Tomcat容器启动org.apache.catalina.util.LifecycleBase#startInternal，根据当前Spring工厂创建一个ServletContextInitializerBeans对象（其实就是收集各种Servlet元素）
@SafeVarargs
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class<? extends ServletContextInitializer>... initializerTypes) {
this.initializers = new LinkedMultiValueMap<>();
this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
: Collections.singletonList(ServletContextInitializer.class);
addServletContextInitializerBeans(beanFactory);
addAdaptableBeans(beanFactory);
List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
logMappings(this.initializers);
}
addServletContextInitializerBeans
org.springframework.boot.web.servlet.ServletContextInitializerBeans#getOrderedBeansOfType(org.springframework.beans.factory.ListableBeanFactory, java.lang.Class<T>, java.util.Set<?>)
private <T> List<Entry<String, T>> getOrderedBeansOfType(ListableBeanFactory beanFactory, Class<T> type,
Set<?> excludes) {
String[] names = beanFactory.getBeanNamesForType(type, true, false);
Map<String, T> map = new LinkedHashMap<>();
for (String name : names) {
if (!excludes.contains(name) && !ScopedProxyUtils.isScopedTarget(name)) {
T bean = beanFactory.getBean(name, type);
if (!excludes.contains(bean)) {
map.put(name, bean);
}
}
}
List<Entry<String, T>> beans = new ArrayList<>();
beans.addAll(map.entrySet());
beans.sort((o1, o2) -> AnnotationAwareOrderComparator.INSTANCE.compare(o1.getValue(), o2.getValue()));
return beans;
}
获取所有ServletContextInitializer类型的Bean名称，然后获取Bean，排序并返回。结果如下
接下来在addServletContextInitializerBeans方法中遍历以上的结果，并根据类型（Servlet、Filter、ServletContextInitializer等类型）进行分组
private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory) {
if (initializer instanceof ServletRegistrationBean) {
Servlet source = ((ServletRegistrationBean<?>) initializer).getServlet();
addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof FilterRegistrationBean) {
Filter source = ((FilterRegistrationBean<?>) initializer).getFilter();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof ServletListenerRegistrationBean) {
EventListener source = ((ServletListenerRegistrationBean<?>) initializer).getListener();
addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
}
else {
addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
initializer);
}
}
分组的结果如下，有两个Filter（分别为监控、安全），一个Servlet（DispatchServlet）和一个Servlet上下文初始器（用于actuator）。
- dispatcherServletRegistration
配置Spring Boot的SERVLET环境
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration.DispatcherServletRegistrationConfiguration#dispatcherServletRegistration
@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet) {
DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
this.webMvcProperties.getServlet().getPath());
registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
registration.setLoadOnStartup(this.webMvcProperties.getServlet().getLoadOnStartup());
if (this.multipartConfig != null) {
registration.setMultipartConfig(this.multipartConfig);
}
return registration;
}
- webMvcMetricsFilter
来源包：spring-boot-actuator-autoconfigure（性能监控）
来源类：org.springframework.boot.actuate.autoconfigure.metrics.web.servlet.WebMvcMetricsAutoConfiguration
@Bean
public FilterRegistrationBean<WebMvcMetricsFilter> webMvcMetricsFilter(MeterRegistry registry,
WebMvcTagsProvider tagsProvider) {
Server serverProperties = this.properties.getWeb().getServer();
WebMvcMetricsFilter filter = new WebMvcMetricsFilter(registry, tagsProvider,
serverProperties.getRequestsMetricName(), serverProperties.isAutoTimeRequests());
FilterRegistrationBean<WebMvcMetricsFilter> registration = new FilterRegistrationBean<>(filter);
registration.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
registration.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.ASYNC);
return registration;
}
- securityFilterChainRegistration
来源包：spring-boot-autoconfigure（认证授权）
来源类：org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration
Auto-configuration for Spring Security’s Filter. Configured separately from SpringBootWebSecurityConfiguration to ensure that the filter’s order is still configured when a user-provided WebSecurityConfiguration exists.
