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本文主要研究一下ShardingSphere进行sql重写的原理
prepareStatement
org/apache/shardingsphere/driver/jdbc/core/connection/ShardingSphereConnection.java
public final class ShardingSphereConnection extends AbstractConnectionAdapter {@Overridepublic PreparedStatement prepareStatement(final String sql) throws SQLException {return new ShardingSpherePreparedStatement(this, sql);}//......
}
ShardingSphereConnection的prepareStatement创建的是ShardingSpherePreparedStatement
ShardingSpherePreparedStatement
org/apache/shardingsphere/driver/jdbc/core/statement/ShardingSpherePreparedStatement.java
public final class ShardingSpherePreparedStatement extends AbstractPreparedStatementAdapter {@Getterprivate final ShardingSphereConnection connection;public ShardingSpherePreparedStatement(final ShardingSphereConnection connection, final String sql) throws SQLException {this(connection, sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY, ResultSet.HOLD_CURSORS_OVER_COMMIT, false, null);}private ShardingSpherePreparedStatement(final ShardingSphereConnection connection, final String sql,final int resultSetType, final int resultSetConcurrency, final int resultSetHoldability, final boolean returnGeneratedKeys,final String[] columns) throws SQLException {if (Strings.isNullOrEmpty(sql)) {throw new EmptySQLException().toSQLException();}this.connection = connection;metaDataContexts = connection.getContextManager().getMetaDataContexts();SQLParserRule sqlParserRule = metaDataContexts.getMetaData().getGlobalRuleMetaData().getSingleRule(SQLParserRule.class);hintValueContext = sqlParserRule.isSqlCommentParseEnabled() ? new HintValueContext() : SQLHintUtils.extractHint(sql).orElseGet(HintValueContext::new);this.sql = sqlParserRule.isSqlCommentParseEnabled() ? sql : SQLHintUtils.removeHint(sql);statements = new ArrayList<>();parameterSets = new ArrayList<>();SQLParserEngine sqlParserEngine = sqlParserRule.getSQLParserEngine(DatabaseTypeEngine.getTrunkDatabaseTypeName(metaDataContexts.getMetaData().getDatabase(connection.getDatabaseName()).getProtocolType()));sqlStatement = sqlParserEngine.parse(this.sql, true);sqlStatementContext = SQLStatementContextFactory.newInstance(metaDataContexts.getMetaData(), sqlStatement, connection.getDatabaseName());parameterMetaData = new ShardingSphereParameterMetaData(sqlStatement);statementOption = returnGeneratedKeys ? new StatementOption(true, columns) : new StatementOption(resultSetType, resultSetConcurrency, resultSetHoldability);executor = new DriverExecutor(connection);JDBCExecutor jdbcExecutor = new JDBCExecutor(connection.getContextManager().getExecutorEngine(), connection.getDatabaseConnectionManager().getConnectionContext());batchPreparedStatementExecutor = new BatchPreparedStatementExecutor(metaDataContexts, jdbcExecutor, connection.getDatabaseName());kernelProcessor = new KernelProcessor();statementsCacheable = isStatementsCacheable(metaDataContexts.getMetaData().getDatabase(connection.getDatabaseName()).getRuleMetaData());trafficRule = metaDataContexts.getMetaData().getGlobalRuleMetaData().getSingleRule(TrafficRule.class);selectContainsEnhancedTable = sqlStatementContext instanceof SelectStatementContext && ((SelectStatementContext) sqlStatementContext).isContainsEnhancedTable();statementManager = new StatementManager();}//......
