大话设计模式之抽象工厂模式总结-java实现

注：示例来自《大话设计模式》

现有如下需求写一个基本的数据访问程序数据库用SqlServer 简单代码实现如下

用户类

package Test15;

public class User {

    private int id;
    private String name;

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

}

操作表类

package Test15;

public class SqlserverUser {

    public void Insert(User user)
    {
        System.out.println("在Sqlserver中给User表增加一条记录");
    }

    public User GetUser(int id)
    {
        System.out.println("在Sqlserver中根据ID得到User表一条记录");
        return null;
    }

}

客户端代码

package Test15;

public class Program {

    public static void main(String[] args) {

        User user = new User();

        SqlserverUser su = new SqlserverUser();
        su.Insert(user);
        su.GetUser(1);

    }

}

上面的写法客户端与SqlServer强耦合如果想要更换数据库为Access 该怎么办呢
下面使用工厂方法模式进行重构代码如下

IUser接口

package Test15;

public interface IUser {

    void Insert(User user);

    User GetUser(int id);

}

SqlserverUser类

package Test15;

public class SqlserverUser implements IUser {

    @Override
    public void Insert(User user)
    {
        System.out.println("在Sqlserver中给User表增加一条记录");
    }

    @Override
    public User GetUser(int id)
    {
        System.out.println("在Sqlserver中根据ID得到User表一条记录");
        return null;
    }

}

AccessUser类

package Test15;

public class AccessUser implements IUser {

    @Override
    public void Insert(User user)
    {
        System.out.println("在Access中给User表增加一条记录");
    }

    @Override
    public User GetUser(int id)
    {
        System.out.println("在Access中根据ID得到User表一条记录");
        return null;
    }

}

IFactory接口

package Test15;

public interface IFactory {

    IUser CreateUser();

}

SqlServerFactory类

package Test15;

public class SqlServerFactory implements IFactory {

    @Override
    public IUser CreateUser() {
        return new SqlserverUser();
    }

}

AccessFactory类

package Test15;

public class AccessFactory implements IFactory {

    @Override
    public IUser CreateUser() {
        return new AccessUser();
    }

}

客户端代码

package Test15;

public class Program {

    public static void main(String[] args) {

        User user = new User();
        //IFactory factory = new SqlServerFactory();
        IFactory factory = new AccessFactory();

        IUser iu = factory.CreateUser();

        iu.Insert(user);
        iu.GetUser(1);

    }

}

现在如果要换数据库只需要把new SqlServerFactory()改成new AccessFactory()
但是问题还没有完全解决数据库里不可能只有一个User表很可能有其他表比如增加部门表此时该怎么办呢修改代码如下

部门类

package Test15;

public class Department {

    private int id;
    private String deptName;;

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

}

IDepartment接口

package Test15;

public interface IDepartment {

    void Insert(Department department);

    Department GetDepartment(int id);

}

SqlserverDepartment类

package Test15;

public class SqlserverDepartment implements IDepartment {

    public void Insert(Department department)
    {
        System.out.println("在Sqlserver中给Department表增加一条记录");
    }

    public Department GetDepartment(int id)
    {
        System.out.println("在Sqlserver中根据ID得到Department表一条记录");
        return null;
    }

}

AccessDepartment类

package Test15;

public class AccessDepartment implements IDepartment {

    public void Insert(Department department)
    {
        System.out.println("在Access中给Department表增加一条记录");
    }

    public Department GetDepartment(int id)
    {
        System.out.println("在Access中根据ID得到Department表一条记录");
        return null;
    }

}

IFactory接口

package Test15;

public interface IFactory {

    IUser CreateUser();

    IDepartment CreateDepartment();

}

SqlServerFactory类

package Test15;

public class SqlServerFactory implements IFactory {

    @Override
    public IUser CreateUser() {
        return new SqlserverUser();
    }

    @Override
    public IDepartment CreateDepartment()
    {
        return new SqlserverDepartment();
    }

}

AccessFactory类

package Test15;

public class AccessFactory implements IFactory {

    @Override
    public IUser CreateUser() {
        return new AccessUser();
    }

    @Override
    public IDepartment CreateDepartment()
    {
        return new AccessDepartment();
    }

}

客户端代码

package Test15;

public class Program {

    public static void main(String[] args) {

        User user = new User();
        Department dept = new Department();

