day22(过滤器Filter)

过滤器

　　生命周期：初始化 -----过滤-------销毁

　　作用：过滤url ，特定字符

　　创建方式：实现一个接口继承Filter　

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package com.baidu.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;     public class Demo01 implements Filter {       public void destroy() {         System.out.println("过滤销毁");     }         public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {         System.out.println("请求过滤");         MyHttpServletRequest msr=new MyHttpServletRequest((HttpServletRequest)request);         chain.doFilter(msr, response);         System.out.println("响应过滤");     }       /**      * @see Filter#init(FilterConfig)      */     public void init(FilterConfig fConfig) throws ServletException {         System.out.println("过滤器初始化");     }   }

　　

　　　　配置过滤器（web.xml）

　　　　　　　　和配置servlet相似。

 

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<filter>     <filter-name>Demo01</filter-name>     <filter-class>com.baidu.filter.Demo01</filter-class>   </filter>   <filter-mapping>     <filter-name>Demo01</filter-name>     <url-pattern>/*</url-pattern>//可以设置经过过滤器的url  /*表示项目下的所有路径都得经过过滤器   </filter-mapping>

 

　　　　　　过滤器在web中的位置

　　　　浏览器        < ------------ >         过滤器              < ------------   >              服务器

 

　　注意事项

　　　　1.配置文件中会配置Filter过滤器的位置只要符合其位置就会经过过滤器    

　　　　2.请求完成以后响应动作也会经过过滤器 

　　使用过滤器来修改编码格式，这样就不需要用每个servlet中去修改编码格式了

　　　　

 

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（使用的装饰者设计模式来实现）package com.baidu.filter;   import java.io.UnsupportedEncodingException;   import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletRequestWrapper;   public class MyHttpServletRequest extends HttpServletRequestWrapper {     private HttpServletRequest request;     public MyHttpServletRequest(HttpServletRequest request) {         super(request);         this.request=request;     }     @Override     public String getParameter(String name) {         //判断提交方式（get/post）         String method = request.getMethod();         if ("Get".equalsIgnoreCase(method)) {             String value = super.getParameter(name);                 try {                     value = new String(value.getBytes("ISO-8859-1"),"UTF-8");                 } catch (UnsupportedEncodingException e) {                     // TODO Auto-generated catch block                     e.printStackTrace();                 }                 return value;         }         if ("post".equalsIgnoreCase(method)) {             try {                 System.out.println(request.getCharacterEncoding());                 request.setCharacterEncoding("UTF-8");                 //value = super.getParameter(name);             } catch (Exception e) {                 // TODO Auto-generated catch block                 e.printStackTrace();             }         }         return super.getParameter(name);     }   }

 

　　使用动态代理来实现实现类的增强

 

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public class GenericEncodingFilter implements Filter {       @Override     public void init(FilterConfig filterConfig) throws ServletException {       }       @Override     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)             throws IOException, ServletException {         final HttpServletRequest req = (HttpServletRequest) request;         // 增强req:（使用匿名内部类）         HttpServletRequest myReq = (HttpServletRequest) Proxy.newProxyInstance(req.getClass().getClassLoader(),                 req.getClass().getInterfaces(), new InvocationHandler() {                                           @Override                     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {                         // 判断执行的方法是否是getParameter:                         if("getParameter".equals(method.getName())){                             // 调用的是getParameter:需要增强这个方法.                             // 判断请求方式是GET还是POST:                             String type = req.getMethod();                             if("get".equalsIgnoreCase(type)){                                 String value = (String) method.invoke(req, args);                                 value = new String(value.getBytes("ISO-8859-1"),"UTF-8");                                 return value;                             }else if("post".equalsIgnoreCase(type)){                                 req.setCharacterEncoding("UTF-8");                             }                         }                         return method.invoke(req, args);                     }                 });                   chain.doFilter(myReq, response);     }       @Override     public void destroy() {       }   }