《大话设计模式--抽象工厂模式》笔记

Myth丶恋晨 2022-04-15 05:05 181阅读 0赞

1、抽象工厂模式（Abstract Factory），提供一个创建一系列相关或者相互依赖对象的接口，而无需指定他们的具体类。

2、抽象工厂模式结构图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNzkwODMz_size_16_color_FFFFFF_t_70]  
3、简单代码实现  
书上例子主要是切换两个不同的数据库。  
user和department实体类

public class User {
    
    	
    	private String id;
    	private String name;
    	
    	public String getId() {
    		return id;
    	}
    	public void setId(String id) {
    		this.id = id;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	
    	
    }

public class Department {
    
    	private String id;
    	private String deptName;
    	public String getId() {
    		return id;
    	}
    	public void setId(String id) {
    		this.id = id;
    	}
    	public String getDeptName() {
    		return deptName;
    	}
    	public void setDeptName(String deptName) {
    		this.deptName = deptName;
    	}
    	
    }

department和user持久层接口

interface IDepartment {
    
    	void insert(Department department);
    	Department getDepartment(int id);
    }

public interface IUser {
    
    	void insert(User user);
    	User getUser(int id);
    }

department持久层实现类，分为access类和sqlserver类；

public class AccessDepartment implements IDepartment {
    
    	@Override
    	public void insert(Department department) {
    		// TODO Auto-generated method stub
    		System.out.println("在Access中增加一条department数据");
    	}
    
    	@Override
    	public Department getDepartment(int id) {
    		// TODO Auto-generated method stub\
    		System.out.println("从Access中获取一条department数据");
    		return null;
    	}
    
    }

public class SqlserverDepartment implements IDepartment {
    
    	@Override
    	public void insert(Department department) {
    		
    		System.out.println("在Sqlserver中增加一条department数据");
    		
    	}
    
    	@Override
    	public Department getDepartment(int id) {
    		System.out.println("从Sqlserver中获取一条department数据");
    		return null;
    	}
    	
    	
    
    }

user持久层实现类，分为access类和sqlserver类；

public class AccessUser implements IUser {
    
    	@Override
    	public void insert(User user) {
    		// TODO Auto-generated method stub
    		System.out.println("在Access中增加一条user数据");
    	}
    
    	@Override
    	public User getUser(int id) {
    		System.out.println("从Access中获取一条user数据");
    		return null;
    	}
    
    }

public class SqlserverUser implements IUser {
    
    	@Override
    	public void insert(User user) {
    		// TODO Auto-generated method stub
    		System.out.println("在Sqlserver中增加一条User数据");
    	}
    
    	@Override
    	public User getUser(int id) {
    		System.out.println("从Sqlserver中获取一条User数据");
    		return null;
    	}
    
    }

IFactory接口，定义一个创建持久层表对象的抽象工厂类

public interface IFactory {
    	
    	IUser createUser();
    	IDepartment createDepartment();
    
    }

Sqlserver类，实现IFactory接口，实例化sqlserver类型的两个持久层对象

public class SqlserverFactory implements IFactory {
    
    	@Override
    	public IUser createUser() {
    		// TODO Auto-generated method stub
    		return new SqlserverUser();
    	}
    
    	@Override
    	public IDepartment createDepartment() {
    		// TODO Auto-generated method stub
    		return new SqlserverDepartment();
    	}
    
    }

Accessserver类，实现IFactory接口，实例化Accessserver类型的两个持久层对象

public class AccessFactoy implements IFactory{
    
    	@Override
    	public IUser createUser() {
    		// TODO Auto-generated method stub
    		return new AccessUser();
    	}
    
    	@Override
    	public IDepartment createDepartment() {
    		// TODO Auto-generated method stub
    		return new AccessDepartment();
    	}
    
    }

客户端代码

public class Client {
    	
    	public static void main(String[] args) {
    		User user=new User();
    		Department dept=new Department();
    		
    		
    		//IFactory fa=new SqlserverFactory();
    		IFactory fa=new AccessFactoy();
    		
    		IUser iu=fa.createUser();
    		
    		iu.insert(user);
    		iu.getUser(1);
    		
    		IDepartment id=fa.createDepartment();
    		
    		id.insert(dept);
    		id.getDepartment(1);
    		
