JavaWeb之过滤器

1.什么是过滤器？

解析：过滤器是向web应用程序的请求和响应（pipeline）添加功能的web服务，过滤器可以统一的集中处理请求和响应。

2. 1〉过滤器是对资源的请求进行过滤的对象，对请求和响应都进行过滤。

　2〉过滤器是一个类，实现了javax.servlet.Filter接口

3. 字符集的过滤器

1）创建form表单

  <form action = "<%=path %>/servlet/uploadServlet" method = "post" >
    用户名：<input name = "uname" type = "text" value = "" />
      <input  type = "submit" value = "提交" >
      </form>

2）创建servlet，即表单提交的地址

public class uploadServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request,response);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

String name = request.getParameter("uname"); //获取用户从前台传过来的数据
        if (name.equals("admin")) {
            request.getSession().setAttribute("name", name);  //把信息放入session中
        //成功跳转到欢迎界面 index.jsp   
       request.getRequestDispatcher("/jsp/index.jsp").forward(request, response); 
        }else{
　　　　　//失败则停留在登陆界面 login.jsp
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        }
    }
    }

3）创建过滤器CharacterEncodingFilter

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;

public class CharacterEncodingFilter  implements Filter{

    public void destroy() {
    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
         request.setCharacterEncoding("utf-8"); //对字符集进行过滤
         chain.doFilter(request, response);   //对拦截到的请求 进行 放行  ，到哪里？ 去下一个过滤器
        
    }

    public void init(FilterConfig filterConfig) throws ServletException {
    }

}

4）在WEB—INF下的web.xml中进行节点的配置（千万不能忘）

<filter>
  <filter-name>CharacterEncodingFilter</filter-name>
  <filter-class>cn.uploadServlet.CharacterEncodingFilter</filter-class>
  </filter>

<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern> //对web工程下的所有项目进行过滤
</filter-mapping>

以上的过滤器可以防止中文乱码，不需要每次都设置字符编码格式

4. 通用的用户登陆过滤器（SessionFilter）

1）功能描述：用于检查用户是否登陆了系统，如未登陆，则重新定向到登陆页面

2），3）步同上述 3 中的一样

4）创建SessionFilter

import java.io.IOException;
import java.util.regex.Pattern;

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 SessionFilter implements Filter {

     Pattern patternUrl;
    public void init(FilterConfig config) throws ServletException {
      String url = config.getInitParameter("execuldeUrl");
    if (url!=null&& !url.equals("")) {
        //在webXml中配置了例外，需要获取一个正则对象
        patternUrl = Pattern.compile(url);
    }
    }
     public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
　　　　 
         HttpServletRequest req = (HttpServletRequest)request;   
         HttpServletResponse res = (HttpServletResponse)response;

        //HttpServletRequest继承自ServletRequest，ServletRequest中没有获取路径的方法，所以进行上面的强转
         String  servletPath = req.getServletPath(); 
         if (patternUrl.matcher(servletPath).matches()) {  
             chain.doFilter(request, response); 
            return; 
        }
　　　　　//获取用户登陆的信息，是否正常登陆
         Object obj = req.getSession().getAttribute("name");
         if (obj!=null) {
            //用户已登陆 ，放行
             chain.doFilter(request, response);
        }else{
            //用户未登陆，返回登陆页面
          res.sendRedirect(req.getContextPath()+"/login.jsp");
        }
    }
 
    public void destroy() {
         
    }
}

5) 在web—xml中配置节点

 <!-- 鉴权过滤 -->
  <filter>
  <filter-name>SessionFilter</filter-name>
  <filter-class>cn.uploadServlet.SessionFilter</filter-class>
  
  <init-param>
  <param-name>execuldeUrl</param-name>
  <param-value>/servlet/uploadServlet</param-value>
  </init-param>
  
  </filter>

<filter-mapping>
<filter-name>SessionFilter</filter-name>
<url-pattern>/jsp/*</url-pattern>
</filter-mapping>

<filter-mapping>
<filter-name>SessionFilter</filter-name>
<url-pattern>/uploadServlet/*</url-pattern>
</filter-mapping>