Springboot2Web原生组件注入

官方文档 - Servlets, Filters, and listeners

使用原生的注解Servlet API

@ServletComponentScan(basePackages = “com.atguigu.admin”) :指定原生Servlet组件都放在那里
@WebServlet(urlPatterns = “/my”):效果:直接响应,没有经过Spring的拦截器?
@WebFilter(urlPatterns ={"/css/","/images/"})
@WebListener

MyServlet 类

@WebServlet(urlPatterns = "/my")
public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("6666");
    }
}

主配置类

//可以将自己写的servlet扫描进来
@ServletComponentScan(basePackages = "com.yujie")
@SpringBootApplication
public class Boot05WebAdminApplication {

    public static void main(String[] args) {
        SpringApplication.run(Boot05WebAdminApplication.class, args);
    }
}

过滤器

@Slf4j
//拦截css下的所有内容
//注意：*是servlet写法，**是spring写法
@WebFilter(urlPatterns ={"/css/*","/images/*"})
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("MyFilter初始化完成");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("MyFilter工作");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
        log.info("MyFilter销毁");
    }
}

监听器

@Slf4j
@WebListener
public class MyServletContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        log.info("监听到项目初始化");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        log.info("监听到项目销毁");
    }
}

Spring方式注入使用RegistrationBean

ServletRegistrationBean, FilterRegistrationBean, and ServletListenerRegistrationBean
可以注解掉前面的3个注解，让后使用RegistrationBean来注册。

@Configuration
public class MyRegistConfig {

    @Bean
    public ServletRegistrationBean myServlet(){
        MyServlet myServlet = new MyServlet();

        return new ServletRegistrationBean(myServlet,"/my","/my02");
    }


    @Bean
    public FilterRegistrationBean myFilter(){

        MyFilter myFilter = new MyFilter();
//        return new FilterRegistrationBean(myFilter,myServlet());
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter);
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/my","/css/*"));
        return filterRegistrationBean;
    }

    @Bean
    public ServletListenerRegistrationBean myListener(){
        MyServletContextListener mySwervletContextListener = new MyServletContextListener();
        return new ServletListenerRegistrationBean(mySwervletContextListener);
    }
}

细节:

@Configuration(proxyBeanMethods=false)
public class MyRegistConfig {

这里没有写proxyBeanMethods=false。如果写了说明当前类每次一调用类里面的方法，servlet都会新建一次。比如我们调用MyFilter的时候，servlet就重新new了一下。(proxyBeanMethods=true)它可以保证依赖的组件始终是单实例的。

【源码分析】DispatcherServlet注入原理

为什么自己写的@WebServlet(urlPatterns = “/my”):不会经过spring的拦截器。

根据上面的分析，我们系统中有两个servlet，一个MyServlet，处理的路径是/my。DispatcherServlet处理的路径是/
我们可以分析它的注入原理

org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration配置类

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {

	/*
	 * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

	/*
	 * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

	@Configuration(proxyBeanMethods = false)
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	protected static class DispatcherServletConfiguration {

        //创建DispatcherServlet类的Bean
		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
			DispatcherServlet dispatcherServlet = new DispatcherServlet();
			dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
			dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
			dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
			dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
			dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
			return dispatcherServlet;
		}

		@Bean
		@ConditionalOnBean(MultipartResolver.class)
		@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
		public MultipartResolver multipartResolver(MultipartResolver resolver) {
			// Detect if the user has created a MultipartResolver but named it incorrectly
			return resolver;
		}

	}
    
    @Configuration(proxyBeanMethods = false)
	@Conditional(DispatcherServletRegistrationCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	@Import(DispatcherServletConfiguration.class)
	protected static class DispatcherServletRegistrationConfiguration {

        //注册DispatcherServlet类
		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
		@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
				WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
			DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
					webMvcProperties.getServlet().getPath());
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}

	}
    
    ...
    
