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JSP一个理解MVC架构的简单的登陆、注册例子

首先我们看看这个目录结构


--+login
----------+WEB-INF
-----------------------+classes
                          -beans
                          -tags
-----------+tlds

login 是主目录放jsp文件，在例子login.jsp,loginFailed.jsp,login_form.jsp,newAccount.jsp,welcome.jsp,accountCreated.jsp

Web-inf下面有web.xml配置文件，classes文件夹放类，tlds文件夹放自定义标签
由于我没有用到数据库，所以没有用LIB文件夹，是来放置*.jar文件的。

classes目录下，有beans,tags文件夹，分别放置User,LoginDB类，和自定义标签类GetRequestParameterTag,classes目录下还直接放了LoginServlet,NewAccountServlet控制器类

我们先看beans下的两个业务对象类
User.java

package beans;

public class User implements java.io.Serializable {
private final String userName,password,hint;
//final强调此属性初始化后，不能修改hint是口令提示
public User(String userName,String password,String hint) {
this.userName = userName;
this.password = password;
this.hint = hint;
}
public String getUserName(){
return userName;
}
public String getPassword(){
return password;
}
public String getHint(){
return hint;
}
//判断当前对象用户名和密码是否相等
public boolean equals(String uname,String upwd) {
return getUserName().equals(uname) &&
getPassword().equals(upwd);
}
}

LoginDB.java



package beans;

import java.util.Iterator;
import java.util.Vector;

public class LoginDB implements java.io.Serializable {
     private Vector users = new Vector();
    //Vector类是同步的，所以addUser就不需要同步了
    public void addUser(String name,String pwd,String hint) {
        users.add(new User(name,pwd,hint));
    }
          //下面方法判断是否存在正确的user
    public User getUser(String name,String pwd) {
        Iterator it = users.iterator();
        User user;
         //迭代需要同步
        synchronized(users) {
	while(it.hasNext()){
	user = (User)it.next();
	if(user.equals(name,pwd))
               	return user;  //如果返回真，就返回当前user
                }
        }	
     return null;
}
     public String getHint(String name) {
         Iterator it = users.iterator();
         User user;
         synchronized(users) {
	while(it.hasNext()){
	     user = (User)it.next();
	     if(user.getUserName().equals(name))
	     return user.getHint();
	}
         }
   return null;
   }
}

login.jsp


<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>Login Page</title>
</head>
<body>
<@ include file="login_form.jsp">
</body>
</html>



被包含的login_form.jsp


<%@ taglib uri="utilities" prefix="util" %>
 <!--调用自定义标签，引用为util，uri的utilities在web.xml映射了-->
<p><font color="#6666CC">请登陆</font></p>
<hr>
<form name="form1" method="post" action="<%=response.encodeURL("login")%>"><!--login是LoginSevlet通过在web.xml映射了-->
  <table width="68%" border="0" cellpadding="2" cellspacing="2">
    <tr> 
      <td width="33%" align="right">用户名：</td>
      <td width="67%">
	  <input type="text" name="userName" value="<util:requestParameter property='userName'/>"></td><!--注意这里用了自定义标签，如果有值就显示-->
    </tr>
    <tr> 
      <td align="right">密码：</td>
      <td><input type="text" name="userPwd" ></td>
    </tr>
    <tr align="center"> 
      <td colspan="2"> 
        <input type="submit" name="Submit" value="登陆">
      </td>
    </tr>
  </table>
</form>



LoginServlet.java


import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

import beans.User;
import beans.LoginDB;

public class LoginServlet extends HttpServlet {
         private LoginDB loginDB;
	
         public void init(ServletConfig config) throws ServletException {
	super.init(config);
	loginDB = new LoginDB();
	config.getServletContext().setAttribute("loginDB",loginDB);
        }
        public void doGet(HttpServletRequest request,HttpServletResponse response)
	                   throws ServletException,IOException{
           String name = request.getParameter("userName");
           //从login_form表单得到值
           String pwd = request.getParameter("userPwd");
           User user = loginDB.getUser(name,pwd);
           if(user != null){　//说明存在用户
	   request.getSession().setAttribute("user",user);
                   //放到session里面
	   request.getRequestDispatcher(response.encodeURL("/welcome.jsp"))
				.forward(request,response);
　　　　　　//成功转发到welcome.jsp
          }else{
	request.getRequestDispatcher(response.encodeURL("/loginFailed.jsp"))
				.forward(request,response);
        }
}
        public void doPost(HttpServletRequest request,HttpServletResponse response)
	                  throws ServletException,IOException{
	doGet(request,response);
        }
}


