在线选课系统 java servlet+ jsp+mysql+css+js制作

/* * This product includes software developed by the * Apache Software Foundation (http://www.apache.org/). */ package ch04.servlet; import java.io.*; import java.util.*; import java.sql.*; import javax.servlet.*; import javax.servlet.http.*; import ch04.*; /** * 针对学生选课登录页面的Servlet * @author ShenYK * @version 1.0 */ public class ChooseCourse extends Common { public void doGet ( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException { //设置提交表单的中文编码 request.setCharacterEncoding("GBK"); HttpSession mySession = request.getSession(true); //清空错误消息 mySession.setAttribute("errMsg",""); //是否进入默认页面 if ( !request.getParameterNames().hasMoreElements() ) { //如果是默认进入页面，则选出所有备选的课程 String sUsername = (String)mySession.getAttribute( "username" ); Vector allCourses = getAllCourses( sUsername ); mySession.setAttribute( "courses", allCourses ); response.sendRedirect("../chooseCourse.jsp"); return; } else { //获取表单变量 String sCourseId = request.getParameter("courseId"); String sUsername = (String)mySession.getAttribute("username"); //尝试进行选择 boolean bChoose = chooseCourse( sUsername, sCourseId ); //如果选课成功，则跳转到选课结果一览页面 if ( bChoose ) { response.sendRedirect("../servlet/ViewCourse"); return; } else { mySession.setAttribute("errMsg","你选择的课程" + sCourseId + "已经满员，请选择其他课程。"); Vector allCourses = getAllCourses( sUsername ); mySession.setAttribute( "courses", allCourses ); response.sendRedirect("../chooseCourse.jsp"); return; } } } public void doPost ( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException { doGet( request, response ); } //获取用户所有可以使用的课程列表 private Vector getAllCourses( String sUsername ) { //获得数据库连接 Connection conn = this.getDBConnection(); if ( conn == null ) { return null; } Statement stmt = null; ResultSet rs = null; try { stmt = conn.createStatement(); //执行SQL语句 String sQuery = "select course.*,IF(elective.course_id, count(*), 0) as amount " + "from course left join elective " + "on course.course_id = elective.course_id " + "where course.course_id not in " + "(select distinct course_id from elective where username='" + sUsername + "') " + "group by course.course_id"; rs = stmt.executeQuery( sQuery ); //留着在页面上显示的课程列表 Vector courses = new Vector(); while ( rs.next() ) { Course course = new Course(); course.setCourseId( rs.getString( "course_id" ) ); course.setCourseName( rs.getString( "course_name" ) ); course.setTeacher( rs.getString( "teacher" ) ); course.setPoint( rs.getInt( "point" ) ); course.setTime1( rs.getString( "time_1" ) ); course.setTime2( rs.getString( "time_2" ) ); course.setLimited( rs.getInt( "limited" ) ); course.setAmount( rs.getInt( "amount" ) ); courses.add(course); } return courses; } catch(Exception e) { e.printStackTrace(); return null; } finally { try { rs.close(); stmt.close(); conn.close(); }catch(Exception ex) { } } } //为用户进行选课 private synchronized boolean chooseCourse( String sUsername, String sCourseId ) { //获得数据库连接 Connection conn = this.getDBConnection(); if ( conn == null ) { return false; } Statement stmt = null; ResultSet rs = null; try { stmt = conn.createStatement(); //执行SQL语句 String sQuery = "select course.limited,IF(elective.course_id, count(*), 0) as amount " + "from course left join elective " + "on course.course_id = elective.course_id " + "where course.course_id = '" + sCourseId + "' " + "group by course.course_id"; rs = stmt.executeQuery( sQuery ); //检查是否选课人数已满 if ( rs.next() ) { int iLimited = rs.getInt("limited"); int iAmount = rs.getInt("amount"); if ( iAmount >= iLimited ) { return false; } } //尝试进行选课 String sUpdateQuery = "insert into elective set " + "username='" + sUsername + "', course_id='" + sCourseId + "'"; stmt.executeUpdate( sUpdateQuery ); return true; } catch(Exception e) { e.printStackTrace(); return false; } finally { try { rs.close(); stmt.close(); conn.close(); }catch(Exception ex) { } } } }