前言
项目发布于半年前（2023年9月），这次是复习~来考古 =_=
点击前往 GitHub 项目页
该项目在之前的 学生管理系统 项目的基础上，增加了三层架构，对项目进行了分层
1. 三层架构
三层架构是一种分层的设计模式，将整个业务分为表示层、业务逻辑层、数据访问层（持久化层）
优点：降低了代码耦合度，层与层更方便管理，维护性和扩展性较高
缺点：开发成本高，系统性能较低（需要中间层）
具体实现如图：
- 表示层（UI）
显示数据和接受用户输入，实现用户与界面的交互
- 业务逻辑层（BLL）
表示层和数据访问层之间的桥梁，主要包含业务逻辑代码，负责数据的传递
- 数据访问层（DAL）
实现对数据库的访问和操作
2. JavaEE 设计模式之 DAO
DAO，Data Access Object（数据访问对象），是 JavaEE 的一种设计模式
只负责数据库表的 CRUD 操作，没有任何业务逻辑
3. 三层架构应用
目录结构
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| src
|--- com.xxx.student_manage
|--- bean
|--- Student
|--- dao 新增：数据访问层
|--- impl
|--- XxxDaoImpl 实现类
|--- XxxDao 接口
|--- filter
|--- LoginCheckFilter
|--- service 新增：业务逻辑层
|--- impl
|--- impl
|--- XxxServiceImpl 实现类
|--- XxxService 接口
|--- utils
|--- DBUtil
|--- web 原有：表示层，代码耦合度降低
|--- StudentServlet
|--- UserServlet
|--- WelcomeServlet
|--- resources
|--- jdbc.properties
web 原有：jsp 也属于表示层
|--- ...
|
代码实现
这里列举学生信息相关
DAO 层
只完成 CRUD 操作
接口：
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public interface StudentDao {
int insert(Student student);
int deleteBySno(String sno);
int update(Student student);
Student selectBySno(String sno);
List<Student> selectAll();
}
|
实现类：
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|
public class StudentDaoImpl implements StudentDao {
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
int count = 0;
@Override
public int insert(Student student) {
try {
conn = DBUtil.getConnection();
String sql = "insert into t_student(sno, sname, ssex, telephone) values (?, ?, ?, ?)";
ps = conn.prepareStatement(sql);
ps.setString(1, student.getSno());
ps.setString(2, student.getSname());
ps.setString(3, student.getSsex());
ps.setString(4, student.getTelephone());
count = 0;
count = ps.executeUpdate();
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
DBUtil.close(conn, ps, null);
}
return count;
}
@Override
public int deleteBySno(String sno) {
try {
conn = DBUtil.getConnection();
String sql = "delete from t_student where sno = ?";
ps = conn.prepareStatement(sql);
ps.setString(1, sno);
count = 0;
count = ps.executeUpdate();
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
DBUtil.close(conn, ps, null);
}
return count;
}
@Override
public int update(Student student) {
try {
conn = DBUtil.getConnection();
String sql = "update t_student set sname=?, telephone=? where sno=?";
ps = conn.prepareStatement(sql);
ps.setString(1, student.getSname());
ps.setString(2, student.getTelephone());
ps.setString(3, student.getSno());
count = 0;
count = ps.executeUpdate();
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
DBUtil.close(conn, ps, null);
}
return count;
}
@Override
public Student selectBySno(String sno) {
Student student = new Student();
try {
conn = DBUtil.getConnection();
String sql = "select sno, sname, ssex, telephone from t_student where sno=?";
ps = conn.prepareStatement(sql);
ps.setString(1, sno);
rs = ps.executeQuery();
if (rs.next()) {
String sname = rs.getString("sname");
String ssex = rs.getString("ssex");
String telephone = rs.getString("telephone");
student.setSno(sno);
student.setSname(sname);
student.setSsex(ssex);
student.setTelephone(telephone);
}
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
DBUtil.close(conn, ps, rs);
}
return student;
}
@Override
public List<Student> selectAll() {
List<Student> studentList = new ArrayList<>();
try {
conn = DBUtil.getConnection();
String sql = "select sno, sname, ssex, telephone from t_student";
ps = conn.prepareStatement(sql);
rs = ps.executeQuery();
while (rs.next()) {
String sno = rs.getString("sno");
String sname = rs.getString("sname");
String ssex = rs.getString("ssex");
String telephone = rs.getString("telephone");
Student student = new Student();
student.setSno(sno);
student.setSname(sname);
student.setSsex(ssex);
student.setTelephone(telephone);
studentList.add(student);
}
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
DBUtil.close(conn, ps, rs);
}
return studentList;
}
}
|
Service 层
实现业务逻辑，传递数据
接口：
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public interface StudentService {
void doList(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException;
void doDetail(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException;
void doDel(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException;
void doAdd(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException;
void doModify(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException;
}
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实现类：
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public class StudentServiceImpl implements StudentService {
StudentDao studentDao = new StudentDaoImpl();
@Override
public void doList(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
List<Student> studentList = studentDao.selectAll();
request.setAttribute("stuList", studentList);
request.getRequestDispatcher("/list.jsp").forward(request, response);
}
@Override
public void doDetail(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String sno = request.getParameter("sno");
Student student = studentDao.selectBySno(sno);
request.setAttribute("student", student);
request.getRequestDispatcher("/" + request.getParameter("f") + ".jsp").forward(request, response);
}
@Override
public void doDel(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String sno = request.getParameter("sno");
if (studentDao.deleteBySno(sno) == 1) {
response.sendRedirect(request.getContextPath() + "/student/list");
}
}
@Override
public void doAdd(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String sno = request.getParameter("sno");
String sname = request.getParameter("sname");
String ssex = request.getParameter("ssex");
String telephone = request.getParameter("telephone");
Student student = new Student(sno, sname, ssex, telephone);
if (studentDao.insert(student) == 1) {
response.sendRedirect(request.getContextPath() + "/student/list");
}
}
@Override
public void doModify(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String sno = request.getParameter("sno");
String sname = request.getParameter("sname");
String ssex = request.getParameter("ssex");
String telephone = request.getParameter("telephone");
Student student = new Student(sno, sname, ssex, telephone);
if (studentDao.update(student) == 1) {
response.sendRedirect(request.getContextPath() + "/student/list");
}
}
}
|
Web 层
StudentServlet：
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@WebServlet({"/student/list", "/student/detail", "/student/delete",
"/student/add", "/student/modify"})
public class StudentServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
StudentService studentService = new StudentServiceImpl();
String servletPath = request.getServletPath();
switch (servletPath) {
case "/student/list" -> studentService.doList(request, response);
case "/student/detail" -> studentService.doDetail(request, response);
case "/student/delete" -> studentService.doDel(request, response);
case "/student/add" -> studentService.doAdd(request, response);
case "/student/modify" -> studentService.doModify(request, response);
}
}
}
|
