【SpringBoot】@SpringBootApplication注解分析

缺乏、安全感 2023-10-15 22:24 38阅读 0赞

> 签名：但行好事，莫问前程。

#### 文章目录 ####

*  前言
 *  @SpringBootApplication
 *   *  @SpringBootConfiguration
     *   *  @Configuration
     *  @EnableAutoConfiguration
     *   *  @AutoConfigurationPackage
         *  @Import(AutoConfigurationImportSelector.class)
     *  @ComponentScan
     *  自动配置流程总结
 *  总结

--------------------

## 前言 ##

@SpringBootApplication的分析

--------------------

## @SpringBootApplication ##

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

> @SpringBootApplication标注在程序的主启动类上面，他由三个注解组成：@SpringBootConfiguration、@EnableAutoConfiguration、@ComponentScan

@SpringBootConfiguration
    @EnableAutoConfiguration
    @ComponentScan(excludeFilters = {
         @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
    public @interface SpringBootApplication {
        }

![在这里插入图片描述][9c42ef25bafc410f8191b6e99a25b1f8.png]

### @SpringBootConfiguration ###

> @SpringBootConfiguration表明该类是SpringBoot的一个核心配置类，他的底层注解是：@Configuration

@Target({
        ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Configuration
    @Indexed
    public @interface SpringBootConfiguration {
        }

![在这里插入图片描述][d829046c3112450dbc23e750df912df1.png]

#### @Configuration ####

> @Configuration：标注在类上面，告诉springboot这是一个配置类。

@Configuration
    public class MyConfig {
        
    
    }

![在这里插入图片描述][b7e54bd22df0462893e0479b3935a62d.png]

> @Bean:给容器中注册组件，以方法名作为组件id，返回类型就是组件类型，返回的值是容器中的实例（默认是单实例）。

@Bean
        public User user (){
        
            return new User("yangcunle", 18);
        }

![在这里插入图片描述][9732809469ae4e6cb03734e7c39209ec.png]  
从容器中获取user组件：

@SpringBootApplication
    @Slf4j
    public class MainApplication {
        
        public static void main(String[] args) {
        
            ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);
            User user = run.getBean("user", User.class);
            log.info(user.toString());
        }
    }

![在这里插入图片描述][802b091ca23044e8ab45c8359def76fe.png]

> @Configuration 中 boolean proxyBeanMethods() default true; （代理bean的方法，默认true）

![在这里插入图片描述][db0261cedf4d4ef791baaebf60610c66.png]  
当我们多次获取组件的时候，获取的是同一个实例。  
![在这里插入图片描述][34202529246b4e4d8221f44c33bed58e.png]

当我们把proxyBeanMethods 改为 false 时，再运行代码：

@Configuration(proxyBeanMethods = false)
    public class MyConfig {
        
    
        @Bean
        public User user (){
        
            return new User("yangcunle", 18);
        }
    
    }

![在这里插入图片描述][7f5814af359d454b8f8e6aef12af8c3b.png]  
此时从容其中获取的就不是同一个实例了。

### @EnableAutoConfiguration ###

> @EnableAutoConfiguration是启用自动配置注解。由两个注解组成：@AutoConfigurationPackage、@Import

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import(AutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration {
        }

![在这里插入图片描述][7b0989f8ba5f44379258aa61bf81d7c1.png]

#### @AutoConfigurationPackage ####

> @AutoConfigurationPackage自动配置包注解。

@Import(AutoConfigurationPackages.Registrar.class)// 给容器导入一个组件
    public @interface AutoConfigurationPackage {
        }

![在这里插入图片描述][ec8ff57866a7445fadbd068a473b4d82.png]

> Registrar.class点击进入源码，发现有一个方法批量注册组件。

![在这里插入图片描述][add548fe87dc444fb2e5fec0e54a3b42.png]

> 将指定包（com.yangcunle.boot）下面的所有组件注册进来。

![在这里插入图片描述][f5c1ed20d701412993643f006dc8af90.png]

