使用JDBC实现数据访问对象层（DAO）代码示例

class User{ private long id; private String name; private String gender; public User(){ super(); } public User(long id,String name,String gender){ super(); this.id = id; this.name = name; this.gender = gender; } //get,set方法 } //DAO类 public class jdbcDao{ static{  try{   Class.forName("com.mysql.jdbc.Driver");  }catch(Exception e){  e.printStackTrace();   }  } private Connection getConn(){  try{   return DriverManager.getConnection("jdbc:mysql://localhost:3306:xe","root","password");   }catch(Exception e){   e.printStackTrace();   }  }  return null; } private void release(ResultSet rs,Statement ps,Connection conn){  if(rs!=null){   try{    rs.close();   }catch(Exception e){    e.printStackTrace();   }  }  if(ps!=null){   try{    ps.close();   }catch(Exception e){    e.printStackTrace();   }  }  if(conn!=null){   try{    conn.close();   }catch(Exception e){    e.printStackTrace();   }  } } //用ID获取用户对象 public User getUserById(long id){  ResultSet rs = null;  PreparedStatement ps = null;  Connection conn = null;  String sql = "select * from user where id = ?";  try{   conn = this.getConnection();   ps = conn.prepareStatement(sql);   ps.setLong(1,id);   rs = ps.executeQuery();   if(rs.next()){    //如果存在，则直接构建并返回用户对象    User user = new User(rs.getLong("id"),rs.getString("name"),rs.getString("gender"));    return user;   }  }catch(Exception e){   e.printStackTrace();  }finally{   this.release(rs,ps,conn);  }  return null; } //查询所有用户 public List<User> getAllUsers(){  List<User> list = new ArrayList<User>();  ResultSet rs = null;  PreparedStatement ps = null;  Connection conn = null;  String sql = "select * from user ";  try{   conn = this.getConnection();   ps = conn.prepareStatement(sql);   rs = ps.executeQuery();   //循环添加用户对象   while(rs.next()){    User user = new User(rs.getLong("id"),rs.getString("name"),rs.getString("gender"));    list.add(user);   }  }catch(Exception e){   e.printStackTrace();  }finally{   this.release(rs,ps,conn);  }  return list; } //修改用户数据 public User updateUser(User user){  PreparedStatement ps = null;  Connection conn = null;  String sql = "update user set id =?,name=?,gender=?"; try{   conn = this.getConnection();   conn.setAutoCommit(false);   ps = conn.prepareStatement(sql);   ps.setLong(1,user.getId());   ps.setString(2,user.getName());   ps.setString(3,user.getGender());   int rst = ps.executeUpdate();   if(rst>0){    return new User(user.getId(),user.getName(),user.getGender());   }   conn.commit();  }catch(Exception e){   e.printStackTrace();   try{    conn.rollback();   }catch(Exception e1){    e1.printStackTrace();   }  }finally{   this.release(null,ps,conn);  }  return null;   }  }  //删除用户数据 public boolean deleteUser(long id){  PreparedStatement ps = null;  Connection conn = null;  String sql = "delete from user where id =?; try{   conn = this.getConnection();   conn.setAutoCommit(false);   ps = conn.prepareStatement(sql);   ps.setLong(1,user.getId());   ps.setString(2,user.getName());   ps.setString(3,user.getGender());   int rst = ps.executeUpdate();   if(rst>0){    return user;   }   conn.commit();  }catch(Exception e){   e.printStackTrace();   try{    conn.rollback();   }catch(Exception e1){    e1.printStackTrace();   }  }finally{   this.release(null,ps,conn);  }  return null;   }  }  //插入用户数据  public User insertUser(User user){  PreparedStatement ps = null;  Connection conn = null;  String sql = "insert into user values(?,?,?)"; try{   conn = this.getConnection();   conn.setAutoCommit(false);   ps = conn.prepareStatement(sql);   ps.setLong(1,user.getId());   ps.setString(2,user.getName());   ps.setString(3,user.getGender());   int rst = ps.executeUpdate();   if(rst>0){    return user;   }   conn.commit();  }catch(Exception e){   e.printStackTrace();   try{    conn.rollback();   }catch(Exception e1){    e1.printStackTrace();   }  }finally{   this.release(null,ps,conn);  }  return null;   }  } } }