web.xml添加


<servlet>
	<servlet-name>Login</servlet-name><!--名字-->
	<servlet-class>LoginServlet</servlet-class><!--指定类-->
  </servlet><servlet>
	<servlet-name>new_account</servlet-name>
	<servlet-class>NewAccountServlet</servlet-class>
  </servlet>
   <servlet-mapping>
	<servlet-name>new_account</servlet-name>
	<url-pattern>/new_account</url-pattern>
  </servlet-mapping>
   <servlet-mapping>
	<servlet-name>Login</servlet-name><!--和上面的名字一致-->
	<url-pattern>/login</url-pattern><!--映射路径-->
  </servlet-mapping>
 <taglib>
	<taglib-uri>utilities</taglib-uri>
	<taglib-location>/WEB-INF/tlds/utilities.tld</taglib-location>
　　　　　　　　　　<!--自定义标签的实际位置-->
  </taglib>



utilities.tld关键部分

<taglib>
<tag>
<name>requestParameter</name>
<tagclass>tags.GetRequestParameterTag</tagclass>
<!--类的位置，如果有包写上-->
<info>Simplest example: inserts one line of output</info>
<bodycontent>Empty</bodycontent>
	<attribute>
	<name>property</name>
	<required>true</required>
	<rtexprvalue>true</rtexprvalue>
	</attribute>
</tag>
</taglib>



自定义标签类GetRequestParameterTag.java



package tags;

import javax.servlet.ServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

public class GetRequestParameterTag extends TagSupport {
       private String property;

      public void setProperty(String property) {
	this.property = property;	
     }
      public int doStartTag() throws JspException {
	ServletRequest reg = pageContext.getRequest();
	String value = reg.getParameter(property);
		
	try{
		pageContext.getOut().print(value == null ? "":value);
	}catch(java.io.IOException e){
		throw new JspException(e.getMessage());
	}
	return SKIP_BODY;
       }
}

 
登陆成功welcome.jsp


<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>Welcome Page</title>
</head>
<body>
<jsp:userBean id="user" scope="session" class="beans.User"/>
<!--也可以
<%
User user = (User)session.getAttribute("user");
%>
-->
欢迎你：<font color=red><%=user.getUserName()%></font>
</body>
</html>



登陆失败loginFailed.jsp


<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>Login Failed</title>
</head>

<body>
<font color="#993366">请输入用户名和密码，或者创建一个新用户！</font> 
<%@ include file="/login_form.jsp"%>
<hr>
<a href="<%=response.encodeURL("newAccount.jsp")%>">创建一个新用户 </a>
</body>
</html>


新建用户newAccount.jsp


<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>New Account</title>
</head>

<body>
<font color="#996633">创建新用户 </font>
<form name="form1" method="post" action="<%=response.encodeURL("new_account")%>">
  <table width="75%" border="0" cellpadding="3">
    <tr> 
      <td width="42%" align="right">用户名：</td>
      <td width="58%"><input type="text" name="userName"></td>
    </tr>
    <tr> 
      <td align="right">密码：</td>
      <td><input type="text" name="userPwd"></td>
    </tr>
    <tr>
      <td align="right">密码问题：</td>
      <td><input type="text" name="hint"></td>
    </tr>
    <tr align="center"> 
      <td colspan="2"> <input type="submit" name="Submit" value="提交"> </td>
    </tr>
  </table>
</form>
</body>
</html>


注册的控制器NewAccountServlet


import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

import beans.LoginDB;

public class NewAccountServlet extends HttpServlet {
	
       public void doPost(HttpServletRequest request,HttpServletResponse response)
	                  throws ServletException,IOException{
	LoginDB loginDB = (LoginDB)getServletContext().getAttribute("loginDB");
	loginDB.addUser(request.getParameter("userName"),
	request.getParameter("userPwd"),
	request.getParameter("hint"));
	request.getRequestDispatcher(response.encodeUrl("accountCreated.jsp"))			.forward(request,response);
     }
}


accountCreated.jsp


<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>无标题文档</title>
</head>

<body>
新用户已经创建！ <font color="#0000FF"><%=request.getParameter("userName")%></font> 
<hr><%@ include file="login_form.jsp"%>
</body>
</html>

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原文地址：https://www.cnblogs.com/KUDO/p/436581.html