}
ShardingSpherePreparedStatement继承了AbstractPreparedStatementAdapter，其构造器主要是通过SQLParserEngine解析sql得到SQLStatement，创建DriverExecutor、BatchPreparedStatementExecutor、KernelProcessor、StatementManager；这里即使useServerPrepStmts=true，也不会触发mysql server的prepare操作
executeUpdate
public int executeUpdate() throws SQLException {try {if (statementsCacheable && !statements.isEmpty()) {resetParameters();return statements.iterator().next().executeUpdate();}clearPrevious();QueryContext queryContext = createQueryContext();trafficInstanceId = getInstanceIdAndSet(queryContext).orElse(null);if (null != trafficInstanceId) {JDBCExecutionUnit executionUnit = createTrafficExecutionUnit(trafficInstanceId, queryContext);return executor.getTrafficExecutor().execute(executionUnit, (statement, sql) -> ((PreparedStatement) statement).executeUpdate());}executionContext = createExecutionContext(queryContext);if (hasRawExecutionRule()) {Collection<ExecuteResult> executeResults = executor.getRawExecutor().execute(createRawExecutionGroupContext(), executionContext.getQueryContext(), new RawSQLExecutorCallback());return accumulate(executeResults);}return isNeedImplicitCommitTransaction(connection, executionContext) ? executeUpdateWithImplicitCommitTransaction() : useDriverToExecuteUpdate();// CHECKSTYLE:OFF} catch (final RuntimeException ex) {// CHECKSTYLE:ONhandleExceptionInTransaction(connection, metaDataContexts);throw SQLExceptionTransformEngine.toSQLException(ex, metaDataContexts.getMetaData().getDatabase(connection.getDatabaseName()).getProtocolType().getType());} finally {clearBatch();}}private void clearPrevious() {statements.clear();parameterSets.clear();generatedValues.clear();}private ExecutionContext createExecutionContext(final QueryContext queryContext) {ShardingSphereRuleMetaData globalRuleMetaData = metaDataContexts.getMetaData().getGlobalRuleMetaData();ShardingSphereDatabase currentDatabase = metaDataContexts.getMetaData().getDatabase(connection.getDatabaseName());SQLAuditEngine.audit(queryContext.getSqlStatementContext(), queryContext.getParameters(), globalRuleMetaData, currentDatabase, null, queryContext.getHintValueContext());ExecutionContext result = kernelProcessor.generateExecutionContext(queryContext, currentDatabase, globalRuleMetaData, metaDataContexts.getMetaData().getProps(), connection.getDatabaseConnectionManager().getConnectionContext());findGeneratedKey(result).ifPresent(optional -> generatedValues.addAll(optional.getGeneratedValues()));return result;}
这里executeUpdate会先执行clearPrevious方法，清空statements、parameterSets、generatedValues，然后createExecutionContext，这里有一步是kernelProcessor.generateExecutionContext
KernelProcessor
generateExecutionContext
shardingsphere-infra-context-5.4.0-sources.jar!/org/apache/shardingsphere/infra/connection/kernel/KernelProcessor.java
public ExecutionContext generateExecutionContext(final QueryContext queryContext, final ShardingSphereDatabase database, final ShardingSphereRuleMetaData globalRuleMetaData,final ConfigurationProperties props, final ConnectionContext connectionContext) {RouteContext routeContext = route(queryContext, database, globalRuleMetaData, props, connectionContext);SQLRewriteResult rewriteResult = rewrite(queryContext, database, globalRuleMetaData, props, routeContext, connectionContext);ExecutionContext result = createExecutionContext(queryContext, database, routeContext, rewriteResult);logSQL(queryContext, props, result);return result;}
KernelProcessor的generateExecutionContext方法先创建routeContext，然后执行rewrite，最后执行createExecutionContext
rewrite
