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