设计模式3---抽象工厂模式
public interface IFactory { IUser CreateUser(); IDepartment CreateDepartment(); }
在工厂模式中，每个工厂类会为特定的操作类型产生操作对象类。
但是如果有产品系列的话，工厂模式就不太适用。
考虑一个数据库的问题。
1.数据库可能有替换
2.每个数据库可以修改多个表，比如user，department。
抽象工厂类就是对于工厂类产生的对象，我其实不需要得到具体的类，只要抽象类（接口）就可以了。
main方法：
public class AbstractFactoryMain extends BasicExample { @Override public void startDemo() { // TODO Auto-generated method stub User user = new User(); Department department = new Department(); IFactory factory = new AccessFactory(); IUser iu = factory.CreateUser(); iu.insertUser(user); iu.getUser(1); IDepartment id = factory.CreateDepartment(); id.insertDepartment(department); id.getDepartment(1); } }
IFactory 是工厂方法接口
IUser 和IDepartment 是对于User和Department的操作接口，具体是access还是SQLserver其实客户端不关心。
其他类具体实现：
public interface IFactory { IUser CreateUser(); IDepartment CreateDepartment(); }
//封装对User表的操作 public interface IUser { void insertUser(User user); User getUser(int id); }
//封装对Department表的操作 public interface IDepartment { void insertDepartment(Department department); Department getDepartment(int id); }
SQLserver工厂类：
public class SqlServerFactory implements IFactory { @Override public IUser CreateUser() { // TODO Auto-generated method stub return new SqlserverUser(); } @Override public IDepartment CreateDepartment() { // TODO Auto-generated method stub return new SqlserverDepartment(); } }
Access工厂类：
public class AccessFactory implements IFactory { @Override public IUser CreateUser() { // TODO Auto-generated method stub return new AccessUser(); } @Override public IDepartment CreateDepartment() { // TODO Auto-generated method stub return new AccessDepartment(); } }
具体操作类：
public class SqlserverUser implements IUser { @Override public void insertUser(User user) { System.out.println("在SQLserver 中给user表添加一条记录"); } @Override public User getUser(int id) { System.out.println("在SQLserver 中根据ID得到user表一条记录"); return null; } }
public class SqlserverDepartment implements IDepartment { @Override public void insertDepartment(Department department) { System.out.println("在SQLserver 中给Department表添加一条记录"); } @Override public Department getDepartment(int id) { System.out.println("在SQLserver 中根据ID得到Department表一条记录"); return null; } }
public class AccessDepartment implements IDepartment { @Override public void insertDepartment(Department department) { // TODO Auto-generated method stub System.out.println("在Access 中给Department表添加一条记录"); } @Override public Department getDepartment(int id) { System.out.println("在Access 中根据ID得到Department表一条记录"); return null; } }
public class AccessUser implements IUser { @Override public void insertUser(User user) { System.out.println("在Access 中给user表添加一条记录"); } @Override public User getUser(int id) { System.out.println("在Access 中根据ID得到user表一条记录"); return null; } }
public class User { private int _id; private String _name; public int getID() { return _id; } public void setID(int _id) { this._id = _id; } public String getName() { return _name; } public void setName(String _name) { this._name = _name; } }
public class Department { private int _id; private String _name; public int getID() { return _id; } public void setID(int _id) { this._id = _id; } public String getName() { return _name; } public void setName(String _name) { this._name = _name; } }
如果需要添加Oracle 数据库，那只要添加 工厂生成类OracleFactory,以及操作OracleUser 和OracleDepartment类。
这样就不会改动原有代码，可以快速替换数据库。
抽象工厂模型：
优点： 1.可以方便的交换产品系列，只需在初始化的地方出现一次，就可以应用一个具体工厂。
2.具体实现隔离客户端，客户端通过抽象接口来操作具体实例。
简单工厂模型优化抽象工厂模型。
把AccessFactory 和SqlserverFactory可以合并成DataAccess方法来处理。
问题：如果上述“ IFactory factory = new AccessFactory();” 有还多处地方，甚至好几百处，这样就需要做大量的修改。
把AccessFactory用DataAccess来代替，客户端彻底杜绝出现数据库字段。
public class DataAccess { // private static final String db = "Sqlserver"; private static final String db = "Access"; public static IUser CreateUser() { IUser result = null; switch(db) { case "Sqlserver": result = new SqlserverUser(); break; case "Access": result = new AccessUser(); break; } return result; } public static IDepartment CreateDepartment() { IDepartment result = null; switch(db) { case "Sqlserver": result = new SqlserverDepartment(); break; case "Access": result = new AccessDepartment(); break; } return result; } }
main方法修改为：
public class AbstractFactoryMain extends BasicExample { @Override public void startDemo() { // TODO Auto-generated method stub User user = new User(); Department department = new Department(); // IFactory factory = new AccessFactory(); IUser iu = DataAccess.CreateUser(); iu.insertUser(user); iu.getUser(1); IDepartment id = DataAccess.CreateDepartment(); id.insertDepartment(department); id.getDepartment(1); } }
从main方法看，根本看不到任何SQL和Access的字段，也就是客户端与业务逻辑隔离了！
但是，如果新增一个Oracle数据库，需要修改DataAccess的switch--case，如何彻底不用switch语句呢？
利用反射，把类对象反射出来，这样只需要添加工厂类定义就可以了。
package com.jayfulmath.designpattern.abstractfactory; import java.lang.reflect.*; public class DataAccessReflection { private static final String AssemblyName = "com.jayfulmath.designpattern.abstractfactory"; private static final String db = "Access"; public static IUser CreateUser() { String className =AssemblyName+"."+db+"User"; IUser result = null; try { Class<?> c = Class.forName(className); Constructor<?> ct = c.getConstructor(); result = (IUser) (ct.newInstance()); } catch (NoSuchMethodException |ClassNotFoundException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) { // TODO Auto-generated catch block e.printStackTrace(); } return result; } public static IDepartment CreateDepartment() { String className = AssemblyName+"."+db+"Department"; IDepartment result = null; try { Class<?> c = Class.forName(className); Constructor<?> ct = c.getConstructor(); result = (IDepartment) (ct.newInstance()); } catch (NoSuchMethodException |ClassNotFoundException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) { // TODO Auto-generated catch block e.printStackTrace(); } return result; } }
自此，完美的解决了switch---case的问题。如果使用配置文件的话，可以彻底不用修改代码，而达到更换数据库的问题。