设计模式之工厂方法模式

工厂方法模式

1.定义

工厂方法模式使用的频率非常高，在我们日常的开发中总能见到它的身影。其定义为：

Define an interface for creating an object,but let subclasses decide which class to instantiate.Factory Method lets a class defer instantiation to subclasses.（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。工厂方法使一个类的实例化延迟到其子类。）

2.特点

1. 良好的封装性，代码结构清晰
2. 工厂方法模式的扩展性非常优秀。在增加产品类的情况下，只要适当地修改具体的工厂类或扩展一个工厂类，就可以完成“拥抱变化”。

3.示例代码

public abstract class Product {public void method1(){}public abstract void method2();
}

public class ConcreteProduct1 extends Product {public void method2() {}
}
public class ConcreteProduct2 extends Product {public void method2() {}
}

public abstract class Creator {public abstract <T extends Product> createProduct(Class<T> clazz);
}

public class ConcreteCreator extends Creator {public <T extends Product> createProduct(Class<T> clazz) {Product product = null;try {product = (Product)Class.forName(clazz.getName()).newInstance();} catch(Exeception e) {}return (T)product;}
}

4.扩展

1. 简单工厂模式

   public class ObjectFactory<T> {private final static Map<String, IDao<?>> DAO_MAP = Maps.newHashMap();private static final String DEFAULT_PROPERTIES_FILE_NAME = "beans.properties";static {// 加载配置文件Properties properties = new Properties();try {properties.load(Thread.currentThread().getContextClassLoader().getResourceAsStream(DEFAULT_PROPERTIES_FILE_NAME));if (CollectionUtils.isEmpty(properties.keySet())) {throw new RuntimeException("properties is empty");}for (Object key : properties.keySet()) {Object o = properties.get(key.toString());Class<?> clazz = Class.forName(o.toString());DAO_MAP.put(key.toString(), (IDao<?>)clazz.newInstance());}} catch (Exception e) {throw new RuntimeException(e);}}public static IDao<?> getDaoByName(String name) {return DAO_MAP.getOrDefault(name, null);}
   }
   

   public class StudentDaoImpl implements IDao<Student> {@Overridepublic boolean save(Student o) {System.out.println("StudentDaoImpl.save");System.out.println(o);return true;}@Overridepublic int update(Student o) {System.out.println("StudentDaoImpl.update");return 0;}@Overridepublic boolean delete(Student o) {System.out.println("StudentDaoImpl.delete");return false;}@Overridepublic Student selectById(String id) {System.out.println("StudentDaoImpl.selectById");return null;}
   }
   public class TeacherDaoImpl implements IDao<Teacher> {@Overridepublic boolean save(Teacher o) {System.out.println("TeacherDaoImpl.save");return false;}@Overridepublic int update(Teacher o) {System.out.println("TeacherDaoImpl.update");return 0;}@Overridepublic boolean delete(Teacher o) {System.out.println("TeacherDaoImpl.delete");return false;}@Overridepublic Teacher selectById(String id) {System.out.println("TeacherDaoImpl.selectById");return null;}
   }
   

   bean.properties

   studentDao=com.yxxmg.gof.create.pattern.factory.impl.StudentDaoImpl
   teacherDao=com.yxxmg.gof.create.pattern.factory.impl.TeacherDaoImpl
   

5.示例代码地址

https://gitee.com/youxiaxiaomage/java-practices/tree/master/yxxmg-gof-sample/src/main/java/com/yxxmg/gof/create/pattern/abstractfactory