一、配置嵌入式 Servlet 容器
SpringBoot默认使用Tomcat作为嵌入式的Servlet容器
引发问题？
1、如何定制和修改Servlet容器的相关配置？
2、注册Servlet三大组件【Servlet、Filter、Listener】？
二、如何定制和修改Servlet容器的相关配置
1、修改和 server 有关的配置（与 ServerProperties 类相对应）
server.port=8081
server.context‐path=/crud
server.tomcat.uri‐encoding=UTF‐8
//通用的Servlet容器设置
server.xxx
//Tomcat的设置
server.tomcat.xxx
2、编写一个EmbeddedServletContainerCustomizer：嵌入式的Servlet容器的定制器；来修改Servlet容器的配置
@Configuration
public class MyMvcConfig extends WebMvcConfigurerAdapter {
@Bean //一定要将这个定制器加入到容器中
public EmbeddedServletContainerCustomizer embeddedServletContainerCustomizer(){
return new EmbeddedServletContainerCustomizer() {
//定制嵌入式的Servlet容器相关的规则
@Override
public void customize(ConfigurableEmbeddedServletContainer container) {
container.setPort(8083);
}
};
}
}
其实这两种方式本质是一样的，ServerProperties 类也实现了 EmbededServletContainerCustomizer 接口，重写了 customize 方法，然后把配置文件中的值设置给 container。
三、注册Servlet三大组件【Servlet、Filter、Listener】
由于SpringBoot默认是以jar包的方式启动嵌入式的Servlet容器来启动SpringBoot的web应用，没有web.xml文件。
注册三大组件：
（1）注册 servlet
public class MyServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.getWriter().write("Hello, MyServlet!");
}
}
---
@Bean
public ServletRegistrationBean myServlet() {
ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new MyServlet(), "/myServlet");
servletRegistrationBean.setLoadOnStartup(1);
return servletRegistrationBean;
}
（2）注册 filter
public class MyFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("MyFilter...process");
filterChain.doFilter(servletRequest, servletResponse);
}
@Override
public void destroy() {
}
}
---
@Bean
public FilterRegistrationBean myFilter() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
filterRegistrationBean.setFilter(new MyFilter());
filterRegistrationBean.setUrlPatterns(Arrays.asList("/hello", "/myServlet"));
return filterRegistrationBean;
}
（3）注册 listener
public class MyListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
System.out.println("contextInitialized... Web 应用启动");
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
System.out.println("contextDestroyed... Web 应用销毁");
}
}
---
@Bean
public ServletListenerRegistrationBean myListener() {
ServletListenerRegistrationBean<MyListener> servletListenerRegistrationBean = new ServletListenerRegistrationBean<>(new MyListener());
return servletListenerRegistrationBean;
}
SpringBoot 中应用
SpringBoot帮我们自动SpringMVC的时候，自动的注册SpringMVC的前端控制器；DIspatcherServlet；
DispatcherServletAutoConfiguration中：
@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public ServletRegistrationBean dispatcherServletRegistration(
DispatcherServlet dispatcherServlet) {
ServletRegistrationBean registration = new ServletRegistrationBean(
dispatcherServlet, this.serverProperties.getServletMapping());
//默认拦截： / 所有请求；包静态资源，但是不拦截jsp请求； /*会拦截jsp
//可以通过server.servletPath来修改SpringMVC前端控制器默认拦截的请求路径
registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
registration.setLoadOnStartup(
this.webMvcProperties.getServlet().getLoadOnStartup());
if (this.multipartConfig != null) {
registration.setMultipartConfig(this.multipartConfig);
}
return registration;
}
四、切换嵌入式 Servlet 容器
1、默认使用 Tomcat 容器
Tomcat 默认使用：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
引入web模块默认就是使用嵌入式的Tomcat作为Servlet容器；
</dependency>
SpringBoot 提供了同时还提供了 Jetty(长连接) 和 Undertow（不支持JSP），可以根据场景进行切换。
2、切换为 Jetty
<!-- 引入web模块 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<artifactId>spring-boot-starter-tomcat</artifactId>
<groupId>org.springframework.boot</groupId>
</exclusion>
</exclusions>
</dependency>
<!--引入其他的Servlet容器-->
<dependency>
<artifactId>spring-boot-starter-jetty</artifactId>
<groupId>org.springframework.boot</groupId>
</dependency>
3、切换为 Undertow
<!-- 引入web模块 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<artifactId>spring-boot-starter-tomcat</artifactId>
<groupId>org.springframework.boot</groupId>
</exclusion>
</exclusions>
</dependency>
<!--引入其他的Servlet容器-->
<dependency>
<artifactId>spring-boot-starter-undertow</artifactId>
<groupId>org.springframework.boot</groupId>
</dependency>
五、嵌入式Servlet容器自动配置原理
SpringBoot 是如何做到嵌入式 Servlet 容器的自动配置呢？
参照 EmbeddedServletContainerAutoConfiguration 类 嵌入式的Servlet容器自动配置
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
//导入BeanPostProcessorsRegistrar：Spring注解版；给容器中导入一些组件
//导入了EmbeddedServletContainerCustomizerBeanPostProcessor：
//后置处理器：bean初始化前后（创建完对象，还没赋值赋值）执行初始化工作
public class EmbeddedServletContainerAutoConfiguration {
/**
* Nested configuration if Tomcat is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class })//判断当前是否引入了Tomcat依赖；
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)//判断当前容器没有用户自己定义EmbeddedServletContainerFactory：嵌入式的Servlet容器工厂；作用：创建嵌入式的Servlet容器
