JDBC笔记 07：DAO及其实现类

Dao

访问数据信息的类和接口，包括了对数据的CRUD，而不包含任何业务相关的信息。作用：为了实现功能的模块化，更有利于代码的维护和升级

BaseDao（基本的对数据库的操作）

public class BaseDao<T> { private Class<T> clazz; { Type type = this.getClass().getGenericSuperclass(); ParameterizedType paramType = (ParameterizedType) type; Type[] typeArguments = paramType.getActualTypeArguments();//获取父类的泛型 clazz = (Class<T>) typeArguments[0];//泛型的第一个参数 } //通用的增删改操作 public int update(Connection connection, String sql, Object... args) { PreparedStatement statement = null; try { //1.预编译SQL语句，返回PreparedStatement对象 statement = connection.prepareStatement(sql); //2.填充占位符 for (int i = 0; i < args.length; i++) { statement.setObject(i + 1, args[i]); } //3.执行操作 return statement.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally { //4.关闭资源 JDBCUtils.closeResource(null, statement); } return -1; } //通用的查询操作，用于返回数据表中的一条记录 public T getInstance(Connection connection, String sql, Object... args) { PreparedStatement statement = null; ResultSet resultSet = null; try { //1.预编译SQL语句，返回PreparedStatement对象 statement = connection.prepareStatement(sql); //2.填充占位符 for (int i = 0; i < args.length; i++) { statement.setObject(i + 1, args[i]); } //3.执行操作，并返回结果集 resultSet = statement.executeQuery(); ResultSetMetaData data = resultSet.getMetaData(); int count = data.getColumnCount(); //4.处理结果集：使用泛型 if (resultSet.next()) { T t = clazz.newInstance(); for (int i = 0; i < count; i++) { Object obj = resultSet.getObject(i + 1); String columnName = data.getColumnLabel(i + 1); Field field = clazz.getDeclaredField(columnName); field.setAccessible(true); field.set(t, obj); } return t; } } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(null, statement, resultSet); } return null; } //通用的查询操作，用于返回数据表中的多条记录 public List<T> getList(Connection connection, String sql, Object... args) { PreparedStatement statement = null; ResultSet resultSet = null; try { //1.预编译SQL语句，返回PreparedStatement对象 statement = connection.prepareStatement(sql); //2.填充占位符 for (int i = 0; i < args.length; i++) { statement.setObject(i + 1, args[i]); } //3.执行操作，并返回结果集 resultSet = statement.executeQuery(); ResultSetMetaData data = resultSet.getMetaData(); int count = data.getColumnCount(); //4.处理结果集：使用泛型 ArrayList<T> results = new ArrayList<>(); while (resultSet.next()) { T t = clazz.newInstance();//为对象的每一个属性赋值 for (int i = 0; i < count; i++) { Object obj = resultSet.getObject(i + 1); String columnName = data.getColumnLabel(i + 1); Field field = clazz.getDeclaredField(columnName); field.setAccessible(true); field.set(t, obj); } results.add(t);//将对象加入集合中去 } return results; } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(null, statement, resultSet); } return null; } //用于查询特殊值的方法 public <E> E getValue(Connection connection, String sql, Object... args) { PreparedStatement statement = null; ResultSet resultSet = null; try { statement = connection.prepareStatement(sql); for (int i = 0; i < args.length; i++) { statement.setObject(i + 1, args[i]); } resultSet = statement.executeQuery(); if (resultSet.next()) { Object obj = resultSet.getObject(1); return (E) obj; } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(null, statement, resultSet); } return null; } }

CustomersDao（规范针对于Customers表的常用操作）

public interface CustomersDao { //添加一个customer void insert(Connection connection, Customers customers); //根据id删除customer void deleteById(Connection connection, int id); //修改customer void update(Connection connection, Customers customers); //根据id获取customer Customers getByID(Connection connection, int id); //获取表中全部数据 List<Customers> getAll(Connection connection); //获取表中数据的条数 Long getCount(Connection connection); //获取最大生日 Date getMaxBirth(Connection connection); }

CustomersDaoImpl（对于常规操作的具体实现）

public class CustomersDaoImpl extends BaseDao<Customers> implements CustomersDao { @Override public void insert(Connection connection, Customers customers) { String sql = "insert into customers (name,email,birth) values (?,?,?)"; update(connection, sql, customers.getName(), customers.getEmail(), customers.getBirth()); } @Override public void deleteById(Connection connection, int id) { String sql = "delete from customers where id = ?"; update(connection, sql, id); } @Override public void update(Connection connection, Customers customers) { String sql = "update customers set name = ? , email = ? , birth = ? where id = ?"; update(connection, sql, customers.getName(), customers.getEmail(), customers.getBirth(), customers.getId()); } @Override public Customers getByID(Connection connection, int id) { String sql = "select id,name,email,birth from customers where id = ?"; Customers customer = getInstance(connection, sql, id); return customer; } @Override public List<Customers> getAll(Connection connection) { String sql = "select id,name,email,birth from customers"; List<Customers> customers = getList(connection, sql); return customers; } @Override public Long getCount(Connection connection) { String sql = "select count(*) from customers"; Long count = getValue(connection, sql); return count; } @Override public Date getMaxBirth(Connection connection) { String sql = "select max(birth) from customers"; Date birth = getValue(connection, sql); return birth; } }