    		
    	}
    
    }

抽象工厂模式的优缺点：  
优点：  
1、易于交换产品系列，具体工厂类，在一个应用中只需要在初始化的时候出现一次，这使得改变一个应用的具体工厂变得非常容易，只需改变工厂，便可以使用不同的产品配置。  
2、他让具体的创建实例与客户端分离，客户端通过抽象接口操作实例，产品的具体类名也被具体工厂的实现分离，不会出现在客户端代码中  
缺点：  
1、当我们需要增加Project实体，需增加Iproject、sqlserverProject、AccessProject。还需要修改IFactory，SqlserverFactory，AccessFactory。

4、使用简单工厂方法改进上面的缺点  
1、增加了dataAccess简单工厂类，客户端只需要createUser()和createDeptment() 。取代了IFactory、SqlserverFactory、AccessFactory。

public class DataAccess {
    
    //	private static final String DB="Sqlserver";
    	private static final String DB="Access";
    	
    	public static IUser createUser() {
    		IUser result=null;
    		
    		switch (DB){
    		case "Sqlserver":
    			result=new SqlserverUser();
    			break;
    		case "Access":
    			result=new AccessUser();
    			break;
    		}
    		
    		return result;
    	}
    	public static IDepartment createDeptment() {
    		IDepartment result=null;
    		
    		switch (DB){
    		case "Sqlserver":
    			result=new SqlserverDepartment();
    			break;
    		case "Access":
    			result=new AccessDepartment();
    			break;
    		}
    		
    		return result;
    	}
    }

客户端代码

public class Client2 {
    	
    		
    		public static void main(String[] args) {
    			User user=new User();
    			Department dept=new Department();
    			
    			
    			IUser iu=DataAccess.createUser();
    			
    			iu.insert(user);
    			iu.getUser(1);
    			
    			IDepartment id=DataAccess.createDeptment();
    			
    			id.insert(dept);
    			id.getDepartment(1);
    			
    			
    		}
    
    	}

但是在添加需求和修改时仍需要修改dataAccess类的switch和case

5、使用反射来取代IFactory、SqlserverFactory、AccessFactory。

public class DataAccess2 {
    
    	private static final String PACKAGE="practice.AbstractFactory";
    //		private static final String DB="Sqlserver";
    		private static final String DB="Access";
    		
    		public static IUser createUser() {
    			IUser result=null;
    			
    			String className=PACKAGE+"."+DB+"User";
    			
    			try {
    				result=	(IUser) Class.forName(className).newInstance();
    			} catch (Exception e) {
    			}
    			
    			return result;
    		}
    		public static IDepartment createDeptment() {
    			IDepartment result=null;
    			
                String className=PACKAGE+"."+DB+"Department";
    			
    			try {
    				result=	(IDepartment) Class.forName(className).newInstance();
    			} catch (Exception e) {
    			}
    			
    			return result;
    		}
    	}

虽然解决了使用简单工厂出现的问题，但是在修改数据库是仍需要修改DB。

6、用反射加配置文件实现访问  
添加一个config.properties

db=Access

修改后的dataAccess

public class DataAccess2 {
    
    	private static final String PACKAGE="practice.AbstractFactory";
    //		private static final String DB="Sqlserver";
    	private static   String db="";
    	//使用properties文件配置
    	
    	
    	static {
    		Properties p=new Properties();
    		try {
    			p.load(new FileInputStream("src/practice/AbstractFactory/reflection/config.properties"));
    		} catch (FileNotFoundException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (IOException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		db=p.getProperty("db");
    	}
    		
    		public static IUser createUser() {
    			IUser result=null;
    			
    			String className=PACKAGE+"."+db+"User";
    			
    			try {
    				result=	(IUser) Class.forName(className).newInstance();
    			} catch (Exception e) {
    			}
    			
    			return result;
    		}
    		public static IDepartment createDeptment() {
    			IDepartment result=null;
    			
                String className=PACKAGE+"."+db+"Department";
    			
    			try {
    				result=	(IDepartment) Class.forName(className).newInstance();
    			} catch (Exception e) {
    			}
    			
    			return result;
    		}
    	}

客户端代码同上。

哇，完美解决

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