@Bean
@ConditionalOnBean(name = DEFAULT_FILTER_NAME)
public DelegatingFilterProxyRegistrationBean securityFilterChainRegistration(
SecurityProperties securityProperties) {
DelegatingFilterProxyRegistrationBean registration = new DelegatingFilterProxyRegistrationBean(
DEFAULT_FILTER_NAME);
registration.setOrder(securityProperties.getFilter().getOrder());
registration.setDispatcherTypes(getDispatcherTypes(securityProperties));
return registration;
}
创建Bean的过程首先会实例化一个DispatcherServletRegistrationBean对象，这里并没有复杂的逻辑不过是设置targetBeanName为springSecurityFilterChain。
然后根据securityProperties设置属性，包括顺序、收集分派类型。
private EnumSet<DispatcherType> getDispatcherTypes(SecurityProperties securityProperties) {
if (securityProperties.getFilter().getDispatcherTypes() == null) {
return null;
}
return securityProperties.getFilter().getDispatcherTypes().stream()
.map((type) -> DispatcherType.valueOf(type.name()))
.collect(Collectors.collectingAndThen(Collectors.toSet(), EnumSet::copyOf));
}
创建流、收集、然后转为EnumSet.实例化对象如下所示
然后这个类又实现了ApplicationContextAware接口，所以在Bean初始化阶段又会进入到setApplicationContext方法当中。
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
这里的逻辑比较简单，仅仅是设置了Spring上下文对象。
- servletEndpointRegistrar
来源包：spring-boot-actuator-autoconfigure（性能监控）
来源类：org.springframework.boot.actuate.autoconfigure.endpoint.web.ServletEndpointManagementContextConfiguration.WebMvcServletEndpointManagementContextConfiguration
ManagementContextConfiguration for servlet endpoints.
@Configuration
@ConditionalOnClass(DispatcherServlet.class)
public static class WebMvcServletEndpointManagementContextConfiguration {
private final ApplicationContext context;
public WebMvcServletEndpointManagementContextConfiguration(ApplicationContext context) {
this.context = context;
}
@Bean
public ServletEndpointRegistrar servletEndpointRegistrar(WebEndpointProperties properties,
ServletEndpointsSupplier servletEndpointsSupplier) {
DispatcherServletPath dispatcherServletPath = this.context.getBean(DispatcherServletPath.class);
return new ServletEndpointRegistrar(dispatcherServletPath.getRelativePath(properties.getBasePath()),
servletEndpointsSupplier.getEndpoints());
}
}
比较简单吗，注册一堆的```EndpointServlet``
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
this.servletEndpoints.forEach((servletEndpoint) -> register(servletContext, servletEndpoint));
}
private void register(ServletContext servletContext, ExposableServletEndpoint endpoint) {
String name = endpoint.getEndpointId().toLowerCaseString() + "-actuator-endpoint";
String path = this.basePath + "/" + endpoint.getRootPath();
String urlMapping = path.endsWith("/") ? path + "*" : path + "/*";
EndpointServlet endpointServlet = endpoint.getEndpointServlet();
Dynamic registration = servletContext.addServlet(name, endpointServlet.getServlet());
registration.addMapping(urlMapping);
registration.setInitParameters(endpointServlet.getInitParameters());
logger.info("Registered '" + path + "' to " + name);
}
首先是读取WebEndpointProperties类型Bean获取配置的属性，这些属性的前缀为management.endpoints.web。接下来获取DispatcherServletPath类型的Bean。而这个实现在默认情况下为DispatcherServletRegistrationBean。其实就上面名称为dispatcherServletRegistration的Bean。
在创建Bean的过程中主要是根据传入的basePath和servlet断点设置值而已。
比较简单，结果如下
addAdaptableBeans
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
new ServletListenerRegistrationBeanAdapter());
}
}
接下来从容器中获取MultipartConfigElement类型Bean，主要是用于文件上传的配置信息。
然后再次到容器中获取Servlet和Filter，前者只有DispatchServlet（已经处理过了），后者还有其他的一些配置，比如以下这些都是系统默认需要的。
接下来还会考虑加载EventListener类型Bean.
其中SUPPORTED_TYPES在类加载的时候添加的，这些都属于Servlet规范了。
public class ServletListenerRegistrationBean<T extends EventListener> extends RegistrationBean {
private static final Set<Class<?>> SUPPORTED_TYPES;
static {
Set<Class<?>> types = new HashSet<>();
types.add(ServletContextAttributeListener.class);
types.add(ServletRequestListener.class);
types.add(ServletRequestAttributeListener.class);
types.add(HttpSessionAttributeListener.class);
types.add(HttpSessionListener.class);
types.add(ServletContextListener.class);
SUPPORTED_TYPES = Collections.unmodifiableSet(types);
}
...
}
通过以上步骤，收集到的Servlet元素如下所示
接下来通过流处理（针对每一个map的条目值排序然后通过flatMap转给一个流收集为列表）为列表，然后转为不可修改列表设置为对象属性，并根据日志级别打印日志（org.springframework.boot.web.servlet.ServletContextInitializerBeans为Debug级别）。
List<ServletContextInitializer> sortedInitializers = this.initializers.values()
.stream()
.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
logMappings(this.initializers);
最后再回过头来看一下ServletContextInitializerBeans这个类的类型。
竟然是一个集合，而针对这个集合的迭代就是迭代上面获取的排序好的列表。
@Override
public Iterator<ServletContextInitializer> iterator() {
return this.sortedList.iterator();
}
@Override
public int size() {
return this.sortedList.size();
}