SpringBoot(七) -- 嵌入式Servlet容器

一.嵌入式Servlet容器
  在传统的开发中,我们在完成开发后需要将项目打成war包,在外部配置好TomCat容器,而这个TomCat就是Servlet容器.在使用SpringBoot开发时,我们无需再外部配置Servlet容器,使用的是嵌入式的Servlet容器(TomCat).如果我们使用嵌入式的Servlet容器,存在以下问题:
  1.如果我们是在外部安装了TomCat,如果我们想要进行自定义的配置优化,可以在其conf文件夹下修改配置文件来实现.在使用内置Servlet容器时,我们可以使用如下方法来修改Servlet容器的相关配置:
  (1)例如我们可以使用server.port=80来修改我们的启用端口号为80;及我们可以通过修改和Server有关的配置来实现(ServerProperties)
  (2)修改通用的设置server.XXX;
  (3)修改和Tomcat相关的设置:server.tomcat.xxx
  2.我们可以编写一个EmbeddedServletContainerCustomizer(嵌入式Servlet容器的定制器):

@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);        //设置端口为8083
            }
        };
    }

二.注册Servlet Filter Listener
  我们可以分别使用ServletRegisterationBean FilterRegisterationBean ServletListenerRegisterationBean完成这三大组件的注册

--Servlet

package com.zhiyun.springboot.web_restfulcrud.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * @author : S K Y
 * @version :0.0.1
 */
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");
    }
}
package com.zhiyun.springboot.web_restfulcrud.config;

import com.zhiyun.springboot.web_restfulcrud.servlet.MyServlet;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author : S K Y
 * @version :0.0.1
 */
@Configuration
public class MyServerConfig {
    //注册三大组件
    @Bean
    public ServletRegistrationBean servletRegistrationBean() {
        return new ServletRegistrationBean(new MyServlet(), "/myServlet");
    }
}

--Filter

package com.zhiyun.springboot.web_restfulcrud.filter;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.*;
import java.io.IOException;

/**
 * @author : S K Y
 * @version :0.0.1
 */
public class MyFilter implements Filter {
    private Logger logger = LoggerFactory.getLogger(this.getClass());

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        logger.debug("自定义的Filter启用了!");
        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {

    }
}

 

 

@Bean
    public FilterRegistrationBean filterRegistrationBean() {
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(new MyFilter());
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/hello", "/myServlet"));
        return filterRegistrationBean;
    }

--Listener

package com.zhiyun.springboot.web_restfulcrud.listener;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * @author : S K Y
 * @version :0.0.1
 */
public class MyListener implements ServletContextListener {
    private Logger logger = LoggerFactory.getLogger(this.getClass());

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        logger.debug("contextInitialized...当前web应用启动了");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        logger.debug("contextDestroyed...当前web项目销毁");
    }
}
@Bean
    public ServletListenerRegistrationBean servletListenerRegistrationBean() {
        return new ServletListenerRegistrationBean<>(new MyListener());
    }

--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.注册三大组件可以采取这样的方法.
--SpringBoot帮我们自动配置SpringMVC的是惠普,自动的注册SpringMVC的前端控制器:DispatcherServlet.默认拦截"/"所有资源包括静态资源,但是不拦截JSP请求,"/*"会拦截JSP.我们可以通过server.servletPath来修改SpringMVC前端控制器默认拦截的请求路径.

三.使用其他的嵌入式容器
  SpringBoot还支持Jetty(适合开发长连接的应用,例如聊天室),Undertow(不支持JSP):
SpringBoot(七) -- 嵌入式Servlet容器

  1.默认使用了TomCat
  2.切换使用其他Servlet容器,首先需要排除其中的spring-boot-starter-web -->spring-boot-starter-tomcat依赖,而后则可以引入其他的Servlet容器

<!--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>

四.嵌入式Servlet容器的自动配置原理
  在SpringBoot中拥有如下自动配置类EmbeddedServletContainerAutoConfiguration:

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
public class EmbeddedServletContainerAutoConfiguration {

