简单工厂+反射+配置文件

用反射+配置文件的方法重新实现大话设计模式课本上15章15.7的例题

问题分析：相比抽象工厂，用DataAccess类代替了工厂接口以及工厂类，再加上使用反射+配置文件的方式，可以做到不对编译好的程序作出改变就能修改数据库种类，客户端可以只是用DateAccess进行数据库访问实例的创建，达到了解耦的目的。

UML图：

package com.cmc;
//用户数据类
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;
    }
}
 
package com.cmc;
//部门数据类
public class Department {
    int id;
    String dept_name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getDept_name() {
        return dept_name;
    }
    public void setDept_name(String dept_name) {
        this.dept_name = dept_name;
    }
    
}
package com.cmc;
//用户数据库操作的接口
public interface IUser {
    void insert(User user);
    User getUser(int id);
}
package com.cmc;
//部门数据库操作接口
public interface IDepartment {
    void insert(Department department);
    
    Department getDepartment(int id);
}
package com.cmc;
//在SqlServer中实现对用户数据库的操作
public class SqlserverUser implements IUser {
 
    public User getUser(int id) {
        System.out.println("在SQL Server中根据ID得到一条记录");
        return null;
    }
 
    public void insert(User u) {
        // TODO Auto-generated method stub
        System.out.println("在SQL Server 中给user表添加一条记录");
 
    }
 
}
package com.cmc;
//在Access中实现对用户数据库的操作
public class AccessUser implements IUser {
 
    public User getUser(int id) {
        System.out.println("在Access中根据ID得到一条记录");
        return null;
    }
 
    public void insert(User user) {
        // TODO Auto-generated method stub
        System.out.println("在Access中给user表添加一条记录");
 
    }
 
}
package com.cmc;
 
public class SqlserverDepartment implements IDepartment {
 
    public Department getDepartment(int id) {
        System.out.println("在SQL Server中根据ID得到一条记录");
        // TODO Auto-generated method stub
        return null;
    }
 
    public void insert(Department department) {
        // TODO Auto-generated method stub
        System.out.println("在SQL Server 中给Department表添加一条记录");
 
    }
 
}
package com.cmc;
 
public class AccessDepartment implements IDepartment {
 
    public Department getDepartment(int id) {
        System.out.println("在Access中根据ID得到一条记录");
        // TODO Auto-generated method stub
        return null;
    }
 
    public void insert(Department department) {
        // TODO Auto-generated method stub
        System.out.println("在Access中给Department表添加一条记录");
    }
 
}
 
package com.cmc;
//通过配置文件+反射对要创建的类进行切换
import java.io.IOException;
import java.util.Properties;
 
import config.RunMain;
 
public class DataAccess {
    public static IUser CreatUser(){
        IUser result = null;
        Properties prop = new Properties();
        try {
            prop.load(RunMain.class.getResourceAsStream("/com/cmc/datebase.properties"));
            Class db = Class.forName("com.cmc."+prop.getProperty("dbuser"));
            result = (IUser)db.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }
    public static IDepartment CreatDepartment(){
        IDepartment result = null;
        Properties properties = new Properties();
        try {
            properties.load(RunMain.class.getResourceAsStream("/com/cmc/datebase.properties"));
            Class db = Class.forName("com.cmc."+properties.getProperty("dbdepartment"));
            result=(IDepartment)db.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }
}

优点：
1.实现了组件的封装，然后让组件外部能真正面向接口编程。
2.通过简单工厂，实现了客户端和具体实现类的解耦。
缺点：不方便扩展子工厂，如果要增加oracle数据库，必须在DateAccess类中增加oracle的方法，在工厂中增加创建case，这一点不符合开闭原则。显然使用反射+配置文件可以解决后者。