@PreDestroy in Spring: What It Is and How It Works

In Spring, the @PreDestroy annotation marks a method to be called just before a bean is removed from the container. It is used to release resources or perform cleanup tasks before the bean is destroyed.

How It Works

The @PreDestroy annotation tells Spring to run a specific method right before the bean is destroyed. Think of it like cleaning up your workspace before leaving: you close files, turn off devices, and tidy up. Similarly, Spring calls the method annotated with @PreDestroy to release resources like open files, database connections, or threads.

This happens automatically when the Spring container shuts down or when the bean is removed. The method must have no parameters and usually returns void. This ensures your application cleans up properly and avoids resource leaks.

Example

This example shows a Spring bean with a method annotated by @PreDestroy. When the application context closes, the cleanup method runs automatically.

java

import jakarta.annotation.PreDestroy;
import org.springframework.stereotype.Component;

@Component
public class ResourceBean {

    public void useResource() {
        System.out.println("Using resource...");
    }

    @PreDestroy
    public void cleanup() {
        System.out.println("Cleaning up resource before bean destruction.");
    }
}

Output

Using resource...
Cleaning up resource before bean destruction.

When to Use

Use @PreDestroy when your Spring bean holds resources that need explicit cleanup. For example:

• Closing database connections
• Stopping background threads
• Releasing file handles or network sockets

This ensures your app frees resources properly and avoids memory leaks or locked files when shutting down or reloading beans.

Key Points

• @PreDestroy marks a method to run before bean destruction.
• The method must have no arguments and usually returns void.
• It helps clean up resources like files, connections, or threads.
• Spring calls it automatically when the context closes or bean is removed.
• Use it to avoid resource leaks and ensure graceful shutdown.

Key Takeaways

@PreDestroy runs a cleanup method before a Spring bean is destroyed.

Use it to release resources like files, connections, or threads.

The annotated method must have no parameters and return void.

Spring calls this method automatically when shutting down or removing beans.

It helps prevent resource leaks and supports graceful application shutdown.