java - 在 Spring Boot 中检索 bean？

Question

我过去曾使用过旧版 Spring。我们通过 xml 配置定义了 beans 并手动连接它们。我的团队最终齐心协力更新注释并使用 Spring Boot，而不是使用 Spring MVC 的“传统”方法。

话虽如此，我无法弄清楚我到底是如何在 Boot 中检索 bean 的。在遗留系统中，Spring 要么使用构造函数/setter 注入(inject)(取决于我们的配置)，要么我们可以直接使用 context.getBean("myBeanID"); 调用 bean，但是，它似乎并不情况不再如此。

我整理了一个小测试用例，尝试在下面的代码中使其正常工作:

package com.ots;


import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
public class GriefUIApplication{

    public static void main(String[] args) {
        SpringApplication.run(GriefUIApplication.class, args);

        SessionFactory factory = new Configuration().configure("hibernate.cfg.xml")
                .addAnnotatedClass(GriefRecord.class).addAnnotatedClass(RecordId.class)
                .addAnnotatedClass(CrossReferenceRecord.class)
                .buildSessionFactory();

        Statics.setSessionFactory(factory);

        TennisCoach tCoach = new TennisCoach();
        tCoach.getCoach();

    }

}



interface Coach{
    public String workout();
}


@Service
class TennisCoach implements Coach{

    private Coach soccerCoach;
    @Autowired
    private ApplicationContext context;


    public TennisCoach() {

    }

    public Coach getCoach() {

        System.out.println(context + " IS THE VALUE OF THE CONTEXT OBJECT");

        soccerCoach = (SoccerCoach)context.getBean("soccerCoach");

        System.out.println(soccerCoach.getClass());

        return soccerCoach;

    }

    @Override
    public String workout() {
        String practice = "practice your backhand!";
        System.out.println(practice);
        return practice;
    }


}

@Service
class SoccerCoach implements Coach{

    public SoccerCoach() {

    }

    @Override
    public String workout() {
        String practice = "practice your footwork!";
        System.out.println(practice);
        return practice;
    }

}

@RestController
class MyController{

    @GetMapping("/")
    public String sayHello() {

        return "Time on server is: " + new java.util.Date();
    }

}

我尝试将 ApplicationContext 对象 Autowiring 到 TennisCoach 类中。当我运行这个时，该对象为空。

我们如何在 Boot 中检索 Bean？

Answer 1

最常见的方法是使用@Autowired注释。另外，由于您有 Coach 接口(interface)的两个不同实现，因此您应该使用 @Qualifier 注释来告诉 Spring 要注入(inject)哪个接口(interface)实现。

一些关于这两个注释的教程，帮助您入门:

• https://www.baeldung.com/spring-autowire
• https://www.baeldung.com/spring-qualifier-annotation

对于您的示例，要将 bean 注入(inject) Controller ，您应该执行以下操作:

@RestController
class MyController {

    @Autowired
    @Qualifier("soccerCoach")
    private Coach coach;

    @GetMapping("/")
    public String sayHello() {
        // this should invoke the workout() from SoccerCoach implementation
        System.out.println(coach.workout());

        return "Time on server is: " + new java.util.Date();
    }

}

或者，如您所愿，使用构造函数注入(inject)将 soccerCoach 注入(inject)到 tennisCoach 中，代码将变为:

@Service
class TennisCoach implements Coach {

    private Coach soccerCoach;

    @Autowired
    public TennisCoach(@Qualifier("soccerCoach") Coach soccerCoach) {
        this.soccerCoach = soccerCoach;
    }

    public Coach getCoach() {
        System.out.println(soccerCoach.getClass());

        return soccerCoach;
    }

}

如果您确实需要使用 ApplicationContext 来检索某些 bean，则不建议在具有 main 函数的类中执行此操作。只需创建另一个 bean(您可以使用 @Componenent 注释)。这是一个例子:

@Component
public class AnyComponent {

    @Autowired
    private ApplicationContext applicationContext;

    public void invokeCoach() {
        System.out.println(applicationContext.getBean("tennisCoach"));
        System.out.println(applicationContext.getBean(SoccerCoach.class));
    }

}

并将此 bean 注入(inject)到您的应用程序流中，可以在 Controller 、服务或存储库中:

@RestController
class MyController {

    @Autowired
    private AnyComponent anyComponent;

    @GetMapping("/")
    public String sayHello() {
        anyComponent.invokeCoach();

        return "Time on server is: " + new java.util.Date();
    }

}

注意:通过注解注入(inject) bean 是 Spring 特有的，一般来说，而不是 Spring Boot 特有的。

来自https://www.baeldung.com/spring-autowire :

Starting with Spring 2.5, the framework introduced a new style of Dependency Injection driven by @Autowired Annotations. This annotation allows Spring to resolve and inject collaborating beans into your bean.