public class LoginFilter implements Filter {
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("过滤器初始化中...");
}
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest httpServletRequest = (HttpServletRequest) request;
HttpServletResponse httpServletResponse = (HttpServletResponse) response;
HttpSession session = httpServletRequest.getSession();
System.out.println("开始过滤....");
if (httpServletRequest.getServletPath().indexOf("login.jsp") > 0) {
System.out.println("放过该请求...");
chain.doFilter(request, response);
} else {
String user = (String) session.getAttribute("login");
if (user != null) {
System.out.println("已登录，取消过滤...");
chain.doFilter(request, response);
} else {
System.out.println("未登录，跳转到登录页面...");
httpServletResponse.sendRedirect(httpServletRequest.getContextPath() + "/login.jsp");
}
}
System.out.println("完成过滤....");
}
}public class LoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public String notNull(String param) {
return param == null ? "" : param;
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
String username = notNull(request.getParameter("username"));
String password = notNull(request.getParameter("password"));
if (username.equals("douya0808") && password.equals("123456")) {// 直接给xxxxLoginTest/servlet/LoginServlet会由于没传值而报出NullPointer
System.out.println("信息正确，跳转页面中...");
session.setAttribute("login", "LoginSuccess!");
response.sendRedirect(request.getContextPath() + "/success.jsp");
} else {
response.sendRedirect(request.getContextPath() + "/login.jsp");
}
}
}<filter>
<filter-name>LoginFilter</filter-name>
<filter-class>filter.LoginFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>LoginFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/servlet/LoginServlet</url-pattern>
</servlet-mapping>
访问：localhost:8090/LoginTest/success.jsp，当然这个success.jsp是不能直接访问的，上面的程序达到了过滤的效果，但是控制台的输出却如下
开始过滤....
未登录，跳转到登录页面...
完成过滤....
开始过滤....
放过该请求...
完成过滤....
但是我预期的输出是
开始过滤....
未登录，跳转到登录页面...
完成过滤....
差在哪里呢，请前辈指点迷津
------解决方案--------------------
httpServletResponse.sendRedirect(httpServletRequest.getContextPath() + "/login.jsp");这个不也是一个请求嘛，所以相当于请求了两次。是不是啊？
------解决方案--------------------
逻辑上没有任何问题。
------解决方案--------------------
正常，你的过滤器拦截所有请求，那么只要和后台打交道的请求都要走一遍过滤器里的逻辑～