Mybatis执行BatchExecutor（四）

BatchExecutor：顾名思义就是进行批量操作，通过批量操作来提高性能

public class BatchExecutor extends BaseExecutor {  public static final int BATCH_UPDATE_RETURN_VALUE = Integer.MIN_VALUE + 1002;  /* Statement链表**/  private final List<Statement> statementList = new ArrayList<Statement>();    /* batch结果链表**/  private final List<BatchResult> batchResultList = new ArrayList<BatchResult>();  private String currentSql;  private MappedStatement currentStatement;  public BatchExecutor(Configuration configuration, Transaction transaction) {    super(configuration, transaction);  }  @Override  public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {//获得配置信息    final Configuration configuration = ms.getConfiguration();//获得StatementHandler    final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);    final BoundSql boundSql = handler.getBoundSql();//获得Sql语句    final String sql = boundSql.getSql();    final Statement stmt;//如果sql语句等于当前sql MappedStatement 等于当前Map碰到Statement    if (sql.equals(currentSql) && ms.equals(currentStatement)) {        int last = statementList.size() - 1;  //获得最后一个      stmt = statementList.get(last);  handler.parameterize(stmt);//fix Issues 322  //有相同的MappedStatement和参数      BatchResult batchResult = batchResultList.get(last);      batchResult.addParameterObject(parameterObject);    } else {  //如果不存在就创建一个批处理操作      Connection connection = getConnection(ms.getStatementLog());      stmt = handler.prepare(connection);      handler.parameterize(stmt);    //fix Issues 322      currentSql = sql;      currentStatement = ms;  //添加批量处理操作      statementList.add(stmt);      batchResultList.add(new BatchResult(ms, sql, parameterObject));    }  // handler.parameterize(stmt);    //最终是调用jdbc的批处理操作    handler.batch(stmt);    return BATCH_UPDATE_RETURN_VALUE;  }  @Override  public <E> List<E> doQuery(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)      throws SQLException {    Statement stmt = null;    try {      flushStatements();  //获得配置信息      Configuration configuration = ms.getConfiguration();  //获得StatementHandler      StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameterObject, rowBounds, resultHandler, boundSql);  //获得连接      Connection connection = getConnection(ms.getStatementLog());      stmt = handler.prepare(connection);  //获得Statement      handler.parameterize(stmt);      return handler.<E>query(stmt, resultHandler);    } finally {      closeStatement(stmt);    }  }  /* 刷新Statement，记录执行次数*/  @Override  public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {    try {      List<BatchResult> results = new ArrayList<BatchResult>();      if (isRollback) {        return Collections.emptyList();      }  //如果进行了批量处理      for (int i = 0, n = statementList.size(); i < n; i++) {        Statement stmt = statementList.get(i);        BatchResult batchResult = batchResultList.get(i);        try {  //记录批量处理执行操作的条数          batchResult.setUpdateCounts(stmt.executeBatch());          MappedStatement ms = batchResult.getMappedStatement();  //参数对象集合          List<Object> parameterObjects = batchResult.getParameterObjects();  //生成key          KeyGenerator keyGenerator = ms.getKeyGenerator();          if (Jdbc3KeyGenerator.class.equals(keyGenerator.getClass())) {            Jdbc3KeyGenerator jdbc3KeyGenerator = (Jdbc3KeyGenerator) keyGenerator;            jdbc3KeyGenerator.processBatch(ms, stmt, parameterObjects);          } else if (!NoKeyGenerator.class.equals(keyGenerator.getClass())) { //issue #141            for (Object parameter : parameterObjects) {              keyGenerator.processAfter(this, ms, stmt, parameter);            }          }        } catch (BatchUpdateException e) {          StringBuilder message = new StringBuilder();          message.append(batchResult.getMappedStatement().getId())              .append(" (batch index #")              .append(i + 1)              .append(")")              .append(" failed.");          if (i > 0) {            message.append(" ")                .append(i)                .append(" prior sub executor(s) completed successfully, but will be rolled back.");          }          throw new BatchExecutorException(message.toString(), e, results, batchResult);        }//记录操作        results.add(batchResult);      }      return results;    } finally {      for (Statement stmt : statementList) {        closeStatement(stmt);      }      currentSql = null;      statementList.clear();      batchResultList.clear();    }  }}