public static class EmbeddedTomcat {
@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}
}
/**
* Nested configuration if Jetty is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
WebAppContext.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedJetty {
@Bean
public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
return new JettyEmbeddedServletContainerFactory();
}
}
/**
* Nested configuration if Undertow is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedUndertow {
@Bean
public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
return new UndertowEmbeddedServletContainerFactory();
}
}
1、EmbeddedServletContainerFactory（嵌入式Servlet容器工厂）
public interface EmbeddedServletContainerFactory {
//获取嵌入式的Servlet容器
EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers);
}
SpringBoot 提供的嵌入式 Servlet 容器工厂：
如果当前容器没有用户自己定义EmbeddedServletContainerFactory：嵌入式的Servlet容器工厂，SpringBoot 就会根据当前依赖创建一个 Servlet容器工厂，每一个嵌入式 Servlet 容器工厂都会创建对应的 servlet 容器；
2、EmbeddedServletContainer：（嵌入式的Servlet容器）
public interface EmbeddedServletContainer {
void start() throws EmbeddedServletContainerException;
void stop() throws EmbeddedServletContainerException;
int getPort();
}
SpringBoot 提供的嵌入的 servlet 容器：
3、SpringBoot 是如何自动配置 servlet 容器的呢？
/**
* Nested configuration if Tomcat is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {
@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}
}
public class TomcatEmbeddedServletContainerFactory
extends AbstractEmbeddedServletContainerFactory implements ResourceLoaderAware {
@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers) {
//创建一个Tomcat
Tomcat tomcat = new Tomcat();
//配置Tomcat的基本环节
File baseDir = (this.baseDirectory != null ? this.baseDirectory
: createTempDir("tomcat"));
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connector connector = new Connector(this.protocol);
tomcat.getService().addConnector(connector);
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
configureEngine(tomcat.getEngine());
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(), initializers);
//将配置好的Tomcat传入进去，返回一个EmbeddedServletContainer；并且启动Tomcat服务器
return getTomcatEmbeddedServletContainer(tomcat);
}
protected TomcatEmbeddedServletContainer getTomcatEmbeddedServletContainer(
Tomcat tomcat) {
return new TomcatEmbeddedServletContainer(tomcat, getPort() >= 0);
}
}
public class TomcatEmbeddedServletContainer implements EmbeddedServletContainer {
public TomcatEmbeddedServletContainer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
initialize();
}
private void initialize() throws EmbeddedServletContainerException {
TomcatEmbeddedServletContainer.logger
.info("Tomcat initialized with port(s): " + getPortsDescription(false));
synchronized (this.monitor) {
try {
addInstanceIdToEngineName();
try {
// Remove service connectors to that protocol binding doesn't happen
// yet
removeServiceConnectors();
// Start the server to trigger initialization listeners
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
rethrowDeferredStartupExceptions();
Context context = findContext();
try {
ContextBindings.bindClassLoader(context, getNamingToken(context),
getClass().getClassLoader());
}
catch (NamingException ex) {
// Naming is not enabled. Continue
}
// Unlike Jetty, all Tomcat threads are daemon threads. We create a
// blocking non-daemon to stop immediate shutdown
startDaemonAwaitThread();
}
catch (Exception ex) {
containerCounter.decrementAndGet();
throw ex;
}
}
catch (Exception ex) {
throw new EmbeddedServletContainerException(
"Unable to start embedded Tomcat", ex);
}
}
}
}
4、我们对嵌入式容器的配置修改是怎么生效？
方式一：在配置文件中进行修改，其实是与 ServerProperties 绑定的；
其实 ServerProperties 也是 EmbeddedServletContainerCustomizer 下的接口，并且重写了 customize 方法：
方式二：配置一个 EmbeddedServletContainerCustomizer 组件；
//一定要将这个定制器加入到容器中
//配置嵌入式的 servlet 容器
@Bean
public EmbeddedServletContainerCustomizer embeddedServletContainerCustomizer(){
return new EmbeddedServletContainerCustomizer() {
//定制嵌入式的Servlet容器相关的规则
@Override
public void customize(ConfigurableEmbeddedServletContainer container) {
container.setPort(8083);
}
};
}
其实都是使用 EmbeddedServletContainerCustomizer 定制器帮我们修改了Servlet容器的配置
5、那么配置是怎么修改的呢？
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
//导入BeanPostProcessorsRegistrar：Spring注解版；给容器中导入一些组件
//导入了EmbeddedServletContainerCustomizerBeanPostProcessor：
//后置处理器：bean初始化前后（创建完对象，还没赋值赋值）执行初始化工作
public class EmbeddedServletContainerAutoConfiguration {}
/**
* Registers a {@link EmbeddedServletContainerCustomizerBeanPostProcessor}. Registered
* via {@link ImportBeanDefinitionRegistrar} for early registration.