#### @Import(AutoConfigurationImportSelector.class) ####

> @Import(AutoConfigurationImportSelector.class)：给容器中批量导入了哪些包？

点击进入AutoConfigurationImportSelector.class查看：  
![在这里插入图片描述][aade4644b7a642daa4a0c83acaa7e447.png]

public String[] selectImports(AnnotationMetadata annotationMetadata) {
        
    		if (!isEnabled(annotationMetadata)) {
        
    			return NO_IMPORTS;
    		}
    		// 使用该方法给容器中批量导入组件
    		AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
    		return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
    	}

> getAutoConfigurationEntry(annotationMetadata) 获取所有配置结合

protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
        
    		if (!isEnabled(annotationMetadata)) {
        
    			return EMPTY_ENTRY;
    		}
    		AnnotationAttributes attributes = getAttributes(annotationMetadata);
    		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
    		configurations = removeDuplicates(configurations);
    		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
    		checkExcludedClasses(configurations, exclusions);
    		configurations.removeAll(exclusions);
    		configurations = getConfigurationClassFilter().filter(configurations);
    		fireAutoConfigurationImportEvents(configurations, exclusions);
    		return new AutoConfigurationEntry(configurations, exclusions);
    	}

> 获取所有需要导入到容器中的配置类  
> List configurations =getCandidateConfigurations(annotationMetadata, attributes);

![在这里插入图片描述][60b85067727745e28d34fcfbff9d5fb7.png]  
![在这里插入图片描述][01ca357509194cdeae32aba70fcc3f6a.png]

> XXXtAutoConfiguration （啥啥啥自动配置类）

这里以RabbitAutoConfiguration为例：

![在这里插入图片描述][2e3e3f0f03ee4a89b4e0afd044445a43.png]

@ConditionalOnClass(\{ RabbitTemplate.class, Channel.class \}) 按条件加载

@Bean
    		@ConditionalOnMissingBean  // 如果这个组件不在容器中，就往容器中注册这个组件
    		RabbitConnectionFactoryBeanConfigurer rabbitConnectionFactoryBeanConfigurer(RabbitProperties properties,
    				ResourceLoader resourceLoader, ObjectProvider<CredentialsProvider> credentialsProvider,
    				ObjectProvider<CredentialsRefreshService> credentialsRefreshService) {
        
    			RabbitConnectionFactoryBeanConfigurer configurer = new RabbitConnectionFactoryBeanConfigurer(resourceLoader,
    					properties);
    			configurer.setCredentialsProvider(credentialsProvider.getIfUnique());
    			configurer.setCredentialsRefreshService(credentialsRefreshService.getIfUnique());
    			return configurer;
    		}

再看看Redis的自动配置类：

![在这里插入图片描述][1d0cda2fb16845bcb860665f7dba6965.png]  
按照条件加载规则，按需加载组件。

### @ComponentScan ###

> @ComponentScan：扫描那些包的注解。

### 自动配置流程总结 ###

*  SpringBoot优先加载所有的自动配置类（xxxAutoConfiguration）
 *  每个自动配置类按条件进行生效，默认都会绑定配置文件指定的值（@EnableConfigurationProperties(xxxProperties.class)）
 *  xxxProperties.class通过@ConfigurationProperties(prefix = “spring.xxx”)与application.properties配置文件绑定
 *  生效的配置类就会给容器中装配对应的组件
 *  定制化配置
    
     *  用@Bean注解去替换底层的组件
     *  去application.properties配置文件里面修改指定的值

> 我们再以我们熟知的 spring-boot-starter-web 里面的 DispatcherServletAutoConfiguration 完整看一遍

1、org.springframework.boot.autoconfigure.web.servlet 包下面的 DispatcherServletAutoConfiguration（xxxAutoConfiguration）

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE) // 配置文件的生效顺序
    @AutoConfiguration(after = ServletWebServerFactoryAutoConfiguration.class) // 在ServletWebServerFactoryAutoConfiguration配置文件生效后生效
    @ConditionalOnWebApplication(type = Type.SERVLET) // WebApplication的类型是SERVLET
    @ConditionalOnClass(DispatcherServlet.class)// 添加判断：DispatcherServlet.class引入才生效
    public class DispatcherServletAutoConfiguration {
        }

