java web实现简单留言板功能

本文实例为大家分享了java web实现简单留言板的具体代码，供大家参考，具体内容如下

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

1、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。

2、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

1、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

2、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" rel="external nofollow" rel="external nofollow" >新增留言</a>

3、添加留言

输入标题、内容 post给WriteServlet

4、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" rel="external nofollow" rel="external nofollow" >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);

}
}

（以上仅为部分代码）

来源：https://blog.csdn.net/weixin_46041475/article/details/109930277