@PostConstruct and @PreDestroy in Spring Boot - Step-by-Step Execution

Concept Flow - @PostConstruct and @PreDestroy

Bean Created

↓

@PostConstruct Method Called

↓

Bean Ready to Use

↓

Application Context Closing

↓

@PreDestroy Method Called

↓

Bean Destroyed

Shows the lifecycle of a Spring bean: after creation, @PostConstruct runs once before use; before destruction, @PreDestroy runs once.

Execution Sample

Spring Boot

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class MyBean {
  @PostConstruct
  public void init() {
    System.out.println("Bean initialized");
  }

  @PreDestroy
  public void cleanup() {
    System.out.println("Bean destroyed");
  }
}

Defines a Spring bean with methods that run after creation and before destruction.

Execution Table

Step	Event	Method Called	Output	Bean State
1	Bean instance created	None	None	Created, not initialized
2	@PostConstruct triggered	init()	"Bean initialized"	Initialized, ready
3	Bean used in application	None	None	In use
4	Application context closing	None	None	Preparing to destroy
5	@PreDestroy triggered	cleanup()	"Bean destroyed"	Destroyed
6	Bean removed from context	None	None	Removed

💡 Bean lifecycle ends after @PreDestroy method runs and bean is removed.

Variable Tracker

Variable	Start	After Step 2	After Step 5	Final
Bean State	Not created	Initialized	Destroyed	Removed

Key Moments - 2 Insights

Why does the @PostConstruct method run only once?

Because it runs right after the bean is created and before it is used, as shown in step 2 of the execution_table.

When exactly is the @PreDestroy method called?

It is called just before the bean is destroyed when the application context is closing, as shown in step 5 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the bean state after step 2?

A Initialized, ready

B Created, not initialized

C Destroyed

D Removed

💡 Hint

Check the 'Bean State' column at step 2 in the execution_table.

At which step does the @PreDestroy method run?

A Step 2

B Step 5

C Step 4

D Step 6

💡 Hint

Look for '@PreDestroy triggered' in the 'Event' column of the execution_table.

If the application context never closes, which method will NOT run?

A @PostConstruct

B Bean constructor

C @PreDestroy

D Bean usage

💡 Hint

Refer to the execution_table steps related to application context closing and @PreDestroy.

Concept Snapshot

@PostConstruct and @PreDestroy in Spring Boot:
- @PostConstruct runs once after bean creation, before use.
- @PreDestroy runs once before bean destruction.
- Used for setup and cleanup tasks.
- Methods must be void, no args.
- Lifecycle tied to Spring application context.

Full Transcript

In Spring Boot, beans have a lifecycle. When a bean is created, the method annotated with @PostConstruct runs once to initialize it. This happens before the bean is used in the application. Later, when the application is shutting down, the method annotated with @PreDestroy runs once to clean up resources before the bean is destroyed. This ensures proper setup and cleanup. The execution table shows these steps clearly: creation, initialization, usage, context closing, cleanup, and removal. Understanding this helps manage resources safely in Spring applications.