Spring Boot best practices

Work in progress, this post is still in ‘work in progress’ status

@Autowired Injection

Avoid field and setter injection

It should be used only for optional dependencies or in test code.

Good

• easy to use

Bad

• the bean can be changed runtime with a new call of the setter;
• the field can reference a null instance, you should add the annotation @Required to enforce the dependency;
• it’s easy to add dependencies, the class risk to violate the single responsibility principle becoming a container of services.

References

• Olivier Gierke: why-field-injection-is-evil

Use constructor injection

Good

• the beans cannot be null;
• the object is immutable;
• the object can be defined final;
• in case the bean has only one constructor you can omit @Autowired;
• force to better think the responsibility of the class.

References

Avoid the use of @Value in Spring Boot

Spring Boot introduced the @ConfigurationProperties annotation that is ‘far more superior than the basic @Value approach’ according to Stéphane Nicoll (Pivotal).

The advantages:

• You inject only an object a POJO and not a list of fields
• There is less risk to do typos in the declaration of the property
• The POJO is TypeSafe and can contain complex structures (e.g. ‘database.configuration.mysql.connection’)

Here you can find the documentation:

• Spring Boot: Type-safe Configuration Properties

Marco Molteni Blog