private SQLRewriteResult rewrite(final QueryContext queryContext, final ShardingSphereDatabase database, final ShardingSphereRuleMetaData globalRuleMetaData,final ConfigurationProperties props, final RouteContext routeContext, final ConnectionContext connectionContext) {SQLRewriteEntry sqlRewriteEntry = new SQLRewriteEntry(database, globalRuleMetaData, props);return sqlRewriteEntry.rewrite(queryContext.getSql(), queryContext.getParameters(), queryContext.getSqlStatementContext(), routeContext, connectionContext, queryContext.getHintValueContext());}
rewrite主要是通过SQLRewriteEntry的rewrite方法进行的
SQLRewriteEntry
shardingsphere-infra-rewrite-5.4.0-sources.jar!/org/apache/shardingsphere/infra/rewrite/SQLRewriteEntry.java
/*** Rewrite.* * @param sql SQL* @param params SQL parameters* @param sqlStatementContext SQL statement context* @param routeContext route context* @param connectionContext connection context* @param hintValueContext hint value context* * @return route unit and SQL rewrite result map*/public SQLRewriteResult rewrite(final String sql, final List<Object> params, final SQLStatementContext sqlStatementContext,final RouteContext routeContext, final ConnectionContext connectionContext, final HintValueContext hintValueContext) {SQLRewriteContext sqlRewriteContext = createSQLRewriteContext(sql, params, sqlStatementContext, routeContext, connectionContext, hintValueContext);SQLTranslatorRule rule = globalRuleMetaData.getSingleRule(SQLTranslatorRule.class);DatabaseType protocolType = database.getProtocolType();Map<String, DatabaseType> storageTypes = database.getResourceMetaData().getStorageTypes();return routeContext.getRouteUnits().isEmpty()? new GenericSQLRewriteEngine(rule, protocolType, storageTypes).rewrite(sqlRewriteContext): new RouteSQLRewriteEngine(rule, protocolType, storageTypes).rewrite(sqlRewriteContext, routeContext);}private SQLRewriteContext createSQLRewriteContext(final String sql, final List<Object> params, final SQLStatementContext sqlStatementContext,final RouteContext routeContext, final ConnectionContext connectionContext, final HintValueContext hintValueContext) {SQLRewriteContext result = new SQLRewriteContext(database.getName(), database.getSchemas(), sqlStatementContext, sql, params, connectionContext, hintValueContext);decorate(decorators, result, routeContext, hintValueContext);result.generateSQLTokens();return result;}private void decorate(final Map<ShardingSphereRule, SQLRewriteContextDecorator> decorators, final SQLRewriteContext sqlRewriteContext,final RouteContext routeContext, final HintValueContext hintValueContext) {if (hintValueContext.isSkipSQLRewrite()) {return;}for (Entry<ShardingSphereRule, SQLRewriteContextDecorator> entry : decorators.entrySet()) {entry.getValue().decorate(entry.getKey(), props, sqlRewriteContext, routeContext);}}
SQLRewriteEntry的rewrite方法，先通过createSQLRewriteContext来创建SQLRewriteContext，这里通过decorate方法遍历decorators，挨个执行SQLRewriteContextDecorator的decorate方法；最后通过GenericSQLRewriteEngine或者RouteSQLRewriteEngine进行rewrite
SQLRewriteContextDecorator
org/apache/shardingsphere/infra/rewrite/context/SQLRewriteContextDecorator.java
@SingletonSPI
public interface SQLRewriteContextDecorator<T extends ShardingSphereRule> extends OrderedSPI<T> {/*** Decorate SQL rewrite context.** @param rule rule* @param props ShardingSphere properties* @param sqlRewriteContext SQL rewrite context to be decorated* @param routeContext route context*/void decorate(T rule, ConfigurationProperties props, SQLRewriteContext sqlRewriteContext, RouteContext routeContext);
}
SQLRewriteContextDecorator定义了decorate方法，它有诸如ShardingSQLRewriteContextDecorator、EncryptSQLRewriteContextDecorator的实现类
EncryptSQLRewriteContextDecorator
org/apache/shardingsphere/encrypt/rewrite/context/EncryptSQLRewriteContextDecorator.java
/*** SQL rewrite context decorator for encrypt.*/
