设计模式四 工厂模式

0、基本定义

工厂模式定义：一个用于创建对象的接口，让子类决定实例化哪一个类。实例化延迟到其子类。‘

抽象工厂模式：为创建一组相关或相互依赖的对象提供一个接口，而且无须指定他们的具体类。（概念略抽象）

只对结果负责。

解耦合

spring 中 AbstractFactoryBean 创建对象使用了工厂模式，很好的诠释了 依赖倒置原则：要依赖抽象，不要依赖具体。

1、类型

1.1 、简单工厂模式：

public class SimpleFactory {


    public Milk getMilk(String name) {

        if ("特仑苏".equals(name)) {
            return new Telunsu();
        } else if ("伊犁".equals(name)) {
            return new Yili();
        } else if ("蒙牛".equals(name)) {
            return new Mengniu();
        }
        return null;
    }
}

1.2、工厂模式

public interface Factory {

    //统一产品出口

    Milk getMilk();
}


public class MengniuFactotry implements Factory {
    @Override
    public Milk getMilk() {
        return new Mengniu();
    }
}


public class TelunsuFactotry implements Factory {
    @Override
    public Milk getMilk() {
        return new Telunsu();
    }
}


public class YiliFactotry implements Factory {
    @Override
    public Milk getMilk() {
        return new Yili();
    }
}

Test

public class FactoryTest {

    public static void main(String[] args) {

        Factory factory = new MengniuFactotry();
        System.out.println(factory.getMilk().getName());
    }

 1.3 抽象工厂模式：

产品登记，产品族

public abstract class AbstractFactory {

    public  abstract Milk getMengniu();
    public  abstract Milk getYili();
    public  abstract Milk getTelunsu();

}


public class MilkFactory extends AbstractFactory {
    @Override
    public Milk getMengniu() {
        return new Mengniu();
    }

    @Override
    public Milk getYili() {
        return new Yili();
    }

    @Override
    public Milk getTelunsu() {
        return new Telunsu();
    }
}

public class AbstractFactoryTest {

    public static void main(String[] args) {


        AbstractFactory factory = new MilkFactory();

        System.out.println(factory.getMengniu());
    }
}

 可通过 反射或者配置文件进行 优化代码

public class DataAccess {

    private static String pack = "com.zzf.design.factory.db.";
    private static String db = "SqlServer";//Access

    //配置文件处理
    private static Properties properties = new Properties();
    static {

        //配置文件获取db
        try {
            ResourceUtils.getFile("classpath:db.properties");
            properties.load(DataAccess.class.getClassLoader().getResourceAsStream("db.properties"));

            db = properties.getProperty("db");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //根据 db 参数选择
    public static IUserDao creatUser() {
        IUserDao userDao = null;

        switch (db) {
            case "SqlServer":
                userDao = new SqlServerUserDao();
                break;
            case "Access":
                userDao = new AccessUserDao();
                break;

        }
        return userDao;
    }

    public static IDepartmentDao creatDepartment() {
        IDepartmentDao departmentDao = null;

        switch (db) {
            case "SqlServer":
                departmentDao = new SqlServerDepartmentDao();
                break;
            case "Access":
                departmentDao = new AccessDepartmentDao();
                break;

        }
        return departmentDao;
    }


    /**
     * 反射实现
     * @return
     */
    public static IUserDao createUserDaoV2() {
        try {
            return (IUserDao) Class.forName(pack + db + "UserDao").newInstance();

        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    public static IDepartmentDao createDepartmentDaoV2() {
        try {
            return (IDepartmentDao) Class.forName(pack + db + "DepartmentDao").newInstance();

        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

}

3、优点

优点：

》良好的封装性，代码结构清晰

》扩展性好

使用场景

》new一个对象的替代品

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抽象工厂模式的概念略抽象， 代码能实现，目前和概念不能有效的结合。。。。。

产品等级

产品族 新增，变动比较大

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参考资料：

咕泡学院

《大话设计模式》