2.4 Spring boot 配置Servelt、Filter、Listener

Spring Boot集成了servlet容器，当我们在pom文件中增加spring- boot-starter-web的maven依赖时，不做任何web相关的配置便能提供web服务，这还得归于spring boot 自动配置的功能（因为加了EnableAutoConfiguration的注解），帮我们创建了一堆默认的配置，以前在web.xml中配置，现在都可以通过spring bean的方式进行配置，由spring来进行生命周期的管理，大多数情况下，我们需要重载这些配置（例如修改服务的启动端口，contextpath,filter,listener,servlet,session超时时间等）

本节讲解在SpringBoot中如何配置Servelt、Filter、Listener。大家可能已经注意到，在SpringBoot中，不光将Spring的配置文件省略了，连web容器的web.xml文件都省略了，而之前，我们通常都是将Servelt、Filter、Listener等配置在web.xml中配置的，而SpringBoot提供了更加简化的配置。在讲解如何配置之前，我们先将演示用Servelt、Filter、Listener的准备好。

DemoServelt.java

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
public class DemoServlet extends HttpServlet{
 
    /**
     * 
     */
    private static final long serialVersionUID = 2600143224322327782L;
 
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
            System.out.println("==>DemoServlet接受请求");
        resp.getWriter().write("DemoServlet access success");
        
    }
 
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        this.doGet(req, resp);
    }
    
}

DemoFilter.java

import java.io.IOException;
 
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
 
public class DemoFilter implements Filter{
 
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("==>DemoFilter启动");
    }
 
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("==>DemoFilter拦截请求");
        chain.doFilter(request, response);
        
    }
 
    @Override
    public void destroy() {
        
    }
}

DemoListener.java

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
 
public class DemoListener implements ServletContextListener{
 
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("==>DemoListener启动");
        
    }
 
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        
    }
 
}

在准备好这些文件之后，我们开始配置。SpringBoot提供了2种方式配置Servlet、Listener、Filter。一种是基于RegistrationBean，另一种是基于注解。

1、基于RegistrationBean的配置

spring boot提供了 ServletRegistrationBean，FilterRegistrationBean，ServletListenerRegistrationBean这3个东西来进行配置Servlet、Filter、Listener

编写配置类WebConfig.java

import java.util.ArrayList;
import java.util.EventListener;
import java.util.List;
 
import org.springframework.boot.context.embedded.FilterRegistrationBean;
import org.springframework.boot.context.embedded.ServletListenerRegistrationBean;
import org.springframework.boot.context.embedded.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
 
import com.tianshouzhi.springbootstudy.web.filter.DemoFilter;
import com.tianshouzhi.springbootstudy.web.listener.DemoListener;
import com.tianshouzhi.springbootstudy.web.servlet.DemoServlet;
 
@Configuration
public class WebConfig extends WebMvcConfigurerAdapter{
    @Bean
    public FilterRegistrationBean getDemoFilter(){
        DemoFilter demoFilter=new DemoFilter();
        FilterRegistrationBean registrationBean=new FilterRegistrationBean();
        registrationBean.setFilter(demoFilter);
        List<String> urlPatterns=new ArrayList<String>();
        urlPatterns.add("/*");//拦截路径，可以添加多个
        registrationBean.setUrlPatterns(urlPatterns);
        registrationBean.setOrder(1);
        return registrationBean;
    }
    @Bean
    public ServletRegistrationBean getDemoServlet(){
        DemoServlet demoServlet=new DemoServlet();
        ServletRegistrationBean registrationBean=new ServletRegistrationBean();
        registrationBean.setServlet(demoServlet);
        List<String> urlMappings=new ArrayList<String>();
        urlMappings.add("/demoservlet");////访问，可以添加多个
        registrationBean.setUrlMappings(urlMappings);
        registrationBean.setLoadOnStartup(1);
        return registrationBean;
    }
    @Bean
    public ServletListenerRegistrationBean<EventListener> getDemoListener(){
        ServletListenerRegistrationBean<EventListener> registrationBean
                                   =new ServletListenerRegistrationBean<>();
        registrationBean.setListener(new DemoListener());
//        registrationBean.setOrder(1);
        return registrationBean;
    }
}