厚积薄发系列之JavaWeb的Filter

Posted 2020-10-14

1.Filter的使用配置

 

• 创建一个类使其实现javax.servlet.Filter接口
• 实现接口方法 destroy() doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)   init(FilterConfig arg0)  
• 配置web.xml 

•     <filter>
          <filter-name>TestFilter</filter-name>
          <filter-class>filter.TestFilter</filter-class>
      </filter>
      <filter-mapping>
          <filter-name>TestFilter</filter-name>
          <url-pattern>/*</url-pattern>
      </filter-mapping>

   

2.Filter的运行流程(两张图来展示)

 

• 
• 

 

3.Filter接口的方法

 

• init(FilterConfig config):初始化操作   
• doFilter(ServletRequest request, ServletResponse response, FilterChain chain):处理业务逻辑
• destroy() :销毁操作

4.Filter的声明周期

 

• 初始化操作 在服务器启动的时候 根据web.xml配置文件创建Filter实例  调用init方法  实现初始化操作  
• 处理业务逻辑  在用户的一次请求 创建一个新的线程 根据路径调用相应的过滤器的doFilter执行业务逻辑
• 结束阶段 当Filter被移除的时候或者服务器正常关闭的时候 调用destory方法 销毁该实例
• 注意Filter是单实例多线程的

5.Filter的常见用法

 

• post和get请求统一utf-8编码 web.xml路径配置为/*
• 

    1 import java.io.IOException;
    2 import java.io.UnsupportedEncodingException;
    3 import java.util.Map;
    4 
    5 import javax.servlet.Filter;
    6 import javax.servlet.FilterChain;
    7 import javax.servlet.FilterConfig;
    8 import javax.servlet.ServletException;
    9 import javax.servlet.ServletRequest;
   10 import javax.servlet.ServletResponse;
   11 import javax.servlet.http.HttpServletRequest;
   12 import javax.servlet.http.HttpServletRequestWrapper;
   13 import javax.servlet.http.HttpServletResponse;
   14 /**
   15  * 统一编码
   16  * @author Administrator
   17  *
   18  */
   19 public class EncodingFilter implements Filter {
   20 
   21     @Override
   22     public void init(FilterConfig filterConfig) throws ServletException {
   23         // TODO Auto-generated method stub
   24 
   25     }
   26 
   27     @Override
   28     public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
   29         //1.强转
   30         HttpServletRequest request=(HttpServletRequest) req;
   31         HttpServletResponse response=(HttpServletResponse) resp;
   32         
   33         //2.放行
   34         chain.doFilter(new MyRequest(request), response);
   35     }
   36 
   37     @Override
   38     public void destroy() {
   39         // TODO Auto-generated method stub
   40 
   41     }
   42 
   43 }
   44 class MyRequest extends HttpServletRequestWrapper{
   45     private HttpServletRequest request;
   46     private boolean flag=true;
   47     
   48     
   49     public MyRequest(HttpServletRequest request) {
   50         super(request);
   51         this.request=request;
   52     }
   53     
   54     @Override
   55     public String getParameter(String name) {  
   56         if(name==null || name.trim().length()==0){
   57             return null;
   58         }
   59         String[] values = getParameterValues(name);
   60         if(values==null || values.length==0){
   61             return null;
   62         }
   63         
   64         return values[0];
   65     }
   66     
   67     @Override
   68     /**
   69      * hobby=[eat,drink]
   70      */
   71     public String[] getParameterValues(String name) {
   72         if(name==null || name.trim().length()==0){
   73             return null;
   74         }
   75         Map<String, String[]> map = getParameterMap();
   76         if(map==null || map.size()==0){
   77             return null;
   78         }
   79         
   80         return map.get(name);
   81     }
   82     
   83     @Override
   84     /**
   85      * map{ username=[tom],password=[123],hobby=[eat,drink]}
   86      */
   87     public Map<String,String[]> getParameterMap() {  
   88         
   89         /**
   90          * 首先判断请求方式
   91          * 若为post  request.setchar...(utf-8)
   92          * 若为get 将map中的值遍历编码就可以了
   93          */
   94         String method = request.getMethod();
   95         if("post".equalsIgnoreCase(method)){
   96             try {
   97                 request.setCharacterEncoding("utf-8");
   98                 return request.getParameterMap();
   99             } catch (UnsupportedEncodingException e) {
  100                 // TODO Auto-generated catch block
  101                 e.printStackTrace();
  102             }
  103         }else if("get".equalsIgnoreCase(method)){
  104             Map<String,String[]> map = request.getParameterMap();
  105             if(flag){
  106                 for (String key:map.keySet()) {
  107                     String[] arr = map.get(key);
  108                     //继续遍历数组
  109                     for(int i=0;i<arr.length;i++){
  110                         //编码
  111                         try {
  112                             arr[i]=new String(arr[i].getBytes("iso8859-1"),"utf-8");
  113                         } catch (UnsupportedEncodingException e) {
  114                             e.printStackTrace();
  115                         }
  116                     }
  117                 }
  118                 flag=false;
  119             }
  120             //需要遍历map 修改value的每一个数据的编码
  121             
  122             return map;
  123         }
  124         
  125         return super.getParameterMap();
  126     }
  127     
  128 }

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• 登陆验证 判断用户是否登陆  web.xml路径配置自己想要用户登陆才能登陆登陆才能访问的页面
• 

   1 public void doFilter(ServletRequest arg0, ServletResponse arg1,
   2             FilterChain arg2) throws IOException, ServletException {
   3         
   4         HttpServletRequest request=(HttpServletRequest) arg0;
   5         HttpServletResponse response=(HttpServletResponse) arg1;
   6         HttpSession session=request.getSession();
   7         
   8         String path=request.getRequestURI();
   9         
  10         Integer uid=(Integer)session.getAttribute("userid");
  11         
  12         if(path.indexOf("/login.jsp")>-1){//登录页面不过滤
  13             arg2.doFilter(arg0, arg1);//递交给下一个过滤器
  14             return;
  15         }
  16         if(path.indexOf("/register.jsp")>-1){//注册页面不过滤
  17             arg2.doFilter(request, response);
  18             return;
  19         }
  20         
  21         if(uid!=null){//已经登录
  22             arg2.doFilter(request, response);//放行，递交给下一个过滤器
  23             
  24         }else{
  25             response.sendRedirect("login.jsp");
  26         }
  27 
  28     }

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• 禁止浏览器缓存动态页面 web.xml路径配置为不想让浏览器缓存的页面
• 

   1  @Override
   2     public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
   3             throws IOException, ServletException {
   4 
   5         HttpServletRequest request = (HttpServletRequest) req;
   6         HttpServletResponse response = (HttpServletResponse) resp;
   7 
   8         response.setDateHeader("Expires",-1);
   9         response.setHeader("Cache-Control","no-cache");
  10         response.setHeader("Pragma","no-cache");
  11 
  12         chain.doFilter(request, response);
  13 
  14     }
  15 
  16     @Override

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