过滤器（Filter）

1.过滤器介绍

 

 

2.过滤器开发三要素

 

 

3.过滤器的配置和注解

 

配置： 
 <filter>
     <filter-name>FilterA</filter-name>
     <filter-class>filter.FilterA</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>FilterA</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>

注解：
@WebFilter(filterName="CharacterEncodingFilter",urlPatterns="/*",
initParams= {
        @WebInitParam(name="encoding" , value="GBK"),
        @WebInitParam(name="p1" , value="v1"),
        @WebInitParam(name="p2" , value="v2")
})

4.过滤器选择

5.字符过滤器

 <filter>
  <filter-name>CharacterEncodingFilter</filter-name>
      <filter-class>filter.CharacterEncodingFilter</filter-class>
      <init-param>
          <param-name>encoding</param-name>
          <param-value>UTF-8</param-value>
      </init-param>
       <init-param>
          <param-name>encode</param-name>
          <param-value>GBK</param-value>
      </init-param>
      <init-param>
          <param-name>p1</param-name>
          <param-value>v1</param-value>
      </init-param>
      <init-param>
          <param-name>p2</param-name>
          <param-value>v2</param-value>
      </init-param>
  </filter>

 
 1 package filter;

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;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//@WebFilter(filterName="CharacterEncodingFilter",urlPatterns="/*",
//initParams= {
//        @WebInitParam(name="encoding" , value="GBK"),
//        @WebInitParam(name="p1" , value="v1"),
//        @WebInitParam(name="p2" , value="v2")
//})
public class CharacterEncodingFilter implements Filter {
    private String encoding;
    
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
        encoding=fConfig.getInitParameter("encoding");
        System.out.println("encoding:"+encoding);
    }

    
    public void destroy() {
        // TODO Auto-generated method stub

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest req=(HttpServletRequest) request;
        req.setCharacterEncoding(encoding);
        HttpServletResponse res=(HttpServletResponse) response;
        res.setContentType("text/html;charset="+encoding);
        
        chain.doFilter(request, response);
    }


}

6.url-pattern设置过滤范围、ServletRequest接口

7.映射问题

 8.注意事项

9.小练习

package filter;

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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DeviceAdapterFilter implements Filter{

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse res = (HttpServletResponse)response;
        /*
         /index.html
         PC: /desktop/index.html
         MOBILE: /mobile/index.html
         /test.html
         PC: /desktop/test.html
         MOBILE: /mobile/test.html
         */
        String uri = req.getRequestURI();
        System.out.println("URI:" + uri);
        if(uri.startsWith("/desktop") || uri.startsWith("/mobile")) {
            chain.doFilter(request, response);
        }else {
            String userAgent = req.getHeader("user-agent").toLowerCase();
            String targetURI="";
            if(userAgent.indexOf("android")!=-1 || userAgent.indexOf("iphone") != -1) {
                targetURI = "/mobile" + uri;
                System.out.println("移动端设备正在访问,重新跳转URI:" + targetURI);
                res.sendRedirect(targetURI);
            }else {
                targetURI = "/desktop" + uri;
                System.out.println("PC端设备正在访问,重新跳转URI:" + targetURI);
                res.sendRedirect(targetURI);
            }
        }
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

}