org.springframework.beans.factory.UnsatisfiedDependencyException：創建名爲'demoRestController'的bean時出錯

Question

我是Spring的新手，我嘗試製作一個學習應用程序，但我在Autowiring中遇到問題，我添加了我的代碼。我正在研究春季引導。

春天引導代碼

public class DemoApplication { 

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

LoginBean.java

@Service 
@Component 
public class LoginBean { 
    private String userId; 
    private String pwd; 

    public String getUserId() { 
     return userId; 
    } 

    public void setUserId(String userId) { 
     this.userId = userId; 
    } 

    public String getPwd() { 
     return pwd; 
    } 

    public void setPwd(String pwd) { 
     this.pwd = pwd; 
    } 

DemoRestController.java

@RestController 
@EnableAutoConfiguration 
@RequestMapping("/demo") 
@Component 
public class DemoRestController { 


    private final LoginBean loginBean; 

    @Autowired 
    public DemoRestController(LoginBean loginBean) { 
     this.loginBean=loginBean; 
    } 

    @RequestMapping(value = "/login/{id},{pwd}", method = RequestMethod.GET, produces = "application/json") 
    public @ResponseBody LoginBean loginService(@PathVariable String id, @PathVariable String pwd) { 
     //LoginBean loginBean = new LoginBean(); 

     loginBean.setUserId(id); 
     loginBean.setPwd(pwd); 
     return loginBean; 
    } 

我想以下情景讓我@Autowired工作：

1. @Autowired LoginBean loginBean;
2. 在Controller類和自動裝配的setter中創建了LoginBean的getter setter;
3. 在上面的代碼中給出了Controller和autowired的創建構造函數;

下面是我得到

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'demoRestController': Unsatisfied dependency expressed through constructor argument with index 0 of type [com.ag.digital.demo.bean.LoginBean]: No qualifying bean of type [com.ag.digital.demo.bean.LoginBean] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.ag.digital.demo.bean.LoginBean] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {} 
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:749) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:185) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1143) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1046) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:510) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:839) ~[spring-context-4.2.6.RELEASE.jar:4.2.6.RELEASE] 
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:538) ~[spring-context-4.2.6.RELEASE.jar:4.2.6.RELEASE] 
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:118) ~[spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE] 
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:766) [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE] 
    at org.springframework.boot.SpringApplication.createAndRefreshContext(SpringApplication.java:361) [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE] 
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE] 
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1191) [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE] 
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1180) [spring-boot-1.3.3.RELEASE.jar:1.3.3.RELEASE] 
    at com.ag.digital.demo.boot.DemoApplication.main(DemoApplication.java:14) [classes/:na] 
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.ag.digital.demo.bean.LoginBean] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {} 
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1373) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1119) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1014) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:813) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741) ~[spring-beans-4.2.5.RELEASE.jar:4.2.5.RELEASE] 
    ... 19 common frames omitted 

Answer 1

你DemoApplication類是在com.ag.digital.demo.boot包和你LoginBean類是com.ag.digital.demo.bean包中的錯誤。默認情況下，如果組件（類別註解爲@Component）位於主應用程序類DemoApplication的相同程序包或子程序包中，則會找到它們。這意味着LoginBean未找到，因此依賴注入失敗。

有一對夫婦的方式來解決問題：

1. 移動LoginBean到com.ag.digital.demo.boot或子包。
2. 使用scanBasePackages屬性@SpringBootApplication配置掃描組件的軟件包，該屬性應爲DemoApplication。

幾個未造成問題的其他東西，但不完全正確的代碼，你已經發布：

• @Service是@Component專業化，所以你不需要無論在LoginBean
• 同樣，@RestController是@Component專業化，這樣你就不需要同時對DemoRestController
• DemoRestController爲@EnableAutoConfiguration一個不尋常的地方。該註釋通常可直接或通過@SpringBootApplication在您的主要應用程序類別（DemoApplication）中找到，它是@ComponentScan,@Configuration和@EnableAutoConfiguration的組合。