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SpringBoot原生組件注入實(shí)現(xiàn)兩種方式介紹

更新時(shí)間：2022年10月20日 16:15:53 作者：劉婉晴

SpringBoot是Spring全家桶的成員之一，基于約定優(yōu)于配置的思想（即有約定默認(rèn)值，在不配置的情況下會(huì)使用默認(rèn)值，在配置文件下配置的話會(huì)使用配置的值）。SpringBoot是一種整合Spring技術(shù)棧的方式(或者說是框架)，同時(shí)也是簡(jiǎn)化Spring的一種快速開發(fā)的腳手架

一、使用 Servlet API

使用 Servlet API 可以實(shí)現(xiàn)原生組件注入，通過在自定義 Servlet 前加入 @WebServlet 注釋，并且在 SpringBoot 啟動(dòng)類前加入 @ServletComponentScan 注釋，可實(shí)現(xiàn)注冊(cè) Servlet

代碼示例：

1、實(shí)現(xiàn)自定義 MyServlet

自定義 Servlet 類：

@WebServlet(urlPatterns = "/my") // 加入 @WebServlet 注釋
public class MyServlet extends HttpServlet { // 注意要繼承 HttpServlet 類
    @Override // 重寫 DoGet 方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().println("haha");
    }
}

項(xiàng)目啟動(dòng)類：

@ServletComponentScan(basePackages = "com.wanqing.admin") //掃描那個(gè)包中有servlet
@SpringBootApplication
public class DemoAdminApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoAdminApplication.class, args);
    }
}

2、實(shí)現(xiàn)自定義 MyFilter

@Slf4j
@WebFilter(urlPatterns = {"/css/*", "/images/*"}) // 攔截靜態(tài)資源
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
        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() {
        Filter.super.destroy();
        log.info("MyFilter銷毀");
    }
}

3、實(shí)現(xiàn)自定義 MyServletContextListener

@WebListener
@Slf4j
public class MyServletContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        log.info("MyServletContextListener 監(jiān)聽到項(xiàng)目初始化完成");
    }
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        log.info("MyServletContextListener 監(jiān)聽到項(xiàng)目銷毀");
    }
}

二、使用 RegistrationBean 的方式注入原生組件

通過編寫 MyRegistConfig 配置類，返回 RegistrationBean 的方式實(shí)現(xiàn)組件的注入，與上一種方式的區(qū)別在于，這種方式不需要給自定義 Servlet 類寫 @WebServlet 注釋。

注意點(diǎn)：要記得使用 @Bean 注釋將 ServletRegistrationBean 注冊(cè)到容器中。

代碼示例：

自定義 MyRegistConfig 配置類，注冊(cè) myServlet 組件，返回 ServletRegistrationBean 對(duì)象（對(duì)象參數(shù)為自定義的 myServlet 對(duì)象實(shí)例）

myFilter 及myListener 的實(shí)現(xiàn)方式同理

@Configuration
public class MyRegistConfig {
    @Bean
    public ServletRegistrationBean myServlet(){
        MyServlet myServlet = new MyServlet();
        return new ServletRegistrationBean(myServlet, "/my","/my02");
    }
    @Bean
    public FilterRegistrationBean myFilter(){
        MyFilter filter = new MyFilter();
        //return new FilterRegistrationBean(filter, myServlet()); // 攔截myServlet()的路徑
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(filter);
        filterRegistrationBean.addUrlPatterns("/my","/css/*");
        return filterRegistrationBean;
    }
    @Bean
    public ServletListenerRegistrationBean myListener(){
        MyServletContextListener myServletContextListener = new MyServletContextListener();
        return new ServletListenerRegistrationBean(myServletContextListener);

    }
}

拓展：為什么攔截器不攔截我們自定義的 MyServlet 請(qǐng)求？

分析 DispatcherServlet 如何注冊(cè)進(jìn)入容器中，從 DispatcherServletAutoConfiguration 類開始

容器中自動(dòng)配置了 DispatcherServlet 組件，其屬性綁定到 WebMvcProperties 中，對(duì)應(yīng)的配置文件是 spring.mvc

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) // 注冊(cè) DispatcherServlet  組件
		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;
		}

通過 ServletRegistrationBean < DispatcherServlet > 機(jī)制（DispatcherServletRegistrationBean.class）將 DispatcherServlet 原生的 Servlet 組件配置進(jìn)來

		@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()); // 拿到默認(rèn)映射路徑為 / 路徑
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}

拿到默認(rèn)映射路徑 /

WebMvcProperties.class 中配置