JDBC的DML增删改查的代码重构设计（下）

JDBC的操作模板：

流程：1.创建ProductResultSetHandler对象：2.作为参数传递给query方法3.在query方法中：rsh.handler,其实调用的是ProductResultSetHanlder方法

结果集处理规范：

//定义一个专门的约束处理结果集的接口：ResultSetHandler：结果集处理器
public interface ResultSetHandler<T> {//同意规定，必须有一个处理结果集的方法：handle,处理之后返回结果T handle(ResultSet rs) throws SQLException;
}

调用的模板方法：

public class JdbcTemplate {private JdbcTemplate() {}/*** *@param sql   DML各自的SQL,由调用者决定*@param params      DML操作需要的参数，由调用者决定*@return     受影响的行数*/public static int update(String sql, Object... params) {Connection conn = null;PreparedStatement ps = null;try {conn = JdbcUtil.INSTANCE.getConn();ps = conn.prepareStatement(sql);for (int i = 0; i < params.length; i++) {ps.setObject(i + 1, params[i]);}return ps.executeUpdate();} catch (SQLException e) {e.printStackTrace();} finally {JdbcUtil.INSTANCE.close(conn, ps, null);}return 0;}public static <T>T query(String sql, ResultSetHandler<T> rsh ,Object... params) {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JdbcUtil.INSTANCE.getConn();ps = conn.prepareStatement(sql);for (int i = 0; i < params.length; i++) {ps.setObject(i + 1, params[i]);}rs = ps.executeQuery();return rsh.handle(rs);} catch (Exception e) {e.printStackTrace();} finally {JdbcUtil.INSTANCE.close(conn, ps, rs);}return null;}

实现类的操作代码：

public class ProductDAOImpl implements IProductDAO {public void save(Product pro) {/*String sql = "insert into product (productName,brand,supplier,salePrice,costPrice,cutoff,dir_id ) values (?,?,?,?,?,?,?)";Object[] params = { pro.getProductName(), pro.getBrand(), pro.getSupplier(), pro.getSalePrice(),pro.getCostPrice(), pro.getCutoff(), pro.getDir_id() };JdbcTemplate.update(sql, params);*///拓展Hibernate的save操作：HibernateMock.save(pro); }public void delete(Long id) {String sql = "delete from product where id =  ? ";JdbcTemplate.update(sql, id);}public void update(Product pro) {String sql = "UPDATE product SET productName = ?, brand = ?, supplier = ?, salePrice = ?, costPrice = ?, cutoff = ?, dir_id = ?  WHERE id = ?";Object[] params = { pro.getProductName(), pro.getBrand(), pro.getSupplier(), pro.getSalePrice(),pro.getCostPrice(), pro.getCutoff(), pro.getDir_id(), pro.getId() };JdbcTemplate.update(sql, params);}public Product get(Long id) {String sql = "select * from product where id = ?";List<Product> list = JdbcTemplate.query(sql, new ProductResultHandler(),id);return list.size()==1? list.get(0):null;}public List<Product> list() {String sql = "SELECT * FROM product";return JdbcTemplate.query(sql,new ProductResultHandler());}//定义处理商品对象的结果集处理器class ProductResultHandler implements ResultSetHandler<List<Product>>{@Overridepublic List<Product> handle(ResultSet rs) throws SQLException {List<Product> list = new ArrayList<>();while (rs.next()) {Product pro = new Product();list.add(pro);pro.setId(rs.getLong("id"));pro.setProductName(rs.getString("productName"));pro.setBrand(rs.getString("brand"));pro.setSupplier(rs.getString("supplier"));pro.setSalePrice(rs.getBigDecimal("salePrice"));pro.setCostPrice(rs.getBigDecimal("costPrice"));pro.setCutoff(rs.getDouble("cutoff"));pro.setDir_id(rs.getLong("dir_id"));}return list;}}

