Sevlet 02: Servlet对比JSP

package com.Jasper2003.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/demo_do")　　
public class DemoServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().append("I'm doGet method!");
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().append("I'm doPost method!");
    }
    
}

2.　　JSP更加适合做展示, Servlet更加适合做处理.

反例: 当用户访问demo_do时, Servlet返回给用户一个网页

@WebServlet("/demo_do")
public class DemoServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().append("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\" \"http://www.w3.org/TR/html4/loose.dtd\">");
        resp.getWriter().append("<html>");
        resp.getWriter().append("<head>");
        resp.getWriter().append("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\">");
        resp.getWriter().append("</head>");
        resp.getWriter().append("<body>");
        resp.getWriter().append("Hi! doGet method!");
        resp.getWriter().append("</body>");
        resp.getWriter().append("</html>");    
    }

效果:

可见, 这是非常麻烦的

正例: 利用Servlet处理注册请求

1.　　利用RegisterServlet.java处理注册请求:

<1>　　在RegisterServlet.java中:

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        int age = Integer.parseInt(request.getParameter("age")); 
        String gender = request.getParameter("gender");

        gender = new String(gender.getBytes("iso-8859-1"), "utf-8");    
        
        boolean isSuccess = DBUtil.addUser(username, password, age, gender);    
        if(isSuccess){
            request.setAttribute("message","你注册成功了,请登录！");
            request.getRequestDispatcher("login.jsp").forward(request,response);
        }else{
            request.setAttribute("message","很遗憾, 由于用户名重复, 注册失败了, 请你重新注册！");
            request.getRequestDispatcher("register.jsp").forward(request,response);
        }
    }

<2>　　在register.jsp中（将表单提交的地址修改为从register_do.jsp修改为register_do）:

　　用户名: <input type="text" name="username"/><br/>
　　密码: <input type="password" name="password"/><br/>
　　年龄: <input type="text" name="age"/><br/>
　　性别: 男<input type="radio" name="gender" value="男的!"/>
　　女<input type="radio" name="gender" value="女的!"/><br/>
　　<input type = "submit" value="我要注册成为新用户!"/>

</form>

效果:

正例2: 利用Servlet 完成登录请求

<1>　　在LoginServlet中:

@WebServlet("/login_do")
public class LoginServlet extends HttpServlet {

　　protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
　　String username = request.getParameter("username");
　　String password = request.getParameter("password");

　　User user = DBUtil.verifyAccount(username,password);
　　if(user == null){
　　　　request.setAttribute("message","<font color='red'>很遗憾,由于用户名或密码错误, 你登录失败了！</font>");
　　　　request.getRequestDispatcher("login.jsp").forward(request,response);
　　}else{

　　　　int number = 0;
　　　　ServletContext application = this.getServletContext();
　　　　if(application.getAttribute("userNumber") != null){
　　　　　　number = (Integer)application.getAttribute("userNumber");
　　　　}
　　　　number++;
　　　　application.setAttribute("userNumber",number);

　　　　request.getSession().setAttribute("user",user);
　　　　request.getRequestDispatcher("personalCenter.jsp").forward(request,response);

　　}
}

<2>　　在login.jsp中：

效果: