目录

架构图

为什么要使用3层架构

各个部分应有的文件

表现层

业务逻辑层

数据访问层

各层示例代码

表现层

jsp

servlet

业务逻辑层

service 接口

service逻辑

数据访问层

dao 接口

dao 操作

entity

dbutils

一图胜万言

架构图

为什么要使用3层架构

1 方便团队分工 利于维护

2 规范代码，在开发软件时对每个层的代码进行规范，固定开发语言的风格。

3 降低更新难度，当软件系统要换数据库时，只要将数据访问层的代码修改就好了。

4 实现”高内聚、低耦合”。易于分配资源。

5 是使得代码逻辑清晰。

各个部分应有的文件

表现层

应该有的文件（jsp+servlet）

业务逻辑层

应该有的文件（service的接口，及其实现的逻辑代码）

具体的逻辑代码应该包括，多次对Dao层的操作（多次查询，修改，登陆的检验，用户在线状态的检验等等）也包括对数据库的连接，关闭等等

数据访问层

应该有的

DAO(全称Data AccessObject，意为数据访问接口/对象)

DAO中也应该定义接口，及其实现（具体指增删改查的代码）

entity(意为实体类是数据库表的映射)

utils是工具集的意思，其中连接数据库，关闭数据库/数据源/对象的一些操作应该写在这里的某个类里面

各层示例代码

表现层

jsp

序号
品牌名称
企业名称
排序
品牌介绍
状态
操作
${brand.id}
${brand.brandName}
${brand.companyName}
${brand.ordered}
${brand.description} 
${brand.status}
修改 删除
document.getElementById("add").onclick = function (){location.href = "addBrand.jsp";}

servlet

package com.teaching.jsp.servlet;import com.teaching.jsp.entity.Brand;import com.teaching.jsp.service.BrandService;import com.teaching.jsp.service.impl.BrandServiceImpl;import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.annotation.*;import java.io.IOException;@WebServlet(name = "AddBrandServlet", value = "/addBrand")public class AddBrandServlet extends HttpServlet {BrandService brandService=new BrandServiceImpl();@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.setCharacterEncoding("utf8");//接收参数String brandName = request.getParameter("brandName");String companyName = request.getParameter("companyName");String ordered = request.getParameter("ordered");String description = request.getParameter("description");String status = request.getParameter("status");//封装BrandBrand brand = new Brand();brand.setBrandName(brandName);brand.setDescription(description);brand.setCompanyName(companyName);brand.setOrdered(Integer.valueOf(ordered));brand.setStatus(Integer.valueOf(status));//调用Service去处理业务brandService.insertBrand(brand);//转发到selectAllresponse.sendRedirect("/teachingJsp/selectBrand");}}

业务逻辑层

service 接口

package com.teaching.jsp.service;import com.teaching.jsp.entity.Brand;import java.util.List;public interface BrandService {List selectAllBrand();boolean insertBrand(Brand brand);Brand selectBrandById(String id);boolean updateBrand(Brand brand);}

service逻辑

package com.web.serivce.impl;import com.web.dao.Impl.UserDaoImpl;import com.web.dao.UserDao;import com.web.entity.User;import com.web.serivce.UserServlet;import com.web.utils.DbUtils;import java.sql.Connection;import java.sql.SQLException;public class UserService implements UserServlet {private UserDao userDao=new UserDaoImpl();//使用Dao查询当前的用户@Overridepublic User getUserByUserEntity(User user) {//service是有多个dao方法组成//和数据库交互相关的方法调用//其中获取数据库连接，关闭连接 应该写在本层User u= null;Connection connection =null;try {connection = DbUtils.getConnection();connection.setAutoCommit(false);u = userDao.selectUserByEntity(user,connection);connection.commit();} catch (SQLException e) {try {connection.rollback();} catch (SQLException ex) {throw new RuntimeException(ex);}throw new RuntimeException(e);} finally {if (connection!=null){try {DbUtils.close(connection);} catch (SQLException e) {throw new RuntimeException(e);}}}return u;}//判断用户是否注册@Overridepublic boolean registryUser(User user) {User u= null;Connection connection =null;int row=0;try {connection = DbUtils.getConnection();connection.setAutoCommit(false);int i=userDao.selectUserByUsername(user.getUsername(),connection);if (i>0){throw new RuntimeException("username已经存在");}row+=userDao.insertUser(user,connection);connection.commit();} catch (SQLException e) {try {connection.rollback();} catch (SQLException ex) {throw new RuntimeException(ex);}throw new RuntimeException(e);} finally {if (connection!=null){try {DbUtils.close(connection);} catch (SQLException e) {throw new RuntimeException(e);}}}return row>0;}}

