《SpringBoot》第05章 Servlet3.0

Servlet 3.0

1.使用Servlet API

@ServletComponentScan

开启Servlet扫描

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({ServletComponentScanRegistrar.class})
public @interface ServletComponentScan {
    @AliasFor("basePackages")
    String[] value() default {};

    @AliasFor("value")
    String[] basePackages() default {};

    Class<?>[] basePackageClasses() default {};
}

@WebServlet

通过@WebServlet来注入Servlet

@WebServlet(urlPatterns = {"/my"})
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setCharacterEncoding("UTF-8");
        response.getWriter().write("@WebServlet注入");
    }
}

@WebFilter

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface WebFilter {
    String description() default "";

    String displayName() default "";

    WebInitParam[] initParams() default {};

    String filterName() default "";

    String smallIcon() default "";

    String largeIcon() default "";

    String[] servletNames() default {};

    String[] value() default {};

    String[] urlPatterns() default {};

    DispatcherType[] dispatcherTypes() default {DispatcherType.REQUEST};

    boolean asyncSupported() default false;
}

@WebFilter(urlPatterns = {"/my"})
public class MyFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("过滤器初始化");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("过滤器工作");
        filterChain.doFilter(request, response);
    }

    @Override
    public void destroy() {

    }
}

@WebListener

@WebListener
public class MyListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println(sce + "监听到初始化");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {

    }
}

2.使用 RegistrationBean

借助@Configuration向容器中注入Bean

@Configuration
public class ServletConfiguration {

    @Bean
    public ServletRegistrationBean myServlet() {
        MyServlet myServlet = new MyServlet();
        return new ServletRegistrationBean(myServlet, "/my");
    }

    @Bean
    public FilterRegistrationBean myFilter() {
        MyFilter myFilter = new MyFilter();
//        return new FilterRegistrationBean(myFilter, myServlet());

        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(myFilter);
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/my"));
        return filterRegistrationBean;
    }

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

}

3.DispatcherServlet 注入原理

1. 在自动配置类向容器中首先注入了DispatcherServlet，但是这种方式只是注入到了容器中
2. 在自动配置类中向容器中注入了DispatcherServletRegistrationBean，通过该类名就可以看到借助了RegistrationBean来注入Servlet，进入到类中一眼就可以看到

自动配置类 DispatcherServletAutoConfiguration

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

DispatcherServletConfiguration

向容器中注入一个DispatcherServlet

	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
	
	@Configuration(proxyBeanMethods = false)
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	protected static class DispatcherServletConfiguration {

         // 这里会向容器中注入一个DispatcherServlet
		@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;
		}

	}

DispatcherServletRegistrationConfiguration

配置类，向容器中注入一个DispatcherServletRegistrationBean

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

   @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
   // 当容器中包含DispatcherServlet.class，因为该配置类就是注入这个Servlet
   @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
   // 参数中包含dispatcherServlet，因为是配置类，所以参数首先从容器中获取，正好就获取到了上面的DispatcherServlet
   public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
         WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
      // 这里创建了RegistrationBean，
      // 第1个参数就是dispatcherServlet
      // 第2个参数就是拦截路径，点进去以后默认就是"/"
      DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
            webMvcProperties.getServlet().getPath());
      // 注入名称
      registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
      // 启动就加载
      registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
      multipartConfig.ifAvailable(registration::setMultipartConfig);
      return registration;
   }

}

DispatcherServletRegistrationBean

// 该类实现了ServletRegistrationBean，通过这种方式向容器中核心类DispatcherServlet
public class DispatcherServletRegistrationBean extends ServletRegistrationBean<DispatcherServlet>
      implements DispatcherServletPath {}