java里面如何在用户登录管理页面时判断用户是否登录

在用户登陆的时候，后台写上：
User user = new User(xxxxxx); //建立user对象
request.getSession().setAttribute("user", user); // 保存到session

在前台，你加上:
User user = session.getAttribute("user");
if(user==null) {
response.sendRedirect("login.jsp");
} else {
// 读取 user信息
}

用户登录后把登录信息存入session，然后可以在web.xml中的filter或者validate中去判断~

你好 可以写一个拦截器, 每次用户请求都将进行拦截,判断是否登录,如果没有登录将返回登录页.这种拦截也是一种很好的解决方案.我们一般都把用户放入session中以便作一些操作,我有一个简单的拦截器例子,当然使用之前是要通过web.xml进行参数配置的 给你作下参考,
package com.manage.filter;

import java.io.IOException;
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.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

/**
* @author RiesLing
*
*/
public class CheckLoginFilter implements Filter {
public static boolean isContains(String container, String[] regx) {
boolean result = false;
for (int i = 0; i < regx.length; i++) {
if (container.indexOf(regx[i]) != -1) {
return true;
}
}
return result;
}
public FilterConfig config;
public void setFilterConfig(FilterConfig config) {
this.config = config;
}
public FilterConfig getFilterConfig() {
return config;
}
@SuppressWarnings("static-access")
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {

HttpServletRequest httpreq = (HttpServletRequest) request;
@SuppressWarnings("unused")
HttpServletResponse httpres = (HttpServletResponse) response;
HttpServletResponseWrapper wrapper = new HttpServletResponseWrapper(
(HttpServletResponse) response);
String logonStrings = config.getInitParameter("logonStrings");
String includeStrings = config.getInitParameter("includeStrings");
String redirectPath = httpreq.getContextPath()
+ config.getInitParameter("redirectPath");
String disabletestfilter = config.getInitParameter("disabletestfilter");

if (disabletestfilter.toUpperCase().equals("Y")) {
chain.doFilter(request, response);
return;
}
String[] logonList = logonStrings.split(";");
String[] includeList = includeStrings.split(";");
Object user = httpreq.getSession().getAttribute("userSession");
if (user == null) {
if (!this.isContains(httpreq.getRequestURI(), includeList)) {
chain.doFilter(request, response);
return;
}
if (this.isContains(httpreq.getRequestURI(), logonList)) {
chain.doFilter(request, response);
return;
}
wrapper.sendRedirect(redirectPath);

} else {
chain.doFilter(request, response);
}
}
public void destroy() {
this.config = null;
}
public void init(FilterConfig filterConfig) throws ServletException {
this.config = filterConfig;
}
}

设置个session 再判断session是否为空追问

能不能写一下关键的几句代码，session理解的不是很透，谢谢！！！！

追答

设置session.setAttribute( "Username", "username的值 ");
获取session.getAttribute( "Username");