三层架构详解-以学生管理系统为例
1.三层架构
与MVC设计模式的目标一致：都是为了解耦合，提高代码复用
区别：二者对项目的理解角度不同
2.三层组成
表示层（USL,User Show Layer:视图层）
-前台：对应于MVC的View，用于和用户交互，界面显示
jsp,html,js,css
代码位置：WebContent
-后台：对应于MVC的Controller，用于控制跳转，调用业务逻辑层
Servlet,SpringMVC，Struts2
位于xxx.servlet包中
业务逻辑层（BLL,Business Logic Layer:Service层）
-接收表示层的请求 调用
-组装数据访问层，逻辑性的操作（增删改查，不可拆）
一般位于xxx.service包中
数据访问层（DAL,Data Access Layer:Dao层）
-直接访问数据库的操作，原子性的操作（增删改查）
一般位于xxx.dao包中
三层间的关系：
上层将请求传递给下层，下层处理后，返回给上层
三层与MVC对比：
案例项目结构：
add.jsp:
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
Insert title here
index.jsp:
<%@page import="org.student.entity.Student"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
学生信息列表
<%
//error:adderror失败
//否则，1.确实执行了增加 2，直接访问查询全部页面 这样都会导致error为null,所以一进查询页面就会有“增加成功！”
String error = (String) request.getAttribute("error");
if (error != null) {
if (error.equals("adderror")) {
out.print("增加失败！");
} else if (error.equals("noadderror")) {
out.print("增加成功！");
}
}
%>
学号
姓名
年龄
操作
<%
//获取request域中的数据
//根据key拿value,从servlet中拿值
List students = (List) request.getAttribute("students");
for (Student student : students) {
%>
<%=student.getSno()%>
<%=student.getSname()%>
<%=student.getSage()%>
删除
<%
}
%>
新增
studentInfo.jsp:
<%@page import="org.student.entity.Student"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
学生个人信息
<%
Student student=(Student)request.getAttribute("student");
%>
Student.java:
package org.student.entity;
public class Student {
private String sno;
private String sname;
private int sage;
private String saddress;
public Student() {
}
public Student(String sname, int sage, String saddress) {
this.sname = sname;
this.sage = sage;
this.saddress = saddress;
}
public Student(String sno, String sname, int sage, String saddress) {
this.sno = sno;
this.sname = sname;
this.sage = sage;
this.saddress = saddress;
}
public String getSno() {
return sno;
}
public void setSno(String sno) {
this.sno = sno;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public int getSage() {
return sage;
}
public void setSage(int sage) {
this.sage = sage;
}
public String getSaddress() {
return saddress;
}
public void setSaddress(String saddress) {
this.saddress = saddress;
}
}
StudentDao.java:
package org.student.dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import org.student.entity.Student;
//数据访问层：原子性的增删改查
public class StudentDao {
String URL = "jdbc:mysql://localhost:3306/threetiersample";
String USERNAME = "root";
String PASSWORD = "";
// 根据学号查此人是否存在
public boolean isExist(String sno) {
return queryStudetByNo(sno) == null ? false : true;
}
// 查询全部学生,用集合表示
public List queryAllStudents() {
List students = new ArrayList<>();
Student student = null;
Connection connection = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
String sql = "select * from student";
pstmt = connection.prepareStatement(sql);
rs = pstmt.executeQuery();
while (rs.next()) {
String no = rs.getString("sno");
String name = rs.getString("sname");
int age = rs.getInt("sage");
String address = rs.getString("saddress");
student = new Student(no, name, age, address);
students.add(student);
}
return students;
} catch (ClassNotFoundException e) {
e.printStackTrace();
return null;
} catch (SQLException e) {
e.printStackTrace();
return null;
} catch (Exception e) {
e.printStackTrace();
return null;
} finally {
try {
if (rs != null)
rs.close();
if (pstmt != null)
pstmt.close();
if (connection != null)
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
// 增加学生
public boolean addStudent(Student student) {
Connection connection = null;
PreparedStatement pstmt = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
String sql = "insert into student values(?,?,?,?)";
pstmt = connection.prepareStatement(sql);
pstmt.setString(1, student.getSno());
pstmt.setString(2, student.getSname());
pstmt.setInt(3, student.getSage());
pstmt.setString(4, student.getSaddress());
int count = pstmt.executeUpdate();
if (count > 0) {
return true;
} else {
return false;
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
return false;
} catch (SQLException e) {
e.printStackTrace();
