MybatisPlus批量保存原理及失效原因排查全过程

@Transactional(rollbackFor = Exception.class)
@Override
public boolean saveBatch(Collection<T> entityList, int batchSize) {
  // ${className}.insert
	String sqlStatement = getSqlStatement(SqlMethod.INSERT_ONE);
  // 函数式编程 BiConsumer<T, U>
	return executeBatch(entityList, batchSize, (sqlSession, entity) -> sqlSession.insert(sqlStatement, entity));
}

@Override
public boolean saveBatch(Collection entityList, int batchSize) {

	BiConsumer<SqlSession, Object> consumer = new EntityConsumer();

	return executeBatch(entityList, batchSize, consumer);
}

class EntityConsumer implements BiConsumer<SqlSession, Object>{

	@Override
	public void accept(SqlSession sqlSession, Object object) {
		sqlSession.insert("${className}.insert", object);
	}
}

public static <E> boolean executeBatch(Class<?> entityClass, Log log, Collection<E> list, int batchSize, BiConsumer<SqlSession, E> consumer) {
	Assert.isFalse(batchSize < 1, "batchSize must not be less than one");
	return !CollectionUtils.isEmpty(list) && executeBatch(entityClass, log, sqlSession -> {
		int size = list.size();
		int i = 1;
		for (E element : list) {
      // 调用sqlSession.insert("${className}.insert", object);
      // 数据最终保存到StatementImpl.batchedArgs中，用于后面做批量保存
			consumer.accept(sqlSession, element);
			if ((i % batchSize == 0) || i == size) {
        // 批量保存StatementImpl.batchedArgs中的数据
				sqlSession.flushStatements();
			}
			i++;
		}
	});
}

 if (sql.equals(currentSql) && ms.equals(currentStatement))

@Override
public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {
	final Configuration configuration = ms.getConfiguration();
	final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);
	final BoundSql boundSql = handler.getBoundSql();
	final String sql = boundSql.getSql();
	final Statement stmt;
  // **
	if (sql.equals(currentSql) && ms.equals(currentStatement)) {
		int last = statementList.size() - 1;
		stmt = statementList.get(last);
		applyTransactionTimeout(stmt);
		handler.parameterize(stmt);//fix Issues 322
		BatchResult batchResult = batchResultList.get(last);
		batchResult.addParameterObject(parameterObject);
	} else {
		Connection connection = getConnection(ms.getStatementLog());
		stmt = handler.prepare(connection, transaction.getTimeout());
		if (stmt == null) {
			return 0;
		}
		handler.parameterize(stmt);    //fix Issues 322
		currentSql = sql;
		currentStatement = ms;
		statementList.add(stmt);
		batchResultList.add(new BatchResult(ms, sql, parameterObject));
	}
	handler.batch(stmt);
	return BATCH_UPDATE_RETURN_VALUE;
}

public void addBatch() throws SQLException {
	synchronized (checkClosed().getConnectionMutex()) {
		if (this.batchedArgs == null) {
			this.batchedArgs = new ArrayList<Object>();
		}

		for (int i = 0; i < this.parameterValues.length; i++) {
			checkAllParametersSet(this.parameterValues[i], this.parameterStreams[i], i);
		}

		this.batchedArgs.add(new BatchParams(this.parameterValues, this.parameterStreams, this.isStream, this.streamLengths, this.isNull));
	}
}

@Override
public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {
	try {
		List<BatchResult> results = new ArrayList<>();
		if (isRollback) {
			return Collections.emptyList();
		}
		for (int i = 0, n = statementList.size(); i < n; i++) {
			Statement stmt = statementList.get(i);
			applyTransactionTimeout(stmt);
			BatchResult batchResult = batchResultList.get(i);
			try {
				batchResult.setUpdateCounts(stmt.executeBatch());
				MappedStatement ms = batchResult.getMappedStatement();
				List<Object> parameterObjects = batchResult.getParameterObjects();
				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);
					}
				}
				// Close statement to close cursor #1109
				closeStatement(stmt);
			} 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);
			}
			results.add(batchResult);
		}
		return results;
	} finally {
		for (Statement stmt : statementList) {
			closeStatement(stmt);
		}
		currentSql = null;
		statementList.clear();
		batchResultList.clear();
	}
}

@Override
protected long[] executeBatchInternal() throws SQLException {
	synchronized (checkClosed().getConnectionMutex()) {

		if (this.connection.isReadOnly()) {
			throw new SQLException(Messages.getString("PreparedStatement.25") + Messages.getString("PreparedStatement.26"),
				SQLError.SQL_STATE_ILLEGAL_ARGUMENT);
		}

		if (this.batchedArgs == null || this.batchedArgs.size() == 0) {
			return new long[0];
		}

		// we timeout the entire batch, not individual statements
		int batchTimeout = this.timeoutInMillis;
		this.timeoutInMillis = 0;

		resetCancelledState();

		try {
			statementBegins();

			clearWarnings();

      // 判断rewriteBatchedStatements参数
			if (!this.batchHasPlainStatements && this.connection.getRewriteBatchedStatements()) {

				if (canRewriteAsMultiValueInsertAtSqlLevel()) {
					return executeBatchedInserts(batchTimeout);
				}

				if (this.connection.versionMeetsMinimum(4, 1, 0) && !this.batchHasPlainStatements && this.batchedArgs != null
					&& this.batchedArgs.size() > 3 ) {
					return executePreparedBatchAsMultiStatement(batchTimeout);
				}
			}

			return executeBatchSerially(batchTimeout);
		} finally {
			this.statementExecuting.set(false);

			clearBatch();
		}
	}
}

if (sql.equals(currentSql) && ms.equals(currentStatement))