1 实战
在Spring Boot项目中,如果使用内嵌Web服务器,可以很方便地注册Servlet
、Filter
和Listener
等组件。
总的来说,包括以下方式:
- 创建实现
ServletContextInitializer
接口的bean,自定义注册逻辑。 - 开启
@ServletCompnentScan
功能,扫描标注@WebServlet
、@WebFilter
或WebListener
的bean。 - 注册实现
Servlet
、Filter
或Listener
接口的bean。
1.1 实现ServletContextInitializer
接口
Spring提供了ServletRegistrationBean
、FilterRegistrationBean
和ServletListenerRegistrationBean
,只需要创建对应bean即可:
@Bean
public ServletRegistrationBean servletRegistrationBean() {
ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean();
// servletRegistrationBean.setServlet(); 设置Servlet
// servletRegistrationBean.addUrlMappings(""); 设置映射地址
return servletRegistrationBean;
}
@Bean
public FilterRegistrationBean filterRegistrationBean() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
// filterRegistrationBean.setFilter(); 设置Filter
return filterRegistrationBean;
}
@Bean
public ServletListenerRegistrationBean servletListenerRegistrationBean() {
ServletListenerRegistrationBean servletListenerRegistrationBean = new ServletListenerRegistrationBean();
// servletListenerRegistrationBean.setListener(); 设置Listener
return servletListenerRegistrationBean;
}
1.2 开启@ServletCompnentScan
功能
在配置类中开启功能:
@Configuration
@ServletComponentScan
public class ServletContextConfig {
}
在对应包下添加对应bean:
@Component
@WebServlet
public class MyServlet implements Servlet {
}
@Component
@WebFilter
public class MyFilter implements Filter {
}
@Component
@WebListener
public class MyListener implements EventListener {
}
1.3 实现Servlet
、Filter
或Listener
接口
实现Servlet
、Filter
或Listener
接口:
@Component
public class MyServlet implements Servlet {
}
@Component
public class MyFilter implements Filter {
}
@Component
public class MyListener implements EventListener {
}
2 源码
2.1 ServletContextInitializer
web服务器在初始化时,会调用ServletContextInitializer#onStartup()方法进行自定义注册。
在ServletWebServerApplicationContext
的onRefresh()
阶段,会创建Web服务器:
protected void onRefresh() {
// 调用父类的onRefresh()方法
super.onRefresh();
try {
// 创建web服务器
createWebServer();
}
catch (Throwable ex) {
// 抛异常
}
}
在ServletWebServerApplicationContext#createWebServer()
方法中,会创建并初始化web服务器:
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
if (webServer == null && servletContext == null) {
// 获取factory
ServletWebServerFactory factory = getWebServerFactory();
// 传入getSelfInitializer(),创建web服务器
this.webServer = factory.getWebServer(getSelfInitializer());
}
else if (servletContext != null) {
// 初始化servletContext
getSelfInitializer().onStartup(servletContext);
}
}
ServletWebServerApplicationContext#getSelfInitializer()
是一个方法引用(匿名对象):
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
return this::selfInitialize;
}
会在后续服务器初始化调用ServletContextInitializer#onStartup()
方法时,触发ServletWebServerApplicationContext#selfInitialize()
方法:
private void selfInitialize(ServletContext servletContext) throws ServletException {
// 遍历调用org.springframework.boot.web.servlet.ServletContextInitializer#onStartup()
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
ServletWebServerApplicationContext#getServletContextInitializerBeans()
方法会返回ServletContextInitializerBeans
对象:
protected Collection<ServletContextInitializer> getServletContextInitializerBeans() {
return new ServletContextInitializerBeans(getBeanFactory());
}
ServletContextInitializerBeans#ServletContextInitializerBeans()
方法中定义了获取ServletContextInitializer的逻辑:
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class<? extends ServletContextInitializer>... initializerTypes) {
this.initializers = new LinkedMultiValueMap<>();
this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
: Collections.singletonList(ServletContextInitializer.class);
// 添加ServletContextInitializer
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);
}
ServletContextInitializerBeans#addServletContextInitializerBeans()
方法会从容器中获取ServletContextInitializer实现类,
