javaweb登陆过滤器实现

在web.xml中配置登陆过滤器：

<!-- 配置登陆过滤器 -->
    <filter>
        <filter-name>loginFilter</filter-name>
        <filter-class>weijiabin.BBS.Utils.LoginFilter</filter-class>
        <init-param>
            <param-name>passUrl</param-name>
            <param-value>index;login;FunctionServlet</param-value>
           </init-param>
    </filter>

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

上边代码中的param-value用来设置不进行拦截的地址关键字（以;作为分隔符），在下边过滤器代码中用passUrl表示

然后写过滤器代码：

public class LoginFilter implements Filter {

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}
	String passUrl = "";
	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
			throws IOException, ServletException {
		 HttpServletRequest httpRequest=(HttpServletRequest)arg0;
	        HttpServletResponse httpResponse=(HttpServletResponse)arg1;
	        HttpSession session=httpRequest.getSession();
	        String[] strArray = passUrl.split(";");
　　　　　　　　　　//下边循环作用是依次检查访问的url中是否包含passurl中的关键字，如果包含则不进行拦截
	        for (String str : strArray) {
	            if (str.equals(""))//如果在上边配置中设置的url为空，则说明都需要进行拦截，跳过此循环
	                continue;
	            if (httpRequest.getRequestURL().indexOf(str) >= 0) {
	                arg2.doFilter(httpRequest, httpResponse);
	                return;
	            }
	        }

	        if(session.getAttribute("sessionUser")!=null){
	            arg2.doFilter(httpRequest, httpResponse);
	        }
	        else{
	            httpResponse.sendRedirect(httpRequest.getContextPath()+"/login.jsp");
	        }
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
		 passUrl = arg0.getInitParameter("passUrl");
	}
}