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Nullable Injected Fields and Parameters Should Provide a Default Value

High
reliabilitystability

What is it?​

This practice is invoked when a nullable field or parameter is annotated with @Value in a Spring application without providing a default value.

Why apply it?​

Without a default value, undefined properties may lead to runtime exceptions when the Spring framework attempts to inject dependencies during bean creation, causing application instabilities.

How to fix it?​

Add a default value to the @Value annotation using the colon (:) operator. For nullable fields, the default value should typically be #{null}.

Examples​

Example 1:​

Negative​

The negative example shows a nullable field with a @Value annotation missing a default value, leading to potential runtime exceptions if the property is undefined.

import org.springframework.beans.factory.annotation.Value;
import org.springframework.lang.Nullable;

public class Config {

    @Nullable
    @Value("${my.property}") // Noncompliant: no default value is provided
    private String myProperty;

    public void displayProperty() {
        System.out.println("Property: " + myProperty);
    }
}

Example 2:​

Positive​

The positive example provides a default value in the @Value annotation for a nullable field, ensuring stability when the property is undefined.

import org.springframework.beans.factory.annotation.Value;
import org.springframework.lang.Nullable;

public class Config {

    @Nullable
    @Value("${my.property:#{null}}") // Compliant: a default value is provided
    private String myProperty;

    public void displayProperty() {
        System.out.println("Property: " + myProperty);
    }
}

Negative​

In this negative example, a method parameter is annotated with @Value but without a default value, risking a null pointer exception when the property is undefined.

import org.springframework.stereotype.Service;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.lang.Nullable;

@Service
public class NotificationService {

    public void sendNotification(
        @Nullable
        @Value("${notification.recipient}") String recipient) { // Noncompliant: no default value is provided
        if (recipient != null) {
            System.out.println("Sending notification to: " + recipient);
        } else {
            System.out.println("No recipient specified.");
        }
    }
}

Example 3:​

Positive​

This positive example ensures that a method parameter uses a default value in the @Value annotation, offering a safeguard against undefined properties.

import org.springframework.stereotype.Service;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.lang.Nullable;

@Service
public class NotificationService {

    public void sendNotification(
        @Nullable
        @Value("${notification.recipient:#{null}}") String recipient) {
        if (recipient != null) {
            System.out.println("Sending notification to: " + recipient);
        } else {
            System.out.println("No recipient specified.");
        }
    }
}