java实训总结3

今天实训内容的小目标就是完成那几个数据库增删改查的功能，由于课时的原因，也因为自己的原因，导致了这里的内容都是没有怎么学习的，所以我在敲代码的过程中首先去认真的看老师的注释，先去理解这个内容的思路，之后再照着敲，因为这个jdbc的思路基本上差不多，我照着先敲了一遍，之后再去背着敲，通过自己对jdbc的理解把代码敲出来，遇到记不住的或者没有理解的再去看老师的代码。通过这样的学习方法，自我感觉已经会了。

看见有一块代码块长达500行，就被下到了，在想着能不能偷懒的情况下，思考着怎么能够把这些代码变少。

import net.sb.student.bean.Student; import net.sb.student.dao.StudentDao; import net.sb.student.dbutil.ConnectionManager; import java.sql.*; import java.util.ArrayList; import java.util.List; import java.util.Vector; public class StudentDaoImpl implements StudentDao { Connection conn = ConnectionManager.getConnection(); /** * 添加学生记录 * @param student * @return */ @Override public int insert(Student student) { int count = 0; String sql = "insert into t_student (id, name, sex, age, department, class, telephone)" + " values (?, ?, ?, ?, ?, ?, ?)"; try{ PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setString(1,student.getId()); pstmt.setString(2,student.getName()); pstmt.setString(3,student.getSex()); pstmt.setInt(4,student.getAge()); pstmt.setString(5,student.getDepartment()); pstmt.setString(7,student.getClazz()); count = pstmt.executeUpdate(); pstmt.close(); } catch (SQLException e) { e.printStackTrace(); }finally { ConnectionManager.closeConnection(conn); } return count; } /** * 按学号删除记录 * @param id * @return */ @Override public int deleteById(String id) { int count = 0; String sql = "delete from t_student where id = ?"; delete(sql, id, count); return count; } /** * 按照班级 删除记录 * @param clazz * @return */ @Override public int deleteByClass(String clazz) { int count = 0; String sql = "delete from t_student where class = ?"; count = delete(sql,clazz,count); return count; } /** * 按照系部删除记录 * @param department * @return */ @Override public int deleteByDepartment(String department) { int count = 0; String sql = "delete from t_student where department = ?"; delete(sql,department,count); return count; } /** * 更新学生记录 * @param student * @return */ @Override public int update(Student student) { int count = 0; Connection conn = ConnectionManager.getConnection(); String sql = "update t_student set name = ?, sex = ?, age = ?," + " department = ?, class = ?, telephone = ? where id = ?"; try{ PreparedStatement pstms = conn.prepareStatement(sql); pstms.setString(1,student.getName()); pstms.setString(2,student.getSex()); pstms.setInt(3,student.getAge()); pstms.setString(4,student.getDepartment()); pstms.setString(5,student.getClazz()); pstms.setString(6,student.getTelephone()); pstms.setString(7,student.getId()); } catch (SQLException e) { e.printStackTrace(); } return count; } /** * 查询学生记录 * @param id * @return */ @Override public Student findById(String id) { Student student = null; String sql = "select * from t_student where id = ?"; student = select(sql,id); ConnectionManager.closeConnection(conn); return student; } List<Student> students = new ArrayList<Student>(); /** * 按照姓名查询学生信息 * @param name * @return */ @Override public List<Student> findByName(String name) { String sql = "select * from t_student where name like ?"; students.add(select(sql, name+"%")); return students; } /** * 按照班级查询学生信息 * @param clazz * @return */ @Override public List<Student> findByClass(String clazz) { String sql = "select * from t_student where class like ?"; students.add(select(sql,"%"+clazz+"%")); ConnectionManager.closeConnection(conn); return students; } /** * 按照系部查询学生记录 * @param department * @return */ @Override public List<Student> findByDepartment(String department) { String sql = "select * from t_student where department like ?"; students.add(select(sql,department+"%")); ConnectionManager.closeConnection(conn); return students; } /** * 查找全部学生 * @return */ @Override public List<Student> findAll() { String sql = "select * from t_student"; try { Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery(sql); while (rs.next()){ Student student = new Student(); student.setId(rs.getString("id")); student.setName(rs.getString("name")); student.setSex(rs.getString("sex")); student.setAge(rs.getInt("age")); student.setDepartment(rs.getString("department")); student.setClazz(rs.getString("class")); student.setTelephone(rs.getString("telephone")); students.add(student); } rs.close(); stmt.close(); } catch (SQLException e) { e.printStackTrace(); }finally { ConnectionManager.closeConnection(conn); } return students; } //定义Vector全局 Vector rows = new Vector(); /** * 按性别统计学生人数 * @return */ @Override public Vector findRowsBySex() { String sql = "select sex as '性别', count(*) as '人数'" + " from t_student group by sex order by sex desc"; try { Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery(sql); while (rs.next()){ Vector<String> currentRow = new Vector(); currentRow.addElement(rs.getString("性别")); currentRow.addElement(rs.getInt("人数") + ""); rows.addElement(currentRow); } } catch (SQLException e) { e.printStackTrace(); }finally { ConnectionManager.closeConnection(conn); } return rows; } /** * 按班级统计人数 * @return */ @Override public Vector findRowsByClass() { String sql = "select class as '班级', count(*) as '人数'" + " from t_student group by class order by class desc"; try{ Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery(sql); while (rs.next()){ Vector<String> currentRow = new Vector(); currentRow.addElement(rs.getString("班级")); currentRow.addElement(rs.getInt("人数") + ""); rows.addElement(currentRow); } } catch (SQLException e) { e.printStackTrace(); }finally { ConnectionManager.closeConnection(conn); } return rows; } /** * 按系部统计人数 * @return */ @Override public Vector findRowsByDepartment() { String sql = "select department as '系部', count(*) as '人数'" + " from t_student group by department order by department desc"; try { Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery(sql); while (rs.next()){ Vector<String> currentRow = new Vector(); currentRow.addElement(rs.getString("系部")); currentRow.addElement(rs.getInt("人数") + ""); rows.addElement(currentRow); } } catch (SQLException e) { e.printStackTrace(); }finally { ConnectionManager.closeConnection(conn); } return rows; } private int delete(String sql, String s, int count){ try{ PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setString(1,s); count = pstmt.executeUpdate(); pstmt.close(); } catch (SQLException e) { e.printStackTrace(); } return count; } private Student select(String sql, String s){ Connection conn = ConnectionManager.getConnection(); Student student = null; try{ PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setString(1,s); ResultSet rs = pstmt.executeQuery(); if (rs.next()){ student = new Student(); student.setId(rs.getString("id")); student.setName(rs.getString("name")); student.setSex(rs.getString("sex")); student.setAge(rs.getInt("age")); student.setDepartment(rs.getString("department")); student.setClazz(rs.getString("class")); student.setTelephone(rs.getString("telephone")); } rs.close(); pstmt.close(); } catch (SQLException e) { e.printStackTrace(); } return student; } }

皇天不负有心人，只要自己努力总会成功的。自己写着的并没有看见那里有语法错误。心里还是有一点小满足的。

不过还是遇到了一些小问题，遇到了一个问题就是：No operations allowed after connection closed，他告诉我说我的数据库连接已经关闭了，可是之前我明明有打开数据库的代码，他却没有打开。问了一下老师，老师告诉我说，他没有试过把打开数据连接的代码当作全局变量来做，都是用的局部变量，让我试一试，是不是因为这个，之后试了一下，果然没有报错了。但是在另一个java文件中，设置了这个，但是却没有报错，然而我找了很久都没有找到原因。但是我不会放弃的，我会下去慢慢找原因的。