return false;
} catch (Exception e) {
e.printStackTrace();
return false;
} finally {
try {
if (pstmt != null)
pstmt.close();
if (connection != null)
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
// 根据学号修改学生:先根据sno找人，然后信息替换为新的student
public boolean updateStudentBySno(String sno, Student student) {
Connection connection = null;
PreparedStatement pstmt = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
String sql = "update student set sname=?,sage=?,saddress=? where sno=?";
pstmt = connection.prepareStatement(sql);
pstmt.setString(1, student.getSname());
pstmt.setInt(2, student.getSage());
pstmt.setString(3, student.getSaddress());
pstmt.setString(4, sno);
int count = pstmt.executeUpdate();
if (count > 0) {
return true;
} else {
return false;
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
return false;
} catch (SQLException e) {
e.printStackTrace();
return false;
} catch (Exception e) {
e.printStackTrace();
return false;
} finally {
try {
if (pstmt != null)
pstmt.close();
if (connection != null)
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
// 根据学号来删除学生
public boolean deleteStudentBySno(String sno) {
Connection connection = null;
PreparedStatement pstmt = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
String sql = "delete from student where sno=?";
pstmt = connection.prepareStatement(sql);
pstmt.setString(1, sno);
int count = pstmt.executeUpdate();
if (count > 0) {
return true;
} else {
return false;
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
return false;
} catch (SQLException e) {
e.printStackTrace();
return false;
} catch (Exception e) {
e.printStackTrace();
return false;
} finally {
try {
if (pstmt != null)
pstmt.close();
if (connection != null)
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
// 根据学号查询学生
public Student queryStudetByNo(String sno) {
Student student = null;
Connection connection = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
String sql = "select * from student where sno=?";
pstmt = connection.prepareStatement(sql);
pstmt.setString(1, sno);
rs = pstmt.executeQuery();
if (rs.next()) {
String no = rs.getString("sno");
String name = rs.getString("sname");
int age = rs.getInt("sage");
String address = rs.getString("saddress");
student = new Student(no, name, age, address);
}
return student;
} catch (ClassNotFoundException e) {
e.printStackTrace();
return null;
} catch (SQLException e) {
e.printStackTrace();
return null;
} catch (Exception e) {
e.printStackTrace();
return null;
} finally {
try {
if (rs != null)
rs.close();
if (pstmt != null)
pstmt.close();
if (connection != null)
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
StudentService.java:
package org.student.service;
import java.util.List;
import org.student.dao.StudentDao;
import org.student.entity.Student;
//业务逻辑层：逻辑性的增删改查(增：查+增)，对dao层进行的组装
public class StudentService {
StudentDao studentDao=new StudentDao();
public boolean addStudent(Student student) {
if(!studentDao.isExist(student.getSno())) { //判断此人是否存在
studentDao.addStudent(student);
return true;
}else {
System.out.println("此人已存在!!!");
return false;
}
}
public boolean deleteStudentBySno(String sno) {
if(studentDao.isExist(sno)) {
return studentDao.deleteStudentBySno(sno);
}
return false;
}
public boolean updateStudentBySno(String sno,Student student) {
if(studentDao.isExist(sno)) {
return studentDao.updateStudentBySno(sno, student);
}
return false;
}
public Student queryStudentBySno(String sno) {
return studentDao.queryStudetByNo(sno);
}
public List queryAllStudent(){
return studentDao.queryAllStudents();
}
}
AddStudentServlet.java:
package org.student.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.student.entity.Student;
import org.student.service.StudentService;
public class AddStudentServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
String no=request.getParameter("sno");
String name=request.getParameter("sname");
int age=Integer.parseInt(request.getParameter("sage"));
String address=request.getParameter("saddress");
Student student=new Student(no,name,age,address);
