SpringBoot初始教程之Servlet、Filter、Listener配置(七)

1.介绍

通过之前的文章来看，SpringBoot涵盖了很多配置，但是往往一些配置是采用原生的Servlet进行的，但是在SpringBoot中不需要配置web.xml的
因为有可能打包之后是一个jar包的形式，这种情况下如何解决？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
通过注解可以完全代替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，需要配置一个核心的注解@ServletComponentScan,具体配置项如下，可以配置扫描的路径



    @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即可



    @SpringBootApplication

    @ServletComponentScan

    public class AppApplication {

        public static void main(String[] args) throws Exception {

            SpringApplication.run(AppApplication.class, args);

        }

    }

2.2 方案二

方案二是采用自己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能够达到统一的效果



    @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别，但是在内部SpringBoot的实现上是无差别的，即使使用的是Servlet3.0注解，也是通过扫描注解
转换成这三种bean的FilterRegistrationBean、ServletRegistrationBean、ServletListenerRegistrationBean

4.扩展

大家在使用的时候有没有发觉，其实SpringBoot在使用SpringMvc的时候不需要配置DispatcherServlet的，因为已经自动配置了，
但是如果想要加一些初始配置参数如何解决，方案如下：



    @Bean

    public ServletRegistrationBean dispatcherRegistration(DispatcherServlet dispatcherServlet) {

        ServletRegistrationBean registration = new ServletRegistrationBean(dispatcherServlet);

        registration.addUrlMappings("*.do");

        registration.addUrlMappings("*.json");

        return registration;

    }

可以通过注入DispatcherServlet 然后用ServletRegistrationBean包裹一层动态的加上一些初始参数

本文代码

https://git.oschina.net/wangkang_daydayup/SpringBoot-Learn/tree/master

springboot-7