1. 系统分层 （扩展）

(1)为什么要分层?（了解)

为了系统好维护，系统的设计应该要做到“高内聚，低耦合”。
“高内聚”：指的是类的职责要单一，这样，一个类就可以会拆分成多个类（比如AccountService拆分成了AccountService和AccountDAO）,这样，就形成了分层的概念。
“低耦合”：指的是类与类之间不要直接依赖。（AccountService要调用AccountDAO，应该使用依赖注入）。

(2)如何分层?

表示层：数据展现和操作界面，以及请求分发。
业务层：封装了业务逻辑。  
持久层: 封装了数据访问逻辑。
注：表示层调用业务层，业务层调用持久层。上一层通过接口来调用下一层提供的服务（这样，下一层的实现发生了改变，不影响上一层）。

案例：

/netctoss-spring/src/main/java/cn/tedu/netctoss/controller/LoginController.java

package cn.tedu.netctoss.controller;import javax.annotation.Resource;
import javax.servlet.http.HttpServletRequest;import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;import cn.tedu.netctoss.entity.Admin;
import cn.tedu.netctoss.service.ApplicationException;
import cn.tedu.netctoss.service.LoginService;@Controller
public class LoginController {@Resource(name="loginService")private LoginService loginService;@RequestMapping("/toLogin.do")public String toLogin(){System.out.println("toLogin()");return "login";}@RequestMapping("/login.do")public String login(HttpServletRequest request){System.out.println("login()");//读取帐号，密码String adminCode = request.getParameter("adminCode");System.out.println("adminCode:"+ adminCode);String pwd = request.getParameter("pwd");//调用业务层提供的服务try{Admin admin = loginService.checkLogin(adminCode, pwd);}catch(Exception e){e.printStackTrace();if(e instanceof ApplicationException){//应用异常，明确提示用户/** getMessage方法继承自* RuntimeException，作用是* 获得异常的描述信息。*/request.setAttribute("login_failed", e.getMessage());return "login";}//系统异常,提示用户稍后重试return "error"; }return "redirect:toIndex.do";}@RequestMapping("/toIndex.do")public String toIndex(){System.out.println("toIndex()");return "index";}
}

/netctoss-spring/src/main/java/cn/tedu/netctoss/dao

AdminDAO.java

package cn.tedu.netctoss.dao;import cn.tedu.netctoss.entity.Admin;
/*** 持久层接口*/
public interface AdminDAO {
    public Admin findByAdminCode(String adminCode);}

AdminDAOJdbcImpl.java

package cn.tedu.netctoss.dao;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;import javax.annotation.Resource;
import javax.sql.DataSource;import org.springframework.stereotype.Repository;import cn.tedu.netctoss.entity.Admin;/*** 持久层实现*/@Repository("adminDAO")
public class AdminDAOJdbcImpl implements AdminDAO{
    @Resource(name="ds")private DataSource ds;public Admin findByAdminCode(String adminCode) {Admin admin = null;Connection conn = null;try {conn = ds.getConnection();String sql = "select * from admin_info_lhh "+ "where admin_code=?";PreparedStatement ps = conn.prepareStatement(sql);ps.setString(1, adminCode);ResultSet rs = ps.executeQuery();if(rs.next()){admin = new Admin();admin.setAdminId(rs.getInt("admin_id"));admin.setAdminCode(rs.getString("admin_code"));admin.setPassword(rs.getString("password"));admin.setName(rs.getString("name"));admin.setTelephone(rs.getString("telephone"));admin.setEmail(rs.getString("email"));admin.setEnrolldate(rs.getTimestamp("enrolldate"));}} catch (SQLException e) {//step1. 记日志（保留现场）e.printStackTrace();/** step2.看异常能否恢复,如果* 不能够恢复(比如数据库服务* 暂停，网络中断，这样的异常* 一般我们称之为系统异常)，* 则提示用户稍后重试。如果能够* 恢复，则立即恢复。* */throw new RuntimeException(e);}finally{if(conn != null){try {conn.close();} catch (SQLException e) {e.printStackTrace();throw new RuntimeException(e);}}}return admin;}}

