Spring中基于构造函数的依赖注入答案

【问题标题】：Constructor-Based Dependency Injection within SpringSpring中基于构造函数的依赖注入
【发布时间】：2021-08-14 17:30:03
【问题描述】：

我有这门课：

@Service     
public class DogUserService  {               
private final ManagerService managerService;
...
}

在我的 context.xml 上：

   <bean id="managerService"
        class="com.dogs.impl.services.ManagerService" />

但是当我运行应用程序时。我有这个错误：

    rvice.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: 
No qualifying bean of type 'com.dogs.impl.services.ManagerService' available: expected at least 1 bean which qualifies as autowire candidate. Dependency a
    nnotations: {}

【问题讨论】：

标签： java spring spring-mvc inversion-of-control ioc-container

【解决方案1】：

您需要使用@Bean 注解将 bean 提供给 WebApplicationContext。我已经从 @Configuration bean 中的 context.xml 创建了 managerService bean，并使用 @Bean 方法使 bean 在 webApplicationContext 中可用。这个将 managerService 自动连接的 UserService 类具有此配置 bean 的属性 @ConditionalOnBean。

以下是我的实现方式。

应用类

@SpringBootApplication public class DemoApplication
{

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

}

用户服务

@Service
@ConditionalOnBean({EnableConfiguration.class})
public class UserService
{
    @Autowired
    private ManagerService managerService;
    
    public String run() {
        System.out.println("Going to Run from manager Service");
        return managerService.run();
    }

}

启用配置

@Configuration
public class EnableConfiguration implements InitializingBean
{

    ManagerService managerService;

    @Bean
    public ManagerService mngrService() {
        return managerService;
    }

    @Override public void afterPropertiesSet() throws Exception
    {
        ApplicationContext ctx = new ClassPathXmlApplicationContext( "context.xml" );
        managerService = (ManagerService) ctx.getBean("managerService");
        System.out.println("manager bean:" + managerService.toString());
        mngrService();

    }
}

ManagerService

public class ManagerService
{
    private int a;
    private int b;

    public ManagerService(int a, int b) {
        this.a = a;
        this.b = b;
    }

    public String run() {
        return this.toString();
    }

    @Override public String toString()
    {
        return "ManagerService{" + "a=" + a + ", b=" + b + '}';
    }
}

服务控制器

@RestController
public class ServiceController
{
    @Autowired
    private UserService userService;

    @GetMapping("/get")
    public String test() {
        return userService.run();
    }
}

context.xml

    <bean id="managerService" class="com.example.demo.ManagerService">
        <constructor-arg index="0" value="2"/>
        <constructor-arg index="1" value="5"/>
    </bean>

【讨论】：