层与层之间的关系表示层依赖于业务逻辑层，业务逻辑层依赖于数据访问层
三层开发遵循的原则（1）上层依赖其下层，依赖关系不跨层1、表示层不能直接访问数据访问层2、上层调用下层的结果，取决于下层的实现（2）下一层不能调用上一层（3）下一层不依赖上一层1、上层的改变不会影响下一层2、下层的改变会影响上一层得到的结果（4）在上一层中不能出现下一层的概念1、分工明确，各司其职分层开发的特点（1）下层不知道上层的存在1、仅完成自身的功能2、不关心结果如何使用（2）每一层仅知道其下层的存在，忽略其他层的存在1、只关心结果的取得2、不关心结果的实现过程3、JSTL通常会与EL表达式合作实现JSP页面的编码分层开发的优势1、职责划分清晰2、无损替换3、复用代码4、降低了系统内部的依赖程度分层开发的案例：package DB;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;/** * 数据库连接帮助类 * @author Administrator * */public class BaseDao { //=======数据库连接信息======== static String url = "jdbc:Oracle:thin:@localhost:1521:orcl"; static String username = "news"; static String passWord = "news"; static String driverClassName = "oracle.jdbc.driver.OracleDriver"; //获取数据库连接 public static Connection getConnection(){ Connection connection = null; try { //加载驱动 Class.forName(driverClassName); //获取连接 connection = DriverManager.getConnection(url,username,password); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.PRintStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return connection; } /* * 释放连接 * */ public void close_con(Connection connection,Statement st,ResultSet rs){ try { if(connection!= null){ connection.close(); } if(st!= null){ st.close(); } if(rs!= null){ rs.close(); } } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } }}package entity;/** * 用户实体 * @author Administrator * */public class User { private String username; private String password; public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } }package Dao;import java.util.List;import entity.User;/** * 用户数据访问层接口 * @author Administrator * */public interface UserDao { /** * 查询用户是否存在 * @param user * @return */ public boolean findUser(User user); /** * 查询用户列表 */ public List<User> findUserList();}package Dao.Impl;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import DB.BaseDao;import Dao.UserDao;import entity.User;/** * 用户数据访问层实现类 * @author Administrator * 继承数据库连接类 */public class UserDaoImpl extends BaseDao implements UserDao { //数据库连接对象 Connection conn = null; PreparedStatement stm = null; ResultSet rs = null; /** * 实现查询用户功能 */ public boolean findUser(User user) { //获得连接 conn = this.getConnection(); //编写sql String sql = "select * from news_users where uname = ? and upwd = ?"; try { //得到预编译对象 stm = conn.prepareStatement(sql); stm.setString(1, user.getUsername()); stm.setString(2, user.getPassword()); //执行sql得到结果集 rs = stm.executeQuery(); return rs.next(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); }finally{ //释放连接 this.close_con(conn, stm, rs); } return false; } /** * 查询用户列表 */ public List<User> findUserList() { //获得连接 conn = this.getConnection(); //编写sql String sql = "select * from news_users"; //创建泛型集合 List<User> userlist = new ArrayList<User>(); try { //得到预编译对象 stm = conn.prepareStatement(sql); //执行sql得到结果集 rs = stm.executeQuery(); while(rs.next()){ User user = new User(); user.setUsername(rs.getString(2)); user.setPassword(rs.getString(3)); userlist.add(user); } } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); return null; }finally{ //释放连接 this.close_con(conn, stm, rs); } return userlist; }}package Biz;import java.util.List;import entity.User;/** * 用户业务逻辑层接口 * @author Administrator * */public interface UserBiz { /** * 用户登录 * @param user * @return */ public boolean login(User user); /** * 查询用户列表 */ public List<User> finduserList();}import Dao.UserDao;import Dao.Impl.UserDaoImpl;import entity.User;/** * 用户业务逻辑实现类 * @author Administrator * */public class UserBizImpl implements UserBiz { //创建数据访问层对象 UserDao userdao = new UserDaoImpl(); /** * 实现登录 */ public boolean login(User user) { //调用数据访问层查询用户 return userdao.findUser(user); } /** * 查询用户列表 */ public List<User> finduserList() { // TODO Auto-generated method stub return userdao.findUserList(); }}JSP页面
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP 'index.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/CSS" href="styles.css"> --> </head> <body> <form action="dologin.jsp" method="post"> <p>用户名:<input type="text" name="username" /></p> <p>密 码:<input type="password" name="password" /></p> <input type="submit" /> </form> </body></html>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@page import="Biz.UserBiz"%><%@page import="Biz.Impl.UserBizImpl"%><%@page import="entity.User"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; //调用业务逻辑层 UserBiz userbiz = new UserBizImpl(); //获取表单项 request.setCharacterEncoding("utf-8"); String username = request.getParameter("username"); String password = request.getParameter("password"); //创建用户实体 User user = new User(); user.setUsername(username); user.setPassword(password); //实现登录 boolean f = userbiz.login(user); if(f){ request.getRequestDispatcher("success.jsp").forward(request,response); }else{ %> <script type="text/Javascript"> alert("用户名或密码错误！"); location.href="index.jsp"; </script> <% } %>新闻热点
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