oceanus-58总体框架理解

1.总体思路：
通过约定的XML规则（分表分库规则）和 封装jdbc的Connection和PreparedStatement来实现SQL解析，sql路由和sql重写。

2.  3个核心类：ConnectionWrapper（JDBC Connection包装），PreparedStatementWrapper( JDBC PreparedStatement包装)，SimpleExecutor(sql执行器，类似mybatis的SimpleExecutor)

3.  3个上下文传参数：ConnectionContext，StatementContext，transactionContext。

4.  真正干活的类：

（1）DefaultStatementContextBuilder类：解析SQL并保存BatchItem到StatementContext，--作者貌似直接用的mycat里面的sql解析的代码，直接拿来主义实现价值啊。

public StatementContext build(String sql, StatementContext context)
			throws SQLException {
		if (context == null) {
			context = new StatementContext();
			StatementContext.setContext(context);
			if (logger.isDebugEnabled()) {
				logger.debug("create context!sql=" + sql);
			}
		}
		if (context.getCurrentBatch().getSql() == null) {
			context.getCurrentBatch().setSql(sql);
		}

		StatementContextHandler handler = null;
		if (context.isBatch()) {
			handler = HandlerFactory.create(StatementType.BATCH);
			StatementContext resultContext = handler.handle(sql, context);
			processPreparedValues(resultContext);
			return resultContext;
		}
		
		TrackerExecutor.trackBegin(TrackPoint.PARSE_SQL, sql);
		SQLParser parser = StatementHelper.createSQLParser();
		try {
			DMLStatementNode statementNode = (DMLStatementNode) parser
					.parseStatement(sql);
			switch (statementNode.getNodeType()) {
			case NodeTypes.CURSOR_NODE:
				handler = HandlerFactory.create(StatementType.SELECT);
				break;
			case NodeTypes.DELETE_NODE:
				handler = HandlerFactory.create(StatementType.DELETE);
				break;
			case NodeTypes.UPDATE_NODE:
				handler = HandlerFactory.create(StatementType.UPDATE);
				break;
			case NodeTypes.INSERT_NODE:
				handler = HandlerFactory.create(StatementType.INSERT);
				break;
			case NodeTypes.CALL_STATEMENT_NODE:
				handler = HandlerFactory.create(StatementType.CALLABLE);
				break;
			}
			
			StatementContext resultContext = handler.handle(statementNode,
					context);
			
			TrackerExecutor.trackEnd(TrackPoint.PARSE_SQL);
			
			processPreparedValues(resultContext);
			return resultContext;

		} catch (StandardException se) {
			System.out.println("sql parse error, sql:"+sql);
			se.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
		processPreparedValues(context);
		return context;
	}

（2）DefaultTargetDispatcher：根据batchItem和batchItem中的tableInfo获取路由信息和重写SQL，达到路由到指定的分库分表的目的

Set<RouteTarget> getSpecifyTargets(TableInfo tableInfo, BatchItem batchItem) {
		Set<RouteTarget> targetSet = new LinkedHashSet<RouteTarget>();
		Configurations configurations = Configurations.getInstance();

		/**
		 * 解析where中符合分库分表字段的值
		 */
		Map<String, List<TableColumn>> resolveColumns = RouteHelper
				.getResolveColumns(tableInfo.getOrgName(),
						batchItem.getAnalyzeResult());
		List<Map<String, Object>> parameters = RouteHelper
				.getParameterValues(resolveColumns);
		Set<Integer> indexs = new HashSet<Integer>();
		TableDescription desc = configurations.getTableDescription(tableInfo
				.getOrgName());
		List<NameNodeHolder> nameNodes = desc.getNameNodes();
		Function func = desc.getFunction();
//分库分表函数，本质就是获取table节点中namenode节点的序号
		for (Map<String, Object> item : parameters) {
			checkParameters(item, batchItem);
			int i = func.execute(nameNodes.size(), item);
			indexs.add(i);
		}

		if (indexs.size() > 0) {
			AnalyzeResult analyzeResult = batchItem.getAnalyzeResult();
			HavingInfo havingInfo = analyzeResult.getHavingInfo();
			if (havingInfo != null) {
				AnalyzerCallback callback = havingInfo.getCallback();
				if (callback != null) {
					callback.call();
				}
			}
		}
		if ((!batchItem.getAnalyzeResult().getAppendResultColumns().isEmpty() || batchItem
				.getAnalyzeResult().getLimit() != null) && indexs.size() > 1) {// 存在limit或者avg等聚集函数,需要重新生成sql
			Collection<AnalyzerCallback> analyzerCallbacks = batchItem
					.getAnalyzeResult().getAnalyzerCallbacks();
			if (batchItem.getAnalyzeResult().getLimit() != null) {
				SqlValueItem limitItem = batchItem.getAnalyzeResult()
						.getLimit();
				SqlValueItem offsetItem = batchItem.getAnalyzeResult()
						.getOffset();
				if(offsetItem==null){
					offsetItem=new SqlValueItem();
					offsetItem.setValue(0);
				}
				if (limitItem.getParameterIndex() > 0
						&& offsetItem.getParameterIndex() > 0) {// limit ?,?
					Integer limitSize = limitItem.getValue()
							+ offsetItem.getValue();
					batchItem.getCallback(limitItem.getParameterIndex())
							.setParameter(limitSize);
					batchItem.getCallback(offsetItem.getParameterIndex())
							.setParameter(0);
					
