The LocalTime.now() method gets the current time.

5fill in blank

hard

Fill all three blanks to create a scheduled task that runs every 10 seconds, prints a message, and uses a component annotation.

Spring Boot

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.[1].Component;

@[2]
public class MessageTask {

    @Scheduled(fixedRate = [3])
    public void printMessage() {
        System.out.println("Hello every 10 seconds");
    }
}

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

Astereotype

BComponent

C10000

DConfiguration

Attempts:

3 left

💡 Hint

Common Mistakes

Wrong import package

Using @Configuration instead of @Component

Wrong fixedRate value

The @Component annotation marks the class as a Spring bean. It is imported from org.springframework.stereotype.Component. The fixedRate is set to 10000 milliseconds for 10 seconds.

Practice

1. What is the main purpose of the @Scheduled annotation in Spring Boot?

easy

A. To run a method automatically at fixed intervals or times

B. To mark a method as a REST endpoint

C. To inject dependencies into a class

D. To configure database connections

Solution

1. Step 1: Understand the role of @Scheduled

   The @Scheduled annotation is used to mark methods that should run automatically on a schedule without manual calls.

2. Step 2: Compare with other options

   Options A, C, and D relate to other Spring features like REST, dependency injection, and database setup, not scheduling.

3. Final Answer:

   To run a method automatically at fixed intervals or times -> Option A

4. Quick Check:

   @Scheduled = automatic method run [OK]

Hint: Remember: @Scheduled means automatic timed method run [OK]

Common Mistakes:

• Confusing @Scheduled with REST or dependency injection annotations
• Thinking @Scheduled configures databases
• Assuming @Scheduled requires manual method calls

2. Which of the following is the correct way to schedule a method to run every 5 seconds using @Scheduled?

easy

A. @Scheduled(fixedDelay = 5000)

B. @Scheduled(rate = 5)

C. @Scheduled(cron = "0 */5 * * * *")

D. @Scheduled(fixedRate = 5000)

Solution

1. Step 1: Understand fixedRate vs fixedDelay

   fixedRate runs the method every specified milliseconds regardless of method duration. fixedDelay waits after method finishes before next run.

2. Step 2: Check the options

   @Scheduled(fixedRate = 5000) uses fixedRate = 5000 which means run every 5 seconds. @Scheduled(fixedDelay = 5000) uses fixedDelay which waits after method ends. @Scheduled(rate = 5) uses invalid attribute rate. @Scheduled(cron = "0 */5 * * * *") uses a cron expression which runs every 5 minutes.

3. Final Answer:

   @Scheduled(fixedRate = 5000) -> Option D

4. Quick Check:

   fixedRate = 5000 means every 5 seconds [OK]

Hint: Use fixedRate for exact interval runs in milliseconds [OK]

Common Mistakes:

• Using 'rate' instead of 'fixedRate'
• Confusing fixedDelay with fixedRate
• Incorrect cron syntax for simple intervals

3. Given the code below, what will be printed and how often?

@Scheduled(fixedDelay = 3000)
public void printMessage() {
    System.out.println("Hello World");
}

medium

A. Method runs only once after 3 seconds delay

B. "Hello World" prints every 3 seconds regardless of method duration

C. "Hello World" prints every 3 seconds after method finishes

D. Code will cause a compilation error

Solution

1. Step 1: Understand fixedDelay behavior

   fixedDelay = 3000 means the method runs, then waits 3 seconds after it finishes before running again.

2. Step 2: Analyze the print output frequency

   Since the method prints "Hello World" each time it runs, it will print every 3 seconds after the previous run completes.

3. Final Answer:

   "Hello World" prints every 3 seconds after method finishes -> Option C

4. Quick Check:

   fixedDelay = wait after method ends [OK]

Hint: fixedDelay waits after method ends before next run [OK]

Common Mistakes:

• Confusing fixedDelay with fixedRate
• Thinking method runs only once
• Assuming compilation error without reason

4. Identify the error in this scheduled task code:

@Scheduled(fixedRate = "5000")
public void task() {
    System.out.println("Running task");
}

medium

A. fixedRate value should be a number, not a string

B. Method must return a value

C. Missing @EnableScheduling annotation on class

D. Method name cannot be 'task'

Solution

1. Step 1: Check fixedRate attribute type

   The fixedRate attribute expects a long number (milliseconds), not a string. Using quotes causes a syntax error.

2. Step 2: Verify other options

   Method can be void, so no return needed. Missing @EnableScheduling is a configuration issue but not a syntax error here. Method name 'task' is valid.

3. Final Answer:

   fixedRate value should be a number, not a string -> Option A

4. Quick Check:

   fixedRate expects number, not string [OK]

Hint: fixedRate and fixedDelay need numbers, no quotes [OK]

Common Mistakes:

• Putting quotes around fixedRate or fixedDelay values
• Assuming method must return a value
• Confusing configuration errors with syntax errors

5. You want a method to run every Monday at 8:30 AM using @Scheduled. Which cron expression is correct?

hard

A. @Scheduled(cron = "30 8 * * 1")

B. @Scheduled(cron = "0 30 8 ? * MON")

C. @Scheduled(cron = "0 8 30 * * MON")

D. @Scheduled(cron = "0 30 8 * * 1")

Solution

1. Step 1: Understand cron format in Spring

   Spring cron has 6 fields: second, minute, hour, day of month, month, day of week.

2. Step 2: Analyze each option

   @Scheduled(cron = "0 30 8 ? * MON"): "0 30 8 ? * MON" means at second 0, minute 30, hour 8, any day of month (?), any month (*), on Monday (MON). This matches 8:30 AM Monday.
   @Scheduled(cron = "30 8 * * 1") is missing seconds field and uses 5 fields.
   @Scheduled(cron = "0 8 30 * * MON") has hour and minute swapped.
   @Scheduled(cron = "0 30 8 * * 1") uses day of week as 1 which is Sunday in some systems, MON is clearer.

3. Final Answer:

   @Scheduled(cron = "0 30 8 ? * MON") -> Option B

4. Quick Check:

   Spring cron: sec min hour day month weekday [OK]

Hint: Spring cron has 6 fields; use '?' for day of month if using day of week [OK]

Common Mistakes:

• Using 5-field cron instead of 6-field in Spring
• Swapping hour and minute positions
• Using numeric day of week without knowing system mapping