Servlet登陆功能的实现
（1）创建动态的Login页面
//登陆界面
package com.lc;
import javax.servlet.http.*;
import java.io.*;
public class Login extends HttpServlet{
public void doGet(HttpServletRequest req,HttpServletResponse res){
//业务逻辑
try{
//解决中文乱码
res.setContentType("text/html;charset=gbk");
PrintWriter pw = res.getWriter();
//返回登陆界面
pw.println("<html>");
pw.println("<body>");
pw.println("<h1>用户登录</h1>");
pw.println("<form action=logincl method=post>"); //action的是servlet的url
pw.println("用户名：<input type=text name=username><br/>");
pw.println("密码：<input type=password name=passwd><br/>");
pw.println("<input type=submit value=loing><br/>");
pw.println("</form>");
pw.println("</body>");
pw.println("</html>");
}
catch(Exception ex){
ex.printStackTrace();
}
}
public void doPost(HttpServletRequest req,HttpServletResponse res){
this.doGet(req,res);
}
}（2）创建接受Login的servlet
//登陆界面
package com.lc;
import javax.servlet.http.*;
import java.io.*;
public class Logincl extends HttpServlet{
public void doGet(HttpServletRequest req,HttpServletResponse res){
//业务逻辑
try{
//解决中文乱码
//接受用户名和password
String u = req.getParameter("username");
String p = req.getParameter("passwd");
//验证
if(u.equals("lc") && p.equals("123"))
{
//合法的情况 跳转到Welcome
res.sendRedirect("welcome");//这里跳转的仍是servlet的url
}
else
{
//不合法的情况
//跳转
res.sendRedirect("login");//跳转的是要到servlet的url
}
}
catch(Exception ex){
ex.printStackTrace();
}
}
public void doPost(HttpServletRequest req,HttpServletResponse res){
this.doGet(req,res);
}
}（3）登陆成功要跳转的welcome页面
//登陆界面
package com.tsinghua;
import javax.servlet.http.*;
import java.io.*;
public class Welcome extends HttpServlet{
public void doGet(HttpServletRequest req,HttpServletResponse res){
//业务逻辑
try{
//解决中文乱码
res.setContentType("text/html;charset=gbk");
PrintWriter pw = res.getWriter();
pw.println("hello welcome！");
}
catch(Exception ex){
ex.printStackTrace();
}
}
public void doPost(HttpServletRequest req,HttpServletResponse res){
this.doGet(req,res);
}
}（4）配置文件web.xml的编写
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0"
metadata-complete="true">
<display-name>Welcome to Tomcat</display-name>
<description>
Welcome to Tomcat
</description>
<!--JSP servlet mappings starts-->
<servlet>
<servlet-name>Login</servlet-name>
<servlet-class>com.lc.Login</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Login</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>Logincl</servlet-name>
<servlet-class>com.<span style="font-family:Arial, Helvetica, sans-serif;">lc</span>.Logincl</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Logincl</servlet-name>
<url-pattern>/logincl</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>Welcome</servlet-name>
<servlet-class>com.lc.Welcome</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Welcome</servlet-name>
<url-pattern>/welcome</url-pattern>
</servlet-mapping>
<!--JSP servlet mappings end-->
</web-app>
（5）执行结果：
