Spring Bean 和依赖注入

您可以自由使用任何标准的 Spring Framework 技术来定义 bean 及其注入的依赖项。我们通常建议使用构造函数注入来连接依赖项，并通过@ComponentScan查找 bean。spring-doc.cn

如果按照上述建议构建代码（将应用程序类放在 top 包中），则可以添加不带任何参数的 @ComponentScan 或使用隐式包含它的 @SpringBootApplication 注释。您的所有应用程序组件（@Service、@Repository、@Controller 等）都将自动注册为 Spring Bean。@Componentspring-doc.cn

以下示例显示了一个 @Service Bean，它使用构造函数注入来获取所需的 Bean：RiskAssessorspring-doc.cn

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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

如果一个 bean 有多个构造函数，则需要标记你希望 Spring 与 @Autowired一起使用的构造函数：spring-doc.cn

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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
	}

	// ...

}

请注意，使用构造函数注入如何让字段被标记为，这表示它随后无法更改。riskAssessorfinal