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