   --该类就是嵌入式的Servlet容器自动配置类

/**
     * 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();
        }

    }

  --如果我们导入了Servlet的相关袭来,那么我们就会存在Servlet.class类以及Tomcat.class类,并且容器中不存在EmbeddedServletContainerFactory嵌入式容器工厂(用户自定义的Servlet容器工厂,那么该配置就会生效),在嵌入式容器工厂中定义了如下类:

public interface EmbeddedServletContainerFactory {

    /**
     * Gets a new fully configured but paused {@link EmbeddedServletContainer} instance.
     * Clients should not be able to connect to the returned server until
     * {@link EmbeddedServletContainer#start()} is called (which happens when the
     * {@link ApplicationContext} has been fully refreshed).
     * @param initializers {@link ServletContextInitializer}s that should be applied as
     * the container starts
     * @return a fully configured and started {@link EmbeddedServletContainer}
     * @see EmbeddedServletContainer#stop()
     */
    EmbeddedServletContainer getEmbeddedServletContainer(
            ServletContextInitializer... initializers);

}

   --获取嵌入式的Servlet容器,在SpringBoot的默认实现中存在如下的实现:
SpringBoot(七) -- 嵌入式Servlet容器

   --以嵌入式Tomcat容器工程为例:

@Override
    public EmbeddedServletContainer getEmbeddedServletContainer(
            ServletContextInitializer... initializers) {
        Tomcat tomcat = new Tomcat();
        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);
        return getTomcatEmbeddedServletContainer(tomcat);
    }

  --可以发现其内部使用Java代码的方式创建了一个Tomcat,并配置了Tomcat工作的基本环境,最终返回一个嵌入式的Tomcat容器

/**
     * Create a new {@link TomcatEmbeddedServletContainer} instance.
     * @param tomcat the underlying Tomcat server
     * @param autoStart if the server should be started
     */
    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);
            }
        }
    }

  --我们对嵌入式容器的配置修改是如何生效的:
  1.修改ServerProperties中的属性
  2.嵌入式Servlet容器定制器:EmbeddedServletContainerCustomizer,帮助我们修改了Sevlet容器的一些默认配置,例如端口号;在EmbeddedServletContainerAutoConfiguration中导入了一个名为BeanPostProcessorsRegistrar,给容器中导入一些组件即嵌入式Servlet容器的后置处理器.后置处理器表示的是在bean初始化前后(创建完对象,还没有赋予初值)执行初始化工作.

  3.EmbeddedServletContainerAutoConfiguration为嵌入式Servlet容器的后置处理器的自动配置类,其存在如下类:

@Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {
        if (bean instanceof ConfigurableEmbeddedServletContainer) {
            postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);
        }
        return bean;
    }
private void postProcessBeforeInitialization(
            ConfigurableEmbeddedServletContainer bean) {
        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
                            .getBeansOfType(EmbeddedServletContainerCustomizer.class,
                                    false, false)
                            .values());
            Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
            this.customizers = Collections.unmodifiableList(this.customizers);
        }
        return this.customizers;
    }  

  4.获取到了所有的定制器,调用了每一个定制器的customer方法来给Servlet容器进行属性赋值.
  5.ServerProperties也是配置器,因此其配置流程如下:
  (1)SpringBoot根据导入的依赖情况,添加响应的配置容器工厂EmbeddedServletCustomerFactory
  (2)容器中某个组件要创建对象就会惊动后置处理器;
  (3)只要是嵌入式的Servlet容器工厂 后置处理器就工作,从容器中获取所有的EmbeddedServletContainerCustomizer调用定制器的定制方法

五.嵌入式Servlet容器启动原理
  获取嵌入式的Servlet容器工厂:
  1.SpringBoot引用启动运行run方法;
  2.refreshContext(context);SpringBoot刷新容器并初始化容器,创建容器中的每一个组件:如果是Web应用,创建web的IOC容器AnnotationConfigEmbeddedWebApplicationContext,如果不是则创建AnnotationConfigApplicationContext;
  3.refreshContext(context)刷新刚才创建好的容器
  4.onRefresh():web的IOC容器重写了onRefresh方法;
  5.webIOC容器会创建嵌入式的servlet容器:createEmbeddedServletContainer();
  6.获取嵌入式的servlet容器工厂:EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
  7.使用容器工厂获取嵌入式的Servlet容器;
  8.嵌入式的Servlet容器创建对象,并启动servlet容器.

