53 lines
2.0 KiB
Plaintext
53 lines
2.0 KiB
Plaintext
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== Why is this an issue?
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Dependency injection frameworks such as Spring support dependency injection by using annotations such as `@Inject` and `@Autowired`.
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These annotation can be used to inject beans via constructor, setter, and field injection.
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Generally speaking, field injection is discouraged.
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It allows the creation of objects in an invalid state and makes testing more difficult.
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The dependencies are not explicit when instantiating a class that uses field injection.
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Apart from that, field injection is not compatible with final fields.
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Keeping dependencies immutable where possible makes the code easier to understand, easing development and maintenance.
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This rule raises an issue when the `@Autowired` or `@Inject` annotations are used on a field.
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== How to fix it
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Use constructor injection instead.
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By using constructor injection, the dependencies are explicit and must be passed during an object's construction.
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This avoids the possibility of instantiating an object in an invalid state and makes types more testable.
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Fields can be declared final, which makes the code easier to understand, as dependencies don't change after instantiation.
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=== Code examples
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==== Noncompliant code example
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[source,text,diff-id=1,diff-type=noncompliant]
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----
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public class SomeService {
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@Autowired
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private SomeDependency someDependency;
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}
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----
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==== Compliant solution
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[source,text,diff-id=1,diff-type=compliant]
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----
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public class SomeService {
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private final SomeDependency someDependency;
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@Autowired
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public SomeService(SomeDependency someDependency) {
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this.someDependency = someDependency;
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}
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}
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----
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== Resources
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=== Articles & blog posts
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* Baeldung - https://www.baeldung.com/java-spring-field-injection-cons[Why Is Field Injection Not Recommended?]
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* Baeldung - https://www.baeldung.com/constructor-injection-in-spring[Constructor Dependency Injection in Spring]
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* Oliver Drotbohm - https://odrotbohm.de/2013/11/why-field-injection-is-evil/[Why field injection is evil]
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