}

扩展: DispatchServlet如何注册进来

容器中自动配置了DispatcherServlet 属性绑定到WebMvcProperties; 对应的配置文件配置项是
spring.mvc。
通过ServletRegistrationBean 把DispatcherServlet配置进来。
默认映射的是/路径。

Tomcat-Servlet;
多个Servlet都能处理到同一层路径, 精确优选原则
A: /my/
B: /my/1

上图中发送/my，按照精确优先原则，来到Tomcat处理。而只有我们触发spring流程，才会有拦截器的作用。所以上面我们自己写的servlet并没有被拦截。

嵌入式Servlet容器

1.切换嵌入式Servlet容器

默认支持的webServer

• Tomcat, Jetty, or Undertow
• ServletWebServerApplicationContext 容器启动寻找ServletwebServerFactory并引导创建服务器

切换服务器

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

原理

SpringBoot应用启动发现当前是Web应用。web场景包-导入tomcat

web应用会创建一个web版的ioc容器 ServletWebServerApplicationContext

ServletWebServerApplicationContext 启动的时候寻找ServletWebServerFactory
(Servlet的web服务器工厂—> Servlet 的web服 务器)

SpringBoot底层默认有很多的WebServerI厂; TomCatServletWebServerFactory,lu.com
JettyServletWebServerFactory, or UndertowServletWebServerFactory

底层直接会有一个自动配置类。ServletWebServerFactoryAutoConfiguration

ServletWebServerFactoryAutoConfiguration导入了ServletWebServerFactoryConfiguration
(配置类)

ServletWebServerFactoryConfiguration 配置类根据动态判断系统中到底导入了那个Web服务器
的包。(默认 是web- starter导入tomcat包)，容器中就有TomcatServletWebServerFactory

TomcatServletWebServerFactory 创建出Tomcat服务器并启动; TomcatWebServer. 的构造器拥有
初始化方法initialize—this . tomcat. start();

内嵌服务器，就是手动把启动服务器的代码调用(tomcat 核心jar包存在)

2.定制Servlet容器

实现WebServerFactoryCustomizer

把配置文件的值和ServletWebServerFactory进行绑定

修改配置文件server.xxx

直接自定义ConfigurableServletWebServerFactory

xxxxxCustomizer:定制化器，可以改变xxx的默认规则

import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;

@Component
public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

    @Override
    public void customize(ConfigurableServletWebServerFactory server) {
        server.setPort(9000);
    }

}

定制化原理

1.定制化的常见方式

修改配置文件;
xxxxxCustomizer;
编写自定义的配置类xxxConfiguration; + @Bean替换、增加容器中默认组件;视图解析器
Web应用编写-个配置类实现WebMvcConfigurer即可定制化web功能; + @Bean给容器中再扩展一 些组件

@Configuration
public class AdminWebConfig implements WebMvcConfigurer

@EnableWebMvc + WebMvcConfigurer一@Bean可以全面接管SpringMVC,所有规则全部自己重新
配置;实现定制和扩展功能

原理
1、WebMvcAutoConfiguration 默认的SpringMVC的自动配置功能类。静态资源、欢迎页…
2、一旦使用@EnableWebMvC、。会@Import(DelegatingWebMvcConfiguration.class)
3、 DelegatingWebMvcConfiguration 的作用，只保证SpringMVC最基本的使用*

• 把所有系统中的WebMvcConfigurer过来。所有功能的定制都是这些WebMvcConfigurer合起来
  一起生效
• 自动配置了一些非常底层的组件。RequestMappingHandlerMapping、 这些组件依赖的组件都是
  从容器中获取
• public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport

4、 WebMvcAutoConfiguration 面的配置要能生效必须@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)

5、@EnableWebMvc导致了WebMvcAutoConfiguration没有生效。

2.原理分析套路

场景starter - xxxxAutoConfiguration -导入xx组件-绑定xxxProperties --绑定配置文件项