Cron expressions for scheduling in Spring Boot - Step-by-Step Execution

Concept Flow - Cron expressions for scheduling

Start

↓

Define cron expression

↓

Spring parses expression

↓

Schedule task at specified times

↓

Task runs

↓

Wait for next scheduled time

↩Back to Schedule task

This flow shows how Spring Boot reads a cron expression, schedules a task, runs it at the right time, then waits for the next run.

Execution Sample

Spring Boot

@Scheduled(cron = "0 0/1 * * * ?")
public void runTask() {
    System.out.println("Task runs every minute");
}

This code schedules a task to run every minute using a cron expression.

Execution Table

Step	Cron Expression Part	Value	Meaning	Action
1	Seconds	0	At second 0	Task triggers at start of minute
2	Minutes	0/1	Every 1 minute starting at 0	Task runs every minute
3	Hours	*	Every hour	No hour restriction
4	Day of Month	*	Every day	No day restriction
5	Month	*	Every month	No month restriction
6	Day of Week	?	No specific day of week	Ignored because day of month is *
7	Year (optional)		Not specified	Runs every year
8	Task runs	N/A	At each matching time	Prints "Task runs every minute"
9	Wait	N/A	Waits until next minute	Cycle repeats
10	Exit	N/A	Never exits	Runs indefinitely

💡 Cron tasks run indefinitely until application stops

Variable Tracker

Variable	Start	After 1 min	After 2 min	After 3 min	Final
Current Time (minute)	0	1	2	3	N/A
Task Triggered	No	Yes	Yes	Yes	N/A

Key Moments - 3 Insights

Why does the task run every minute and not every second?

Because the cron expression sets seconds to 0 and minutes to 0/1, so it triggers only at second 0 of every minute (see execution_table step 1 and 2).

What does the '?' symbol mean in the day of week field?

It means 'no specific value' and is used when day of month is specified as '*', so Spring ignores day of week (see execution_table step 6).

Why does the task never stop running?

Because cron schedules repeat indefinitely until the app stops (see execution_table step 10).

Visual Quiz - 3 Questions

Look at the execution table, at which step does the task actually run?

A Step 2

B Step 8

C Step 6

D Step 10

💡 Hint

Check the 'Action' column for when the task prints output.

According to variable_tracker, what is the value of 'Task Triggered' after 2 minutes?

A Maybe

B No

C Yes

D Undefined

💡 Hint

Look at the 'After 2 min' column for 'Task Triggered'.

If the minutes part changed from '0/1' to '0/5', how would the execution table change?

A Task runs every 5 minutes instead of every minute

B Task runs every second

C Task runs only once

D Task runs every hour

💡 Hint

Look at step 2 where minutes are defined.

Concept Snapshot

Cron expressions schedule tasks by specifying time parts:
Seconds Minutes Hours DayOfMonth Month DayOfWeek Year(optional)
Use * for any value, / for intervals, ? for no specific value.
Spring Boot reads this to run tasks repeatedly at matching times.
Example: "0 0/1 * * * ?" runs task every minute at second 0.

Full Transcript

Cron expressions let you schedule tasks by defining when they run using six or seven parts: seconds, minutes, hours, day of month, month, day of week, and optionally year. In Spring Boot, you use @Scheduled with a cron string. For example, "0 0/1 * * * ?" means run at second 0, every 1 minute, every hour, every day, every month, ignoring day of week. The task runs at these times repeatedly until the app stops. The '?' means no specific value for day of week because day of month is '*'. This way, Spring parses the expression, schedules the task, runs it at the right times, then waits for the next scheduled time. Beginners often wonder why the task runs every minute and not every second; that is because seconds is fixed at 0. They also ask about '?', which means no specific value. Finally, cron tasks run indefinitely unless stopped.