SpringBoot初始教程之Servlet、Filter、Listener配置

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);        }    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

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) {        }    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14

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() {        }    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23

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 {};    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

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);        }    }
1
2
3
4
5
6
7
8
9
10
11

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;    }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

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;    }
1
2
3
4
5
6
7
8
9

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