Springboot自动装配
万物皆字节 人气:0原理概述
Springboot向外界提供web服务,底层依赖了springframework中的web模块(包含但不限于spring mvc核心类DispatcherServlet)来实现
那么springboot在什么时机向容器注入DispatcherServlet这个核心类的呢
注入的流程还是遵循了自动装配流程,在springboot框架里默认提供了该自动装配的支持
在jar包里的spring.factories文件里有个 org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration配置
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE) @Configuration(proxyBeanMethods = false) @ConditionalOnWebApplication(type = Type.SERVLET) @ConditionalOnClass(DispatcherServlet.class) @AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class) public class DispatcherServletAutoConfiguration { /* * The bean name for a DispatcherServlet that will be mapped to the root URL "/" */ public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet"; /* * The bean name for a ServletRegistrationBean for the DispatcherServlet "/" * public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration"; // ... 省略代码 }
在DispatcherServletAutoConfiguration中有两个内部类(配置类) DispatcherServletConfiguration、DispatcherServletRegistrationConfiguration和两个对应的Condition类DefaultDispatcherServletCondition、DispatcherServletRegistrationCondition
DispatcherServletConfiguration
DispatcherServletConfiguration是DispatcherServletAutoConfiguration 的一个内部类,并被 @Configuration标注,会被容器自动扫描到;其有两个方法: 1、dispatcherServlet;2、multipartResolver
@Configuration(proxyBeanMethods = false) @Conditional(DefaultDispatcherServletCondition.class) @ConditionalOnClass(ServletRegistration.class) @EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class }) protected static class DispatcherServletConfiguration { // @A @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) public DispatcherServlet dispatcherServlet(HttpProperties httpProperties, WebMvcProperties webMvcProperties) { DispatcherServlet dispatcherServlet = new DispatcherServlet(); dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest()); dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest()); dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound()); dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents()); dispatcherServlet.setEnableLoggingRequestDetails(httpProperties.isLogRequestDetails()); return dispatcherServlet; } // @B @Bean @ConditionalOnBean(MultipartResolver.class) @ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME) public MultipartResolver multipartResolver(MultipartResolver resolver) { // Detect if the user has created a MultipartResolver but named it incorrectly return resolver; } }
@A:
- @Configuration(proxyBeanMethods = false):配置类采用Lite模式
- @Conditional(DefaultDispatcherServletCondition.class):根据DefaultDispatcherServletCondition类返回值计算是否要注入,主要逻辑是检验Spring容器中是否已经存在一个名字为"dispatcherServlet"的DispatcherServlet
- @ConditionalOnClass(ServletRegistration.class):容器中必须要有ServletRegistration类
- @EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class }):加载HttpProperties和WebMvcProperties
@B:注入 MultipartResolver 解析类
DispatcherServletRegistrationConfiguration
该类注入的逻辑与DispatcherServletConfiguration 相同,只不过在类上注解了 @Import(DispatcherServletConfiguration.class)那么这两个类定义就有了先后顺序
@Configuration(proxyBeanMethods = false) @Conditional(DispatcherServletRegistrationCondition.class) @ConditionalOnClass(ServletRegistration.class) @EnableConfigurationProperties(WebMvcProperties.class) @Import(DispatcherServletConfiguration.class) //@A protected static class DispatcherServletRegistrationConfiguration { @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME) @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) { DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet, webMvcProperties.getServlet().getPath()); // 设置名称 registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME); registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup()); multipartConfig.ifAvailable(registration::setMultipartConfig); return registration; } }
其中,DispatcherServletRegistrationBean继承自ServletRegistrationBean,主要为DispatcherServlet提供服务。DispatcherServletRegistrationBean和DispatcherServlet都提供了注册Servlet并公开DispatcherServletPath信息的功能
面试点
spring mvc和spring boot的关系,相信读了上面的文章会说出一两点;
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