web.xml 配置Filter

public class AuthorityFilter implements Filter
{
//FilterConfig可用于访问Filter的配置信息
private FilterConfig config;
//实现初始化方法
public void init(FilterConfig config)
{
this.config = config;
}
//实现销毁方法
public void destroy()
{
this.config = null;
}
//执行过滤的核心方法
public void doFilter(ServletRequest request,
ServletResponse response, FilterChain chain)
throws IOException,ServletException
{
//获取该Filter的配置参数
String encoding = config.getInitParameter("encoding");
String loginPage = config.getInitParameter("loginPage");
String proLogin = config.getInitParameter("proLogin");
//设置request编码用的字符集
request.setCharacterEncoding(encoding);                    //①
HttpServletRequest requ = (HttpServletRequest)request;
HttpSession session = requ.getSession(true);
//获取客户请求的页面
String requestPath = requ.getServletPath();
//如果session范围的user为null，即表明没有登录
//且用户请求的既不是登录页面，也不是处理登录的页面
if( session.getAttribute("user") == null
&& !requestPath.endsWith(loginPage)
&& !requestPath.endsWith(proLogin))
{
//forward到登录页面
request.setAttribute("tip" , "您还没有登录");
request.getRequestDispatcher(loginPage)
.forward(request, response);
}
//“放行”请求
else
{
chain.doFilter(request, response);
}
}
}

<!-- 定义Filter -->
<filter>
<!-- Filter的名字 -->
<filter-name>authority</filter-name>
<!-- Filter的实现类 -->
<filter-class>lee.AuthorityFilter</filter-class>
<!-- 下面3个init-param元素配置了3个参数 -->
<init-param>
<param-name>encoding</param-name>
<param-value>GBK</param-value>
</init-param>
<init-param>
<param-name>loginPage</param-name>
<param-value>/login.jsp</param-value>
</init-param>
<init-param>
<param-name>proLogin</param-name>
<param-value>/proLogin.jsp</param-value>
</init-param>
</filter>
<!-- 定义Filter拦截的URL地址 -->
<filter-mapping>
<!-- Filter的名字 -->
<filter-name>authority</filter-name>
<!-- Filter负责拦截的URL -->
<url-pattern>/*</url-pattern>
</filter-mapping>