*/
public static class BeanPostProcessorsRegistrar
implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
private ConfigurableListableBeanFactory beanFactory;
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
if (beanFactory instanceof ConfigurableListableBeanFactory) {
this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
}
}
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
if (this.beanFactory == null) {
return;
}
registerSyntheticBeanIfMissing(registry,
"embeddedServletContainerCustomizerBeanPostProcessor",
EmbeddedServletContainerCustomizerBeanPostProcessor.class);
registerSyntheticBeanIfMissing(registry,
"errorPageRegistrarBeanPostProcessor",
ErrorPageRegistrarBeanPostProcessor.class);
}
private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry,
String name, Class<?> beanClass) {
if (ObjectUtils.isEmpty(
this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
beanDefinition.setSynthetic(true);
registry.registerBeanDefinition(name, beanDefinition);
}
}
}
public class EmbeddedServletContainerCustomizerBeanPostProcessor
implements BeanPostProcessor, BeanFactoryAware {
private ListableBeanFactory beanFactory;
private List<EmbeddedServletContainerCustomizer> customizers;
@Override
public void setBeanFactory(BeanFactory beanFactory) {
Assert.isInstanceOf(ListableBeanFactory.class, beanFactory,
"EmbeddedServletContainerCustomizerBeanPostProcessor can only be used "
+ "with a ListableBeanFactory");
this.beanFactory = (ListableBeanFactory) beanFactory;
}
//初始化之前
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
throws BeansException {
//如果当前初始化的是一个 ConfigurableEmbeddedServletContainer 类型的组件
if (bean instanceof ConfigurableEmbeddedServletContainer) {
postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName)
throws BeansException {
return bean;
}
private void postProcessBeforeInitialization(
ConfigurableEmbeddedServletContainer bean) {
//获取所有的定制器，调用每一个定制器的customize方法来给Servlet容器进行属性赋值；
for (EmbeddedServletContainerCustomizer customizer : getCustomizers()) {
customizer.customize(bean);
}
}
private Collection<EmbeddedServletContainerCustomizer> getCustomizers() {
if (this.customizers == null) {
// Look up does not include the parent context
this.customizers = new ArrayList<EmbeddedServletContainerCustomizer>(
this.beanFactory
//从容器中获取所有这个类型的组件：EmbeddedServletContainerCustomizer
//定制Servlet容器，给容器中可以添加一个EmbeddedServletContainerCustomizer类型的组件
.getBeansOfType(EmbeddedServletContainerCustomizer.class,
false, false)
.values());
Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
this.customizers = Collections.unmodifiableList(this.customizers);
}
return this.customizers;
}
}
6、总结步骤
（1）SpringBoot根据导入的依赖情况，给容器中添加相应的EmbeddedServletContainerFactory【TomcatEmbeddedServletContainerFactory】，会创建对应的Servlet容器工厂，然后由Servlet容器工厂来创建对应的servlet容器；
（2）容器中某个组件要创建对象就会惊动后置处理器；EmbeddedServletContainerCustomizerBeanPostProcessor；
只要是嵌入式的Servlet容器工厂，后置处理器就工作；
（3）后置处理器，从容器中获取所有的EmbeddedServletContainerCustomizer，调用定制器的定制方法；
六、嵌入式Servlet容器启动原理
什么时候创建嵌入式的Servlet容器工厂？什么时候获取嵌入式的Servlet容器并启动Tomcat？
在下面两处打上断点：
1、SpringBoot应用启动运行run方法
2、
（1）创建容器：如果是 web 环境，创建一个org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext 容器，否则创建默认的 org.springframework.context.annotation.AnnotationConfigApplicationContext
（2）刷新容器
3、
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
4、onRefresh()：web的ioc容器重写了onRefresh方法
5、
6、获取嵌入式的Servlet容器工厂：
EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
从ioc容器中获取EmbeddedServletContainerFactory 组件；
TomcatEmbeddedServletContainerFactory创建对象，后置处理器一看是这个对象，就获取所有的定制器来先定制Servlet容器的相关配置；
7、使用容器工厂获取嵌入式的Servlet容器
this.embeddedServletContainer = containerFactory .getEmbeddedServletContainer(getSelfInitializer());
8、嵌入式的Servlet容器创建对象并启动Servlet容器；
9、小结
先启动嵌入式的Servlet容器，再将 ioc 容器中剩下没有创建出的对象获取出来；
IOC容器启动创建嵌入式的Servlet容器
