Mybatis源碼之Statement處理器BaseStatementHandler（二）

BaseStatementHandler是一個抽象類，并沒有實作和CURD相關的類，隻是更多的設定了一些參數相關。

/**
 * @author Clinton Begin
 */
public abstract class BaseStatementHandler implements StatementHandler {

  protected final Configuration configuration;
  protected final ObjectFactory objectFactory;
  protected final TypeHandlerRegistry typeHandlerRegistry;
  protected final ResultSetHandler resultSetHandler;
  protected final ParameterHandler parameterHandler;

  protected final Executor executor;
  protected final MappedStatement mappedStatement;
  protected final RowBounds rowBounds;

  protected BoundSql boundSql;

  protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    this.configuration = mappedStatement.getConfiguration();
    this.executor = executor;
    this.mappedStatement = mappedStatement;
    this.rowBounds = rowBounds;

    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
    this.objectFactory = configuration.getObjectFactory();

    if (boundSql == null) { // issue #435, get the key before calculating the statement
      generateKeys(parameterObject);
      boundSql = mappedStatement.getBoundSql(parameterObject);
    }

    this.boundSql = boundSql;

    this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
    this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
  }
  //擷取BoundSql
  public BoundSql getBoundSql() {
    return boundSql;
  }
  //擷取ParameterHandler
  public ParameterHandler getParameterHandler() {
    return parameterHandler;
  }

  //準備語句
  public Statement prepare(Connection connection) throws SQLException {
    ErrorContext.instance().sql(boundSql.getSql());
    Statement statement = null;
    try {
    //執行個體化Statement
      statement = instantiateStatement(connection);
    //設定逾時
      setStatementTimeout(statement);
    //設定讀取條數
      setFetchSize(statement);
      return statement;
    } catch (SQLException e) {
      closeStatement(statement);
      throw e;
    } catch (Exception e) {
      closeStatement(statement);
      throw new ExecutorException("Error preparing statement.  Cause: " + e, e);
    }
  }
  //如何執行個體化Statement，交給子類去做
  protected abstract Statement instantiateStatement(Connection connection) throws SQLException;

  //設定逾時，實際就是調用Statement.setQueryTimeout
  protected void setStatementTimeout(Statement stmt) throws SQLException {
    Integer timeout = mappedStatement.getTimeout();
    Integer defaultTimeout = configuration.getDefaultStatementTimeout();
    if (timeout != null) {
      stmt.setQueryTimeout(timeout);
    } else if (defaultTimeout != null) {
      stmt.setQueryTimeout(defaultTimeout);
    }
  }
  //設定讀取條數，其實就是調用Statement.setFetchSize
  protected void setFetchSize(Statement stmt) throws SQLException {
    Integer fetchSize = mappedStatement.getFetchSize();
    if (fetchSize != null) {
      stmt.setFetchSize(fetchSize);
    }
  }
  //關閉Statement
  protected void closeStatement(Statement statement) {
    try {
      if (statement != null) {
        statement.close();
      }
    } catch (SQLException e) {
      //ignore
    }
  }
   
  protected void generateKeys(Object parameter) {
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    ErrorContext.instance().store();
    keyGenerator.processBefore(executor, mappedStatement, null, parameter);
    ErrorContext.instance().recall();
  }

}