private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) {
// 从容器中获取ServletContextInitializer实现类
for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory,
initializerType)) {
addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
}
}
}
ServletContextInitializerBeans#addServletContextInitializerBean()
会注册ServletContextInitializer实现类:
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);
}
}
三种内嵌容器的初始化流程都很相似。对于内嵌Tomcat,它的初始化流程如下:
TomcatServletWebServerFactory#getWebServer()
和TomcatWebServer#TomcatWebServer()
方法创建服务器。- 在创建服务器过程中,将
selfInitialize
添加到TomcatStarter
中。 TomcatWebServer#initialize()
方法初始化服务器。Tomcat#start()
和LifecycleBase#start()
启动服务器。StandardContext#startInternal()
启动上下文。javax.servlet.ServletContainerInitializer#onStartup()
初始化容器。
org.springframework.boot.web.embedded.tomcat.TomcatStarter
实现了javax.servlet.ServletContainerInitializer
,所以会直接触发前者的onStartup()
方法。需要注意全限定类名的不同,TomcatStarter
在这里起着适配器的作用:
public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {
try {
// 遍历所有org.springframework.boot.web.servlet.ServletContextInitializer
for (ServletContextInitializer initializer : this.initializers) {
initializer.onStartup(servletContext);
}
}
catch (Exception ex) {
}
}
理论上,我们只需要注册实现org.springframework.boot.web.servlet.ServletContextInitializer
的bean,就可以在服务器初始化时进行额外操作,例如注册Servlet
、Filter
和Listener
。
实际上,Spring提供了专门用来注册Servlet
、Filter
和Listener
的实现类,它们定义好了注册三大组件的模板方法,更加方便开发人员使用:
org.springframework.boot.web.servlet.ServletRegistrationBean
:注册Servlet。org.springframework.boot.web.servlet.FilterRegistrationBean
:注册Filter。org.springframework.boot.web.servlet.ServletListenerRegistrationBean
:注册Listener。
这些实现的使用方式都十分简单,只需要设置对应成员变量即可。
org.springframework.boot.web.servlet.ServletRegistrationBean:
org.springframework.boot.web.servlet.FilterRegistrationBean:
org.springframework.boot.web.servlet.ServletListenerRegistrationBean
2.2 @ServletComponentScan
@ServletComponentScan
会将指定路径下标注@WebServlet、@WebFilter或@WebListener的bean注册成三大组件。
将@ServletComponentScan
标注到配置类上,会将指定路径下标注@WebServlet
、@WebFilter
或@WebListener
的bean注册到web服务器中。
@ServletComponentScan
源码如下,它会导入ServletComponentScanRegistrar
:
@Import(ServletComponentScanRegistrar.class)
public @interface ServletComponentScan {
@AliasFor("basePackages")
String[] value() default {};
@AliasFor("value")
String[] basePackages() default {};
Class<?>[] basePackageClasses() default {};
}
ServletComponentScanRegistrar
会注册servletComponentRegisteringPostProcessor
作为BeanFactoryPostProcessor。ServletComponentScanRegistrar#registerBeanDefinitions()
:
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
Set<String> packagesToScan = getPackagesToScan(importingClassMetadata);
if (registry.containsBeanDefinition(BEAN_NAME)) {
updatePostProcessor(registry, packagesToScan);
}
else {
addPostProcessor(registry, packagesToScan);
}
}
ServletComponentRegisteringPostProcessor#postProcessBeanFactory()
方法会从容器中获取指定路径下、标注@WebServlet
、@WebFilter
或@WebListener
的BeanDefinition,然后使用ServletComponentHandler进行处理:
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
if (isRunningInEmbeddedWebServer()) {
ClassPathScanningCandidateComponentProvider componentProvider = createComponentProvider();
for (String packageToScan : this.packagesToScan) {
// 扫描指定路径
scanPackage(componentProvider, packageToScan);
}
}
}
ServletComponentRegisteringPostProcessor#scanPackage()
方法中定义了实际扫描逻辑:
private void scanPackage(ClassPathScanningCandidateComponentProvider componentProvider, String packageToScan) {
// 获取指定路径下的BeanDefinition
for (BeanDefinition candidate : componentProvider.findCandidateComponents(packageToScan)) {
// 过滤注解标注的BeanDefinition
if (candidate instanceof AnnotatedBeanDefinition) {
// 使用ServletComponentHandler进行分别处理
for (ServletComponentHandler handler : HANDLERS) {
handler.handle(((AnnotatedBeanDefinition) candidate),