public final class EncryptSQLRewriteContextDecorator implements SQLRewriteContextDecorator<EncryptRule> {@Overridepublic void decorate(final EncryptRule encryptRule, final ConfigurationProperties props, final SQLRewriteContext sqlRewriteContext, final RouteContext routeContext) {SQLStatementContext sqlStatementContext = sqlRewriteContext.getSqlStatementContext();if (!containsEncryptTable(encryptRule, sqlStatementContext)) {return;}Collection<EncryptCondition> encryptConditions = createEncryptConditions(encryptRule, sqlRewriteContext);if (!sqlRewriteContext.getParameters().isEmpty()) {Collection<ParameterRewriter> parameterRewriters = new EncryptParameterRewriterBuilder(encryptRule,sqlRewriteContext.getDatabaseName(), sqlRewriteContext.getSchemas(), sqlStatementContext, encryptConditions).getParameterRewriters();rewriteParameters(sqlRewriteContext, parameterRewriters);}Collection<SQLTokenGenerator> sqlTokenGenerators = new EncryptTokenGenerateBuilder(encryptRule,sqlStatementContext, encryptConditions, sqlRewriteContext.getDatabaseName()).getSQLTokenGenerators();sqlRewriteContext.addSQLTokenGenerators(sqlTokenGenerators);}private Collection<EncryptCondition> createEncryptConditions(final EncryptRule encryptRule, final SQLRewriteContext sqlRewriteContext) {SQLStatementContext sqlStatementContext = sqlRewriteContext.getSqlStatementContext();if (!(sqlStatementContext instanceof WhereAvailable)) {return Collections.emptyList();}Collection<WhereSegment> whereSegments = ((WhereAvailable) sqlStatementContext).getWhereSegments();Collection<ColumnSegment> columnSegments = ((WhereAvailable) sqlStatementContext).getColumnSegments();return new EncryptConditionEngine(encryptRule, sqlRewriteContext.getSchemas()).createEncryptConditions(whereSegments, columnSegments, sqlStatementContext, sqlRewriteContext.getDatabaseName());}private boolean containsEncryptTable(final EncryptRule encryptRule, final SQLStatementContext sqlStatementContext) {for (String each : sqlStatementContext.getTablesContext().getTableNames()) {if (encryptRule.findEncryptTable(each).isPresent()) {return true;}}return false;}private void rewriteParameters(final SQLRewriteContext sqlRewriteContext, final Collection<ParameterRewriter> parameterRewriters) {for (ParameterRewriter each : parameterRewriters) {each.rewrite(sqlRewriteContext.getParameterBuilder(), sqlRewriteContext.getSqlStatementContext(), sqlRewriteContext.getParameters());}}@Overridepublic int getOrder() {return EncryptOrder.ORDER;}@Overridepublic Class<EncryptRule> getTypeClass() {return EncryptRule.class;}
}
rewriteParameters是通过ParameterRewriter进行rewrite，主要是修改ParameterBuilder；而具体sql语句的修改则通过sqlTokenGenerators进行
SQLToken
@RequiredArgsConstructor
@Getter
public abstract class SQLToken implements Comparable<SQLToken> {private final int startIndex;@Overridepublic final int compareTo(final SQLToken sqlToken) {return startIndex - sqlToken.startIndex;}
}
SQLToken它有诸如InsertValuesToken、SubstitutableColumnNameToken、InsertColumnsToken之类的实现类
RouteSQLRewriteEngine
/*** Rewrite SQL and parameters.** @param sqlRewriteContext SQL rewrite context* @param routeContext route context* @return SQL rewrite result*/public RouteSQLRewriteResult rewrite(final SQLRewriteContext sqlRewriteContext, final RouteContext routeContext) {Map<RouteUnit, SQLRewriteUnit> sqlRewriteUnits = new LinkedHashMap<>(routeContext.getRouteUnits().size(), 1F);for (Entry<String, Collection<RouteUnit>> entry : aggregateRouteUnitGroups(routeContext.getRouteUnits()).entrySet()) {Collection<RouteUnit> routeUnits = entry.getValue();if (isNeedAggregateRewrite(sqlRewriteContext.getSqlStatementContext(), routeUnits)) {sqlRewriteUnits.put(routeUnits.iterator().next(), createSQLRewriteUnit(sqlRewriteContext, routeContext, routeUnits));} else {addSQLRewriteUnits(sqlRewriteUnits, sqlRewriteContext, routeContext, routeUnits);}}return new RouteSQLRewriteResult(translate(sqlRewriteContext.getSqlStatementContext().getSqlStatement(), sqlRewriteUnits));}private void addSQLRewriteUnits(final Map<RouteUnit, SQLRewriteUnit> sqlRewriteUnits, final SQLRewriteContext sqlRewriteContext,final RouteContext routeContext, final Collection<RouteUnit> routeUnits) {for (RouteUnit each : routeUnits) {sqlRewriteUnits.put(each, new SQLRewriteUnit(new RouteSQLBuilder(sqlRewriteContext, each).toSQL(), getParameters(sqlRewriteContext.getParameterBuilder(), routeContext, each)));}}private Map<RouteUnit, SQLRewriteUnit> translate(final SQLStatement sqlStatement, final Map<RouteUnit, SQLRewriteUnit> sqlRewriteUnits) {Map<RouteUnit, SQLRewriteUnit> result = new LinkedHashMap<>(sqlRewriteUnits.size(), 1F);for (Entry<RouteUnit, SQLRewriteUnit> entry : sqlRewriteUnits.entrySet()) {DatabaseType storageType = storageTypes.get(entry.getKey().getDataSourceMapper().getActualName());String sql = translatorRule.translate(entry.getValue().getSql(), sqlStatement, protocolType, storageType);SQLRewriteUnit sqlRewriteUnit = new SQLRewriteUnit(sql, entry.getValue().getParameters());result.put(entry.getKey(), sqlRewriteUnit);}return result;}
addSQLRewriteUnits是往sqlRewriteUnits添加SQLRewriteUnit，最后translate方法构建SQLRewriteUnit；SQLRewriteUnit包含了更改之后的sql以及对应改动后的参数
useDriverToExecuteUpdate
org/apache/shardingsphere/driver/jdbc/core/statement/ShardingSpherePreparedStatement.java
private int useDriverToExecuteUpdate() throws SQLException {ExecutionGroupContext<JDBCExecutionUnit> executionGroupContext = createExecutionGroupContext();cacheStatements(executionGroupContext.getInputGroups());return executor.getRegularExecutor().executeUpdate(executionGroupContext,executionContext.getQueryContext(), executionContext.getRouteContext().getRouteUnits(), createExecuteUpdateCallback());}private ExecutionGroupContext<JDBCExecutionUnit> createExecutionGroupContext() throws SQLException {DriverExecutionPrepareEngine<JDBCExecutionUnit, Connection> prepareEngine = createDriverExecutionPrepareEngine();return prepareEngine.prepare(executionContext.getRouteContext(), executionContext.getExecutionUnits(), new ExecutionGroupReportContext(connection.getDatabaseName()));} private void cacheStatements(final Collection<ExecutionGroup<JDBCExecutionUnit>> executionGroups) throws SQLException {for (ExecutionGroup<JDBCExecutionUnit> each : executionGroups) {each.getInputs().forEach(eachInput -> {statements.add((PreparedStatement) eachInput.getStorageResource());parameterSets.add(eachInput.getExecutionUnit().getSqlUnit().getParameters());});}replay();}private void replay() throws SQLException {replaySetParameter();for (Statement each : statements) {getMethodInvocationRecorder().replay(each);}}private void replaySetParameter() throws SQLException {for (int i = 0; i < statements.size(); i++) {replaySetParameter(statements.get(i), parameterSets.get(i));}}protected final void replaySetParameter(final PreparedStatement preparedStatement, final List<Object> params) throws SQLException {setParameterMethodInvocations.clear();addParameters(params);for (PreparedStatementInvocationReplayer each : setParameterMethodInvocations) {each.replayOn(preparedStatement);}}private void addParameters(final List<Object> params) {int i = 0;for (Object each : params) {int index = ++i;setParameterMethodInvocations.add(preparedStatement -> preparedStatement.setObject(index, each));}}
useDriverToExecuteUpdate方法会执行createExecutionGroupContext(
