用 servlet 来创建一个用户登录界面

代码如下：

1、首先创建一个表单

package com.mx.servlet1;

import java.io.IOException;
import java.io.PrintWriter;

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

public class myservlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		out.println("<h1>用户登录</h1>");
		out.println("<form action='/Servlet1/Clservlet' method='post'>");
		//这是一个表单，action 就是把表单提交到什么地方，提交表单的过程就是向服务器发送
		//请求的过程，其中 action 里面的书写方式为：/web 应用名/servlet 名
		out.println("用户名<input type='text' name='username'/></br>");
		out.println("密	    码<input type='password' name='password'/></br>");
		out.println("<input type='submit' value='登录'/></br>");
		out.println("</form>");
		
	}

	
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}

}

2、表单提交后，由再创建一个 servlet  Clservlet来处理表单，如下：

package com.mx.servletCl;

import java.io.IOException;
import java.io.PrintWriter;

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

public class Clservlet extends HttpServlet {

	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		String username=request.getParameter("username");
		String password=request.getParameter("password");
		out.println(username+"  "+password);
		//用户名和密码验证，如果成功，则跳转到下一个页面，一般吧常量写在 equals 的前面
		//可以避免空字符串的问题，比如 username 如果为空，那么就没有equals 方法
		if("maxiao".equals(username)&& "123".equals(password)){
			// sendRedirect 函数的URL 写法：/web 应用名/servlet 名，后面的
			//这个servlet 名 是要跳转到的 servlet
			response.sendRedirect("/Servlet1/MainFrame");
		}else{
			response.sendRedirect("/Servlet1/myservlet");
		}
	}

	
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}

}

3、处理表单的结果是如果登录验证成功，则跳转到 MainFrame 界面，如果不成功，则返回登录界面，（就是验证用户名和密码是否一致），下面是验证成功后跳转的页面

输出一句话：登录界面

package com.mx.view;

import java.io.IOException;
import java.io.PrintWriter;

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

public class MainFrame extends HttpServlet {

	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		out.println("<h1>登录界面</h1>");
		
	}

	
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}

}

整个项目框架如下图：