数据访问层

dao 接口

package com.teaching.jsp.dao;import com.teaching.jsp.entity.Brand;import java.util.List;//DAO 的全称是Data Access Objectpublic interface BrandDao {List selectAll();boolean insert(Brand brand);Brand selectBrandById(String id);boolean updateBrand(Brand brand);}

dao 操作

对数据库的连接不应该写在此层，应该写在serivce层

package com.teaching.web.dao;import com.teaching.web.entity.User;import com.teaching.web.utils.DbUtils;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;public class UserDaoImpl implements UserDao {@Overridepublic User selectUserByEntity(User user, Connection connection) throws SQLException {String sql="select id,username,password from user where username=" />

entity

package com.teaching.jsp.entity;public class Brand {// id 主键private Integer id;// 品牌名称private String brandName;// 企业名称private String companyName;// 排序字段private Integer ordered;// 描述信息private String description;// 状态：0：禁用1：启用private Integer status;public Brand() {}public Brand(Integer id, String brandName, String companyName, String description) {this.id = id;this.brandName = brandName;this.companyName = companyName;this.description = description;}public Brand(Integer id, String brandName, String companyName, Integer ordered, String description, Integer status) {this.id = id;this.brandName = brandName;this.companyName = companyName;this.ordered = ordered;this.description = description;this.status = status;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getBrandName() {return brandName;}public void setBrandName(String brandName) {this.brandName = brandName;}public String getCompanyName() {return companyName;}public void setCompanyName(String companyName) {this.companyName = companyName;}public Integer getOrdered() {return ordered;}public void setOrdered(Integer ordered) {this.ordered = ordered;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public Integer getStatus() {return status;}public void setStatus(Integer status) {this.status = status;}@Overridepublic String toString() {return "Brand{" +"id=" + id +", brandName='" + brandName + '\'' +", companyName='" + companyName + '\'' +", ordered=" + ordered +", description='" + description + '\'' +", status=" + status +'}';}}

dbutils

package com.teaching.jsp.utils;import com.alibaba.druid.pool.DruidDataSourceFactory;import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;import javax.sql.DataSource;import java.io.FileInputStream;import java.io.IOException;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.Properties;public class DbUtils {private static DataSource dataSource;static {Properties prop=new Properties();try {prop.load(new FileInputStream("F:\\JAVA EE Preject\\课堂练习\\src\\com\\teaching\\jsp\\db.properties"));System.out.println("iiii");dataSource = DruidDataSourceFactory.createDataSource(prop);} catch (IOException e) {throw new RuntimeException(e);} catch (Exception e) {throw new RuntimeException(e);}}public static void test(){System.out.println(DbUtils.class.getClassLoader().getResource("db.properties"));}public static Connection getConnection() throws SQLException {System.out.println("iiii111");return dataSource.getConnection();}public static void close(Connection connection) throws SQLException {if (connection!=null){connection.close();}}public static void close(PreparedStatement ps, ResultSet rs,Connection connection) throws SQLException {if (rs!=null){rs.close();}if (ps!=null){ps.close();}if (connection!=null){connection.close();}}}