手写一个MyBatis框架

手写一个MyBatis框架

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• ​​MyBatis框架分析​​
• ​​手写简单的MyBatis框架​​

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• ​​Configuration​​
• ​​SqlSession​​
• ​​Executor​​
• ​​ExecutorImpl​​
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• ​​Executor​​

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MyBatis框架分析

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• ​MyBatis框架结构图:
• ​MyBatis框架组件调用关系图:
• ​MyBatis框架运行时序图:
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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);
  }
}