SpringBoot中servlet三大组件的注册[Servlet,Filter,Listener]

╰+攻爆jí腚メ 2021-11-22 15:56 437阅读 0赞

由于SpringBoot默认是以jar包的方式启动嵌入式的Servlet容器来启动SpringBoot的web应用，没有web.xml文  
件。所以三大组件的注册也有相应的改变，接下来看一下，springboot中是如何注册的：

# 一、Servlet的注册 #

Servlet是一种独立于平台和协议的处于服务器端的Java应用程序，利用他可以实现业务层和表现层的分离，同时又可以生成动态页面

## 1. 创建一个Servlet类继承HttpServlet ##

import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    public class MyServlet extends HttpServlet { 
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
            resp.getWriter().write("<h1>Hello World,servlet!</h1>");
        }
    }

## 2. 在配置类中配置Servlet ##

import com.infosec.netsafess.servlet.MyServlet;
    import org.springframework.boot.web.servlet.ServletRegistrationBean;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    
    @Configuration
    public class ServletComponentConfiguration { 
    
        @Bean
        public ServletRegistrationBean myServlet(){ 
            ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new MyServlet(),"/myServlet");
            return servletRegistrationBean;
        }
    }
    接下来的几个配置都添加在这个配置类中！

执行结果如下：  
![image][]

# 二、Filter的注册 #

Filter称之为过滤器，可以通过它对web服务器管理的所有web资源，通常用来实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等。

## 1. 创建一个filter类实现Filter类 ##

import javax.servlet.*;
    import java.io.IOException;
    
    public class MyFilter implements Filter { 
        @Override
        public void init(FilterConfig filterConfig) throws ServletException { 
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { 
            System.out.println("过滤器逻辑运行中");
            chain.doFilter(request,response); //放行
        }
    
        @Override
        public void destroy() { 
        }
    }

## 2. 将Filter注册到SpringBoot容器中 ##

@Bean
    public FilterRegistrationBean myFilter(){ 
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();
        registrationBean.setFilter(new MyFilter()); //设置过滤类
        registrationBean.setUrlPatterns(Arrays.asList("/myServlet")); //这里是一个数组，里面都是过滤的路径
        return registrationBean;
    }

# 三、 Listener的注册 #

## 1. 创建一个类实现监听器,以ServletContextListener为例 ##

import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    public class MyListener implements ServletContextListener {
        @Override
        public void contextInitialized(ServletContextEvent sce) {
            System.out.println("监听器开始运行了");
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent sce) {
            System.out.println("监听器开始销毁了");
        }
    
    }

## 2. 将监听器注册到spring容器中 ##

import com.university.subject.jsp_component.MyListener;
    import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    
    @Configuration
    public class MyWebConfig {
        @Bean
        public ServletListenerRegistrationBean myListener(){
            ServletListenerRegistrationBean<MyListener> registrationBean = new ServletListenerRegistrationBean<>(new MyListener());
            return registrationBean;
        }
    }
    
    //这个监听器是监听上下文的初始化，服务启动和关闭就会触发这个监听器
    2019-07-24 23:37:37.867  INFO 1412 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.21]
    2019-07-24 23:37:37.977  INFO 1412 --- [  restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
    2019-07-24 23:37:37.977  INFO 1412 --- [  restartedMain] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 2400 ms
    监听器开始运行了
    2019-07-24 23:37:38.827  INFO 1412 --- [  restartedMain] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'

## 3. 支持的监听器类型 ##

static {
            Set<Class<?>> types = new HashSet();
            types.add(ServletContextAttributeListener.class);
            types.add(ServletRequestListener.class);
            types.add(ServletRequestAttributeListener.class);
            types.add(HttpSessionAttributeListener.class);
            types.add(HttpSessionListener.class);
            types.add(ServletContextListener.class);
            SUPPORTED_TYPES = Collections.unmodifiableSet(types);
        }

<table> 
 <thead> 
  <tr> 
   <th>监听器类型</th> 
   <th>功能</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>ServletContextAttributeListener</td> 
   <td>监听spring上下文的属性增加和减少</td> 
  </tr> 
  <tr> 
   <td>ServletRequestListener</td> 
   <td>监听ServletRequest请求</td> 
  </tr> 
  <tr> 
   <td>ServletRequestAttributeListener</td> 
   <td>监听ServletRequest请求属性值的变化</td> 
  </tr> 
  <tr> 
   <td>HttpSessionAttributeListener</td> 
   <td>监听HttpSession的属性</td> 
  </tr> 
  <tr> 
   <td>HttpSessionListener</td> 
   <td>监听HttpSession</td> 
  </tr> 
  <tr> 
   <td>ServletContextListener</td> 
   <td>监听spring的上下文的创建和销毁</td> 
  </tr> 
 </tbody> 
</table>

HttpSessionAttributeListener | 监听HttpSession的属性  
HttpSessionListener | 监听HttpSession  
ServletContextListener | 监听spring的上下文的创建和销毁

[image]: /images/20211122/4fc3654335fe4118abd1541de5b0704f.png