- servlet只实例化一次
- 单例模型
- 全局变量的值不确定，线程不安全====避免声明全局变量
- 第一次：构造块 构造函数 init() service() super.service() doGet()/doPost()
第二次：super.service() doGet()/doPost()
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@WebServlet("/Life.action")
public class LifeServlet extends HttpServlet {
//servlet只实例化一次，单例模型 全局变量的值不确定，线程不安全====避免声明全局变量
{
//实例块，在构造方法之前调用
System.out.println("1.构造代码块");
}
public LifeServlet(){
System.out.println("2.构造方法");
}
@Override
public void init() throws ServletException {
System.out.println("3.初始化init()");
}
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("4.service()");
super.service(req, resp);//5.判断请求方法是post还是get
//get====>doGet
//post===>doPost
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("6.doGet");
}
@Override
public void destroy() {
//关闭容器时
System.out.println("7.servlet销毁");
super.destroy();
}
}
HTML-JAVA-数据库
1.html====>关键active2.Servlet====> 关键1：@WebServlet("/reg.action")====>连接HTML 关键2：request.setCharacterEncoding("utf-8")====>解决参数编码问题 关键3：String uname = request.getParameter("uname")====>接收html中的数据 uname：标签中name属性的命名 关键4：中间连接数据库部分参考之前写过的文章JDBC部分 关键5：在HTML中显示（添加补充框架） response.setContentType("text/html;charset=utf-8");//设置编码 PrintWriter out = response.getWriter(); out.println(""); out.println("
封装代码汇总
调错思路看是哪一端的错误
- 客户端：在开发者工具
- 服务端：看自己的代码
- 获取session：客户端与服务器多次请求和响应的共享空间
HttpSession session = request.getSession();
session.getAttribute("userid");
session.setAttribute("userid",userid);
2.ServletContext
ServletContext application = request.getSession().getServletContext();
application.getAttribute("onlineuserList");
application.setAttribute("onlineuserList",onlineuserList);
3.显示本机ID+在线ID
private void number(HttpServletRequest request, HttpServletResponse response){
JsonModel jsonModel = new JsonModel();
int userid = 0;
String ip = getIpAddress(request);
String addr = "";
//获取session：客户端与服务器多次请求和响应的共享空间
HttpSession session = request.getSession();
if(session.getAttribute("userid")==null){
//如果id为空，则给一个随机数作为id
userid = new Random().nextInt(1000);
session.setAttribute("userid",userid);
//获取application存这个用户编号====所有访问的用户编号
ServletContext application = request.getSession().getServletContext();
Map onlineuserMap = new HashMap();
List> onlineuserList = null;
if(application.getAttribute("onlineuserList")==null){
onlineuserList = new ArrayList>();
application.setAttribute("onlineuserList",onlineuserList);
}
onlineuserMap.put("userid",userid);//添加在线人数
onlineuserMap.put("ip",ip);//添加IP
onlineuserList = (List>) application.getAttribute("onlineuserList");
onlineuserList.add(onlineuserMap);
//System.out.println(onlineuserList);
}
userid = Integer.parseInt(session.getAttribute("userid").toString());
try {
jsonModel.setCode(1);
jsonModel.setData(userid);
super.writeJson(jsonModel,response);
} catch (IOException e) {
e.printStackTrace();
jsonModel.setCode(0);
jsonModel.setMsg(e.getMessage());
}
}
4.本ID退出
private void quit(HttpServletRequest request,HttpServletResponse response){
HttpSession session = request.getSession();
int id = Integer.parseInt(session.getAttribute("userid").toString());
//取出在线用户列表
ServletContext application = request.getServletContext();
List> onlineuserList = (List>) application.getAttribute("onlineuserList");
//在线用户列表中移出退出的id
for (int i=0;i
5.保存聊天记录
private void sendMessage(HttpServletRequest request,HttpServletResponse response){
//取出在线用户列表
ServletContext application = request.getServletContext();
HttpSession session = request.getSession();
//取出用户id
int userid = Integer.parseInt(session.getAttribute("userid").toString());
//取出该id说的话
String message = request.getParameter("message");
//获取现在的时间
Date date = new Date();
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String time = simpleDateFormat.format(date);
//历史聊天记录
List messageList = null;
if (application.getAttribute("messageList")==null){
messageList = new ArrayList();
application.setAttribute("messageList",messageList);
}
messageList = (List) application.getAttribute("messageList");
//拼接样式信息
StringBuffer stringBuffer = new StringBuffer();
stringBuffer.append(userid+"说：
");
stringBuffer.append(message+"
");
stringBuffer.append(""+time+"");
messageList.add(stringBuffer.toString());
//System.out.println(messageList);
JsonModel jsonModel = new JsonModel();
jsonModel.setCode(1);
jsonModel.setData(messageList);
try {
super.writeJson(jsonModel,response);//json只有数组和对象，而list没有键，所以以数组形式保存
} catch (IOException e) {
e.printStackTrace();
}
}