2、因为我们引入了spring-boot-starter-web依赖，所以以上条件都满足，接着往下看

@Configuration(proxyBeanMethods = false) // 不启动代理
    	@Conditional(DefaultDispatcherServletCondition.class) // 满足DefaultDispatcherServletCondition里面的条件
    	@ConditionalOnClass(ServletRegistration.class) // 是否存在ServletRegistration类
    	@EnableConfigurationProperties(WebMvcProperties.class) // 绑定WebMvcProperties配置文件（xxxProperties.class）
    	protected static class DispatcherServletConfiguration {
        
    
            // 给容器中注册组件dispatcherServlet
    		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
    		public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
        
    			DispatcherServlet dispatcherServlet = new DispatcherServlet();
    			// 一系列的默认配置都是从WebMvcProperties配置文件类里面读取的
    			dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
    			dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
    			dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
    			dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
    			dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
    			// 配置好了基本的参数之后，返回dispatcherServlet对象
    			return dispatcherServlet;
    		}
    
            // 给容器中注册文件上传组件multipartResolver
    		@Bean
    		@ConditionalOnBean(MultipartResolver.class) // 系统中有没有MultipartResolver这个bean
    		@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME) // 有没有不叫这个名字“MULTIPART_RESOLVER_BEAN_NAME”的DispatcherServlet类型的bean
    		public MultipartResolver multipartResolver(MultipartResolver resolver) {
        
    			// Detect if the user has created a MultipartResolver but named it incorrectly
    			// 把用户自定义的，不叫“MULTIPART_RESOLVER_BEAN_NAME”的bean注册到容器（已用户自定义的bean优先）
    			return resolver;
    		}
    
    	}

3、细看一下 @EnableConfigurationProperties(WebMvcProperties.class)

// 通过@ConfigurationProperties注解绑定前缀为："spring.mvc"的配置文件，并且每个属性都有一个默认值
    @ConfigurationProperties(prefix = "spring.mvc")
    public class WebMvcProperties {
        
    
    	/**
    	 * Formatting strategy for message codes. For instance, 'PREFIX_ERROR_CODE'.
    	 */
    	private DefaultMessageCodesResolver.Format messageCodesResolverFormat;
    
    	private final Format format = new Format();
    
    	/**
    	 * Whether to dispatch TRACE requests to the FrameworkServlet doService method.
    	 */
    	private boolean dispatchTraceRequest = false;
    
    	/**
    	 * Whether to dispatch OPTIONS requests to the FrameworkServlet doService method.
    	 */
    	private boolean dispatchOptionsRequest = true;
    
    	/**
    	 * Whether the content of the "default" model should be ignored during redirect
    	 * scenarios.
    	 */
    	private boolean ignoreDefaultModelOnRedirect = true;
    
    	/**
    	 * Whether to publish a ServletRequestHandledEvent at the end of each request.
    	 */
    	private boolean publishRequestHandledEvents = true;
    
    	/**
    	 * Whether a "NoHandlerFoundException" should be thrown if no Handler was found to
    	 * process a request.
    	 */
    	private boolean throwExceptionIfNoHandlerFound = false;
    
    	/**
    	 * Whether logging of (potentially sensitive) request details at DEBUG and TRACE level
    	 * is allowed.
    	 */
    	private boolean logRequestDetails;
    
    	/**
    	 * Whether to enable warn logging of exceptions resolved by a
    	 * "HandlerExceptionResolver", except for "DefaultHandlerExceptionResolver".
    	 */
    	private boolean logResolvedException = false;
    
    	/**
    	 * Path pattern used for static resources.
    	 */
    	private String staticPathPattern = "/**";
    
    	private final Async async = new Async();
    
    	private final Servlet servlet = new Servlet();
    
    	private final View view = new View();
    
    	private final Contentnegotiation contentnegotiation = new Contentnegotiation();
    
    	private final Pathmatch pathmatch = new Pathmatch();

可以在配置文件中修改配置文件的默认值，达到定制化修改组件的需求。  
![在这里插入图片描述][8d13a7e8637f4dbe8e542d693700486d.png]

--------------------

## 总结 ##

博客主要记录了@SpringBootApplication的分析，有啥错误或不足地方请指正，如果对你有所帮助，请一键三连。

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