iBatis batch处理那些事

   昨天应同事要求在框架中（Spring+iBatis2.3.4）加入Batch处理，于是满足之，由于需要更灵活并且不想为批量插入、批量更新、批量删除等操作单独写对应的方法，于是写了这样的一个方法

	public Object batchExecute(final CallBack callBack) {
		Object result = getSqlMapClientTemplate().execute(new SqlMapClientCallback<Object>() {

			@Override
			public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
				executor.startBatch();
				Object obj = callBack.execute(new IbatisSqlExecutor(executor));
				executor.executeBatch();
				return obj;
			}
		});
		return result;
	}

不想将SqlMapExecutor侵入到业务代码中，于是又有了如下3个类，在今天的主题中不是关键，可以忽略，只是为了将代码贴完整

public interface SqlExecutor {
	Object insert(String id, Object parameterObject) throws SQLException;
	Object insert(String id) throws SQLException;
	int update(String id, Object parameterObject) throws SQLException;
	int update(String id) throws SQLException;
	int delete(String id, Object parameterObject) throws SQLException;
	int delete(String id) throws SQLException;
	Object queryForObject(String id, Object parameterObject) throws SQLException;
	Object queryForObject(String id) throws SQLException;
	Object queryForObject(String id, Object parameterObject, Object resultObject) throws SQLException;
}

class IbatisSqlExecutor implements SqlExecutor {
	private SqlMapExecutor executor;
	IbatisSqlExecutor(SqlMapExecutor executor) {
		this.executor = executor;
	}
	@Override
	public Object insert(String id, Object parameterObject) throws SQLException {
		return executor.insert(id, parameterObject);
	}
	// 剩下的就省略了，和insert都类似
}

public interface CallBack {
		Object execute(SqlExecutor executor);
}

然后执行了一个类似以下伪代码行为的操作：

getDao().batchExecute(new CallBack() {
        @Override
        public Object execute(SqlExecutor executor) {
                for (int i = 0; i < 10000; ++i) {
                        // 注意每个sql_id的sql语句都是不相同的
                        executor.insert("id1", obj1);
                        executor.insert("id2", obj2);
                        // ...
                        executor.insert("idn", objn);
                }
                return null;
        }
});

再然后...尼玛不但速度没变快还异常了，原因竟然是生成了太多的PreparedStatement，你妹不是批处理吗？不是应该一个sql只有一个PreparedStatement吗？
跟踪iBatis代码，发现了iBatis是这样处理的

// 以下代码来自com.ibatis.sqlmap.engine.execution.SqlExecutor$Batch

    public void addBatch(StatementScope statementScope, Connection conn, String sql, Object[] parameters) throws SQLException {
      PreparedStatement ps = null;
// 就是它：currentSql
      if (currentSql != null && currentSql.equals(sql)) {
        int last = statementList.size() - 1;
        ps = (PreparedStatement) statementList.get(last);
      } else {
        ps = prepareStatement(statementScope.getSession(), conn, sql);
        setStatementTimeout(statementScope.getStatement(), ps);
// 就是它：currentSql
        currentSql = sql;
        statementList.add(ps);
        batchResultList.add(new BatchResult(statementScope.getStatement().getId(), sql));
      }
      statementScope.getParameterMap().setParameters(statementScope, ps, parameters);
      ps.addBatch();
      size++;
    }

不细解释了，只看currentSql这个实例变量就知道了，如果sql与前一次不同那么会新建一个PreparedStatement，所以刚才的伪代码应该这样写：

getDao().batchExecute(new CallBack() {
        @Override
        public Object execute(SqlExecutor executor) {
                for (int i = 0; i < 10000; ++i) {
                        executor.insert("id1", obj1);
                }
                for (int i = 0; i < 10000; ++i) {
                        executor.insert("id2", obj2);
                }
                // ...你就反复写for循环吧
                return null;
        }
});

很不爽是不？反正我是决了一个定，改iBatis的源码
改源码最好这么来：
1.复制对应类的源码到工程下，本例中要复制的是com.ibatis.sqlmap.engine.execution.SqlExecutor
注意要保持包名，其实是类的全限定名称要一样哇，这样根据ClassLoader的类加载机制会先加载你工程中的SqlExecutor而不加载iBatis jar包中的对应SqlExecutor
如图：



2.改之，只改static class Batch这个内部类即可，策略是去掉currentSql，将PreparedStatement放入HashMap
如下：

public void addBatch(StatementScope statementScope, Connection conn, String sql, Object[] parameters) throws SQLException {
			PreparedStatement ps = statementMap.get(sql);
			if (ps == null) {
				ps = prepareStatement(statementScope.getSession(), conn, sql);
				setStatementTimeout(statementScope.getStatement(), ps);
				statementMap.put(sql, ps);
				batchResultMap.put(sql, new BatchResult(statementScope.getStatement().getId(), sql));
			}
			statementScope.getParameterMap().setParameters(statementScope, ps, parameters);
			ps.addBatch();
			++size;
		}