//service层写好后，开始在servlet调用service
StudentService studentService=new StudentService();
boolean result=studentService.addStudent(student);
/*
* out request response session application
* out:PrintWriter out = response.getWriter();
* session:request.getSession()
* application:request.getServletContext()
*/
//设置响应编码
response.setContentType("text/html; charset=UTF-8");
response.setCharacterEncoding("utf-8");
//由于out是jsp的内置对象，所以要先拿到out
PrintWriter out = response.getWriter();
/*
if(result) {
//out.println("增加成功!");
//response.sendRedirect("QueryAllStudentServlet");
}else {
//out.println("增加失败!");
//response.sendRedirect("QueryAllStudentServlet");
}
*/
if(!result) { //如果增加失败，给request域放入一条数据
request.setAttribute("error", "adderror");
}else {//增加成功
request.setAttribute("error", "noadderror");
}
//增加成功失败，都会跳转查询页
//response.sendRedirect("QueryAllStudentServlet");
//如果增加成功,跳转到查询页
request.getRequestDispatcher("QueryAllStudentServlet").forward(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
DeleteStudentServlet.java:
package org.student.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.student.service.StudentService;
public class DeleteStudentServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//删除功能
request.setCharacterEncoding("utf-8");
//接收前端传来的学号
String no = request.getParameter("sno");
//servlet直接掉service去删
StudentService service=new StudentService();
boolean result=service.deleteStudentBySno(no);
//设置响应编码
response.setContentType("text/html; charset=UTF-8");
response.setCharacterEncoding("utf-8");
PrintWriter out = response.getWriter();
if(result) {
//out.println("删除成功!!!");
response.sendRedirect("QueryAllStudentServlet");//删除学生之后重新查询，然后数据返回jsp，而不是直接跳到index.jsp
}else {
out.println("删除失败!!!");
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
UpdateStudentServlet.java:
package org.student.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.student.entity.Student;
import org.student.service.StudentService;
public class UpdateStudentServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
// 获取修改的人的学号
String no = request.getParameter("sno");
// 获取修改后的内容
String name = request.getParameter("sname");
int age = Integer.parseInt(request.getParameter("sage"));
String address = request.getParameter("saddress");
// 将修改后的内容封装到一个实体类中
Student student = new Student(name, age, address);
// Servlet调Service(上层调下层)
StudentService service = new StudentService();
boolean result = service.updateStudentBySno(no, student);
// 设置响应编码
response.setContentType("text/html; charset=UTF-8");
response.setCharacterEncoding("utf-8");
PrintWriter out = response.getWriter();
if (result) {
//out.println("修改成功!!!");
response.sendRedirect("QueryAllStudentServlet");//修改完后跳转到QueryAllStudentServlet
} else {
out.println("修改失败!!!");
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
QueryStudentBySnoServlet.java:
package org.student.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.student.entity.Student;
import org.student.service.StudentService;
public class QueryStudentBySnoServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
String no=request.getParameter("sno");
StudentService service=new StudentService();
Student student=service.queryStudentBySno(no);
System.out.println(student.toString());
//将此人的信息传到前台studentInfo.jsp显示
request.setAttribute("student", student); //将查到的学生信息放在request域中
//如果request域没有数据，使用重定向跳转response.sendRedirect();
//如果request域有数据(request.setAttribute() ),使用请求转发跳转
request.getRequestDispatcher("studentInfo.jsp").forward(request,response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
QueryAllStudentServlet.java:
package org.student.servlet;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.student.entity.Student;
import org.student.service.StudentService;
public class QueryAllStudentServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
StudentService service=new StudentService();
List students=service.queryAllStudent();
System.out.println(students.toString());
//将Servlet传给jsp
request.setAttribute("students", students);
//因为request域中有数据，因此需要通过请求转发的方式跳转（重定向会丢失request域数据)
//pageContext