78 lines
2.5 KiB
Plaintext
78 lines
2.5 KiB
Plaintext
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The `@Autowired` annotation in Spring is used for automatic dependency injection.
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It allows Spring to resolve and inject the required beans into your bean.
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For example to inject a `@Repository` object into a `@Service`.
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== Why is this an issue?
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The Spring dependency injection mechanism cannot identify which constructor to use for auto-wiring when multiple constructors are present in a class.
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This ambiguity can cause the application to crash at runtime, and it makes the code less clear to understand and more complex to extend and maintain.
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=== What is the potential impact?
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* *Incorrect Instantiation*: the wrong constructor is selected for instantiation, leading to a bean not being correctly initialized.
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* *Unsatisfied Dependency Exception*: the constructor selected by Spring requires beans that are not available in the Spring context.
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* *Non-Deterministic Behavior*: the constructor selected by Spring can vary, based on the number of dependencies that can be satisfied at runtime, leading to unpredictable application behavior.
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* *Maintainability Issues*: adding more constructors in the future could lead to further confusion and potential bugs.
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== How to fix it
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Use the `@Autowired` annotation to specify which constructor to use for auto-wiring.
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=== Code examples
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==== Noncompliant code example
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[source,java,diff-id=1,diff-type=noncompliant]
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----
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@Component
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public class ExampleClass { // Noncompliant, multiple constructors present and no @Autowired annotation to specify which one to use
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private final DependencyClass1 dependency1;
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public ExampleClass() {
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throw new UnsupportedOperationException("Not supported yet.");
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}
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public ExampleClass(DependencyClass1 dependency1) {
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this.dependency1 = dependency1;
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}
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// ...
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}
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----
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==== Compliant solution
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[source,java,diff-id=1,diff-type=compliant]
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----
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@Component
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public class ExampleClass {
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private final DependencyClass1 dependency1;
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public ExampleClass() {
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throw new UnsupportedOperationException("Not supported yet.");
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}
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@Autowired
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public ExampleClass(DependencyClass1 dependency1) {
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this.dependency1 = dependency1;
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}
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// ...
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}
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----
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== Resources
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=== Documentation
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* Spring - https://docs.spring.io/spring-framework/reference/core/beans/annotation-config/autowired.html[Annotation Config: Autowired]
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=== Articles & blog posts
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* Java Guides - https://www.javaguides.net/2023/08/unsatisfieddependencyexception-in.html[UnsatisfiedDependencyException in Spring Boot]
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