JavaWeb开发之JDBC

Posted 2021-12-01 luojack

项目搭建的包命名和类命名：

 

首先导入数据库的驱动架包，并添加依赖

 

 

1.Dao层是专门负责和数据库交互，数据处理的代码层

2.Dao是接口，DaoImpl是Dao接口的实现类

3.Java代码连接数据库的步骤：“贾琏欲执事”口诀

　　（1）贾：加载数据库注册驱动,将数据库驱动注册到DriverManager中去。

　　　　Class.forName("com.mysql.jdbc.Driver");

 

　　（2）琏：创建连接数据库的对象，通过DriverManager获取

　　Connection conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbcdemo", "root", "123456");

 

　　（3）欲：创建预编译或非预编译 SQL语句对象

　　String sql="update t_student set name = ?,age = ? where id = ?";

　　PrepardStatment ps =conn.preparedStatment(sql);

　　ps.setString(1，"小明");

　　ps.setInt(2，20)；

　　ps.setInt(3，2)；

 

　　（4）执：执行SQL语句

　　int row =ps.executeUpdate();

 

　　（5）事：释放资源（先创后放）

　　conn.close();

　　ps.close();

　

具体代码：

	@Override
	public int insert(Student stu) {

		String sql = "insert into t_student(name,age)values(?,?)";
		Connection conn = null;
		PreparedStatement ps = null;
		try {
			// 1.加载注册驱动
			Class.forName("com.mysql.jdbc.Driver");

			// 2.获取数据库连接对象
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbcdemo", "root", "root");
			// 3.创建预编译语句对象
			ps = conn.prepareStatement(sql);

			// 3.1设置预编译语句对象占位符对应的参数值
			ps.setString(1, stu.getName());
			ps.setInt(2, stu.getAge());
			// 4.执行SQL语句 (注意：方法不能带sql参数)
			int row = ps.executeUpdate();
			return row;

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (ps != null) {
					ps.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			} finally {
				try {
					if (conn != null) {
						conn.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
		return 0;
	}

	@Override
	public int delete(Integer id) {
		String sql = "delete from t_student where id = ?";
		Connection conn = null;
		PreparedStatement ps = null;
		try {
			// 1.加载注册驱动
			Class.forName("com.mysql.jdbc.Driver");

			// 2.获取数据库连接对象
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbcdemo", "root", "root");
			// 3.创建预编译语句对象
			ps = conn.prepareStatement(sql);

			// 3.1设置预编译语句对象占位符对应的参数值
			ps.setInt(1, id);
			// 4.执行SQL语句 (注意：方法不能带sql参数)
			int row = ps.executeUpdate();
			return row;

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (ps != null) {
					ps.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			} finally {
				try {
					if (conn != null) {
						conn.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
		return 0;
	}

	@Override
	public int update(Student stu) {
		String sql = "update t_student set name = ?,age = ? where id = ?";
		Connection conn = null;
		PreparedStatement ps = null;
		try {
			// 1.加载注册驱动
			Class.forName("com.mysql.jdbc.Driver");

			// 2.获取数据库连接对象
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbcdemo", "root", "root");
			// 3.创建预编译语句对象
			ps = conn.prepareStatement(sql);

			// 3.1设置预编译语句对象占位符对应的参数值
			ps.setString(1, stu.getName());
			ps.setInt(2, stu.getAge());
			ps.setInt(3, stu.getId());
			// 4.执行SQL语句 (注意：方法不能带sql参数)
			int row = ps.executeUpdate();
			return row;

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (ps != null) {
					ps.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			} finally {
				try {
					if (conn != null) {
						conn.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
		return 0;
	}

	@Override
	public Student selectByPrimaryKey(Integer id) {

		String sql = "select * from t_student where id = ?";

		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		try {
			// 1.加载注册驱动
			Class.forName("com.mysql.jdbc.Driver");
			// 2.获取数据库连接对象
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbcdemo", "root", "root");
			// 3.创建预编译语句对象
			ps = conn.prepareStatement(sql);
			ps.setInt(1, id);
			// 4.执行sql语句
			rs = ps.executeQuery();

			while (rs.next()) {
				String name = rs.getString("name");
				int age = rs.getInt("age");

				// 封装Student对象
				Student stu = new Student(id, name, age);
				//返回Student对象
				return stu;
			}

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (rs != null) {
					rs.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			} finally {
				try {
					if (ps != null) {
						ps.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				} finally {
					try {
						if (conn != null) {
							conn.close();
						}
					} catch (SQLException e) {
						e.printStackTrace();
					}
				}
			}
		}
		return null;
	}

	@Override
	public List<Student> selectList() {

		List<Student> students = new ArrayList<>();

		String sql = "select * from t_student";

		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		try {
			// 1.加载注册驱动
			Class.forName("com.mysql.jdbc.Driver");
			// 2.获取数据库连接对象
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbcdemo", "root", "root");
			// 3.创建预编译语句对象
			ps = conn.prepareStatement(sql);

			// 4.执行sql语句
			rs = ps.executeQuery();

			while (rs.next()) {
				int id = rs.getInt("id");
				String name = rs.getString("name");
				int age = rs.getInt("age");

				// 封装Student对象
				Student stu = new Student(id, name, age);

				// 学生对象添加到集合中
				students.add(stu);
			}

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (rs != null) {
					rs.close();
				}
			} catch (SQLException e) {
				e.printStackTrace();
			} finally {
				try {
					if (ps != null) {
						ps.close();
					}
				} catch (SQLException e) {
					e.printStackTrace();
				} finally {
					try {
						if (conn != null) {
							conn.close();
						}
					} catch (SQLException e) {
						e.printStackTrace();
					}
				}
			}
		}

		return students;
	}