浅谈设计模式之简单工厂模式

简单工厂模式简介

简单工厂模式是属于创建型模式，又叫做静态工厂方法（Static Factory Method）模式，但不属于23种GOF设计模式之一。简单工厂模式是由一个工厂对象决定创建出哪一种产品类的实例。简单工厂模式是工厂模式家族中最简单实用的模式，可以理解为是不同工厂模式的一个特殊实现。(简而言之，就是有一个专门生产某个产品的类。比如下图中的鼠标工厂，专业生产鼠标，给参数0，生产戴尔鼠标，给参数1，生产惠普鼠标)

简单工厂模式的UML类图

简单工厂模式简单实现

生产某个产品的工厂 如mouse鼠标工厂 MouseFactory

/**
 * @Description 鼠标工厂
 * @Author xiaoqx 
 * @Version V1.0.0
 * @Since 1.0
 * @Date 2018/1/27
 */
public class MouseFactory {
    private static Mouse mouse;
    //传入什么品牌就生产对应得品牌
    public static Mouse produceMouse(String flag){
        if("lenovo".equals(flag))
            mouse =new LenovoMouse();
        else if("asus".equals(flag))
            mouse =new AsusMouse();
        else
            mouse =null;
        return mouse;
    }
 }

产品的抽象角色(如：鼠标mouse)

public abstract class Mouse{
}

具体产品如联想鼠标LenoveMouse，华硕鼠标 AsusMouse

/**
 * @Description 联想鼠标
 * @Author xiaoqx 
 * @Version V1.0.0
 * @Since 1.0
 * @Date 2018/1/27
 */
public class LenovoMouse extends Mouse{
    private String name;
    private Double price;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "{\"LenovoMouse\":{"
                + "\"name\":\"" + name + "\""
                + ", \"price\":\"" + price + "\""
                + "}}";
    }
}
/**
 * @Description 华硕鼠标
 * @Author xiaoqx 
 * @Version V1.0.0
 * @Since 1.0
 * @Date 2018/1/27
 */
public class AsusMouse  extends Mouse {
    private String name;
    private Double price;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "{\"AsusMouse\":{"
                + "\"name\":\"" + name + "\""
                + ", \"price\":\"" + price + "\""
                + "}}";
    }
}

缺点

• 每增加一个具体产品，都需要修改源码，违反面向对象原则的开闭原则；
• 所有的产品都是由 MouseFactory来生产的，比较臃肿比较难维护；

在jdk中的应用

 /**
     * Gets a calendar with the specified time zone and locale.
     * The Calendar returned is based on the current time
     * in the given time zone with the given locale.
     *
     * @param zone the time zone to use
     * @param aLocale the locale for the week data
     * @return a Calendar.
     */
    public static Calendar getInstance(TimeZone zone,
                                       Locale aLocale)
    {
        return createCalendar(zone, aLocale);
    }

    private static Calendar createCalendar(TimeZone zone,
                                           Locale aLocale)
    {
        CalendarProvider provider =
            LocaleProviderAdapter.getAdapter(CalendarProvider.class, aLocale)
                                 .getCalendarProvider();
        if (provider != null) {
            try {
                return provider.getInstance(zone, aLocale);
            } catch (IllegalArgumentException iae) {
                // fall back to the default instantiation
            }
        }

        Calendar cal = null;
    //根据传入的aLocale来 new Calendar,采用简单工厂模式的实现
        if (aLocale.hasExtensions()) {
            String caltype = aLocale.getUnicodeLocaleType("ca");
            if (caltype != null) {
                switch (caltype) {
                case "buddhist":
                cal = new BuddhistCalendar(zone, aLocale);
                    break;
                case "japanese":
                    cal = new JapaneseImperialCalendar(zone, aLocale);
                    break;
                case "gregory":
                    cal = new GregorianCalendar(zone, aLocale);
                    break;
                }
            }
        }
        if (cal == null) {
            // If no known calendar type is explicitly specified,
            // perform the traditional way to create a Calendar:
            // create a BuddhistCalendar for th_TH locale,
            // a JapaneseImperialCalendar for ja_JP_JP locale, or
            // a GregorianCalendar for any other locales.
            // NOTE: The language, country and variant strings are interned.
            if (aLocale.getLanguage() == "th" && aLocale.getCountry() == "TH") {
                cal = new BuddhistCalendar(zone, aLocale);
            } else if (aLocale.getVariant() == "JP" && aLocale.getLanguage() == "ja"
                       && aLocale.getCountry() == "JP") {
                cal = new JapaneseImperialCalendar(zone, aLocale);
            } else {
                cal = new GregorianCalendar(zone, aLocale);
            }
        }
        return cal;
    }