public boolean check()
{
/*
   if(username==null || userpass==null)
     return false;
   if(username.equals("zhangsan") && userpass.equals("lisi"))
   {
     return true;
   }else{
     return false;
   }
*/
   Connection con = null;
   Statement stmt = null;
   ResultSet rs = null;
   boolean b = true;
   try{
     // 指出连接数据库所需要的驱动程序
     Class.forName("oracle.jdbc.driver.OracleDriver");
    // 建立与数据库之间的连接
// myserver修改为数据库服务器IP，mydb为数据库名
    con = DriverManager.getConnection("jdbc:oracle:thin:@myserver:1521:mydb","scott","tiger");
    // 编写查询数据库信息的SQL语句
    String sql="select * from usertable where username='"+username+"' and userpass='"+userpass+"'";
    System.err.println(sql);
    // 创建语句对象，用于执行SQL语句
    stmt = con.createStatement();
    // 执行SQL语句得到结果集
    rs = stmt.executeQuery(sql);   
    // 判断rs中是否有数据
    if(rs.next())
     b = true;
    else
     b = false;
   }catch(Exception e){
     System.out.println(e.getMessage());
   }
   finally{
    // 关闭相关对象
    if(rs!=null) try{ rs.close(); }catch(Exception ee){}
    if(stmt!=null) try{ stmt.close(); }catch(Exception ee){}
    if(con!=null) try{ con.close(); }catch(Exception ee){}
   }
   return b;
}

public ArrayList getAllUser()
{
   Connection con = null;
   Statement stmt = null;
   ResultSet rs = null;
   ArrayList users = new ArrayList();
   try{
    // 指出连接数据库所需要的驱动程序
    Class.forName("oracle.jdbc.driver.OracleDriver");
    // 建立与数据库之间的连接
    con = DriverManager.getConnection("jdbc:oracle:thin:@myserver:1521:mydb","scott","tiger");
    // 编写查询数据库信息的SQL语句
    String sql="select * from usertable";
    // 创建语句对象，用于执行SQL语句
    stmt = con.createStatement();
    // 执行SQL语句得到结果集
    rs = stmt.executeQuery(sql);   
    // 遍历结果集
    while(rs.next())
    {
      String username = rs.getString(1);
      String userpass = rs.getString(2);
      // java.util.Date birthday = rs.getDate(3);
      // int age = rs.getInt(4);
      User user = new User();
      user.setUsername(username);
      user.setUserpass(userpass);
      users.add(user);
    }
   }catch(Exception e){
     System.out.println(e.getMessage());
   }
   finally{
    // 关闭相关对象
    if(rs!=null) try{ rs.close(); }catch(Exception ee){}
    if(stmt!=null) try{ stmt.close(); }catch(Exception ee){}
    if(con!=null) try{ con.close(); }catch(Exception ee){}
   }   
   return users;
}

package servlet;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javabean.*;
import java.util.*;
public class GetAllUser extends HttpServlet
{
  public void doGet(HttpServletRequest request,HttpServletResponse response)
  throws IOException,ServletException
  {
   // 第一步：获取用户的输入信息，这里不需要
   // 第二步：调用JavaBean
   User user = new User();
   ArrayList users=null;
   users = user.getAllUser();
   // 第三步：传值
   request.setAttribute("users",users);
   // 第四步：选择一个界面对用户进行响应
   String forward="userlist.jsp";
   RequestDispatcher rd = request.getRequestDispatcher(forward);
   rd.forward(request,response);
  }
  public void doPost(HttpServletRequest request,HttpServletResponse response)
  throws IOException,ServletException
  {
   doGet(request,response);
  }
}

  <servlet>
   <servlet-name>getAllUser</servlet-name>
   <servlet-class>servlet.GetAllUser</servlet-class>
  </servlet>
  <servlet-mapping>
   <servlet-name>getAllUser</servlet-name>
   <url-pattern>/getAllUser</url-pattern>
  </servlet-mapping>

<%@ page contentType="text/html;charset=gb2312"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<c:forEach var="user" items="${users}">
  用户名：${user.username} 口令：${user.userpass} <br>
</c:forEach>