SpringBoot之Servlet、Filter、Listener配置

1.介绍

经过以前的文章来看，SpringBoot涵盖了不少配置，可是每每一些配置是采用原生的Servlet进行的，可是在SpringBoot中不须要配置web.xml的
由于有可能打包以后是一个jar包的形式，这种状况下如何解决？SpringBoot 提供了两种方案进行解决

2.快速开始

2.1 方案一

方案一采用原生Servlet3.0的注解进行配置、@WebServlet 、@WebListener、@WebFilter是Servlet3.0 api中提供的注解
经过注解能够彻底代替web.xml中的配置，下面是一个简单的配置

IndexServlet

@WebServlet(name = "IndexServlet",urlPatterns = "/hello")
    public class IndexServlet extends HttpServlet {
            @Override
            public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
                    resp.getWriter().print("hello word");
                    resp.getWriter().flush();
                    resp.getWriter().close();
            }

            @Override
            protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
                    this.doGet(req, resp);
            }
    }

IndexListener

@WebListener
    public class IndexListener implements ServletContextListener {
            private Log log = LogFactory.getLog(IndexListener.class);

            @Override
            public void contextInitialized(ServletContextEvent servletContextEvent) {
                    log.info("IndexListener contextInitialized");
            }

            @Override
            public void contextDestroyed(ServletContextEvent servletContextEvent) {

            }
    }

IndexFilter

@WebFilter(urlPatterns = "/*", filterName = "indexFilter")
    public class IndexFilter implements Filter {
        Log log = LogFactory.getLog(IndexFilter.class);

        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            log.info("init IndexFilter");
        }

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

        }

        @Override
        public void destroy() {

        }
    }

上面配置完了，须要配置一个核心的注解@ServletComponentScan,具体配置项以下，能够配置扫描的路径

@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 {};

    }

把注解加到入口处启动便可

@SpringBootApplication
    @ServletComponentScan
    public class AppApplication {

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

    }

2.2 方案二

方案二是采用本身SpringBoot 配置bean的方式进行配置的，SpringBoot提供了三种BeanFilterRegistrationBean、ServletRegistrationBean、ServletListenerRegistrationBean
分别对应配置原生的Filter、Servlet、Listener,下面提供的三个配置和方案一采用的方式可以达到统一的效果

@Bean
    public ServletRegistrationBean indexServletRegistration() {
        ServletRegistrationBean registration = new ServletRegistrationBean(new IndexServlet());
        registration.addUrlMappings("/hello");
        return registration;
    }

    @Bean
    public FilterRegistrationBean indexFilterRegistration() {
        FilterRegistrationBean registration = new FilterRegistrationBean(new IndexFilter());
        registration.addUrlPatterns("/");
        return registration;
    }
    @Bean
    public ServletListenerRegistrationBean servletListenerRegistrationBean(){
        ServletListenerRegistrationBean servletListenerRegistrationBean = new ServletListenerRegistrationBean();
        servletListenerRegistrationBean.setListener(new IndexListener());
        return servletListenerRegistrationBean;
    }

3.总结

两种方案在使用上有差异，可是在内部SpringBoot的实现上是无差异的，即便使用的是Servlet3.0注解，也是经过扫描注解
转换成这三种bean的FilterRegistrationBean、ServletRegistrationBean、ServletListenerRegistrationBean

4.扩展

你们在使用的时候有没有发觉，其实SpringBoot在使用SpringMvc的时候不须要配置DispatcherServlet的，由于已经自动配置了，
可是若是想要加一些初始配置参数如何解决，方案以下：

@Bean
    public ServletRegistrationBean dispatcherRegistration(DispatcherServlet dispatcherServlet) {
        ServletRegistrationBean registration = new ServletRegistrationBean(dispatcherServlet);
        registration.addUrlMappings("*.do");
        registration.addUrlMappings("*.json");
        return registration;
    }

能够经过注入DispatcherServlet 而后用ServletRegistrationBean包裹一层 动态的加上一些初始参数

出处：https://blog.csdn.net/king_is_everyone/article/details/53116744