/netctoss-spring/src/main/java/cn/tedu/netctoss/entity/Admin.java

package cn.tedu.netctoss.entity;import java.io.Serializable;
import java.sql.Timestamp;public class Admin implements Serializable{
    private Integer adminId;private String adminCode;private String password;private String name;private String telephone;private String email;private Timestamp enrolldate;@Overridepublic String toString() {return "Admin [adminId=" + adminId + ", adminCode=" + adminCode + ", password=" + password + ", name=" + name+ ", telephone=" + telephone + ", email=" + email + ", enrolldate=" + enrolldate + "]";}public Integer getAdminId() {return adminId;}public void setAdminId(Integer adminId) {this.adminId = adminId;}public String getAdminCode() {return adminCode;}public void setAdminCode(String adminCode) {this.adminCode = adminCode;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getTelephone() {return telephone;}public void setTelephone(String telephone) {this.telephone = telephone;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public Timestamp getEnrolldate() {return enrolldate;}public void setEnrolldate(Timestamp enrolldate) {this.enrolldate = enrolldate;}}

/netctoss-spring/src/main/java/cn/tedu/netctoss/service

ApplicationException.java

package cn.tedu.netctoss.service;
/*** 应用异常类**/
public class ApplicationException extends RuntimeException {
    public ApplicationException() {}public ApplicationException(String message) {super(message);}}

LoginService.java

package cn.tedu.netctoss.service;import cn.tedu.netctoss.entity.Admin;/*** 业务层接口**/
public interface LoginService {
    public Admin checkLogin(String adminCode,String pwd);
}

LoginServiceImpl.java

package cn.tedu.netctoss.service;import javax.annotation.Resource;import org.springframework.stereotype.Service;import cn.tedu.netctoss.dao.AdminDAO;
import cn.tedu.netctoss.entity.Admin;/*** 业务层实现**/
@Service("loginService")
public class LoginServiceImpl implements LoginService{
    @Resource(name="adminDAO")private AdminDAO aDAO;public Admin checkLogin(String adminCode, String pwd) {Admin admin = aDAO.findByAdminCode(adminCode);if(admin == null){//帐号不存在,抛一个应用异常。//注：应用异常，指的是因为用户//不正确的操作引起的异常，比如//帐号、密码填写错误。需要明确//提示用户采取正确的操作。throw new ApplicationException("帐号错误");}if(!admin.getPassword().equals(pwd)){//密码错误throw new ApplicationException("密码错误");}//登录成功return admin;}   
}

/netctoss-spring/src/main/resources

db.properties

# db connection parameters
driver=oracle.jdbc.driver.OracleDriver
url=jdbc:oracle:thin:@localhost:1521:xe
user= 
pwd= 
# datasource parameters
initsize=1
maxsize=2

spring-mvc.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee"xmlns:tx="http://www.springframework.org/schema/tx" xmlns:aop="http://www.springframework.org/schema/aop"xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:util="http://www.springframework.org/schema/util"xmlns:jpa="http://www.springframework.org/schema/data/jpa"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsdhttp://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.2.xsdhttp://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.3.xsdhttp://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsdhttp://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd"><!-- 配置组件扫描 --><context:component-scan base-package="cn.tedu.netctoss" /><!-- 配置MVC注解扫描 --><mvc:annotation-driven /><!-- 配置视图解析器 --><bean  class="org.springframework.web.servlet.view.InternalResourceViewResolver"><property name="prefix" value="/WEB-INF/" /><property name="suffix" value=".jsp" /></bean><!-- 读取db.properties文件 --><util:properties id="db" location="classpath:db.properties" /><!-- 配置连接池 --><bean id="ds" class="org.apache.commons.dbcp.BasicDataSource"destroy-method="close"><property name="driverClassName" value="#{db.driver}" /><property name="url" value="#{db.url}" /><property name="username" value="#{db.user}" /><property name="password" value="#{db.pwd}" /></bean></beans>