下面贴出修改后完整的代码，方便有同样需求的同学修改，只贴出内部类com.ibatis.sqlmap.engine.execution.SqlExecutor$Batch，com.ibatis.sqlmap.engine.execution.SqlExecutor没有做出任何修改

	private static class Batch {

		private Map<String, PreparedStatement> statementMap = new HashMap<String, PreparedStatement>();
		private Map<String, BatchResult> batchResultMap = new HashMap<String, BatchResult>();
		private int size;

		/**
		 * Create a new batch
		 */
		public Batch() {
			size = 0;
		}

		/**
		 * Getter for the batch size
		 * @return - the batch size
		 */
		@SuppressWarnings("unused")
		public int getSize() {
			return size;
		}

		/**
		 * Add a prepared statement to the batch
		 * @param statementScope - the request scope
		 * @param conn - the database connection
		 * @param sql - the SQL to add
		 * @param parameters - the parameters for the SQL
		 * @throws SQLException - if the prepare for the SQL fails
		 */
		public void addBatch(StatementScope statementScope, Connection conn, String sql, Object[] parameters) throws SQLException {
			PreparedStatement ps = statementMap.get(sql);
			if (ps == null) {
				ps = prepareStatement(statementScope.getSession(), conn, sql);
				setStatementTimeout(statementScope.getStatement(), ps);
				statementMap.put(sql, ps);
				batchResultMap.put(sql, new BatchResult(statementScope.getStatement().getId(), sql));
			}
			statementScope.getParameterMap().setParameters(statementScope, ps, parameters);
			ps.addBatch();
			++size;
		}

		/**
		 * TODO (Jeff Butler) - maybe this method should be deprecated in some release,
		 * and then removed in some even later release. executeBatchDetailed gives
		 * much more complete information.
		 * <p/>
		 * Execute the current session's batch
		 * @return - the number of rows updated
		 * @throws SQLException - if the batch fails
		 */
		public int executeBatch() throws SQLException {
			int totalRowCount = 0;
			for (Map.Entry<String, PreparedStatement> iter : statementMap.entrySet()) {
				PreparedStatement ps = iter.getValue();
				int[] rowCounts = ps.executeBatch();
				for (int j = 0; j < rowCounts.length; j++) {
					if (rowCounts[j] == Statement.SUCCESS_NO_INFO) {
						// do nothing
					} else if (rowCounts[j] == Statement.EXECUTE_FAILED) {
						throw new SQLException("The batched statement at index " + j + " failed to execute.");
					} else {
						totalRowCount += rowCounts[j];
					}
				}
			}
			return totalRowCount;
		}

		/**
		 * Batch execution method that returns all the information
		 * the driver has to offer.
		 * @return a List of BatchResult objects
		 * @throws BatchException (an SQLException sub class) if any nested
		 *             batch fails
		 * @throws SQLException if a database access error occurs, or the drive
		 *             does not support batch statements
		 * @throws BatchException if the driver throws BatchUpdateException
		 */
		@SuppressWarnings({ "rawtypes", "unchecked" })
		public List executeBatchDetailed() throws SQLException, BatchException {
			List answer = new ArrayList();
			int i = 0;
			for (String sql : statementMap.keySet()) {
				BatchResult br = batchResultMap.get(sql);
				PreparedStatement ps = statementMap.get(sql);
				try {
					br.setUpdateCounts(ps.executeBatch());
				} catch (BatchUpdateException e) {
					StringBuffer message = new StringBuffer();
					message.append("Sub batch number ");
					message.append(i + 1);
					message.append(" failed.");
					if (i > 0) {
						message.append(" ");
						message.append(i);
						message.append(" prior sub batch(s) completed successfully, but will be rolled back.");
					}
					throw new BatchException(message.toString(), e, answer, br.getStatementId(), br.getSql());
				}
				++i;
				answer.add(br);
			}
			return answer;
		}

		/**
		 * Close all the statements in the batch and clear all the statements
		 * @param sessionScope
		 */
		public void cleanupBatch(SessionScope sessionScope) {
			for (Map.Entry<String, PreparedStatement> iter : statementMap.entrySet()) {
				PreparedStatement ps = iter.getValue();
				closeStatement(sessionScope, ps);
			}
			statementMap.clear();
			batchResultMap.clear();
			size = 0;
		}
	}