会执行prepare方法)，cacheStatements这里主要是把eachInput.getStorageResource()真正的PrepareStatement赋值到ShardingSpherePreparedStatement的statements变量中，把eachInput.getExecutionUnit().getSqlUnit().getParameters()赋值到parameterSets，然后执行replay方法通过PreparedStatementInvocationReplayer把修改后的变量replay到真正的PrepareStatement
该方法委托给executor.getRegularExecutor().executeUpdate，最后一个参数为callback，即createExecuteUpdateCallback
DriverExecutionPrepareEngine.prepare
org/apache/shardingsphere/infra/executor/sql/prepare/AbstractExecutionPrepareEngine.java
public final ExecutionGroupContext<T> prepare(final RouteContext routeContext, final Collection<ExecutionUnit> executionUnits,final ExecutionGroupReportContext reportContext) throws SQLException {return prepare(routeContext, Collections.emptyMap(), executionUnits, reportContext);}public final ExecutionGroupContext<T> prepare(final RouteContext routeContext, final Map<String, Integer> connectionOffsets, final Collection<ExecutionUnit> executionUnits,final ExecutionGroupReportContext reportContext) throws SQLException {Collection<ExecutionGroup<T>> result = new LinkedList<>();for (Entry<String, List<SQLUnit>> entry : aggregateSQLUnitGroups(executionUnits).entrySet()) {String dataSourceName = entry.getKey();List<SQLUnit> sqlUnits = entry.getValue();List<List<SQLUnit>> sqlUnitGroups = group(sqlUnits);ConnectionMode connectionMode = maxConnectionsSizePerQuery < sqlUnits.size() ? ConnectionMode.CONNECTION_STRICTLY : ConnectionMode.MEMORY_STRICTLY;result.addAll(group(dataSourceName, connectionOffsets.getOrDefault(dataSourceName, 0), sqlUnitGroups, connectionMode));}return decorate(routeContext, result, reportContext);}protected List<ExecutionGroup<T>> group(final String dataSourceName, final int connectionOffset, final List<List<SQLUnit>> sqlUnitGroups, final ConnectionMode connectionMode) throws SQLException {List<ExecutionGroup<T>> result = new LinkedList<>();List<C> connections = databaseConnectionManager.getConnections(dataSourceName, connectionOffset, sqlUnitGroups.size(), connectionMode);int count = 0;for (List<SQLUnit> each : sqlUnitGroups) {result.add(createExecutionGroup(dataSourceName, each, connections.get(count++), connectionMode));}return result;}private ExecutionGroup<T> createExecutionGroup(final String dataSourceName, final List<SQLUnit> sqlUnits, final C connection, final ConnectionMode connectionMode) throws SQLException {List<T> result = new LinkedList<>();for (SQLUnit each : sqlUnits) {result.add((T) sqlExecutionUnitBuilder.build(new ExecutionUnit(dataSourceName, each), statementManager, connection, connectionMode, option, databaseTypes.get(dataSourceName)));}return new ExecutionGroup<>(result);}
group方法调用遍历SQLUnit执行createExecutionGroup，而后者则执行sqlExecutionUnitBuilder.build；这里databaseConnectionManager.getConnections获取的connection是通过真正driver获取的connection(
com.mysql.jdbc.Driver)
PreparedStatementExecutionUnitBuilder
org/apache/shardingsphere/infra/executor/sql/prepare/driver/jdbc/builder/PreparedStatementExecutionUnitBuilder.java
public JDBCExecutionUnit build(final ExecutionUnit executionUnit, final ExecutorJDBCStatementManager statementManager,final Connection connection, final ConnectionMode connectionMode, final StatementOption option, final DatabaseType databaseType) throws SQLException {PreparedStatement preparedStatement = createPreparedStatement(executionUnit, statementManager, connection, connectionMode, option, databaseType);return new JDBCExecutionUnit(executionUnit, connectionMode, preparedStatement);}private PreparedStatement createPreparedStatement(final ExecutionUnit executionUnit, final ExecutorJDBCStatementManager statementManager, final Connection connection,final ConnectionMode connectionMode, final StatementOption option, final DatabaseType databaseType) throws SQLException {return (PreparedStatement) statementManager.createStorageResource(executionUnit, connection, connectionMode, option, databaseType);}
