SpringBoot---web 应用开发-Servlets, Filters, listeners-蒲公英云

一.Web 开发使用 Controller 基本上可以完成大部分需求，但是我们还可能会用到 Servlet、 Filter、Listener 等等。

二.在 spring boot 中的三种实现方式

   (1) 1.通过注册 ServletRegistrationBean、 FilterRegistrationBean 和 ServletListenerRegistrationBean 获得控制,
     CustomServlet,java 如下：
package com.nyist.demo.utils.servlet;
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 CustomServlet extends HttpServlet {
 private static final long serialVersionUID = 1L; 
 @Override 
 protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   System.out.println("servlet get method");
   doPost(request, response);
 } 
 @Override 
 protected void doPost(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
   System.out.println("servlet post method");
   response.getWriter().write("hello world");
 } 
}
  在启动类中注册ServletRegistrationBean 获得访问路径
package com.nyist.demo;
import com.nyist.demo.utils.filter.CustomFilter;
import com.nyist.demo.utils.listener.CustomListener;
import com.nyist.demo.utils.servlet.CustomServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import javax.swing.*;
@SpringBootApplication
public class DemoApplication {
    @Bean
    public ServletRegistrationBean servletRegistrationBean() {
        return new ServletRegistrationBean(new CustomServlet(), "/nyist");
    }
}
2. 定义一个CustomFileterlei类 实现Filter接口
    CustomFilter.java 如下：
package com.nyist.demo.utils.filter; /**
 * 自定义 filter 
 *  
 * @author wujing 
 */
import javax.servlet.*;
import java.io.IOException;
public class CustomFilter implements Filter { 
  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    System.out.println("init filter");
  }
  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
    throws IOException, ServletException {
    System.out.println("do filter");
    chain.doFilter(request, response);
  }
  @Override
  public void destroy() {
    System.out.println("destroy filter");
  }
}
  在启动类中注册，FilterRegistrationBean 来设置需要拦截的servlet
package com.nyist.demo;
import com.nyist.demo.utils.filter.CustomFilter;
import com.nyist.demo.utils.listener.CustomListener;
import com.nyist.demo.utils.servlet.CustomServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import javax.swing.*;
@SpringBootApplication
public class DemoApplication {
    @Bean
    public FilterRegistrationBean filterRegistrationBean() {
        return new FilterRegistrationBean(new CustomFilter());
    }
}
 3.CustomListener 实现 Listener 接口，用来监听servlet
package com.nyist.demo.utils.listener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
/**
 * 自定义 listener 
 *  
 * @author wujing 
 */ 
public class CustomListener implements ServletContextListener {
   @Override
   public void contextInitialized(ServletContextEvent sce) {
    System.out.println("contextInitialized");
   }
   @Override
   public void contextDestroyed(ServletContextEvent sce) {
    System.out.println("contextDestroyed");
   }
}
    在启动类注册，ListenerRegistrationBean 
package com.nyist.demo;
import com.nyist.demo.utils.filter.CustomFilter;
import com.nyist.demo.utils.listener.CustomListener;
import com.nyist.demo.utils.servlet.CustomServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import javax.swing.*;
@SpringBootApplication
public class DemoApplication {
    @Bean
    public ServletListenerRegistrationBean<CustomListener> servletListenerRegistrationBean() {
        return new ServletListenerRegistrationBean<CustomListener>(new CustomListener());
    }
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

访问结果：do filter
servlet get method
servlet post method

(2)第二种方法： ServletContextInitializer 接口直接注册需要的Servlet和Fileter和Listener

package com.nyist.demo;
import com.nyist.demo.utils.filter.CustomFilter;
import com.nyist.demo.utils.listener.CustomListener;
import com.nyist.demo.utils.servlet.CustomServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletContextInitializer;
import javax.servlet.DispatcherType;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import java.util.EnumSet;
@SpringBootApplication
public class DemoApplication implements ServletContextInitializer {
        @Override  public void onStartup(ServletContext servletContext) throws ServletException {
            servletContext.addServlet("customServlet", new CustomServlet()).addMapping("/nyist");
            servletContext.addFilter("customFilter", new CustomFilter()).addMappingForServletNames(EnumSet.of(DispatcherType.REQUEST), true,"customServlet");
            servletContext.addListener(new CustomListener());
        }
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}
  (3)第三种方法：在 SpringBootApplication 上使用@ServletComponentScan 注解后，直接通过@WebServlet、@WebFilter、@WebListener 注解自动注册 
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