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Spring Beans and Dependency Injection
You are free to use any of the standard Spring Framework techniques to define your beans and their injected dependencies.
We generally recommend using constructor injection to wire up dependencies and @ComponentScan
to find beans.
If you structure your code as suggested above (locating your application class in a top package), you can add @ComponentScan
without any arguments or use the @SpringBootApplication
annotation which implicitly includes it.
All of your application components (@Component
, @Service
, @Repository
, @Controller
, and others) are automatically registered as Spring Beans.
The following example shows a @Service
Bean that uses constructor injection to obtain a required RiskAssessor
bean:
-
Java
-
Kotlin
import org.springframework.stereotype.Service;
@Service
public class MyAccountService implements AccountService {
private final RiskAssessor riskAssessor;
public MyAccountService(RiskAssessor riskAssessor) {
this.riskAssessor = riskAssessor;
}
// ...
}
import org.springframework.stereotype.Service
@Service
class MyAccountService(private val riskAssessor: RiskAssessor) : AccountService
If a bean has more than one constructor, you will need to mark the one you want Spring to use with @Autowired
:
-
Java
-
Kotlin
import java.io.PrintStream;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class MyAccountService implements AccountService {
private final RiskAssessor riskAssessor;
private final PrintStream out;
@Autowired
public MyAccountService(RiskAssessor riskAssessor) {
this.riskAssessor = riskAssessor;
this.out = System.out;
}
public MyAccountService(RiskAssessor riskAssessor, PrintStream out) {
this.riskAssessor = riskAssessor;
this.out = out;
}
// ...
}
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Service
import java.io.PrintStream
@Service
class MyAccountService : AccountService {
private val riskAssessor: RiskAssessor
private val out: PrintStream
@Autowired
constructor(riskAssessor: RiskAssessor) {
this.riskAssessor = riskAssessor
out = System.out
}
constructor(riskAssessor: RiskAssessor, out: PrintStream) {
this.riskAssessor = riskAssessor
this.out = out
}
// ...
}
Notice how using constructor injection lets the riskAssessor field be marked as final , indicating that it cannot be subsequently changed.
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