拓展Hibernate的save操作：

public class HibernateMock {/*** 保存操作* @param obj* 1.拼SQL* 2.设置封装参数*///约定优于配置：//要求：表中的列和对象的属性相同public static void save(Object obj){//使用内省机制获取JivaBean对象的属性try {BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass(),Object.class);PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();StringBuilder sqlBuilder = new StringBuilder();//拼接SQLList<Object> params = new ArrayList<>();//封装属性的值/参数值String tableName = obj.getClass().getSimpleName();sqlBuilder.append("INSERT INTO ").append(tableName).append("(");StringBuilder sign = new StringBuilder();//拼接占位符for (PropertyDescriptor pd : pds) {String propertyName = pd.getName();//属性名/表中的列名sqlBuilder.append(propertyName).append(",");//拼接列名sign.append("?").append(",");Object value = pd.getReadMethod().invoke(obj);//获取每个属性的值params.add(value);}sqlBuilder.deleteCharAt(sqlBuilder.length()-1);sign.deleteCharAt(sign.length()-1);sqlBuilder.append(")VALUES(").append(sign);sqlBuilder.append(")");//封装参数,执行SQL//调用之前编写的MDL操作模板JdbcTemplate.update(sqlBuilder.toString(),params.toArray());} catch (Exception e) {e.printStackTrace();}}

测试类

public class ProductDAOTest {private IProductDAO dao = new ProductDAOImpl();@Testpublic void testSave() {Product pro = new Product();pro.setProductName("iphone8s");pro.setBrand("apple");pro.setSupplier("苹果公司");pro.setSalePrice(new BigDecimal("7000"));pro.setCostPrice(new BigDecimal("2000"));pro.setCutoff(0.9);pro.setDir_id(3L);//pro.setId(12L);dao.save(pro);}@Testpublic void testDelete() {dao.delete(26L);}@Testpublic void testUpdate() {Product pro = new Product();pro.setProductName("iphone6s");pro.setBrand("apple9s");pro.setSupplier("苹果公司2");pro.setSalePrice(new BigDecimal("6000"));pro.setCostPrice(new BigDecimal("1000"));pro.setCutoff(0.8);pro.setDir_id(5L);pro.setId(8L);dao.update(pro);}@Testpublic void testGet() {Product pro = dao.get(6L);System.out.println(pro);}@Testpublic void testList() {List<Product> list = dao.list();for (Product p : list) {System.out.println(p);}}
}

JdbcUtil工具类

public enum JdbcUtil {INSTANCE;private static Properties p = new Properties();//只需要注册一次驱动即可，没必要每次都注册，放到jdbcutil类的静态代码块中（当字节码被加载进jvm，就会执行）static {try {//从classpath的根路径去加载db.properties文件InputStream inStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties");p.load(inStream);Class.forName(p.getProperty("driverClassName"));} catch (Exception e) {e.printStackTrace();}}/*** 创建connection对象* @return*/public Connection getConn() {try {return DriverManager.getConnection(p.getProperty("url"), p.getProperty("usename"),p.getProperty("password"));} catch (Exception e) {e.printStackTrace();}return null;}public void close(Connection conn, Statement st, ResultSet rs) {try {if (rs != null) {rs.close();}} catch (Exception e) {e.printStackTrace();} finally {try {if (st != null) {st.close();}} catch (Exception e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (Exception e) {e.printStackTrace();}}}}
}

db.properties文件

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbcdemo?useSSL=false
usename=root
password=111111

商品对象

public class Product {private Long id;private String productName;private String brand;private String supplier;private BigDecimal salePrice;private BigDecimal costPrice;private Double cutoff;private Long dir_id;//分类编号public Long getId() {return id;}public void setId(Long id) {this.id = id;}public String getProductName() {return productName;}public void setProductName(String productName) {this.productName = productName;}public String getBrand() {return brand;}public void setBrand(String brand) {this.brand = brand;}public String getSupplier() {return supplier;}public void setSupplier(String supplier) {this.supplier = supplier;}public BigDecimal getSalePrice() {return salePrice;}public void setSalePrice(BigDecimal salePrice) {this.salePrice = salePrice;}public BigDecimal getCostPrice() {return costPrice;}public void setCostPrice(BigDecimal costPrice) {this.costPrice = costPrice;}public Double getCutoff() {return cutoff;}public void setCutoff(Double cutoff) {this.cutoff = cutoff;}public Long getDir_id() {return dir_id;}public void setDir_id(Long dir_id) {this.dir_id = dir_id;}@Overridepublic String toString() {return "Product [id=" + id + ", productName=" + productName + ", brand=" + brand + ", supplier=" + supplier+ ", salePrice=" + salePrice + ", costPrice=" + costPrice + ", cutoff=" + cutoff + ", dir_id=" + dir_id+ "]";}
}

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