(BeanDefinitionRegistry) this.applicationContext);
}
}
}
}
org.springframework.boot.web.servlet.ServletComponentHandler#handle()
方法会对@WebServlet
、@WebFilter
或@WebListener
进行过滤:
void handle(AnnotatedBeanDefinition beanDefinition, BeanDefinitionRegistry registry) {
Map<String, Object> attributes = beanDefinition.getMetadata()
.getAnnotationAttributes(this.annotationType.getName());
if (attributes != null) {
doHandle(attributes, beanDefinition, registry);
}
}
WebServletHandler#doHandle()
方法会注册一个ServletRegistrationBean
:
public void doHandle(Map<String, Object> attributes, AnnotatedBeanDefinition beanDefinition,
BeanDefinitionRegistry registry) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(ServletRegistrationBean.class);
builder.addPropertyValue("asyncSupported", attributes.get("asyncSupported"));
builder.addPropertyValue("initParameters", extractInitParameters(attributes));
builder.addPropertyValue("loadOnStartup", attributes.get("loadOnStartup"));
String name = determineName(attributes, beanDefinition);
builder.addPropertyValue("name", name);
// 设置servlet
builder.addPropertyValue("servlet", beanDefinition);
builder.addPropertyValue("urlMappings", extractUrlPatterns(attributes));
builder.addPropertyValue("multipartConfig", determineMultipartConfig(beanDefinition));
registry.registerBeanDefinition(name, builder.getBeanDefinition());
}
WebFilterHandler#doHandle()
方法会注册一个FilterRegistrationBean
:
public void doHandle(Map<String, Object> attributes, AnnotatedBeanDefinition beanDefinition,
BeanDefinitionRegistry registry) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(FilterRegistrationBean.class);
builder.addPropertyValue("asyncSupported", attributes.get("asyncSupported"));
builder.addPropertyValue("dispatcherTypes", extractDispatcherTypes(attributes));
builder.addPropertyValue("filter", beanDefinition);
builder.addPropertyValue("initParameters", extractInitParameters(attributes));
String name = determineName(attributes, beanDefinition);
builder.addPropertyValue("name", name);
builder.addPropertyValue("servletNames", attributes.get("servletNames"));
builder.addPropertyValue("urlPatterns", extractUrlPatterns(attributes));
registry.registerBeanDefinition(name, builder.getBeanDefinition());
}
WebListenerHandler#doHandle()
方法会注册一个ServletComponentWebListenerRegistrar
:
protected void doHandle(Map<String, Object> attributes, AnnotatedBeanDefinition beanDefinition,
BeanDefinitionRegistry registry) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder
.rootBeanDefinition(ServletComponentWebListenerRegistrar.class);
builder.addConstructorArgValue(beanDefinition.getBeanClassName());
registry.registerBeanDefinition(beanDefinition.getBeanClassName() + "Registrar", builder.getBeanDefinition());
}
不同于其他两个,ServletComponentWebListenerRegistrar实现了WebListenerRegistrar
接口,会在org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryCustomizer#customize()
方法被触发:
public void customize(ConfigurableServletWebServerFactory factory) {
for (WebListenerRegistrar registrar : this.webListenerRegistrars) {
registrar.register(factory);
}
}
ServletWebServerFactoryCustomizer
会被Spring Boot自动配置机制注入,并添加上述WebListenerRegistrar实现类。同时,还会注册ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar
:
// 注册ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class})
public class ServletWebServerFactoryAutoConfiguration {
// 注册ServletWebServerFactoryCustomizer
@Bean
public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(ServerProperties serverProperties,
ObjectProvider<WebListenerRegistrar> webListenerRegistrars,
ObjectProvider<CookieSameSiteSupplier> cookieSameSiteSuppliers) {
return new ServletWebServerFactoryCustomizer(serverProperties,
webListenerRegistrars.orderedStream().collect(Collectors.toList()),
cookieSameSiteSuppliers.orderedStream().collect(Collectors.toList()));
}
}
