一、注册
@Bean
public FilterRegistrationBean filterTestRegistrationBean(){
FilterRegistrationBean filterRegistry = new FilterRegistrationBean();
filterRegistry.setOrder(Ordered.HIGHEST_PRECEDENCE + 3);
//注册过滤器
filterRegistry.setFilter(new ShallowEtagHeaderFilter());
filterRegistry.addUrlPatterns("/*");
filterRegistry.setName("eTagFilter");
return filterRegistry;
}
二、流程分析
1.加载ServletContextInitializer
（1）项目中使用的服务是undertow，所以就以服务undertow为例，
服务创建工厂UndertowServletWebServerFactory中的内部类Initializer，实现了ServletContainerInitializer接口，接口中就一个onStartup( )方法，会在服务创建过程中调用
public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {
for (ServletContextInitializer initializer : this.initializers) {
initializer.onStartup(servletContext);
}
}
（2）这里的initializers列表，其中之一是ServletWebServerApplicationContext中的lambda表达式，如下
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
//lambda表达式
return this::selfInitialize;
}
//具体实现
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
registerApplicationScope(servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
//调用ServletContextInitializer 的onStartup()
beans.onStartup(servletContext);
}
}
（3）ServletContextInitializer 的获取
protected Collection<ServletContextInitializer> getServletContextInitializerBeans() {
return new ServletContextInitializerBeans(getBeanFactory());
}
（4）ServletContextInitializerBeans的构造方法
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class<? extends ServletContextInitializer>... initializerTypes) {
this.initializers = new LinkedMultiValueMap<>();
this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
: Collections.singletonList(ServletContextInitializer.class);
//从beanFactory获取ServletContextInitializerBeans
addServletContextInitializerBeans(beanFactory);
//从beanFactory获取Servlet、Filter、EventListener，注册为RegistrationBean
addAdaptableBeans(beanFactory);
//根据@Order排序
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);
}
（5）addServletContextInitializerBeans(beanFactory)，通过ServletContextInitializer类型从beanFactory中获取bean，实现接口ServletContextInitializer的bean如FilterRegistrationBean、ServletListenerRegistrationBean等bean会被获取到，然后调用addServletContextInitializerBean( )方法注册bean
private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) {
for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory,
initializerType)) {
addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
}
}
}
（6）addServletContextInitializerBean( )
private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory) {
if (initializer instanceof ServletRegistrationBean) {
Servlet source = ((ServletRegistrationBean<?>) initializer).getServlet();
//ServletRegistrationBean Servlet.class
addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof FilterRegistrationBean) {
Filter source = ((FilterRegistrationBean<?>) initializer).getFilter();
//过滤器 FilterRegistrationBean Filter.class
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
//过滤器 DelegatingFilterProxyRegistrationBean Filter.class
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof ServletListenerRegistrationBean) {
EventListener source = ((ServletListenerRegistrationBean<?>) initializer).getListener();
//监听器 ServletListenerRegistrationBean EventListener.class
addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
}
else {
//ServletContextInitializer.class
addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
initializer);
}
}
private void addServletContextInitializerBean(Class<?> type, String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory, Object source) {
//保存到多值的map中 MultiValueMap
this.initializers.add(type, initializer);
if (source != null) {
// Mark the underlying source as seen in case it wraps an existing bean
this.seen.add(source);
}
if (logger.isTraceEnabled()) {
String resourceDescription = getResourceDescription(beanName, beanFactory);
int order = getOrder(initializer);
logger.trace("Added existing " + type.getSimpleName() + " initializer bean '" + beanName + "'; order="
+ order + ", resource=" + resourceDescription);
}
}
2.注册ServletContextInitializer
（7）获取ServletContextInitializer后，回到第（2）步中，调用onStartup( )，将Servlet、Filter、EventListener注册到servletContext中，源码不展开分析了
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
//调用ServletContextInitializer 的onStartup()
beans.onStartup(servletContext);
}
（8）RegistrationBean.onStartup( )
@Override
public final void onStartup(ServletContext servletContext) throws ServletException {
//获取描述信息
String description = getDescription();
if (!isEnabled()) {
logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
return;
}
//注册，以Filter为例
register(description, servletContext);
}
（9）register( )
DynamicRegistrationBean.java
protected final void register(String description, ServletContext servletContext) {
//注册
D registration = addRegistration(description, servletContext);
if (registration == null) {
logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
return;
}
//配置
configure(registration);
}
protected Dynamic addRegistration(String description, ServletContext servletContext) {
//获取到Filter
Filter filter = getFilter();
//注册Filter
return servletContext.addFilter(getOrDeduceName(filter), filter);
}
public FilterRegistration.Dynamic addFilter(final String filterName, final Filter filter) {
ensureNotProgramaticListener();
ensureNotInitialized();
final DeploymentInfo deploymentInfo = getDeploymentInfo();
if (deploymentInfo.getFilters().containsKey(filterName)) {
return null;
}
//创建FilterInfo
FilterInfo f = new FilterInfo(filterName, filter.getClass(), new ImmediateInstanceFactory<>(filter));
//添加到DeploymentInfo中filters
deploymentInfo.addFilter(f);
//添加到DeploymentImpl的filters中
deployment.getFilters().addFilter(f);
return new FilterRegistrationImpl(f, deployment, this);
}
总结
ServletContextInitializer onStartup 注册Filter、Servlet、EventListener。