7 Servlet 介绍
7.1 Servlet 的开发
@WebServlet(name = "helloServlet", urlPatterns = {"/helloServlet"})
public class HelloServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
resp.setCharacterEncoding("UTF-8");
String username = req.getParameter("username");
PrintStream out = new PrintStream(resp.getOutputStream());
out.println(username);
}
}
启动 tomcat 后使用链接 http://localhost/helloServlet?username=admin 即可。
7.2 Servlet 的配置
从 Servlet 3.0 开始，配置 Servlet 有两种方式：@WebServlet 注解或 web.xml 配置。
7.3 Servlet 的生命周期
7.4 load-on-startup Servlet
创建 Servlet 有两个时机：应用启动时或用户请求时。load-on-startup 参数配置 Servlet 实例化优先级，值越小，越优先。
7.5 访问 Servlet 的配置参数
为 Servlet 配置参数也有两种方式：@WebServlet 的 initParams 属性或 web.xml 中 <servlet> 元素的 <init-param> 子元素。
@WebServlet(name = "helloServlet", urlPatterns = {"/helloServlet"},
initParams = {
@WebInitParam(name = "password", value = "admin123")
}
)
public class HelloServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
resp.setCharacterEncoding("UTF-8");
PrintStream out = new PrintStream(resp.getOutputStream());
ServletConfig config = getServletConfig();
out.println(config.getInitParameter("password"));
}
}
7.6 使用 Servlet 作为控制器
在标准的 MVC 模式中，JSP 仅作为表现层技术负责收集用户请求参数并展现数据，Servlet 仅作为控制器使用，所有请求都发给 Servlet，Servlet 调用 Model 处理请求，并调用 JSP 呈现处理结果。
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>用户登录</title>
</head>
<body>
<span>
<%
String message = (String) request.getAttribute("message");
if (message != null) {
out.println(message);
}
%>
</span>
请输入用户名和密码：<br>
<form id="login" method="post" action="/loginServlet">
用户名：<input type="text" name="username"><br>
密码：<input type="password" name="password"><br>
<input type="submit" value="登陆">
</form>
</body>
</html>
login.jsp
@WebServlet(name = "loginServlet", urlPatterns = {"/loginServlet"})
public class LoginServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
String username = req.getParameter("username");
String password = req.getParameter("password");
String message = "";
DBUtil dbUtil = new DBUtil();
try {
ResultSet resultSet = dbUtil.query("select password from t_user where username = ?", username);
if (resultSet.next()) {
if (resultSet.getString("password").equals(password)) {
// 保存username至会话
HttpSession session = req.getSession();
session.setAttribute("username", username);
// 转发到欢迎页面
req.getRequestDispatcher("/welcome.jsp").forward(req, resp);
} else {
message = "密码错误";
}
} else {
message = "用户名不存在";
}
} catch (Exception e) {
e.printStackTrace();
}
if (!message.equals("")) {
req.setAttribute("message", message);
req.getRequestDispatcher("/login.jsp").forward(req, resp);
}
}
}
LoginServlet.java
8 JSP 2 的自动用标签
时间： 2024-11-05 18:57:06