WebServerFactoryCustomizerBeanPostProcessor#postProcessBeforeInitialization()
方法会触发ServletWebServerFactoryCustomizer#customize()
的执行:
private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
LambdaSafe.callbacks(WebServerFactoryCustomizer.class, getCustomizers(), webServerFactory)
.withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
.invoke((customizer) -> customizer.customize(webServerFactory));
}
2.3 ServletContextInitializerBeans#addAdaptableBeans
ServletContextInitializerBeans#addAdaptableBeans()
方法会注册实现Servlet、Filter或Listener接口的bean作为三大组件。
之前说过,会在服务器初始化调用ServletContextInitializer#onStartup()
方法时,触发ServletWebServerApplicationContext#selfInitialize()
方法:
private void selfInitialize(ServletContext servletContext) throws ServletException {
// 遍历调用org.springframework.boot.web.servlet.ServletContextInitializer#onStartup()
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
getServletContextInitializerBeans()
方法会创建ServletContextInitializerBeans
对象。
ServletContextInitializerBeans#ServletContextInitializerBeans()
方法中定义了获取ServletContextInitializer的逻辑:
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);
// 扫描实现Servlet、Filter或EventListener的bean
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);
}
ServletContextInitializerBeans#addAdaptableBeans()
方法会从容器获取所有实现javax.servlet.Servlet
、javax.servlet.Filter
或java.util.EventListener
的bean,为它们创建对应的RegistrationBean
实现类:
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
// 扫描&注册Servlet实现类
addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
// 扫描&注册Filter实现类
addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
// 扫描&注册EventListener实现类
for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
new ServletListenerRegistrationBeanAdapter());
}
}
ServletContextInitializerBeans#addAsRegistrationBean()
定义了具体扫描&注册逻辑:
private <T, B extends T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type,
Class<B> beanType, RegistrationBeanAdapter<T> adapter) {
// 从容器中获取指定类型的bean
List<Map.Entry<String, B>> entries = getOrderedBeansOfType(beanFactory, beanType, this.seen);
for (Entry<String, B> entry : entries) {
String beanName = entry.getKey();
B bean = entry.getValue();
// 添加缓存
if (this.seen.add(bean)) {
// 创建对应RegistrationBean实现类
RegistrationBean registration = adapter.createRegistrationBean(beanName, bean, entries.size());
// 根据@Order注解设置执行顺序
int order = getOrder(bean);
registration.setOrder(order);
this.initializers.add(type, registration);
}
}
}
创建RegistrationBean实现类的逻辑位于对应的RegistrationBeanAdapter
实现类中。
ServletContextInitializerBeans.ServletRegistrationBeanAdapter#createRegistrationBean()
方法创建ServletRegistrationBean:
public RegistrationBean createRegistrationBean(String name, Servlet source, int totalNumberOfSourceBeans) {
String url = (totalNumberOfSourceBeans != 1) ? "/" + name + "/" : "/";
if (name.equals(DISPATCHER_SERVLET_NAME)) {
url = "/"; // always map the main dispatcherServlet to "/"
}
ServletRegistrationBean<Servlet> bean = new ServletRegistrationBean<>(source, url);
bean.setName(name);
bean.setMultipartConfig(this.multipartConfig);
return bean;
}
ServletContextInitializerBeans.FilterRegistrationBeanAdapter#createRegistrationBean()
方法创建FilterRegistrationBean:
public RegistrationBean createRegistrationBean(String name, Filter source, int totalNumberOfSourceBeans) {
FilterRegistrationBean<Filter> bean = new FilterRegistrationBean<>(source);
bean.setName(name);
return bean;
}
ServletContextInitializerBeans.ServletListenerRegistrationBeanAdapter#createRegistrationBean()
方法创建ServletListenerRegistrationBean:
public RegistrationBean createRegistrationBean(String name, EventListener source,
int totalNumberOfSourceBeans) {
return new ServletListenerRegistrationBean<>(source);
}
标签:Filter,SpringBoot,beanFactory,builder,class,Listener,bean,public,ServletContextI
From: https://www.cnblogs.com/Xianhuii/p/17124058.html