用户登录(login)过滤器(Filter)

在一个web应用中，通常需要用户认证，通过了用户认证才能访问网页。
几乎所有网页在访问前，都需要通过用户认证，所以用户认证可以做成一个过滤器。访问一个Servlet或JSP时，会自动的调用过滤器，过滤器里判断是否已经用户认证过了，如果已经认证通过，则显示页面，如果没有通过，则跳转至用户登录页面。

下面是用户登录过滤器的代码：

（根据网上搜索到的一个例子，修改而成）

------ LoginFilter.java ------
package common.filter;

import javax.servlet.*;

import javax.servlet.http.*;

import java.util.*;

import java.io.*;

/**

 * 检测用户是否登录，如果没有登录，则重定向到登录页面

 */

public class LoginFilter implements Filter

{
private String loginURL = null;
private List notCheckURLList = null;
private String loginSessionKey = null;

@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
{
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;

String servletPath = request.getServletPath();

// Pass if not need to check login
if (loginSessionKey == null) {
filterChain.doFilter(request, response);
return;
}

// Pass if already logged in
HttpSession session = request.getSession();
if (session.getAttribute(loginSessionKey) != null) {
filterChain.doFilter(servletRequest, servletResponse);
return;
}

// Pass if it is configured not checking
if (checkRequestURIIntNotFilterList(request)) {
filterChain.doFilter(servletRequest, servletResponse);
return;
}

// Redirect to login page
response.sendRedirect(request.getContextPath() + loginURL);
return;
}

private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) {
String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo());
return notCheckURLList.contains(uri);
}

@Override
public void destroy() {
}

@Override
public void init(FilterConfig filterConfig) throws ServletException {
notCheckURLList = new ArrayList();

loginURL = filterConfig.getServletContext().getInitParameter("loginURL");
loginSessionKey = filterConfig.getServletContext().getInitParameter("loginSessionKey");

String notCheckURLListStr = filterConfig.getServletContext().getInitParameter("notCheckURLList");

if (notCheckURLListStr != null) {
StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");
while (st.hasMoreTokens()) {
notCheckURLList.add(st.nextToken());
}
}
}

}

------ web.xml ------

  <context-param>

    <param-name>loginURL</param-name>

    <param-value>/login.jsp</param-value>

  </context-param>

  <context-param>

    <param-name>loginSessionKey</param-name>

    <param-value>userName</param-value>

  </context-param>

  <context-param>

    <param-name>notCheckURLList</param-name>

    <param-value>/login.jsp;/login;/jsp/NewFile.jsp</param-value>

  </context-param>

  <filter>

    <filter-name>loginFilter</filter-name>

    <filter-class>common.filter.LoginFilter</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>loginFilter</filter-name>

    <url-pattern>/*</url-pattern>

  </filter-mapping>