Cron expressions for scheduling in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to schedule a method to run every minute using a cron expression.

Spring Boot

@Scheduled(cron = "[1]")
public void runEveryMinute() {
    System.out.println("Running every minute");
}

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

A"* * * * *"

B"*/5 * * * * ?"

C"0 0/1 * * * ?"

D"0 * * * * *"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5 fields instead of 6 in the cron expression

Setting the wrong field for seconds

The cron expression "0 * * * * *" means the method runs at the 0th second of every minute.

2fill in blank

medium

Complete the cron expression to schedule a task to run at 3:30 AM every day.

Spring Boot

@Scheduled(cron = "[1]")
public void runDailyAt330() {
    System.out.println("Running daily at 3:30 AM");
}

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

A"30 0 3 * * *"

B"0 30 3 * * *"

C"0 3 30 * * *"

D"0 30 15 * * *"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping minutes and hours

Using 24-hour format incorrectly

The cron expression "0 30 3 * * *" means at second 0, minute 30, hour 3 every day.

3fill in blank

hard

Fix the error in the cron expression to run a task every Monday at 8 AM.

Spring Boot

@Scheduled(cron = "[1]")
public void runEveryMondayAt8() {
    System.out.println("Running every Monday at 8 AM");
}

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

A"0 0 8 ? * MON"

B"0 0 8 * * MON"

C"0 0 8 * * 1"

D"0 0 8 ? * 2"

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '?' for day-of-month

Using numeric day-of-week incorrectly

In Spring cron, '?' is used for day-of-month when specifying day-of-week. "0 0 8 ? * MON" runs at 8 AM every Monday.

4fill in blank

hard

Fill both blanks to schedule a task to run every 15 minutes between 9 AM and 5 PM on weekdays.

Spring Boot

@Scheduled(cron = "[1] [2] 9-17 * * MON-FRI")
public void runEvery15MinWeekdays() {
    System.out.println("Running every 15 minutes on weekdays between 9 AM and 5 PM");
}

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

A0

B0/15

C9-17

D*/15

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' for seconds causing multiple triggers

Incorrect hour range or day specification

The expression "0 0/15 9-17 * * MON-FRI" means at second 0, every 15 minutes, hours 9 to 17, Monday to Friday.

5fill in blank

hard

Fill all three blanks to schedule a task to run at 10:15 PM on the last day of every month.

Spring Boot

@Scheduled(cron = "[1] [2] [3] L * ?")
public void runMonthlyLastDay() {
    System.out.println("Running at 10:15 PM on the last day of every month");
}

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

A0

B15

C22

D59

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong hour or minute values

Misplacing 'L' in the expression

The cron expression "0 15 22 L * ?" means at second 0, minute 15, hour 22 (10 PM), on the last day (L) of every month.

Practice

1. What does a cron expression in Spring Boot primarily specify?

easy

A. The output format of the task

B. When a scheduled task should run

C. The name of the scheduled task

D. The priority of the task

Solution

1. Step 1: Understand the purpose of cron expressions

   Cron expressions define timing details for scheduling tasks.

2. Step 2: Identify what cron expressions control in Spring Boot

   They tell Spring Boot exactly when to run a method automatically.

3. Final Answer:

   When a scheduled task should run -> Option B

4. Quick Check:

   Cron expression = schedule time [OK]

Hint: Cron expressions set task run times, not names or outputs [OK]

Common Mistakes:

• Thinking cron sets task names
• Confusing cron with output formatting
• Assuming cron controls task priority

2. Which of the following is the correct syntax to schedule a method to run every minute using Spring Boot's @Scheduled annotation with a cron expression?

easy

A. @Scheduled(cron = "*/1 * * * *")

B. @Scheduled(cron = "* * * * *")

C. @Scheduled(cron = "0 0/1 * * ?")

D. @Scheduled(cron = "0 * * * * *")

Solution

1. Step 1: Recall Spring Boot cron format

   Spring Boot cron uses 6 fields: seconds, minutes, hours, day, month, weekday.

2. Step 2: Identify correct expression for every minute

   "0 * * * * *" means at 0 seconds every minute, every hour, every day.

3. Final Answer:

   @Scheduled(cron = "0 * * * * *") -> Option D

4. Quick Check:

   6-field cron with 0 seconds = every minute [OK]

Hint: Spring Boot cron needs 6 fields; seconds first [OK]

Common Mistakes:

• Using 5-field cron (missing seconds)
• Misplacing seconds field
• Using '?' in wrong position

3. Given the cron expression "0 15 10 * * ?" in a Spring Boot @Scheduled annotation, when will the scheduled method run?

medium

A. Every day at 10:15 AM

B. Every hour at 15 minutes past

C. Every day at 10:00 AM

D. Every minute at 15 seconds past

Solution

1. Step 1: Break down the cron fields

   Fields: seconds=0, minutes=15, hours=10, day=any, month=any, weekday=? (no specific day)

2. Step 2: Interpret the timing

   Means run at 10:15:00 every day, ignoring weekday.

3. Final Answer:

   Every day at 10:15 AM -> Option A

4. Quick Check:

   0 15 10 * * ? = daily 10:15 AM [OK]

Hint: Seconds first, then minutes, then hours in Spring cron [OK]

Common Mistakes:

• Confusing minutes and hours positions
• Ignoring '?' meaning in weekday
• Assuming it runs every hour

4. Identify the error in this Spring Boot cron expression: @Scheduled(cron = "0 0 25 * * ?")

medium

A. Seconds field missing

B. Day of month field is invalid

C. Hour value 25 is invalid

D. Weekday field cannot be '?'

Solution

1. Step 1: Check each cron field's valid range

   Seconds: 0-59, Minutes: 0-59, Hours: 0-23, Day: 1-31, Month: 1-12, Weekday: 1-7 or ?

2. Step 2: Identify invalid value

   Hour field is 25, which is outside 0-23 range, causing error.

3. Final Answer:

   Hour value 25 is invalid -> Option C

4. Quick Check:

   Hour must be 0-23, 25 is invalid [OK]

Hint: Hours max 23 in cron, check all field ranges [OK]

Common Mistakes:

• Using hour > 23
• Forgetting seconds field
• Misusing '?' in day or weekday

5. You want to schedule a Spring Boot task to run every Monday at 8:30 AM, but only during the months of June, July, and August. Which cron expression correctly achieves this?

hard

A. "0 30 8 ? 6,7,8 MON"

B. "0 30 8 * 6-8 *"

C. "0 30 8 ? 5-8 MON"

D. "0 30 8 ? 6-8 1"

Solution

1. Step 1: Understand cron fields needed

   Seconds=0, Minutes=30, Hours=8, Day=? (no specific day), Month=6,7,8 (June-Aug), Weekday=MON (Monday)

2. Step 2: Check options for correct syntax

   "0 30 8 ? 6,7,8 MON" uses '?' for day, lists months as 6,7,8, and weekday as MON, which is correct.

3. Final Answer:

   "0 30 8 ? 6,7,8 MON" -> Option A

4. Quick Check:

   Use '?' for day, list months, specify MON weekday [OK]

Hint: Use '?' for day when specifying weekday, list months with commas [OK]

Common Mistakes:

• Using '*' for day and weekday together
• Using range '-' instead of commas for months
• Using numeric weekday instead of MON