SpringBoot原生组件注入实现两种方式介绍-Java开发

SpringBoot是Spring全家桶的成员之一，基于约定优于配置的思想（即有约定默认值，在不配置的情况下会使用默认值，在配置文件下配置的话会使用配置的值）。SpringBoot是一种整合Spring技术栈的方式(或者说是框架)，同时也是简化Spring的一种快速开发

一、使用 Servlet API

使用 Servlet API 可以实现原生组件注入，通过在自定义 Servlet 前加入 @WebServlet 注释，并且在 SpringBoot 启动类前加入 @ServletComponentScan 注释，可实现注册 Servlet

代码示例：

1、实现自定义 MyServlet

自定义 Servlet 类：

@WebServlet(urlPatterns = "/my") // 加入 @WebServlet 注释
public class MyServlet extends HttpServlet { // 注意要继承 HttpServlet 类
    @Override // 重写 DoGet 方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().println("haha");
    }
}

项目启动类：

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

2、实现自定义 MyFilter

@Slf4j
@WebFilter(urlPatterns = {"/css/*", "/images/*"}) // 拦截静态资源
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销毁");
    }
}

3、实现自定义 MyServletContextListener

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

二、使用 RegistrationBean 的方式注入原生组件

通过编写 MyRegistConfig 配置类，返回 RegistrationBean 的方式实现组件的注入，与上一种方式的区别在于，这种方式不需要给自定义 Servlet 类写 @WebServlet 注释。

注意点：要记得使用 @Bean 注释将 ServletRegistrationBean 注册到容器中。

代码示例：

自定义 MyRegistConfig 配置类，注册 myServlet 组件，返回 ServletRegistrationBean 对象（对象参数为自定义的 myServlet 对象实例）

myFilter 及myListener 的实现方式同理

@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()); // 拦截myServlet()的路径
        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：为什么拦截器不拦截我们自定义的 MyServlet 请求？

分析 DispatcherServlet 如何注册进入容器中，从 DispatcherServletAutoConfiguration 类开始

容器中自动配置了 DispatcherServlet 组件，其属性绑定到 WebMvcProperties 中，对应的配置文件是 spring.mvc

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) // 注册 DispatcherServlet  组件
		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;
		}

通过 ServletRegistrationBean < DispatcherServlet > 机制（DispatcherServletRegistrationBean.class）将 DispatcherServlet 原生的 Servlet 组件配置进来

		@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()); // 拿到默认映射路径为 / 路径
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}

拿到默认映射路径 /

WebMvcProperties.class 中配置