一个登录页面设置查看Cookie中的数据（Cookie不为null）;然后将页面提交到另一个页面去，在这个页面中的到是否选择记住用户名，如果选择了，
就创建Cookie对象，将用户名存储起来，下次登录时，用户名直接显示在上面，注意：路径一定要一致，且都能访问。
登录页面
package com.itheima.cookie;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.itheima.myConstant;
//模拟登录时，记住用户名和密码
@WebServlet(
urlPatterns = { "/CookieDemo2" },
initParams = {
@WebInitParam(name = "CookieDemo2", value = "com.itheima.cookie.CookieDemo2")
})
public class CookieDemo2 extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//读取记住的用户名
String name="";
String rem="";
Cookie[] cookies=request.getCookies();
for(int i=0;cookies!=null&&i<cookies.length;i++){
Cookie c=cookies[i];
if(myConstant.USER_NAME.equals(c.getName())){
//找到了
String value=c.getValue();
name=value;
rem="checked='checked'";
}
}
//显示出登陆界面
response.setContentType("text/html;charset=utf-8");
PrintWriter out=response.getWriter();
out.println("<html>");
out.println("<head><title>用户登陆</title></head>");
out.println("<body>");
out.println("<form action='/CookieTest/CookieDemo3' method='post'>");
out.println("<table width='400' border='1'>");
out.println("<tr>");
out.println("<td>用户名</td>");
out.println("<td><input type='text' name='username' value="+name+"/></td>");
out.println("</tr>");
out.println("<tr>");
out.println("<td>密码</td>");
out.println("<td><input type='password' name='password'/></td>");
out.println("</tr>");
out.println("<tr>");
out.println("<td colspan='2'><input type='checkbox' name='remember'"+rem+"/>记住用户名</td>");
out.println("</tr>");
out.println("<tr>");
out.println("<td colspan='2'><input type='submit' value='go'/></td>");
out.println("</tr>");
out.println("</table></form></body></html>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
处理页面
package com.itheima.cookie;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.itheima.myConstant;
/**
* 接收用户名和密码，验证是否是合法用户
*看用户是否选中了checkbox,如果选中，将数据写入Cookie
*/
@WebServlet(
urlPatterns = { "/CookieDemo3" },
initParams = {
@WebInitParam(name = "CookieDemo3", value = "com.itheima.cookie.CookieDemo3")
})
public class CookieDemo3 extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String remember=request.getParameter("remember");
// System.out.println(remember);//选中输出on，不选中输出null(value的值)
if(remember!=null){
//如果选中,把用户名写入Cookie
Cookie c=new Cookie(myConstant.USER_NAME,request.getParameter("username"));
c.setPath(request.getContextPath());
c.setMaxAge(Integer.MAX_VALUE);//永久保存
response.addCookie(c);
}
response.setContentType("text/html;charset=utf-8");
response.getWriter().write("登陆成功，这是主页");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request,response);
}
}