Field XX required a bean of type 使用@componentscan 解决

很少写博客了，似乎就为了让自己不断加深印象来写博客啦~ 

遇到的问题 是 spring boot 启动不起来 问题 是 

Field XXX  that could not be found.

给出的建议Action:

Consider defining a bean of type 'XX ‘ in your configuration.

Spring加载外部Bean两种方式
将定义在另外一个带有@Configuration的类中的Bean加载
1. 在Application类中使用@Import指定该类，
2.让@ComponentScan扫描到该类。

大多数使用的2. 实际上是要在spring boot 初始化前加入该类所在的包 进行扫描

在spring boot 主启动main函数上面加上默认的 扫描就好

@ComponentScan(basePackageClasses = {"XX", "XX.XX"})

这句会将相应的包进行扫描

如果想用自己的注解时可以使用SpringBootApplication 进行中间转化 

自己封装一个启动注解时 

public @interface App {       @AliasFor(annotation = SpringBootApplication.class, attribute = "scanBasePackages")    String[] scanBasePackages() default {};    @AliasFor(annotation = SpringBootApplication.class, attribute = "scanBasePackageClasses")    Class<?>[] scanBasePackageClasses() default {};}

当然如果就为了这个两个注解就咩有必要封装啦~ 就是启动是如果加入了其余的还要用这个注解时可以这样封装 

要不就直接用

SpringBootApplication

//// Source code recreated from a .class file by IntelliJ IDEA// (powered by Fernflower decompiler)//package org.springframework.boot.autoconfigure;import java.lang.annotation.Documented;import java.lang.annotation.ElementType;import java.lang.annotation.Inherited;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import org.springframework.boot.SpringBootConfiguration;import org.springframework.boot.autoconfigure.EnableAutoConfiguration;import org.springframework.boot.context.TypeExcludeFilter;import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.FilterType;import org.springframework.context.annotation.ComponentScan.Filter;import org.springframework.core.annotation.AliasFor;@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan(    excludeFilters = {@Filter(    type = FilterType.CUSTOM,    classes = {TypeExcludeFilter.class})})public @interface SpringBootApplication {    Class<?>[] exclude() default {};    String[] excludeName() default {};    @AliasFor(        annotation = ComponentScan.class,        attribute = "basePackages"    )    String[] scanBasePackages() default {};    @AliasFor(        annotation = ComponentScan.class,        attribute = "basePackageClasses"    )    Class<?>[] scanBasePackageClasses() default {};}