public void init(FilterConfig filterConfig) throws ServletException;//初始化

public void destroy();//销毁

String getFilterName();//得到filter的名称。 
String getInitParameter(String name);//返回在部署描述中指定名称的初始化参数的值。如果不存在返回null. 
Enumeration getInitParameterNames();//返回过滤器的所有初始化参数的名字的枚举集合。 
public ServletContext getServletContext();//返回Servlet上下文对象的引用。

<filter>
  <filter-name>SessionFilter</filter-name>
  <filter-class>com.action.login.SessionFilter</filter-class>
  <init-param>
    <param-name>logonStrings</param-name><!-- 对登录页面不进行过滤 -->
    <param-value>/project/index.jsp;login.do</param-value>
  </init-param>
  <init-param>
    <param-name>includeStrings</param-name><!-- 只对指定过滤参数后缀进行过滤 -->
    <param-value>.do;.jsp</param-value>
  </init-param>
  <init-param>
    <param-name>redirectPath</param-name><!-- 未通过跳转到登录界面 -->
    <param-value>/index.jsp</param-value>
  </init-param>
  <init-param>
    <param-name>disabletestfilter</param-name><!-- Y:过滤无效 -->
    <param-value>N</param-value>
  </init-param>
</filter>
<filter-mapping>
  <filter-name>SessionFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

package com.action.login;

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;
import javax.servlet.http.HttpServletResponseWrapper;

/**
 *  判断用户是否登录,未登录则退出系统
 */
public class SessionFilter implements Filter {

  public FilterConfig config;

  public void destroy() {
    this.config = null;
  }

  public static boolean isContains(String container, String[] regx) {
    boolean result = false;

    for (int i = 0; i < regx.length; i++) {
      if (container.indexOf(regx[i]) != -1) {
        return true;
      }
    }
    return result;
  }

  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest hrequest = (HttpServletRequest)request;
    HttpServletResponseWrapper wrapper = new HttpServletResponseWrapper((HttpServletResponse) response);

    String logonStrings = config.getInitParameter("logonStrings");    // 登录登陆页面
    String includeStrings = config.getInitParameter("includeStrings");  // 过滤资源后缀参数
    String redirectPath = hrequest.getContextPath() + config.getInitParameter("redirectPath");// 没有登陆转向页面
    String disabletestfilter = config.getInitParameter("disabletestfilter");// 过滤器是否有效

    if (disabletestfilter.toUpperCase().equals("Y")) {  // 过滤无效
      chain.doFilter(request, response);
      return;
    }
    String[] logonList = logonStrings.split(";");
    String[] includeList = includeStrings.split(";");

    if (!this.isContains(hrequest.getRequestURI(), includeList)) {// 只对指定过滤参数后缀进行过滤
      chain.doFilter(request, response);
      return;
    }

    if (this.isContains(hrequest.getRequestURI(), logonList)) {// 对登录页面不进行过滤
      chain.doFilter(request, response);
      return;
    }

    String user = ( String ) hrequest.getSession().getAttribute("useronly");//判断用户是否登录
    if (user == null) {
      wrapper.sendRedirect(redirectPath);
      return;
    }else {
      chain.doFilter(request, response);
      return;
    }
  }

  public void init(FilterConfig filterConfig) throws ServletException {
    config = filterConfig;
  }
}

<filter>
  <filter-name>encoding</filter-name>
  <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
  <init-param>
    <param-name>encoding</param-name><!--用来指定一个具体的字符集-->
    <param-value>UTF-8</param-value>
  </init-param>
  <init-param>
    <param-name>forceEncoding</param-name><!--true：无论request是否指定了字符集，都是用encoding；false：如果request已指定一个字符集，则不使用encoding-->
    <param-value>false</param-value>
  </init-param>
</filter>
<filter-mapping>
  <filter-name>encoding</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>