手写一个MyBatis框架

爱被打了一巴掌 2023-02-21 14:19 44阅读 0赞

### 手写一个MyBatis框架 ###

*  MyBatis框架分析
 *  手写简单的MyBatis框架
 *   *   *  Configuration
         *  SqlSession
         *  Executor
         *  ExecutorImpl
 *  手写完整的MyBatis框架
 *   *   *  Executor
         *   *   *  ExecutorImpl

# MyBatis框架分析 #

*  **MyBatis框架结构图:**  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pld2F2ZU94Zm9yZA_size_16_color_FFFFFF_t_70_pic_center]
 *  **MyBatis框架组件调用关系图:**  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pld2F2ZU94Zm9yZA_size_16_color_FFFFFF_t_70_pic_center 1]
 *  **MyBatis框架运行时序图:**  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pld2F2ZU94Zm9yZA_size_16_color_FFFFFF_t_70]

# 手写简单的MyBatis框架 #

*  根据框架组件调用关系图开发Mybatis框架代码
    
     *  **一个组件实体就对应一个实体类**

### Configuration ###

public class Configuration { 
    	public <T> T getMapper(Class<T> clazz, SqlSession sqlSession) { 
    		return <T> Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{ clazz}, new MapperProxy(sqlSession));
    	} 
    }

### SqlSession ###

public class SqlSession { 
    	private Configuration configuration;
    	private Executor executor;
    
    	/** * 通过构造函数建立Configuration以及Executor和SqlSession的关系 */
    	public SqlSession(Configuration configuration, Executor executor) { 
    		this.configuration = configuration;
    		this.executor = executor;
    	}
    
    	/** * getMapper * @param clazz */
    	 public <T> getMapper(class<T> calzz) { 
    	 	return configuration.getMapper(calzz, this);
    	 }
    
    	/** * selectOne * * @param statement SQL语句 * @param parameter SQL参数 * @return <T> T 查询结果 */
    	 public <T> T selectOne(String statement, String parameter) { 
    	 	return executor.query(statement, parameter);
    	 }
    }

### Executor ###

public interface Executor { 
    	<T> T query(String statement, String parameter);
    }

### ExecutorImpl ###

public class ExecutorImpl implements Executor { 
    	@Override
    	public <T> T query(String statement, String parameter) { 
    		Connection connection = null;
    		PreparedStatement preparedStatement = null;
    		try { 
    			Class.forName("com.mysql.cj.jdbc.Driver");
    			connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/db?useUnicode=true&characterEncoding=utf-8");
    			String sql = String.format(statement, Integer.parseInt(parameter));
    			PreparedStatement ps = connection.prepareStatement(sql);
    			ResultSet rs = ps.executeQuery();
    			while (rs.hasNext()) { 
    				test = new Test();
    				test.setId(rs.getInt(1));
    				test.setNum(rs.getInt(2));
    				test.setName(rs.getString(3));
    			}
    		} catch (ClassNotFoundException e) { 
    			e.printStackTrace();
    		} finally { 
    			try { 
    				if (null != connection) { 
    					connection.close();
    				}
    			} catch (SQLException e) { 
    				e.printStackTrace();
    			}
    		}
    		return (T)test;
    	}
    }

# 手写完整的MyBatis框架 #

>  *  简单的**MyBatis**框架中的**Executor**采用**JDBC**实现,采用了硬编码的方式,一次只能操作一张表:
> 
>     ...
>     while (rs.hasNext()) { 
>     		test = new Test();
>     		test.setId(rs.getInt(1));
>     		test.setNum(rs.getInt(2));
>     		test.setName(rs.getString(3));
>     }
>     ...

### Executor ###

##### ExecutorImpl #####

public class ExecutorImpl implements Executor { 
    	private Configuration configuration;
    
    	public ExecutorImpl(Configuration configuration) { 
    		this.configuration = configuration;
    	}
    
    	public Configuration getConfiguration() { 
    		return configuration;
    	}
    
    	public void setConfiguration(Configuration configuration) { 
    		this.configuration = configuration;
    	}
    
    	public <E> E query(MapperRegistry.MapperData, Object parameter) throws Exception { 
    		/* * 初始化 StatementHandler -> ParameterHandler -> ResultHandler */
    		 StatementHandler handler = new StatementHandler(configuration);
    		 return (E) handler.query(mapperData, parameter);
    	}
    }

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