springboot 無法掃描到父類模塊中Bean

現(xiàn)象：

我定義了兩個模塊 A 和 B 。B模塊依賴A模塊

A模塊中我定義了一個@Component

卻發(fā)現(xiàn)在B模塊中我無法掃描到這個Bean導入注入失敗

如何解決

查閱得知，在springboot中的bean掃描是掃描同級目錄或者下級目錄，也就是不會掃描到依賴包里面的東西。

但是我又想定義公共Bean，該怎么做呢。

解決方案

手動注入 @Bean

如果你定義的是實體類之類的Bean，那么可以在子類中手動Bean

@Bean
Result result(){
 new Result;
}

配置掃描 @ComponentScan

但是如果你定義的Bean是類似于接口的文件，那你使用手動定義的方法就會發(fā)現(xiàn)要寫很長一段，把所有的方法都定義一下。所以還有另一種方法

@SpringBootApplication
@ComponentScan(basePackages = {"cn.o"})
public class ProxyDataSourceApplication {
 ...main(){
 }
}

如果定義了@ComponentScan掃描路徑，注意不要讓@Bean多處定義，否則會報重復注入的錯誤。

spring boot 啟動就自動關閉 之 找不到bean

創(chuàng)建的bean

package com.springboot.entity; 
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.Component;
 
/**
 * Created by ASUS on 2018/3/20.
 */
@Component
@ConfigurationProperties(prefix = "author")
public class AuthorBean {
    private String name;
    private Long age;
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getName() {
        return name;
    }
 
    public void setAge(Long age) {
        this.age = age;
    }
 
    public Long getAge() {
        return age;
    }
}

寫的application類

package com.springboot.demo; 
import com.springboot.entity.AuthorBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
/**
 * Created by ASUS on 2018/3/20.
 */
@RestController
@org.springframework.boot.autoconfigure.SpringBootApplication
 
public class ApplicationDemo {
    @Autowired
    private AuthorBean authorBean;
 
    @RequestMapping("/kkk")
    String index(){
        return "author name ="+authorBean.getName()+"author age="+authorBean.getAge();
    }
 
    public static void main(String[] args) {
        SpringApplication.run(ApplicationDemo.class,args);
    }
}

控制臺報錯：

2018-03-20 22:22:02.070 INFO 11360 --- [ main] com.springboot.demo.ApplicationDemo : Starting ApplicationDemo on DESKTOP-IV2AEJK with PID 11360 (D:\IDEA\IDEAWorkSpace\SpringBootDemo\target\classes started by ASUS in D:\IDEA\IDEAWorkSpace\SpringBootDemo)
2018-03-20 22:22:02.074 INFO 11360 --- [ main] com.springboot.demo.ApplicationDemo : No active profile set, falling back to default profiles: default
2018-03-20 22:22:02.144 INFO 11360 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@3fa980b: startup date [Tue Mar 20 22:22:02 CST 2018]; root of context hierarchy
2018-03-20 22:22:03.453 INFO 11360 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 9090 (http)
2018-03-20 22:22:03.462 INFO 11360 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2018-03-20 22:22:03.463 INFO 11360 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.27
2018-03-20 22:22:03.557 INFO 11360 --- [ost-startStop-1] o.a.c.c.C.[.[localhost].[/helloboot] : Initializing Spring embedded WebApplicationContext
2018-03-20 22:22:03.558 INFO 11360 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1416 ms
2018-03-20 22:22:03.704 INFO 11360 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/]
2018-03-20 22:22:03.707 INFO 11360 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]
2018-03-20 22:22:03.707 INFO 11360 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2018-03-20 22:22:03.707 INFO 11360 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2018-03-20 22:22:03.708 INFO 11360 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]
2018-03-20 22:22:03.741 WARN 11360 --- [ main] ationConfigEmbeddedWebApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'applicationDemo': Unsatisfied dependency expressed through field 'authorBean'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.springboot.entity.AuthorBean' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
2018-03-20 22:22:03.742 INFO 11360 --- [ main] o.apache.catalina.core.StandardService : Stopping service [Tomcat]
2018-03-20 22:22:03.761 INFO 11360 --- [ main] utoConfigurationReportLoggingInitializer :

Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2018-03-20 22:22:03.858 ERROR 11360 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter :

***************************
APPLICATION FAILED TO START
***************************
Description:
Field authorBean in com.springboot.demo.ApplicationDemo required a bean of type 'com.springboot.entity.AuthorBean' that could not be found.
Action:
Consider defining a bean of type 'com.springboot.entity.AuthorBean' in your configuration.
Process finished with exit code 1

其中：

意思就是找不到bean，沒有注入進去。

解決方法：

@RestController
@org.springframework.boot.autoconfigure.SpringBootApplication
@ComponentScan(basePackages = {"com.springboot.entity"})
public class ApplicationDemo {
    @Autowired
    private AuthorBean authorBean;

加注解

@ComponentScan(basePackages = {"com.springboot.entity"})

原因：

@SpringBootApplication 注解組合了@Configuration @EnableAutoConfiguration，@ComponentScan.

spring boot 會自動掃描@SpringBootApplication 所在類的同級包以及下級包里的Bean ，建議入口類放置在groupid+arctifactId 組合的包名下

以下收集別的解釋：

正常情況下加上@Component注解的類會自動被Spring掃描到生成Bean注冊到spring容器中，既然他說沒找到，也就是該注解被沒有被spring識別，問題的核心關鍵就在application類的注解SpringBootApplication上

這個注解其實相當于下面這一堆注解的效果，其中一個注解就是@Component，在默認情況下只能掃描與控制器在同一個包下以及其子包下的@Component注解，以及能將指定注解的類自動注冊為Bean的@Service@Controller和@ Repository，至此明白問題所在，之前我將接口與對應實現(xiàn)類放在了與控制器所在包的同一級目錄下，這樣的注解自然是無法被識別的

所以有兩種解決辦法：

1 .將接口與對應的實現(xiàn)類放在與application啟動類的同一個目錄或者他的子目錄下，這樣注解可以被掃描到，這是最省事的辦法

2 .在指定的application類上加上這么一行注解，手動指定application類要掃描哪些包下的注解。

以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。

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