SpringBoot配置嵌入式的Servlet

owenbbkp 2020-03-27

SpringBoot默认使用Tomcat作为嵌入式的Servlet

SpringBoot配置嵌入式的Servlet

问题?

1)、如何定制和修改Servlet容器的相关配置;

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

 注:在2.0之前的版本当中可以使用以下方式修改 Servlet  (EmbeddedServletContainerCustomizer   为 ServerProperties  父类)

@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);
        }
    };
}

 2)、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。

注册三大组件用以下方式

ServletRegistrationBean

@Bean
public ServletRegistrationBean myServlet(){
    ServletRegistrationBean registrationBean = new ServletRegistrationBean(new MyServlet(),"/myServlet");
    return registrationBean;
}public class MyServlet extends HttpServlet {    //处理get请求    @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");    }}

 FilterRegistrationBean

@Bean
public FilterRegistrationBean myFilter(){
    FilterRegistrationBean registrationBean = new FilterRegistrationBean();
    registrationBean.setFilter(new MyFilter());
    registrationBean.setUrlPatterns(Arrays.asList("/hello","/myServlet"));
    return registrationBean;
}public class MyFilter implements Filter {    @Override    public void init(FilterConfig filterConfig) throws ServletException {    }    @Override    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {        System.out.println("MyFilter process...");        chain.doFilter(request,response);    }    @Override    public void destroy() {    }}

 ServletListenerRegistrationBean

@Bean
public ServletListenerRegistrationBean myListener(){
    ServletListenerRegistrationBean<MyListener> registrationBean = new ServletListenerRegistrationBean<>(new MyListener());
    return registrationBean;
}public class MyListener implements ServletContextListener {    @Override    public void contextInitialized(ServletContextEvent sce) {        System.out.println("contextInitialized...web应用启动");    }    @Override    public void contextDestroyed(ServletContextEvent sce) {        System.out.println("contextDestroyed...当前web项目销毁");    }}

这种注册方式最好的例子(注册  DIspatcherServlet

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 = {"dispatcherServletRegistration"}
        )
        @ConditionalOnBean(
            value = {DispatcherServlet.class},
            name = {"dispatcherServlet"}
        )
        public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
     //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  spring.mvc.servlet.path  (之前版本是server.servletPath)  来修改SpringMVC前端控制器默认拦截的请求路径 DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet, webMvcProperties.getServlet().getPath());
            registration.setName("dispatcherServlet");
            registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
            multipartConfig.ifAvailable(registration::setMultipartConfig);
            return registration;
        }

 2)、SpringBoot能不能支持其他的Servlet容器;

Spring Boot 的 web 项目默认使用嵌入式的 Tomcat 服务器,同时它也支持程序员自己切换 内置的 Servlet 容器,如 Jetty 、Undertow 

Jetty 支持长连接,对于页面与服务器类似建立长连接聊天式的性能很好,

Undertow   高性能非阻塞的,并发性能非常好,但是不支持JSP

Tomcat 与 Undertow 对比
1、Tomcat 是 Apache 基金下的一个轻量级的 Servlet 容器,支持 Servlet 和 JSP。Tomcat 具有 Web 服务器特有的功能,包括 Tomcat 管理和控制平台、安全局管理和 Tomcat 阀等。Tomcat 本身包含了 HTTP 服务器,因此也可以视作单独的 Web 服务器。
2、但是,Tomcat 和 ApacheHTTP 服务器不是同一个东西,ApacheHTTP 服务器是用 C 语言实现的 HTTP Web 服务器。Tomcat 是完全免费的,深受开发者的喜爱。
3、Undertow 是 Red Hat 公司的开源产品, 它完全采用 Java 语言开发,是一款灵活的高性能 Web 服务器,支持阻塞 IO 和非阻塞 IO。由于 Undertow 采用 Java 语言开发,可以直接嵌入到 Java 项目中使用。同时,Undertow 完全支持 Servlet 和 Web Socket,在高并发情况下表现非常出色。

3)、替换为其他嵌入式Servlet容器

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnWebApplication
@EnableConfigurationProperties({ServerProperties.class})
public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {
    public EmbeddedWebServerFactoryCustomizerAutoConfiguration() {

默认支持:

Tomcat(默认使用)

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>引入web模块默认就是使用嵌入式的Tomcat作为Servlet容器;

 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>

 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>

 4)、嵌入式Servlet容器自动配置原理;

  springboot2.x前后在配置化 Servlet 容器的方式是不同的,

  创建工厂之前容器属性的配置方式

    ①2.x之前采用后置处理器的方式

    ②2.x之后直接采用启用配置的方式

2.x之后的方式

@AutoConfigureOrder(-2147483648)
@ConditionalOnClass({ServletRequest.class})
@ConditionalOnWebApplication(
    type = Type.SERVLET
)//启动自动配置
@EnableConfigurationProperties({ServerProperties.class})//根据条件给容器中导入嵌入式的容器
@Import({ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class, EmbeddedTomcat.class, EmbeddedJetty.class, EmbeddedUndertow.class})
public class ServletWebServerFactoryAutoConfiguration {
    public ServletWebServerFactoryAutoConfiguration() {
    }

    @Bean
    public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(ServerProperties serverProperties) {
        return new ServletWebServerFactoryCustomizer(serverProperties);
    }以导入Tomcat为例,查看Tomcat依赖组件,如果满足则导入tomcat工厂,以此获取Tomcat容器
 

 通过Tomcat工厂获取tomcat容器的代码如下

@Override
	public WebServer getWebServer(ServletContextInitializer... initializers) {
		if (this.disableMBeanRegistry) {
			Registry.disableRegistry();
		} //创建一个Tomcat
		Tomcat tomcat = new Tomcat();
		File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");//配置Tomcat的基本环节
		tomcat.setBaseDir(baseDir.getAbsolutePath());
		Connector connector = new Connector(this.protocol);
		connector.setThrowOnFailure(true);
		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 TomcatWebServer ;并且启动Tomcat服务器
		return getTomcatWebServer(tomcat);
	}

 启动tomcat的整个调用链路如下

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
		return new TomcatWebServer(tomcat, getPort() >= 0);
	}

	public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
		Assert.notNull(tomcat, "Tomcat Server must not be null");
		this.tomcat = tomcat;
		this.autoStart = autoStart;
		initialize();
	}

private void initialize() throws WebServerException {
		logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
		synchronized (this.monitor) {
			try {
				addInstanceIdToEngineName();

				Context context = findContext();
				context.addLifecycleListener((event) -> {
					if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
						// Remove service connectors so that protocol binding doesn‘t
						// happen when the service is started.
						removeServiceConnectors();
					}
				});

				// Start the server to trigger initialization listeners
				this.tomcat.start();

				// We can re-throw failure exception directly in the main thread
				rethrowDeferredStartupExceptions();

				try {
					ContextBindings.bindClassLoader(context, context.getNamingToken(), 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) {
				stopSilently();
				destroySilently();
				throw new WebServerException("Unable to start embedded Tomcat", ex);
			}
		}
	}

 2.0之后的启动步骤

   配置文件初始化----》容器工厂的初始化

2.x之前的方式

@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 {
    
    @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();
		}

	}
//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;
}

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葛类型的组件: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;
}

ServerProperties也是定制器

2.x之前的初始化步骤:

1)、SpringBoot根据导入的依赖情况,给容器中添加相应的EmbeddedServletContainerFactory【TomcatEmbeddedServletContainerFactory】

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

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