Java用反射+配置文件结合抽象工厂模式实现数据库访问程序

前言：本文需对反射和抽象工厂模式有一定了解。
了解->Java反射
了解->抽象工厂模式

IUser接口

public interface IUser {
    
    
 void Insert(User user);
 User getUser(String id);
}

SqlserverUser

public class SqlserverUser implements IUser {
    
    

	@Override
	public void Insert(User user) {
    
    
		System.out.println("在SqlserverUser中插入一条数据");
	}

	@Override
	public User getUser(String id) {
    
    
		System.out.println("在SqlserverUser中查询一条数据");
		return null;
	}

}

AccessUser

public class AccessUser implements IUser {
    
    

	@Override
	public void Insert(User user) {
    
    
		System.out.println("在AccessUser中插入一条数据");
		
	}

	@Override
	public User getUser(String id) {
    
    
		System.out.println("在AccessUser中查询一条数据");
		return null;
	}

}

IDepartment

public interface IDepartment {
    
    
 void Insert(Department department);
 Department getDepartment(String id);
}

SqlserverDepartment

public class SqlserverDepartment implements IDepartment{
    
    

	@Override
	public void Insert(Department department) {
    
    
		System.out.println("在SqlserverDepartment中插入一条数据");
		
	}

	@Override
	public Department getDepartment(String id) {
    
    
		System.out.println("在SqlserverDepartment中查询一条数据");
		return null;
	}

}

AccessDepartment

public class AccessDepartment implements IDepartment {
    
    

	@Override
	public void Insert(Department department) {
    
    
		System.out.println("在AccessDepartment中插入一条数据");
		
	}

	@Override
	public Department getDepartment(String id) {
    
    
		System.out.println("在AccessDepartment中查询一条数据");
		return null;
	}

}

DataAccess

public class Data {
    
    

private static String db;

  public static IUser CreateUser() throws IOException, InstantiationException, IllegalAccessException
  {
    
    
	 Properties p = new Properties();
	 
	 try {
    
     
		
		  InputStream in =Data.class.getClassLoader().getResourceAsStream("database.properties");
	      p.load(in);}
	 catch (Exception e) {
    
    
			
			e.printStackTrace();
			
		}
	  db=p.getProperty("DB");
	  String className = "抽象工厂模式." + db +"User";
		//获取以className字符串为名的类
		Class<IUser> userDaoImplClass = null;
		try {
    
    
			userDaoImplClass = (Class<IUser>) Class.forName(className);
		} catch (ClassNotFoundException e1) {
    
    
			
			e1.printStackTrace();
		}
		//返回类的实例
		try {
    
    
			return userDaoImplClass.getConstructor().newInstance();
		} catch (Exception e) {
    
    
			
			e.printStackTrace();
		}
		return null;
		
  }
  public static IDepartment CreateDepartment() throws IOException, InstantiationException, IllegalAccessException
  {
    
    
	 Properties p = new Properties();
	 
	 try {
    
     
		
		  InputStream in =Data.class.getClassLoader().getResourceAsStream("database.properties");
	      p.load(in);}
	 catch (Exception e) {
    
    
			
			e.printStackTrace();
			
		}
	  db=p.getProperty("DB");
	  String className = "抽象工厂模式." + db +"User";
		//获取以className字符串为名的类
		Class<IDepartment> DepartmentDaoImplClass = null;
		try {
    
    
			DepartmentDaoImplClass = (Class<IDepartment>) Class.forName(className);
		} catch (ClassNotFoundException e1) {
    
    
			
			e1.printStackTrace();
		}
		//返回类的实例
		try {
    
    
			return DepartmentDaoImplClass.getConstructor().newInstance();
		} catch (Exception e) {
    
    
			
			e.printStackTrace();
		}
		return null;
		
  }
}

配置文件需注意的问题
getClassLoader().getResourceAsStream()的参数是根目录src下的路径，即使配置文件在同目录下，也不能下成getClassLoader().getResourceAsStream(“配置文件”)，这样程序会报错，得到的InputStream是null值。
getClassLoader()和getURLClassLoader()的区别：ClassLoader（）只能查找src目录下的文件，而URLClassLoader()则能查找任意目录下的文件。