此版本仍在开发中，尚未被视为稳定版本。对于最新的稳定版本，请使用 Spring Boot 3.4.3！spring-doc.cadn.net.cn

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和@ComponentScan查找 Beans。spring-doc.cadn.net.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@ComponentScan不使用任何参数或使用@SpringBootApplication注解，其中隐式包含它。 您的所有应用程序组件 （@Component,@Service,@Repository,@Controller等）将自动注册为 Spring Bean。spring-doc.cadn.net.cn

以下示例显示了@Service使用构造函数注入来获取所需的RiskAssessor豆：spring-doc.cadn.net.cn

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:spring-doc.cadn.net.cn

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.