					if(limitItem.getParameterIndex() > offsetItem.getParameterIndex()){
						batchItem.getCallback(offsetItem.getParameterIndex())
							.setParameterIndex(limitItem.getParameterIndex());
						
						batchItem.getCallback(limitItem.getParameterIndex())
							.setParameterIndex(offsetItem.getParameterIndex());
					}
				} else if (limitItem.getParameterIndex() > 0) {// limit 1,?
					Integer limitSize = limitItem.getValue()
							+ offsetItem.getValue();
					batchItem.getCallback(limitItem.getParameterIndex())
							.setParameter(limitSize);
				} else if (offsetItem.getParameterIndex() > 0) {// limit ?,10
					batchItem.getCallback(offsetItem.getParameterIndex())
							.setParameter(0);
				}
			}
			for (AnalyzerCallback callback : analyzerCallbacks) {
				callback.call();
			}
		} else {// 在单库路由的情况下，如果检测到是limit ?,?，就置换Parameter顺序
			SqlValueItem limitItem = batchItem.getAnalyzeResult()
					.getLimit();
			SqlValueItem offsetItem = batchItem.getAnalyzeResult()
					.getOffset();
			
			if(limitItem !=null && offsetItem !=null && 
					limitItem.getParameterIndex() > offsetItem.getParameterIndex()){
				
				batchItem.getCallback(offsetItem.getParameterIndex())
					.setParameterIndex(limitItem.getParameterIndex());
				
				batchItem.getCallback(limitItem.getParameterIndex())
					.setParameterIndex(offsetItem.getParameterIndex());
			}
		}
		for (Integer i : indexs) {// 生成target
			NameNode nameNode = configurations.getNameNode(
					tableInfo.getOrgName(), i);
			DefaultRouteTarget target = this.createTarget(batchItem, nameNode, tableInfo);
			targetSet.add(target);
		}

		
		for (RouteTarget item : targetSet) {
			DefaultRouteTarget target = (DefaultRouteTarget) item;
			SqlExecuteInfo info = new SqlExecuteInfo();
			info.setCallbacks(new LinkedHashSet<ParameterCallback<?>>(batchItem
					.getCallbacks()));

			if (desc.isDifferentName()) {
				info.setExecuteSql(configurations.getGenerator().generate(
						(NameNodeHolder) target.getNameNode(),
						batchItem.getAnalyzeResult()));
			} else if ((!batchItem.getAnalyzeResult().getAppendResultColumns().isEmpty() || batchItem
					.getAnalyzeResult().getLimit() != null) && nameNodes.size() > 1) {// 存在limit或者avg等聚集函数,需要重新生成sql,必须要超过1个路由结果
				info.setExecuteSql(configurations.getLimitAvgGenerator()
						.generate((NameNodeHolder) target.getNameNode(),
								batchItem.getAnalyzeResult()));
			} else {
				info.setExecuteSql(batchItem.getSql());
			}
			target.setExecuteInfo(info);
		}
		return targetSet;
	}

(3)SimpleExecutor 和 HandlerFactory:

根据StatementContext的RouteTarget（路由数据），

新建事务并获取数据库连接，   实际执行JDBC curd操作的类.

兴趣点：发现doUpdate的时候有用同步工具类：

CyclicBarrier barrier = new CyclicBarrier(n);

@SuppressWarnings({ "rawtypes", "unchecked" })
public class SimpleExecutor implements Executor {
	static Logger logger = LoggerFactory.getLogger(SimpleExecutor.class);
	static final ExecuteHandler<Integer> deleteHandler = new DeleteExecuteHandler();
	static final ExecuteHandler<Integer> insertHandler = new InsertExecuteHandler();
	static final ExecuteHandler<Integer> updateHandler = new UpdateExecuteHandler();
	static final ExecuteHandler<ResultSet> queryHandler = new QueryExecuteHandler();

	@Override
	public Object execute(StatementContext context, ExecuteCallback callback)
			throws SQLException {

		switch (context.getCurrentBatch().getAnalyzeResult().getStatementType()) {
		case SELECT:
			return this.doQuery(context, callback);
		case INSERT:
		case UPDATE:
		case DELETE:
			return doUpdate(context, callback);
		default:
			break;
		}
		return null;
	}

	ExecuteHandler<?> getHandler(StatementType statementType) {
		switch (statementType) {
		case SELECT:
			return queryHandler;
		case INSERT:
			return insertHandler;
		case UPDATE:
			return updateHandler;
		case DELETE:
			return deleteHandler;
		default:
			break;
		}
		return null;
	}
...

5.集成Mybatis:

因为Mybatis获取连接是通过PooledDataSource或UnpooledDataSource获取的，所以写个插件：包装下DataSource，把oceanus的connentionWrap包装进去即可实现整合。