六.使用外置的Servlet容器
  嵌入式Servlet容器:
    优点: 简单,快捷
    缺点:默认不支持JSP,优化定制复杂(使用定制器,自定义配置servlet容器的创建工厂);
  --外部的Servlet容器,:外面安装Tomcat-应用war包的方式打包.
  --我们使用war包的形式创建SpringBoot工程可以发现其目录结构如下:
SpringBoot(七) -- 嵌入式Servlet容器

   --创建项目webapp路径及web-XML文件:
SpringBoot(七) -- 嵌入式Servlet容器

   --部署Tomcat服务器:
SpringBoot(七) -- 嵌入式Servlet容器

 SpringBoot(七) -- 嵌入式Servlet容器

  --创建步骤:
  1.必须创建一个war项目;
  2.将嵌入式的Tomcat指定为provided

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>

   3.必须编写一个SpringBootServletInitializer的子类,目的就是调用config方法

package com.skykuqi.springboot.exteralservlet;

import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.support.SpringBootServletInitializer;

public class ServletInitializer extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        //传入SpringBoot应用的主程序
        return application.sources(ExteralservletApplication.class);
    }

}

 七.外置Servlet容器的启动原理
  1.jar包:当我们的应用是使用SpringBoot的jar包形式的话,我们可以直接通过执行SpringBoot主类的main方法,启动IOC容器,创建嵌入式的Servlet容器;
  2.war包:启动服务器,服务器启动SpringBoot应用,启用IOC容器:
  3.在Servlet3.0中有一项规范:
SpringBoot(七) -- 嵌入式Servlet容器
  (1)服务器启动(web应用启动)会创建当前web应用里面每一个jar包里面ServletContainerInitializer的实例;
  (2)ServletContainerInitializer的实现必须放在META-INF/services文件夹下,该文件夹下还必须有一个文件名为javax.servlet.ServletContainerInitializer的文件,文件的内容就是ServletContainerInitializer实现的全类名.
  (3)可以使用@HandlesTypes注解来实现,容器在应用启动的时候,加载我们所感兴趣的类.
  4.启动流程:
  (1)启动Tomcat服务器,Spring的Web模块中存在该文件:
SpringBoot(七) -- 嵌入式Servlet容器

SpringBoot(七) -- 嵌入式Servlet容器   

  (2)SpringServletContainerInitializer将@HandlesTypes(WebApplicationInitializer.class)所标注的所有这个类型的类都传入到onStartup方法的集合中为这些不是接口不是抽象类类型的类创建实例;
  (3)每一个WebApplicationInitializer的实现类都调用自己的onStartup方法.
SpringBoot(七) -- 嵌入式Servlet容器

   (4)相当于我们的SpringServletContainerInitializer的类会被创建对象,并执行onStartup方法;
  (6)SpringServletContainerInitializer执行onStartup的时候会创建容器

protected WebApplicationContext createRootApplicationContext(
            ServletContext servletContext) {
        SpringApplicationBuilder builder = createSpringApplicationBuilder();
        StandardServletEnvironment environment = new StandardServletEnvironment();
        environment.initPropertySources(servletContext, null);
        builder.environment(environment);
        builder.main(getClass());
        ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
        if (parent != null) {
            this.logger.info("Root context already created (using as parent).");
            servletContext.setAttribute(
                    WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null);
            builder.initializers(new ParentContextApplicationContextInitializer(parent));
        }
        builder.initializers(
                new ServletContextApplicationContextInitializer(servletContext));
        builder.contextClass(AnnotationConfigEmbeddedWebApplicationContext.class);
        builder = configure(builder);
        SpringApplication application = builder.build();
        if (application.getSources().isEmpty() && AnnotationUtils
                .findAnnotation(getClass(), Configuration.class) != null) {
            application.getSources().add(getClass());
        }
        Assert.state(!application.getSources().isEmpty(),
                "No SpringApplication sources have been defined. Either override the "
                        + "configure method or add an @Configuration annotation");
        // Ensure error pages are registered
        if (this.registerErrorPageFilter) {
            application.getSources().add(ErrorPageFilterConfiguration.class);
        }
        return run(application);
    }

   --将创建RootApplicationContext容器,在创建容器时会进行如下操作:
  a.创建SpringApplicationBuilder
  b.在18行调用了configer(),将SpringBoot的主程序类传入了进来
  c.使用builder创建一个Spring应用

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