        //IFactory factory = new SqlServerFactory();
        IFactory factory = new AccessFactory();
        IUser iu = factory.CreateUser();

        iu.Insert(user);
        iu.GetUser(1);

        IDepartment id = factory.CreateDepartment();
        id.Insert(dept);
        id.GetDepartment(1);

    }

}

不知不觉间我们已经重构出了抽象工厂模式

抽象工厂模式提供一个创建一系列相关或相互依赖对象的接口而无需指定它们具体的类

抽象工厂模式最大的好处便是易于交换产品系列由于具体工厂类例如IFactory factory = new AccessFactory() 在一个应用中只需要在初始化的时候出现一次这就使得改变一个应用的具体工厂变得非常容易它只需要改变具体工厂即可使用不同的产品配置
第二大好处是它让具体的创建实例过程与客户端分离客户端是通过它们的抽象接口操纵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代码中

缺点如果需要增加新的表那么就要新增三个类并且要修改三个工厂类这样大批量的改动显然是非常丑陋的做法

下面我们用简单工厂来改进抽象工厂代码如下

DataAccess类

package Test15;

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 CreateDepartment()
    {
        IDepartment result = null;
        switch (db)
        {
            case "Sqlserver":
                result = new SqlserverDepartment();
                break;
            case "Access":
                result = new AccessDepartment();
                break;
        }
        return result;
    }

}

客户端代码

package Test15;

public class Program {

    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.CreateDepartment();
        id.Insert(dept);
        id.GetDepartment(1);

    }

}

现在客户端已经不再受改动数据库访问的影响了但是如果我需要增加Oracle数据库访问本来抽象工厂只增加一个OracleFactory工厂类就可以了现在就比较麻烦了
下面我们用反射+抽象工厂的方式进行重构代码如下

修改DataAccess类

package Test15;

public class DataAccess {

    private static final String AssemblyName = "Test15";
    private static final String db = "Sqlserver";
    //private static final String db = "Access";

    public static IUser CreateUser() throws ClassNotFoundException, InstantiationException, IllegalAccessException
    {
        String className = AssemblyName+"."+db+"User";
        Class<IUser> forName = (Class<IUser>) Class.forName(className); 
        return forName.newInstance();
    }

    public static IDepartment CreateDepartment() throws ClassNotFoundException, InstantiationException, IllegalAccessException
    {
        String className = AssemblyName+"."+db+"Department";
        Class<IDepartment> forName = (Class<IDepartment>) Class.forName(className); 
        return forName.newInstance();
    }

}

现在如果增加Oracle数据访问我们只需更改private static final String db = “Sqlserver”;为private static final String db = “Oracle”;
但是总感觉还是有点遗憾因为在更换数据库访问时我还是需要去改程序重编译
下面我们用反射+配置文件的方式进行重构

添加一个sql.properties文件内容如下

db=Sqlserver

DataAccess类

package Test15;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Properties;

public class DataAccess {

    private static final String AssemblyName = "Test15";

    public static String getDb() throws IOException {

        Properties properties = new Properties();
        String db = "";
        // 使用BufferedReader加载properties配置文件生成对应的输入流
        BufferedReader bufferedReader = new BufferedReader(new FileReader(System.getProperty("user.dir")+"/src/test/java/Test15/sql.properties"));
        // 使用properties对象加载输入流
        properties.load(bufferedReader);
        //获取key对应的value值
        db = properties.getProperty("db");
        return db;

    }

    public static IUser CreateUser() throws ClassNotFoundException, InstantiationException, IllegalAccessException, IOException
    {   
        String className = AssemblyName+"."+getDb()+"User";
        Class<IUser> forName = (Class<IUser>) Class.forName(className);
        return forName.newInstance();
    }

    public static IDepartment CreateDepartment() throws ClassNotFoundException, InstantiationException, IllegalAccessException, IOException
    {
        String className = AssemblyName+"."+getDb()+"Department";
        Class<IDepartment> forName = (Class<IDepartment>) Class.forName(className); 
        return forName.newInstance();
    }

}

现在如果需要更换数据库只需要修改配置文件就可以了从这个角度上说所有在用简单工厂的地方都可以考虑用反射技术来去除switch或if 解除分支判断带来的耦合

大话设计模式之抽象工厂模式总结-java实现

猜你喜欢