数据库中间件-Sharding-JDBC（跟踪一次insert语句的执行过程）

SQL解析部分:
组件解析顺序
DDL -> TCL -> DAL –> DCL -> DML –>DQL
数据操纵语言（DML）: SELECT(查询)INSERT(插入) UPDATE(更新) DELETE(删除）
数据定义语言（DDL）：CREATE(创建数据库或表或索引）ALTER(修改表或者数据库）DROP(删除表或索引）
数据控制语言（DCL）：GRANT(赋予用户权限） REVOKE(收回权限） DENY(禁止权限)
数据查询语言（DQL）：是由SELECT子句，FROM子句，WHERE子句组成的查询块
事务控制语言（TCL）：SAVEPOINT (设置保存点）ROLLBACK (回滚) COMMIT(提交)

SQL路由部分:

ShardingRouteDecorator
装饰器模式，组合选择不同的路由

public RouteContext decorate(final RouteContext routeContext, final ShardingSphereMetaData metaData, final ShardingRule shardingRule, final ConfigurationProperties properties) {
        SQLStatementContext sqlStatementContext = routeContext.getSqlStatementContext();
        List<Object> parameters = routeContext.getParameters();
        ShardingStatementValidatorFactory.newInstance(
                sqlStatementContext.getSqlStatement()).ifPresent(validator -> validator.validate(shardingRule, sqlStatementContext.getSqlStatement(), parameters));
        ShardingConditions shardingConditions = getShardingConditions(parameters, sqlStatementContext, metaData.getSchema(), shardingRule);
        boolean needMergeShardingValues = isNeedMergeShardingValues(sqlStatementContext, shardingRule);
        if (sqlStatementContext.getSqlStatement() instanceof DMLStatement && needMergeShardingValues) {
            checkSubqueryShardingValues(sqlStatementContext, shardingRule, shardingConditions);
            mergeShardingConditions(shardingConditions);
        }
        ShardingRouteEngine shardingRouteEngine = ShardingRouteEngineFactory.newInstance(shardingRule, metaData, sqlStatementContext, shardingConditions, properties);
	//执行路由
        RouteResult routeResult = shardingRouteEngine.route(shardingRule);
        if (needMergeShardingValues) {
            Preconditions.checkState(1 == routeResult.getRouteUnits().size(), "Must have one sharding with subquery.");
        }
        return new RouteContext(sqlStatementContext, parameters, routeResult);
    }

ShardingStandardRoutingEngine
路由的方法

public RouteResult route(final ShardingRule shardingRule) {
        if (isDMLForModify(sqlStatementContext) && 1 != ((TableAvailable) sqlStatementContext).getAllTables().size()) {
            throw new ShardingSphereException("Cannot support Multiple-Table for '%s'.", sqlStatementContext.getSqlStatement());
        }
        return generateRouteResult(getDataNodes(shardingRule, shardingRule.getTableRule(logicTableName)));
    }

private Collection<DataNode> routeByShardingConditionsWithCondition(final ShardingRule shardingRule, final TableRule tableRule) {
        Collection<DataNode> result = new LinkedList<>();
        for (ShardingCondition each : shardingConditions.getConditions()) {
	//根据分片规则找到具体的数据库表dataNodes
            Collection<DataNode> dataNodes = route0(shardingRule, tableRule, 
                    getShardingValuesFromShardingConditions(shardingRule, shardingRule.getDatabaseShardingStrategy(tableRule).getShardingColumns(), each),
                    getShardingValuesFromShardingConditions(shardingRule, shardingRule.getTableShardingStrategy(tableRule).getShardingColumns(), each));
            result.addAll(dataNodes);
            originalDataNodes.add(dataNodes);
        }
        return result;
    }

SQL改写部分：
package org.apache.shardingsphere.underlying.pluggble.prepare
BasePrepareEngine.java

/**
     * Prepare to execute.
     *
     * @param sql SQL
     * @param parameters SQL parameters
     * @return execution context
     */
    public ExecutionContext prepare(final String sql, final List<Object> parameters) {
        List<Object> clonedParameters = cloneParameters(parameters);
        RouteContext routeContext = executeRoute(sql, clonedParameters);
	//executeRewrite 执行改写
        ExecutionContext result = new ExecutionContext(routeContext.getSqlStatementContext());
        	result.getExecutionUnits().addAll(executeRewrite(sql, clonedParameters, routeContext));
        if (properties.<Boolean>getValue(ConfigurationPropertyKey.SQL_SHOW)) {
            SQLLogger.logSQL(sql, properties.<Boolean>getValue(ConfigurationPropertyKey.SQL_SIMPLE), result.getSqlStatementContext(), result.getExecutionUnits());
        }
        return result;
    }

private Collection<ExecutionUnit> executeRewrite(final String sql, final List<Object> parameters, final RouteContext routeContext) {
        registerRewriteDecorator();
        SQLRewriteContext sqlRewriteContext = rewriter.createSQLRewriteContext(sql, parameters, routeContext.getSqlStatementContext(), routeContext);
        return routeContext.getRouteResult().getRouteUnits().isEmpty() ? rewrite(sqlRewriteContext) : rewrite(routeContext, sqlRewriteContext);
    }

private Collection<ExecutionUnit> rewrite(final RouteContext routeContext, final SQLRewriteContext sqlRewriteContext) {
        Collection<ExecutionUnit> result = new LinkedHashSet<>();
        for (Entry<RouteUnit, SQLRewriteResult> entry : new SQLRouteRewriteEngine().rewrite(sqlRewriteContext, routeContext.getRouteResult()).entrySet()) {
            result.add(new ExecutionUnit(entry.getKey().getDataSourceMapper().getActualName(), new SQLUnit(entry.getValue().getSql(), entry.getValue().getParameters())));
        }
        return result;
    }

SQL执行部分:
package org.apache.shardingsphere.shardingjdbc.executor
PreparedStatementExecutor.java

/**
     * Execute SQL.
     *
     * @return return true if is DQL, false if is DML
     * @throws SQLException SQL exception
     */
    public boolean execute() throws SQLException {
        boolean isExceptionThrown = ExecutorExceptionHandler.isExceptionThrown();
        SQLExecuteCallback<Boolean> executeCallback = SQLExecuteCallbackFactory.getPreparedSQLExecuteCallback(getDatabaseType(), isExceptionThrown);
        List<Boolean> result = executeCallback(executeCallback);
        if (null == result || result.isEmpty() || null == result.get(0)) {
            return false;
        }
        return result.get(0);
    }

参考: https://segmentfault.com/a/1190000038225441