java servlet过滤器使用示例

    <filter-class>com.filter.Filter/class</filter-class>

       <init-param>
   <param-name>file</param-name>
   <param-value>filename</param-value>
       </init-param>
    </filter>

    <filter-mapping>
 <filter-name>Filtername</filter-name>
<url-pattern>/*</url-pattern>
   </filter-mapping>

  config = null;

}

public void doFilter(ServletRequest request, ServletResponse response ,

   FilterChain chain) throws IOException, ServletException {

  request.setCharacterEncoding(encoding);

  chain.doFilter(request, response);

}

public void init(FilterConfig config) throws ServletException {

  this.config  = config;

  String s = config.getInitParameter("encoding");

  if(s!=null){

   encoding = s;

  }

}

}

    <filter-name>encodingFilter</filter-name>

    <filter-class>com.filter.CharacterEncodingFilter</filter-class>

    <init-param>

      <param-name>encoding</param-name>

      <param-value>utf-8</param-value>

    </init-param>

  </filter>

  <filter-mapping>

    <filter-name>encodingFilter</filter-name>

    <url-pattern>/*</url-pattern>

  </filter-mapping>
 

      密码:<c:out value="${param.userpassword}" default="none"></c:out><br>

      <form action="MyJsp.jsp" method="post">

        用户名：<input type="test" name="username"> <br>

        密码:<input type="password" name="userpassword"><br>

        <input type="submit" value="提交">

      </form>
 

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

import java.text.SimpleDateFormat;
import java.util.Date;
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.HttpSession;

import com.sun.org.apache.bcel.internal.generic.NEW;

public class LoginFilter implements Filter{

  private FilterConfig config =null;
  private String filename = null;
  private String filtername = null;
  public void destroy() {
    this.config = null;
    this.filename = null;
    this.filtername = null;
  }

  public void doFilter(ServletRequest request , ServletResponse response,
      FilterChain chain ) throws IOException, ServletException {
    HttpServletRequest hRequest = (HttpServletRequest) request;
    // 获取session对象
    HttpSession session = hRequest.getSession();
    // 先判断session中的LOGGED是否有值，如没有则说明是新的请求
    if(null==session.getAttribute("LOGGED")){
      session.setAttribute("LOGGED", "yes");    // 设置LOGGED的值为yes，防止同一会话重复记录
      File file = new File(this.filename);
      if(!file.exists())
        file.createNewFile();        // 判断文件是否存在，如果不存在，就建立一个新的

      /*
       * 创建日志记录内容logContent包括访问者的IP， 访问的页面URL和访问的时间以及日志过滤器的名字
       */
      String logContent = hRequest.getRemoteHost()+"->"+hRequest.getRequestURI()+" Logged "+getTime()+" By s"+this.filtername+"\r\n";
      RandomAccessFile rf = new RandomAccessFile(this.filename,"rw");   // 建立一个随机文件操作对象
      rf.seek(rf.length());   // 将写入指针指向文件的尾部，rf.length()获得文件的长度，seek文件长度这么长得距离正好是文件的尾部
      rf.writeBytes(logContent);   // 将日志写入到文件中去
      rf.close();   // 关闭文件
    }
    chain.doFilter(request, response);
  }

  public void init(FilterConfig config) throws ServletException {
    this.config = config;
    this.filename = this.config.getInitParameter("file");
    this.filtername = this.config.getFilterName();
  }

  // 获取时间
  private String getTime(){
    SimpleDateFormat sdf  = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss");
    return sdf.format(new Date());
  }

}