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);
}
}
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
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作者：夜宿山寺
来源：CSDN
原文：https://blog.csdn.net/king_is_everyone/article/details/53116744
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