一、目标

用户可以登录并记住密码进入留言板，添加留言，点击留言列表中的标题可显示该条留言全部内容。

二、相关知识

使用Cookie实现自动登录
用户第一次登录网站，服务器将用户名和密码以Cookie的形式发送到客户端。当客户之后再次访问该网站时，浏览器自动将Cookie文件中的用户名和密码随请求一起发送到服务器，服务器从Cookie中取出用户名和密码并且通过验证。
java类的定义与使用
定义java类时注意属性的定义、构造方法的重写，定义两个方法，一个是访问方法（getter），一个是修改方法（setter）。

三、实现思路

登录
输入用户名、密码登录，对应检测登录BoardLoginServlet
可实现记住登录信息 Cookie实现
登录成功显示留言板标题列表页面board-title.jsp，登录失败返回登录页面
显示留言标题
标题列表为上下文变量lists，其中标题为链接，点击可显示留言具体信息界面（跳转到MessageServlet处理）。

 list = username+":"+"<a href='MessageServlet?title="+title+"'target='_parent'>"+title+"</a>";

页面下方有新增留言的链接，点击后跳转到写留言页面

 <a href="board-write.jsp">新增留言</a>

添加留言
输入标题、内容 post给WriteServlet
显示留言具体信息
在MessageServlet中遍历查找留言并传递变量，显示留言信息在board-message.jsp

四、代码实现

board-login.jsp

<form action="board.do" method="post">
    <br>
    <h1 class="text" >登录界面</h1>
            昵称：<input type="text" name="username" value="${cookie.username.value}"/><br>
            密码：<input type="password" name="password" value="${cookie.password.value}"/><br><br>
            <input type="checkbox" name="check" value="check"/>记住密码<br>  <br>
            <input type="submit" value="登录"/>
            <input type="reset" value="取消"/>
</form>

board-title.jsp

 <h2>留言板</h2>
    ${lists}
    <a href="board-write.jsp">新增留言</a>

boarrd-write.jsp

<form action="write.do" method="post">
    标题:<input type="text" name="title"/><br>
    内容:<input type="text" name="text"/><br>
    <input type="submit"/>
</form>

board-message.jsp

<h2>留言详情</h2>
    用户名：${name}<br>
    标题：${title}<br>
    内容：${text}<br>
    时间：${date}<br>

Message.java（将留言信息存储在Message类中）

package board;

import java.util.Date;

public class Message {
    private String title;//标题
    private String time;//时间
    private String username;//用户名
    private String text;//内容
    public Message(){}
    //初始化
    public Message(String title,String time,String username,String text){
        this.title = title;
        this.time = time;
        this.username = username;
        this.text = text;
    }

    public String getTitle(){
        return title;
    }
    public String getUsername(){
        return username;
    }
    public String getTime(){
        return time;
    }
    public String getText(){
        return text;
    }
}

BoardLoginServlet.java（用Cookie登录）

package board;

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

@javax.servlet.annotation.WebServlet(name = "BoardLoginServlet",urlPatterns = "/board.do")
public class BoardLoginServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset = utf-8");
        request.setCharacterEncoding("UTF-8");
        HttpSession session=request.getSession();
        String username = request.getParameter("username").trim();
        String password = request.getParameter("password").trim();
        session.setAttribute("username",username);
        if (!(username.equals("admin") &&password.equals("admin"))&&!(username.equals("123") &&password.equals("123"))) {
            response.sendRedirect("board-login.jsp");
        } else {

            if ((request.getParameter("check") != null) && (request.getParameter("check").equals("check"))) {
                Cookie nameCookie = new Cookie("username", username);
                Cookie pswdCookie = new Cookie("password", password);
                nameCookie.setMaxAge(60 * 60);
                pswdCookie.setMaxAge(60 * 60);
                nameCookie.setPath("/");
                pswdCookie.setPath("/");
                response.addCookie(nameCookie);
                response.addCookie(pswdCookie);
                String value1 = "", value2 = "";
                Cookie cookie = null;
                Cookie[] cookies = request.getCookies();
                if (cookies != null) {
                    for (int i = 0; i < cookies.length; i++) {
                        cookie = cookies[i];
                        if (cookie.getName().equals("username"))
                            value1 = cookie.getValue();
                        if (cookie.getName().equals("password"))
                            value2 = cookie.getValue();
                    }
                    if (value1.equals("admin") && value2.equals("admin")||value1.equals("123") && value2.equals("123")) {
                        response.sendRedirect("board-title.jsp");
                    } else {
                        response.sendRedirect("board-login.jsp");
                    }

                }
            }
            else
            {
                response.sendRedirect("board-title.jsp");
            }
        }

    }
}

WriteServlet.java（新增留言）

package board;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

@WebServlet(name = "WriteServlet",urlPatterns = "/write.do")
public class WriteServlet extends HttpServlet {
	//messages列表中存放Message类对象
    public List<Message> messages = new ArrayList<Message>();
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        ServletContext context = request.getServletContext();
        HttpSession session = request.getSession();
        //用户名存储到session中
        String username =(String)session.getAttribute("username");
        String title = request.getParameter("title");
        String text = request.getParameter("text");
        //获取当前时间
        SimpleDateFormat formatter= new SimpleDateFormat("yyyy-MM-dd 'at' HH:mm:ss");
        Date date = new Date(System.currentTimeMillis());
        String time = formatter.format(date);
		//在messages列表中添加留言对象
        messages.add(new Message(title,time,username,text));
        context.setAttribute("messages",messages);

        String list = new String();
        //list中存放留言用户名+留言标题，标题为链接，可跳转到留言具体信息，并传参title
        list = username+":"+"<a href='MessageServlet?title="+title+"'target='_parent'>"+title+"</a>";
        String lists = new String();
        //将留言标题列表信息存到上下文对象
        if(context.getAttribute("lists")!=null){
            lists = context.getAttribute("lists") + list + "<br>";
        }
        else{
            lists = list + "<br>";
        }
        context.setAttribute("lists", lists);
        request.setAttribute("lists", lists);
		//转发
        RequestDispatcher dispatcher = request.getRequestDispatcher("/board-title.jsp");
        dispatcher.forward(request, response);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

MessageServlet.java

package board;

import com.sun.net.httpserver.HttpContext;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

@WebServlet(name = "MessageServlet",urlPatterns = "/MessageServlet")
public class MessageServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        ServletContext context = request.getServletContext();
        List<Message> messages = new ArrayList<Message>();
        //获取列表
        messages = (List<Message>)context.getAttribute("messages");
        //获取链接中的参数title
        String title =request.getParameter("title");
        String name = new String();
        String date = new String();
        String text = new String();
		//遍历列表，查找该title的具体信息
        for(Message message : messages){
            if((message.getTitle()).equals(title)){
                name = message.getUsername();
                date = message.getTime();
                text = message.getText();
                title = message.getTitle();
                request.setAttribute("name",name);
                request.setAttribute("title",title);
                request.setAttribute("text",text);
                request.setAttribute("date",date);
                break;
            }
        }
        //将留言信息转发到board-message.jsp
        RequestDispatcher dispatcher = request.getRequestDispatcher("/board-message.jsp");
        dispatcher.forward(request, response);




    }
}