本例主要练习jdbc技术以及sql语句对数据库进行增删改查的操作
四张表
grade（班级表）
表中数据
result(成绩表)
表中数据
student(学生表)
表中数据
subject(科目表)
java代码实现
Util.java
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLClientInfoException;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Timestamp;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;
public class Util {
Connection conn =null;
Statement st = null;
Scanner input = new Scanner(System.in);
//建立连接
public void getConn() throws Exception {
//加载驱动
Class.forName("com.mysql.cj.jdbc.Driver");
//连接数据库
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/java27?characterEncoding=utf-8&serverTimezone=GMT%2B8",
"root","root");
}
//关闭连接
public void closeConn() throws Exception {
conn.close();
if(st!=null) {
st.close();
}
}
//选课系统
public void courseSystem() throws Exception {
int isLoop = 1;
System.out.println("欢迎进入学生选课系统！");
do {
System.out.println("请输入学号：");
int studentNo = input.nextInt();
System.out.println("请输入密码：");
String pwd = input.next();
//判断学生是否存在
if(login(studentNo,pwd)) {
isLoop=4;
boolean isContinue = false;
do {
showData();
int choice = input.nextInt();
switch (choice) {
case 1:
subjectInfo();
break;
case 2:
selectCourse(studentNo);
break;
case 3:
subjectInfo();
addCourse(studentNo);
break;
case 4:
lookResult(studentNo);
break;
case 5:
gradeInfo(studentNo);
break;
case 6:
classmates(studentNo);
break;
case 7:
selectCourse(studentNo);
deleteCourse(studentNo);
break;
case 8:
updatePwd(studentNo);
break;
default:
break;
}
System.out.println("请输入0继续1退出");
int a = input.nextInt();
if(a==0) {
isContinue=true;
}else {
System.out.println("系统已退出");
System.exit(0);
}
} while (isContinue);
}else {
System.out.println("你还有"+(3-isLoop)+"次输入机会后系统将退出");
isLoop++;
if(isLoop==4) {
System.out.println("3次机会已用完，系统退出");
System.exit(0);
}
}
} while (isLoop<4);
}
//检查学生是否在表中
public boolean login(int studentNo,String pwd) throws Exception {
try {
getConn();
st = conn.createStatement();
String sql="select * from student where studentNo="+studentNo+" and loginPwd='"
+pwd+"'";
ResultSet rs = st.executeQuery(sql);
if(rs.next()) {
return true;
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
closeConn();
}
return false;
}
//展示数据
public void showData() {
System.out.println("1.查看所有课程信息");
System.out.println("2.查看自己已经选择的课程");
System.out.println("3.新增选课（不能重复）");
System.out.println("4.查看自己每门课的成绩");
System.out.println("5.查看自己的班级信息");
System.out.println("6.查看自己班级的同学");
System.out.println("7.作废某门课程");
System.out.println("8.修改自己的信息（密码）");
System.out.println("请输入编号：");
}
//1.查看所有课程信息
public void subjectInfo() throws Exception {
getConn();
st = conn.createStatement();
String sql = "select * from subject";
ResultSet rs = st.executeQuery(sql);
System.out.println("课程编号\t课程名称\t学分\t所属班级");
while(rs.next()) {
System.out.println(rs.getInt("SubjectNo")+"\t"+rs.getString("SubjectName")
+"\t"+rs.getInt("ClassHour")+"\t"+rs.getInt("GradeId"));
}
closeConn();
}
//2.查看自己选择的课程信息
public void selectCourse(int studentNo) throws Exception {
getConn();
st = conn.createStatement();
String sql = "select * from subject where subjectNo in ((select subjectNo from result where studentNo="+studentNo+"))";
ResultSet rs = st.executeQuery(sql);
System.out.println("课程编号\t课程名称\t学分\t所属班级");
while(rs.next()) {
System.out.println(rs.getInt("SubjectNo")+"\t"+rs.getString("SubjectName")
+"\t"+rs.getInt("ClassHour")+"\t"+rs.getInt("GradeId"));
}
closeConn();
}
//3.新增选课
public void addCourse(int studentNo) throws Exception {
System.out.println("请输入要选择的课程编号:");
int subjectNo = input.nextInt();
//判断课程是否在课程表上
if(!isSubject(subjectNo)) {
System.out.println("你要选的课程不存在");
}else {
//判断该课程是否属于该学生所在班级的可以选择的课程
if(isGrade(subjectNo, studentNo)) {
//判断该课程是否已经被该学生选过
if(isExist(subjectNo, studentNo)) {
System.out.println("你已经选择过这门课程");
}
else {
//新增课程成功，存入result表
addSubject(subjectNo, studentNo);
System.out.println("新增科目成功");
}
}else{
System.out.println("该班级的学生不可以选择该课程");
}
}
}
//3.判断课程是否在课程表上
public boolean isSubject(int subjectNo) throws Exception {
