SpringBoot初始教程之Servlet、Filter、Listener配置详解

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;

									  }