关于接口在J2EE编程中的小运用及一些体会

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关于接口

接口是一些列方法的抽象，并没有给出具体的实现，需要特定的类去实现它，在J2EE编程中，通常分为三块，前台的显示，业务逻辑部分以及数据库访问部分，也就是DAO层。在DAO层，则可以定义一个接口，这样换底层是数据库的话，更改起来也比较方便

代码块

例如定义一个将产品存入数据库的接口ProductDAO.java，例如：

@requires_authorizationimport java.sql.Timestamp;import java.util.List;import com.bandc.shopping.Product;public interface ProductDAO {    public List<Product> getProductlist();    public boolean addProduct(Product p);    public List<Product> findProducts(int id,                                      String name,                                      String descr,                                      double lownormalprice,                                      double highnormalprice,                                      double lowmembershipprice,                                      double highmembershiprice,                                      Timestamp pdate,                                      int categoryid);    public void deleteProductByCategoryId(int categoryid);    public void deleteProductById(int id);    public boolean updateProduct(Product p);}

这里定义了一个接口，然后定义一个类去实现它ProductMySQLDAO.java，这就是一个基于MySQL数据库的一个具体的实现

package com.bandc.shopping.DAO;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.SQLException;import java.sql.Timestamp;import java.util.*;import com.bandc.shopping.Product;import com.bandc.shopping.util.DB;public class ProductMySQLDAO implements ProductDAO {    public List<Product> getProductlist() {        return null;    }    public boolean addProduct(Product p) {        int id = p.getId();        String name = p.getName();        String descr = p.getDescr();        double normalprice = p.getNormalprice();        double memberprice = p.getMemberprice();         Timestamp pdate =p.getPdate();        int categoryid = p.getCategoryid();        Connection conn =null;        String sql = null;        PreparedStatement pstmt = null;         try{            conn = DB.getConn();            if(id == -1){                sql = "insert into product values(null,?,?,?,?,?,?)";            }else{                sql = "insert into product values("+id+",?,?,?,?,?,?)";            }            pstmt = conn.prepareStatement(sql);            pstmt.setString(1, name);            pstmt.setString(2, descr);            pstmt.setDouble(3, normalprice);            pstmt.setDouble(4, memberprice);            pstmt.setTimestamp(5, pdate);            pstmt.setInt(6, categoryid);            //System.out.println(sql);            pstmt.executeUpdate();            System.out.println("插入成功");        }catch(SQLException e){            e.printStackTrace();            return false;        }finally{            DB.closePstmt(pstmt);            DB.closeConn(conn);        }   //System.out.println("插入成功");        return true;    }    public List<Product> findProducts(int id, String name, String descr,            double lownormalprice, double highnormalprice,            double lowmembershipprice, double highmembershiprice,            Timestamp pdate, int categoryid) {        // TODO Auto-generated method stub        return null;    }    public void deleteProductByCategoryId(int categoryid) {        // TODO Auto-generated method stub    }    public void deleteProductById(int id) {        // TODO Auto-generated method stub    }    public boolean updateProduct(Product p) {        // TODO Auto-generated method stub        return false;    }    public List<Product> findProducts(int id, String name, String descr,            double lownormalprice, double highnormalprice,            double lowmembershipprice, double highmembershiprice,            com.sun.jmx.snmp.Timestamp pdate, int categoryid) {        // TODO Auto-generated method stub        return null;    }    ```然后在业务逻辑层，有一个关于产品的管理类ProductManager.java``` pythonpackage com.bandc.shopping;import java.util.List;import com.bandc.shopping.DAO.ProductDAO;import com.bandc.shopping.DAO.ProductMySQLDAO;public class ProductManager {    ProductDAO dao = null;    private static ProductManager pm = null;    static{        if(pm == null){            pm = new ProductManager();            pm.setDAO(new ProductMySQLDAO());//只要改变这一句话，并生成相应的数据库的DAO，那么改变就完成了        }    }    public static ProductManager getInstance(){        return pm;    }    public List<Product> getProductlist() {        return dao.getProductlist();    }    public ProductDAO getDAO(){        return dao;    }    private void setDAO(ProductDAO dao) {        this.dao = dao;    }    public boolean addProduct(Product p) {        return dao.addProduct(p);    }    public List<Product> findProducts(int id, String name, String descr,            double lownormalprice, double highnormalprice,            double lowmembershipprice, double highmembershiprice,            Timestamp pdate, int categoryid) {        // TODO Auto-generated method stub        return null;    }    public void deleteProductByCategoryId(int categoryid) {        // TODO Auto-generated method stub    }    public void deleteProductById(int id) {        // TODO Auto-generated method stub    }    public boolean updateProduct(Product p) {        // TODO Auto-generated method stub        return false;    }}

这样可以大大的提高代码的灵活性。