MyBatis源码分析（二）语句处理器

StatementHandler

语句处理器，主要负责语句的创建、参数的设置、语句的执行。不负责结果集的处理。

Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException
void parameterize(Statement statement) throws SQLException
void batch(Statement statement) throws SQLException
int update(Statement statement) throws SQLException
List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException
Cursor<E> queryCursor(Statement statement) throws SQLException

BaseStatementHandler

实现公共部分，具体差异通过抽象方法，留给子类实现。

@Override
  public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
    ErrorContext.instance().sql(boundSql.getSql());
    Statement statement = null;
    try {
      statement = instantiateStatement(connection);
      setStatementTimeout(statement, transactionTimeout);
      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);
    }
  }

protected abstract Statement instantiateStatement(Connection connection) throws SQLException;

首先语句级别的配置，其次配置文件中的配置。

protected void setStatementTimeout(Statement stmt, Integer transactionTimeout) throws SQLException {
    Integer queryTimeout = null;
    if (mappedStatement.getTimeout() != null) {
      queryTimeout = mappedStatement.getTimeout();
    } else if (configuration.getDefaultStatementTimeout() != null) {
      queryTimeout = configuration.getDefaultStatementTimeout();
    }
    if (queryTimeout != null) {
      stmt.setQueryTimeout(queryTimeout);
    }
    StatementUtil.applyTransactionTimeout(stmt, queryTimeout, transactionTimeout);
  }

首先语句级别的配置，其次配置文件中的配置。

 protected void setFetchSize(Statement stmt) throws SQLException {
    Integer fetchSize = mappedStatement.getFetchSize();
    if (fetchSize != null) {
      stmt.setFetchSize(fetchSize);
      return;
    }
    Integer defaultFetchSize = configuration.getDefaultFetchSize();
    if (defaultFetchSize != null) {
      stmt.setFetchSize(defaultFetchSize);
    }
  }

StatementUtil

如果两个参数都有值，设置较小的那一个。

public static void applyTransactionTimeout(Statement statement, Integer queryTimeout, Integer transactionTimeout) throws SQLException {
    if (transactionTimeout == null){
      return;
    }
    Integer timeToLiveOfQuery = null;
    if (queryTimeout == null || queryTimeout == 0) {
      timeToLiveOfQuery = transactionTimeout;
    } else if (transactionTimeout < queryTimeout) {
      timeToLiveOfQuery = transactionTimeout;
    }
    if (timeToLiveOfQuery != null) {
      statement.setQueryTimeout(timeToLiveOfQuery);
    }
  }

SimpleStatementHandler

无参数sql语句的执行。

@Override
  protected Statement instantiateStatement(Connection connection) throws SQLException {
    if (mappedStatement.getResultSetType() != null) {
      return connection.createStatement(mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
    } else {
      return connection.createStatement();
    }
  }

  @Override
  public void parameterize(Statement statement) throws SQLException {
    // N/A
  }

@Override
  public int update(Statement statement) throws SQLException {
    String sql = boundSql.getSql();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    int rows;
    if (keyGenerator instanceof Jdbc3KeyGenerator) {
      statement.execute(sql, Statement.RETURN_GENERATED_KEYS);
      rows = statement.getUpdateCount();
      keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);
    } else if (keyGenerator instanceof SelectKeyGenerator) {
      statement.execute(sql);
      rows = statement.getUpdateCount();
      keyGenerator.processAfter(executor, mappedStatement, statement, parameterObject);
    } else {
      statement.execute(sql);
      rows = statement.getUpdateCount();
    }
    return rows;
  }

  @Override
  public void batch(Statement statement) throws SQLException {
    String sql = boundSql.getSql();
    statement.addBatch(sql);
  }

  @Override
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    String sql = boundSql.getSql();
    statement.execute(sql);
    return resultSetHandler.<E>handleResultSets(statement);
  }

  @Override
  public <E> Cursor<E> queryCursor(Statement statement) throws SQLException {
    String sql = boundSql.getSql();
    statement.execute(sql);
    return resultSetHandler.<E>handleCursorResultSets(statement);
  }

PreparedStatementHandler

参数化sql语句的执行。

@Override
  protected Statement instantiateStatement(Connection connection) throws SQLException {
    String sql = boundSql.getSql();
    if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
      String[] keyColumnNames = mappedStatement.getKeyColumns();
      if (keyColumnNames == null) {
        return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
      } else {
        return connection.prepareStatement(sql, keyColumnNames);
      }
    } else if (mappedStatement.getResultSetType() != null) {
      return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
    } else {
      return connection.prepareStatement(sql);
    }
  }

  @Override
  public void parameterize(Statement statement) throws SQLException {
    parameterHandler.setParameters((PreparedStatement) statement);
  }

@Override
  public int update(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    int rows = ps.getUpdateCount();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);
    return rows;
  }

  @Override
  public void batch(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.addBatch();
  }

  @Override
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    return resultSetHandler.<E> handleResultSets(ps);
  }

  @Override
  public <E> Cursor<E> queryCursor(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    return resultSetHandler.<E> handleCursorResultSets(ps);
  }

CallableStatementHandler

存储过程的执行。

@Override
  protected Statement instantiateStatement(Connection connection) throws SQLException {
    String sql = boundSql.getSql();
    if (mappedStatement.getResultSetType() != null) {
      return connection.prepareCall(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
    } else {
      return connection.prepareCall(sql);
    }
  }

  @Override
  public void parameterize(Statement statement) throws SQLException {
    registerOutputParameters((CallableStatement) statement);
    parameterHandler.setParameters((CallableStatement) statement);
  }

@Override
  public int update(Statement statement) throws SQLException {
    CallableStatement cs = (CallableStatement) statement;
    cs.execute();
    int rows = cs.getUpdateCount();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    keyGenerator.processAfter(executor, mappedStatement, cs, parameterObject);
    resultSetHandler.handleOutputParameters(cs);
    return rows;
  }

  @Override
  public void batch(Statement statement) throws SQLException {
    CallableStatement cs = (CallableStatement) statement;
    cs.addBatch();
  }

  @Override
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    CallableStatement cs = (CallableStatement) statement;
    cs.execute();
    List<E> resultList = resultSetHandler.<E>handleResultSets(cs);
    resultSetHandler.handleOutputParameters(cs);
    return resultList;
  }

  @Override
  public <E> Cursor<E> queryCursor(Statement statement) throws SQLException {
    CallableStatement cs = (CallableStatement) statement;
    cs.execute();
    Cursor<E> resultList = resultSetHandler.<E>handleCursorResultSets(cs);
    resultSetHandler.handleOutputParameters(cs);
    return resultList;
  }

RoutingStatementHandler

根据语句类型，自动路由到正确的语句处理器。

public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {

    switch (ms.getStatementType()) {
      case STATEMENT:
        delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case PREPARED:
        delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case CALLABLE:
        delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      default:
        throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
    }

  }