PreparedStatementExecutionUnitBuilder的build方法这里才真正创建PreparedStatement
StatementManager
org/apache/shardingsphere/driver/jdbc/core/statement/StatementManager.java
public Statement createStorageResource(final ExecutionUnit executionUnit, final Connection connection, final ConnectionMode connectionMode, final StatementOption option,final DatabaseType databaseType) throws SQLException {Statement result = cachedStatements.get(new CacheKey(executionUnit, connectionMode));if (null == result || result.isClosed() || result.getConnection().isClosed()) {String sql = executionUnit.getSqlUnit().getSql();if (option.isReturnGeneratedKeys()) {result = null == option.getColumns() || 0 == option.getColumns().length? connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS): connection.prepareStatement(sql, option.getColumns());} else {result = connection.prepareStatement(sql, option.getResultSetType(), option.getResultSetConcurrency(), option.getResultSetHoldability());}cachedStatements.put(new CacheKey(executionUnit, connectionMode), result);}return result;}
createStorageResource则是通过connection.prepareStatement来创建真正的PrepareStatement，而此时传入的sql也是经过重写之后的sql
createExecuteUpdateCallback
org/apache/shardingsphere/driver/jdbc/core/statement/ShardingSpherePreparedStatement.java
private JDBCExecutorCallback<Integer> createExecuteUpdateCallback() {boolean isExceptionThrown = SQLExecutorExceptionHandler.isExceptionThrown();return new JDBCExecutorCallback<Integer>(metaDataContexts.getMetaData().getDatabase(connection.getDatabaseName()).getProtocolType(),metaDataContexts.getMetaData().getDatabase(connection.getDatabaseName()).getResourceMetaData().getStorageTypes(), sqlStatement, isExceptionThrown) {@Overrideprotected Integer executeSQL(final String sql, final Statement statement, final ConnectionMode connectionMode, final DatabaseType storageType) throws SQLException {return ((PreparedStatement) statement).executeUpdate();}@Overrideprotected Optional<Integer> getSaneResult(final SQLStatement sqlStatement, final SQLException ex) {return Optional.empty();}};}
createExecuteUpdateCallback创建的JDBCExecutorCallback，其executeSQL方法则是通过((PreparedStatement) statement).executeUpdate()来执行，即委托给了真正的PreparedStatement
小结
- ShardingSphereConnection的prepareStatement创建的是ShardingSpherePreparedStatement，它在ShardingSpherePreparedStatement的executeUpdate的时候进行sql重写，然后prepare，最后执行的时候是通过JDBCExecutorCallback，其executeSQL方法则是通过((PreparedStatement) statement).executeUpdate()来执行，即委托给了真正的PreparedStatement
- rewriteParameters是通过ParameterRewriter进行rewrite，主要是修改ParameterBuilder；而具体sql语句的修改则通过sqlTokenGenerators进行
- PreparedStatementExecutionUnitBuilder的build方法这里才真正创建PreparedStatement：它通过StatementManager.createStorageResource则是通过connection.prepareStatement来创建真正的PrepareStatement，而此时传入的sql也是经过重写之后的sql
- useDriverToExecuteUpdate方法会执行createExecutionGroupContext(
会执行prepare方法)，cacheStatements这里主要是把eachInput.getStorageResource()真正的PrepareStatement赋值到ShardingSpherePreparedStatement的statements变量中，把eachInput.getExecutionUnit().getSqlUnit().getParameters()赋值到parameterSets，然后执行replay方法通过PreparedStatementInvocationReplayer把修改后的变量replay到真正的PrepareStatement
ShardingSpherePreparedStatement实现了java.sql.PreparedStatement接口，其sql属性是用户传入的sql，即未经过重写的sql，而实际execute的时候，会触发sql重写(包括重写sql语句及参数)，最后会通过connection.prepareStatement(传入重写之后的sql)来创建真正的PrepareStatement，然后有一步replay操作，把重写后的参数作用到真正的PrepareStatement，最后通过((PreparedStatement) statement).executeUpdate()来触发执行
至此我们可以得到sql重写的一个基本思路：通过实现java.sql.PreparedStatement接口伪装一个PreparedStatement类，其创建和set参数先内存缓存起来，之后在execute的时候进行sql重写，创建真正的PreparedStatement，replay参数，执行execute方法
