springboot 自动注入servlet原理

前置内容： servlet的多种注册方式

SpringBoot启用 ServletContainerInitializer

ServletContainerInitializer-SPI

SPI部分内容参照 servlet的多种注册方式

开启SPI

默认情况下，springboot 使用 embedded-tomcat,没有启用ServletContainerInitializer，这就需要我们做改造。

pom.xml

 <dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId><exclusions><exclusion><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-tomcat</artifactId></exclusion></exclusions></dependency><!--添加servlet的依赖--><dependency><groupId>javax.servlet</groupId><artifactId>javax.servlet-api</artifactId><version>3.1.0</version><scope>provided</scope></dependency>

App.java 继承 SpringBootServletInitializer

@SpringBootApplication
public class App extends SpringBootServletInitializer {/*   public static void main(String[] args) {SpringApplication.run(App.class, args);}
*//*    @Overrideprotected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {return builder.sources(App.class);}*/
}

springboot SPI

增加Filter配置类

@Configuration
public class SpringFilterConfiguration {@Beanpublic FilterRegistrationBean<SpringFilter1> SpringFilter1() {FilterRegistrationBean<SpringFilter1> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new SpringFilter1());registrationBean.setName("springfilter11");registrationBean.addUrlPatterns("/*");registrationBean.setOrder(11);return registrationBean;}@Beanpublic FilterRegistrationBean<SpringFilter2> SpringFilter2() {FilterRegistrationBean<SpringFilter2> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new SpringFilter2());registrationBean.setName("springfilter22");registrationBean.addUrlPatterns("/*");registrationBean.setOrder(22);return registrationBean;}
}

源码分析

1. SpringServletContainerInitializer

@HandlesTypes(WebApplicationInitializer.class) //lookup 实现WebApplicationInitializer的类
public class SpringServletContainerInitializer implements ServletContainerInitializer {@Overridepublic void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)throws ServletException {List<WebApplicationInitializer> initializers = new ArrayList<>(webAppInitializerClasses.size());for (Class<?> waiClass : webAppInitializerClasses) {initializers.add((WebApplicationInitializer) ReflectionUtils.accessibleConstructor(waiClass).newInstance());}AnnotationAwareOrderComparator.sort(initializers);for (WebApplicationInitializer initializer : initializers) { //  2. 此时值为App.classinitializer.onStartup(servletContext); }}
}

2.App

类图

App为我们的主类，它的泪如如下。

3.SpringBootServletInitializer.onStartup(servletContext)

程序的最终入口就在此了。

public abstract class SpringBootServletInitializer implements WebApplicationInitializer {@Overridepublic void onStartup(ServletContext servletContext) throws ServletException {WebApplicationContext rootApplicationContext = createRootApplicationContext(servletContext); // 3.1if (rootApplicationContext != null) {servletContext.addListener(new SpringBootContextLoaderListener(rootApplicationContext, servletContext)); //3.2}}//3.1protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) {SpringApplicationBuilder builder = createSpringApplicationBuilder(); // new SpringApplicationBuilder()builder.main(getClass()); // getClass() == App.class//parent部分略....builder.initializers(new ServletContextApplicationContextInitializer(servletContext));  //3.1.1builder.contextFactory((webApplicationType) -> new AnnotationConfigServletWebServerApplicationContext()); //3.1.2 factory 直接返回new AnnotationConfigServletWebServerApplicationContext(); extends ServletWebServerApplicationContextbuilder = configure(builder); //do nothingbuilder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext)); //3.1.3SpringApplication application = builder.build(); // 返回 SpringApplicationapplication.addPrimarySources(Collections.singleton(getClass())); //3.1.4application.setRegisterShutdownHook(false);return run(application);}protected WebApplicationContext run(SpringApplication application) {return (WebApplicationContext) application.run(); //执行 SpringApplication.run()}}

4. SpringApplication.run()

SpringApplication.run()的逻辑不再赘述，最终会调用AbstractApplicationContext.onRefresh(),而此时的ApplicationContext的具体实现类为AnnotationConfigServletWebServerApplicationContext

public class SpringApplication {private List<ApplicationContextInitializer<?>> initializers;         //3.1.1private List<ApplicationListener<?>> listeners;                //3.1.3private ApplicationContextFactory applicationContextFactory = ApplicationContextFactory.DEFAULT; //3.1.2private Set<Class<?>> primarySources;  //3.1.4public ConfigurableApplicationContext run(String... args) {DefaultBootstrapContext bootstrapContext = createBootstrapContext();ConfigurableApplicationContext context = null;configureHeadlessProperty();SpringApplicationRunListeners listeners = getRunListeners(args);listeners.starting(bootstrapContext, this.mainApplicationClass);ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext(); // applicationContextFactory.create()//3.1.2 return AnnotationConfigServletWebServerApplicationContext();context.setApplicationStartup(this.applicationStartup);prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);refreshContext(context); // ConfigurableApplicationContext.refresh();   ---> AbstractApplicationContext.onRefresh();afterRefresh(context, applicationArguments);Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);}listeners.started(context, timeTakenToStartup);callRunners(context, applicationArguments);return context;}}

5.AnnotationConfigServletWebServerApplicationContext.onRefresh()

类图

ServletWebServerApplicationContext.onRefresh()

public class ServletWebServerApplicationContext extends GenericWebApplicationContextimplements ConfigurableWebServerApplicationContext {@Overrideprotected void onRefresh() {super.onRefresh();createWebServer(); // factory.getWebServer(getSelfInitializer());}private void selfInitialize(ServletContext servletContext) throws ServletException {prepareWebApplicationContext(servletContext);registerApplicationScope(servletContext);WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);for (ServletContextInitializer beans : getServletContextInitializerBeans()) {  beanFactory.getBeanNamesForType(ServletContextInitializer.class);beans.onStartup(servletContext); //6}}
}

6.ServletContextInitializer.onStartup

类图

AbstractFilterRegistrationBean.addRegistration()

//6. FilterRegistrationBean -> AbstractFilterRegistrationBean -> DynamicRegistrationBean  -> RegistrationBean
public abstract class AbstractFilterRegistrationBean<T extends Filter> extends DynamicRegistrationBean<Dynamic> {@Overrideprotected Dynamic addRegistration(String description, ServletContext servletContext) {Filter filter = getFilter();return servletContext.addFilter(getOrDeduceName(filter), filter);}}

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