try {
getConn();
st=conn.createStatement();
String sql = "select SubjectName from subject where SubjectNo="+subjectNo;
ResultSet rs = st.executeQuery(sql);
if(rs.next()) {
return true;
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
closeConn();
}
return false;
}
//3.判断该课程是否属于该学生所在班级可以选择的课程
public boolean isGrade(int SubjectNo,int studentNo) throws Exception {
try {
getConn();
st = conn.createStatement();
String sql = "select * from student where GradeId="
+ "(select GradeId from subject where SubjectNo="+SubjectNo+") and studentNo="+studentNo;
ResultSet rs = st.executeQuery(sql);
if(rs.next()) {
return true;
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
closeConn();
}
return false;
}
//3.判断该课程是否已经被该学生选过
public boolean isExist(int subjectNo,int studentNo) throws Exception {
try {
getConn();
st = conn.createStatement();
String sql = "select studentNo from result where studentNo="+
studentNo+" and subjectNo="+subjectNo;
ResultSet rs = st.executeQuery(sql);
if(rs.next()) {
return true;
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
closeConn();
}
return false;
}
//3.新增成功，存入result表
public void addSubject(int subjectNo,int studentNo) throws Exception {
getConn();
st=conn.createStatement();
//获得系统时间
Date date = new Date();
//将时间格式转换成符合Timestamp要求的格式
String nowTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(date);
String sql = "insert into result(studentNo,subjectNo,examDate) values("+studentNo+","+subjectNo+",'"+nowTime+"')";
st.executeUpdate(sql);
closeConn();
}
//4.查看自己每门课程的成绩
public void lookResult(int studentNo) throws Exception {
getConn();
st = conn.createStatement();
String sql = "select s.subjectNo,SubjectName,studentResult from \r\n" +
"(select * from result where StudentNo="+studentNo+") s left join subject\r\n" +
"on s.subjectNo=subject.SubjectNo";
ResultSet rs = st.executeQuery(sql);
System.out.println("课程编号\t课程名称\t成绩");
while(rs.next()) {
System.out.println(rs.getInt("s.SubjectNo")+"\t"+rs.getString("SubjectName")
+"\t"+rs.getInt("studentResult"));
}
closeConn();
}
//5.查看自己班级信息
public void gradeInfo(int studentNo) throws Exception {
getConn();
st = conn.createStatement();
String sql = "select s.gradeid,gradename from (select gradeid from student where studentno="+studentNo+") s \r\n" +
"left join grade on s.gradeid=grade.GradeId";
ResultSet rs = st.executeQuery(sql);
System.out.println("班级编号\t班级名称");
while(rs.next()) {
System.out.println(rs.getInt("gradeid")+"\t"+rs.getString("gradename"));
}
closeConn();
}
//6.查看自己班级的同学
public void classmates(int studentNo) throws Exception {
getConn();
st = conn.createStatement();
String sql = "select studentno,studentname,sex,gradeid from student WHERE\r\n" +
"gradeid=(select gradeid from student where studentno="+studentNo+") ";
ResultSet rs = st.executeQuery(sql);
System.out.println("学号\t名字\t性别\t班级编号");
while(rs.next()) {
System.out.println(rs.getInt("studentno")+"\t"+rs.getString("studentname")+"\t"
+rs.getInt("sex")+"\t"+rs.getInt("gradeid"));
}
closeConn();
}
//7.作废某门课程
public void deleteCourse(int studentNo) throws Exception {
System.out.println("请输入要作废的课程的编号:");
int subjectNo = input.nextInt();
//判断该门课程是否已经被该学生选过
if(isExist(subjectNo, studentNo)) {
getConn();
st = conn.createStatement();
String sql = "delete from result where studentno="+studentNo+" and subjectno="+subjectNo;
int rs = st.executeUpdate(sql);
if(rs>0) {
System.out.println("该门课程作废成功");
}
closeConn();
}else {
System.out.println("该学生没有选择过该门课程");
}
}
//8.修改密码
public void updatePwd(int studentNo) throws Exception {
System.out.println("请输入修改后的密码");
String pwd = input.next();
getConn();
st = conn.createStatement();
String sql = "update student set loginPwd='"+pwd+"' where studentno="+studentNo;
int rs=st.executeUpdate(sql);
if(rs>0) {
System.out.println("修改成功");
}
closeConn();
}
}
Test.java
测试
package studentSelect;
public class Test {
public static void main(String[] args) throws Exception {
Util util = new Util();
util.courseSystem();
}
}
效果图：
