文章摘要
这篇文章介绍了一个基于Javax Servlet API实现的过滤器类`LoginFilter`，用于在Servlet生命周期中进行身份验证。该过滤器通过检查请求路径和会话属性来判断用户是否已登录。如果用户未登录，则提示用户登录并重定向。文章重点描述了过滤器的构造、核心方法（`doFilter`）的处理逻辑及其关键字密度控制在2%左右。
package filter;
import java.io.IOException;
import java.io.PrintWriter;
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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
@WebFilter(filterName=”loginFilter”, urlPatterns={ “/*” })
public class LoginFilter implements Filter {
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req=(HttpServletRequest) request;
HttpServletResponse resp=(HttpServletResponse) response;
HttpSession session=req.getSession(true);
resp.setContentType(“text/html;”);
resp.setCharacterEncoding(“utf-8”);
PrintWriter out=resp.getWriter();
String request_uri=req.getRequestURI();
String ctxPath=req.getContextPath();
String uri=request_uri.substring(ctxPath.length());
if (uri.contains(“login.jsp”) || uri.contains(“loginServlet”)) {
chain.doFilter(request, response);
} else {
if (session.getAttribute(“user”) !=null) {
chain.doFilter(request, response);
} else {
out.println(“您没有登录，请先登录！3秒后回到登录页面。”);
resp.setHeader(“refresh”, “3;url=” + ctxPath + “/login.jsp”);
return;
}
}
}
public void init(FilterConfig fConfig) throws ServletException {
}
}