一、介绍

抽象工厂模式(Abstract Factory)，提供一个创建一系列相关或相互依赖对象的接口，而无须指定它们具体的类。

AbstractProductA和AbstractProductB是两个抽象产品，之所以为抽象，是因为它们都有可能有两种不同的实现；

IFactory是一个抽象工厂接口，它里面应该包含所有的产品创建的抽象方法。而ConcreteFactory1和ConcreteFactory2就是具体的工厂了。

通常是在运行时刻再创建一个ConcreteFactory类的实例，这个具体的工厂再创建具有特定实现的产品对象，也就是说，为创建不同的产品对象，客户端应使用不同的具体工厂。

二、代码实现

需求：有两种数据库(mysql、access)需要插入数据和查询数据，SQL有区别。

基础类

public class User {
    private int _id;
    private String _name;

    public int get_id() {
        return _id;
    }

    public void set_id(int _id) {
        this._id = _id;
    }

    public String get_name() {
        return _name;
    }

    public void set_name(String _name) {
        this._name = _name;
    }
}
public class Department {
    private int _id;
    private String _name;

    public int get_id() {
        return _id;
    }

    public void set_id(int _id) {
        this._id = _id;
    }

    public String get_name() {
        return _name;
    }

    public void set_name(String _name) {
        this._name = _name;
    }
}

 产品类

//抽象产品
public interface IUser {
    public void insert(User user);
    public User getUser(int id);
}

//抽象产品
public interface IDepartment {
    public void insert(Department department);
    public Department getDepartment(int id);
}

public class AccessDepartment implements IDepartment {
    //新增用户
    @Override
    public void insert(Department user){
        System.out.println("在Access中给Department表增加一条记录");
    }

    @Override
    public Department getDepartment(int id) {
        System.out.println("在Access中根据用户ID得到一条记录");
        return null;
    }
}

public class AccessUser implements IUser {
    //新增用户
    @Override
    public void insert(User user){
        System.out.println("在Access中给User表增加一条记录");
    }
    //查询用户
    @Override
    public User getUser(int id){
        System.out.println("在Access中根据用户ID得到一条记录");
        return null;
    }
}

public class SqlserverDepartment implements IDepartment {
    //新增用户
    @Override
    public void insert(Department department){
        System.out.println("在SQL Server中给Department表增加一条记录");
    }
    //查询用户
    @Override
    public Department getDepartment(int id){
        System.out.println("在SQL Server中根据用户ID得到一条记录");
        return null;
    }
}

public class SqlserverUser implements IUser {
    //新增用户
    @Override
    public void insert(User user){
        System.out.println("在SQL Server中给User表增加一条记录");
    }
    //查询用户
    @Override
    public User getUser(int id){
        System.out.println("在SQL Server中根据用户ID得到一条记录");
        return null;
    }
}

工厂类

//抽象工厂
public interface IFactory {
    public IUser createUser();

    public IDepartment createDepartment();
}

//具体工厂
public class AccessFactory implements IFactory{
    @Override
    public IUser createUser() {
        return new AccessUser();
    }

    @Override
    public IDepartment createDepartment() {
        return new AccessDepartment();
    }
}

//具体工厂
public class SqlserverFactory implements IFactory{
    @Override
    public IUser createUser() {
        return new SqlserverUser();
    }

    @Override
    public IDepartment createDepartment() {
        return new SqlserverDepartment();
    }
}

测试代码

两种数据切换只需切换具体工厂类

//客户端
public class Client {
    public static void main(String[] args) {
        //数据
        User user = new User();
        Department department = new Department();

        //IFactory sqlserverFactory = new AccessFactory();
        IFactory sqlserverFactory = new SqlserverFactory();
        IUser sqlUser = sqlserverFactory.createUser();
        sqlUser.insert(user);
        sqlUser.getUser(1);
        IDepartment sqlDepartment = sqlserverFactory.createDepartment();
        sqlDepartment.insert(department);
        sqlDepartment.getDepartment(1);


    }
}

在Access中给User表增加一条记录
在Access中根据用户ID得到一条记录
在Access中给Department表增加一条记录
在Access中根据用户ID得到一条记录

在SQL Server中给User表增加一条记录
在SQL Server中根据用户ID得到一条记录
在SQL Server中给Department表增加一条记录
在SQL Server中根据用户ID得到一条记录

调试小技巧:使用Ctrl+Alt点击进入实现类的方法。

随着产品越来越多，可以使用反射，取消工厂类的维护：

import java.lang.reflect.InvocationTargetException;

public class FactoryAll {
    private String db;

    public FactoryAll(String db) {
        this.db = db;
    }

    public IUser createUser(){
        IUser result=null;
        try {
            result=(IUser)Class.forName("org.minos.chapter15.inter.impl"+"."+db+"User").getDeclaredConstructor().newInstance();
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (IllegalArgumentException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (SecurityException e) {
            throw new RuntimeException(e);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }

        return result;
    }


    public IDepartment createDepartment() {
        IDepartment result=null;
        try {
            result=(IDepartment)Class.forName("org.minos.chapter15.inter.impl"+"."+db+"Department").getDeclaredConstructor().newInstance();
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (IllegalArgumentException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (SecurityException e) {
            throw new RuntimeException(e);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        }

        return result;
    }
}

 public static void main(String[] args) {
        //数据
        User user = new User();
        Department department = new Department();

        //IFactory sqlserverFactory = new AccessFactory();
        FactoryAll sqlserverFactory = new FactoryAll("Sqlserver");
        //IFactory sqlserverFactory = new SqlserverFactory();
        IUser sqlUser = sqlserverFactory.createUser();
        sqlUser.insert(user);
        sqlUser.getUser(1);
        IDepartment sqlDepartment = sqlserverFactory.createDepartment();
        sqlDepartment.insert(department);
        sqlDepartment.getDepartment(1);


    }

在SQL Server中给User表增加一条记录
在SQL Server中根据用户ID得到一条记录
在SQL Server中给Department表增加一条记录
在SQL Server中根据用户ID得到一条记录