[Solved] Examine the following Spring component:@Component public class EventSender { private ApplicationEventPublisher publisher;... } }What is the main issue with this code? | Spring Boot

Spring Boot - Advanced Patterns

Examine the following Spring component:

@Component
public class EventSender {
    private ApplicationEventPublisher publisher;

    public void sendEvent() {
        publisher.publishEvent(new CustomEvent(this));
    }
}

What is the main issue with this code?

AThe <code>publishEvent</code> method does not exist in <code>ApplicationEventPublisher</code>

BThe <code>ApplicationEventPublisher</code> is not injected, so <code>publisher</code> is null

CThe <code>CustomEvent</code> class must extend <code>ApplicationListener</code> instead of <code>ApplicationEvent</code>

DThe <code>sendEvent</code> method must be annotated with <code>@EventListener</code>

Step-by-Step Solution

Solution:

Step 1: Check field injection
The publisher field is declared but not injected via @Autowired or constructor.
Step 2: Consequence
Without injection, publisher remains null, causing a NullPointerException when publishEvent is called.
Step 3: Verify other options
The publishEvent method does not exist in ApplicationEventPublisher is false; publishEvent exists. The CustomEvent class must extend ApplicationListener instead of ApplicationEvent is incorrect; events extend ApplicationEvent. The sendEvent method must be annotated with @EventListener is wrong; @EventListener is for listener methods, not publishers.
Final Answer:
The ApplicationEventPublisher is not injected, so publisher is null -> Option B
Quick Check:
Always inject ApplicationEventPublisher before use [OK]

Quick Trick: Missing @Autowired causes null ApplicationEventPublisher [OK]

Common Mistakes:

Forgetting to inject ApplicationEventPublisher
Confusing event and listener classes
Misusing @EventListener annotation

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More Spring Boot Quizzes

Examine the following Spring component:

Step 1: Check field injection

Step 2: Consequence

Step 3: Verify other options

Final Answer:

Quick Check:

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