15 Servlet——利用ServletContext制作网站访问计数器

背景

我们以 第13节 的案例为背景，添加网站访问的计数功能。

设计思路

创建一个文件：用来存储网站访问的次数

从文件获取：在初始化InitServlet中的init()方法中，从文件获取已经存好的值作为已经访问的数量

在用户登录的LoginServlet和3天免登陆的CookieServlet中添加往ServletContext对象中添加获取和自增计数变量的代码。（-_-||好长的一句话）

• 获取：通过getAttribute()获取目标数据变量
• 自增：获取之后变量自增，又通过setAttribute()覆盖原有值

写入值到文件：当服务器关闭，ServletContext对象会被销毁，所以我们需要在InitServlet的destroy方法中向文件中写入ServletContext中的用来计数的变量的值。（-_-||）

演示

演示说明：启动服务器->登录->主页看到1->注销，再次登录->主页看到2->关闭服务器->重启服务器->登录->主页看到3

 

代码

InitServlet

public class InitServlet extends HttpServlet {
	@Override
	public void init() throws ServletException {
		//ServletContext对象
		ServletContext sc = this.getServletContext();
		//从文件中获取值
		InputStream is = sc.getResourceAsStream("/doc/count.txt");//保存访问次数的文件路径
		BufferedReader br = null;
		try{
			br = new BufferedReader(new InputStreamReader(is));
			String countor= br.readLine();
			System.out.println("读取countor:"+countor);
			sc.setAttribute("countor", countor);
		}catch(IOException e) {
			e.printStackTrace();
		}finally {
			try {
				if(br!=null) {
					br.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		//赋值到ServletContext对象中去
		
	}
	@Override
	public void destroy() {
		System.out.println("我被执行了1");
		//从ServeltContext中获取值
			//ServletContext对象
		ServletContext sc = this.getServletContext();
			//获取值
		String countor = (String)sc.getAttribute("countor");
		System.out.println("写入countor:"+countor);
		//写入文件
		String path = sc.getRealPath("/doc/count.txt");//保存访问次数的文件路径

FileWriter fw = null; BufferedWriter bw = null; System.out.println("我被执行了2"); try{ System.out.println("我被执行了3"); bw = new BufferedWriter(fw = new FileWriter(path)); bw.write(countor); bw.flush(); System.out.println("我被执行了4"); }catch(IOException e) { e.printStackTrace(); }finally { try { if(bw!=null) { bw.close(); } } catch (IOException e) { e.printStackTrace(); } try { if(fw!=null) { fw.close(); } } catch (IOException e) { e.printStackTrace(); } } } }

　　

LoginServlet

public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
    private static String username;
    private static String password;
    private static boolean flag =false;//账号密码是否正确
	@Override
		protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
			//设置请求编码
			req.setCharacterEncoding("utf-8");
			//设置响应编码
			resp.setContentType("text/html;charset=utf-8");
			//获取请求数据
				username = req.getParameter("uname");
				password = req.getParameter("pwd");
			//处理请求
				LoginService ls = new LoginServiceImpl();
				User user = ls.checkLoginService(username, password);
			//响应
			if(null != user) {
				//创建cookie，实现3天免登陆
					//我们不直接存账号密码，而是存用户的uid
					Cookie c = new Cookie("uid",user.getUid()+"");
					//设置有效期为3天
					c.setMaxAge(3*24*3600);
					//设置指定url
					c.setPath("/200222-CookieLogin/ck");
					//添加
					resp.addCookie(c);
					//创建session
					HttpSession hs = req.getSession();
					//设置时效
					//将用户对象保存到session中
					hs.setAttribute("user", user);
					//ServletContext对象获取网站访问计数器
					ServletContext cs = this.getServletContext();
					int countor = Integer.valueOf((String)cs.getAttribute("countor"));
					countor++;
					cs.setAttribute("countor", countor+"");
					
				resp.sendRedirect("main");
				return;
			}else {
				//请求转发
				req.setAttribute("msg", "账号或密码错误");
				req.getRequestDispatcher("page").forward(req, resp);
				return;
			}
		}
}

　　

CookieServlet

public class CookieServlet extends HttpServlet {
	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		//设置请求编码
		req.setCharacterEncoding("utf-8");
		//设置响应类型及编码
		resp.setContentType("text/html;charset=utf-8");
		//获取请求
			//判断是否有cookie
			Cookie[] cks = req.getCookies();
			//处理请求
			if(null!=cks) {
				//从cookie中获取uid
				String uid = "";
				for(Cookie c : cks) {
					if("uid".equals(c.getName())) {
						uid = c.getValue();
					}
				}
				//校验用户是否存在（使用uid）
				CookieService ls = new CookieServiceImpl();
				User u = ls.checkUidService(uid);
				if(null!=u) {
					//设置session
					HttpSession hs = req.getSession();
					//将用户数据保存到session
					hs.setAttribute("user", u);
					//ServletContext对象获取网站访问计数器
					ServletContext cs = this.getServletContext();
					int countor = Integer.valueOf((String)cs.getAttribute("countor"));
					countor++;
					cs.setAttribute("countor", countor+"");
					//跳转主页
					resp.sendRedirect("main");
					return;
				}else {
					req.getRequestDispatcher("/page").forward(req, resp);
					return;
				}
			}else {
				req.getRequestDispatcher("/page").forward(req, resp);
				return;
			}
	}
}

　　

MainSerlvet

public class MainServlet extends HttpServlet{
	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		//设置请求编码格式
		req.setCharacterEncoding("utf-8");
		//设置响应类型及编码
		resp.setContentType("text/html;charset=utf-8");
		//获取session对象
		HttpSession hs = req.getSession();
		//获取用户对象
		User user = (User)hs.getAttribute("user");
		//获取用户名
		String username = null;
		if(user!=null) {
			username = user.getUsername();
		}
		//ServletContext对象获取网站访问计数器
		ServletContext cs = this.getServletContext();
		String countor = (String)cs.getAttribute("countor");
		resp.getWriter().write("<html>");
		resp.getWriter().write("<head>");
		resp.getWriter().write("</head>");
		resp.getWriter().write("<body>");
		resp.getWriter().write("欢迎登录"+username+"管理系统<hr>");
		resp.getWriter().write("<form action='logout' method='get'>");
		resp.getWriter().write("<input type='submit' value='注销'> ");
		resp.getWriter().write("</form>");
		resp.getWriter().write("<form action='page' method='get'>");
		resp.getWriter().write("<input type='submit' value='登录'><hr>");
		resp.getWriter().write("</form>");
		resp.getWriter().write("网站访问次数："+countor);
		resp.getWriter().write("</body>");
		resp.getWriter().write("</html>");
	}
}