MyBatis框架分析

MyBatis框架结构图:
MyBatis框架组件调用关系图:
MyBatis框架运行时序图:

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);
    }
}