Mysql JDBC驱动源码分析(Statement,ResultSet的创建)四

一，当连接创建完成时，接着就创建Statement进行sql查询，并返回相应的ResultSet

进入ConnectionImpl类下的，createStatement(..)

 

 

	
public java.sql.Statement createStatement(int resultSetType,
			int resultSetConcurrency, int resultSetHoldability)
			throws SQLException {
               //对返回的结果集进行指定相应的模式功能,可参照ResultSet的常量设置
		if (getPedantic()) {
			if (resultSetHoldability != java.sql.ResultSet.HOLD_CURSORS_OVER_COMMIT) {
				throw SQLError.createSQLException(
						"HOLD_CUSRORS_OVER_COMMIT is only supported holdability level",
						SQLError.SQL_STATE_ILLEGAL_ARGUMENT, getExceptionInterceptor());
			}
		}

		return createStatement(resultSetType, resultSetConcurrency);
	}





public java.sql.Statement createStatement(int resultSetType,
			int resultSetConcurrency) throws SQLException {
		checkClosed();
                //getLoadBalanceSafeProxy() 为相应的连接
		StatementImpl stmt = new 
StatementImpl(getLoadBalanceSafeProxy(), this.database);
		stmt.setResultSetType(resultSetType);
		stmt.setResultSetConcurrency(resultSetConcurrency);

		return stmt;
	}

 

进入StatementImpl .executeQuery(..)

 

public synchronized java.sql.ResultSet executeQuery(String sql)
			throws SQLException {
		checkClosed();
		//参数所传的连接对象
		MySQLConnection locallyScopedConn = this.connection;

		synchronized (locallyScopedConn) {
			this.retrieveGeneratedKeys = false;
			
			resetCancelledState();

			checkNullOrEmptyQuery(sql);

			//We only stream result sets when they are forward-only, read-only, and thefetch size has been set to Integer.MIN_VALUE
			boolean doStreaming = createStreamingResultSet();


			if (doStreaming
					&& this.connection.getNetTimeoutForStreamingResults() > 0) {
				executeSimpleNonQuery(locallyScopedConn, "SET net_write_timeout="
						+ this.connection.getNetTimeoutForStreamingResults());
			}

			if (this.doEscapeProcessing) {
				Object escapedSqlResult = EscapeProcessor.escapeSQL(sql,
						locallyScopedConn.serverSupportsConvertFn(), this.connection);

				if (escapedSqlResult instanceof String) {
					sql = (String) escapedSqlResult;
				} else {
					sql = ((EscapeProcessorResult) escapedSqlResult).escapedSql;
				}
			}

			char firstStatementChar = StringUtils.firstNonWsCharUc(sql,
					findStartOfStatement(sql));

			if (sql.charAt(0) == '/') {
				if (sql.startsWith(PING_MARKER)) {
					doPingInstead();
				
					return this.results;
				}
			}
			
			checkForDml(sql, firstStatementChar);

			if (this.results != null) {
				if (!locallyScopedConn.getHoldResultsOpenOverStatementClose()) {
					this.results.realClose(false);
				}
			}

			CachedResultSetMetaData cachedMetaData = null;

			// If there isn't a limit clause in the SQL
			// then limit the number of rows to return in
			// an efficient manner. Only do this if
			// setMaxRows() hasn't been used on any Statements
			// generated from the current Connection (saves
			// a query, and network traffic).

			if (useServerFetch()) {
				this.results = createResultSetUsingServerFetch(sql);

				return this.results;
			}

			CancelTask timeoutTask = null;

			String oldCatalog = null;

			try {
				if (locallyScopedConn.getEnableQueryTimeouts() &&
						this.timeoutInMillis != 0
						&& locallyScopedConn.versionMeetsMinimum(5, 0, 0)) {
					timeoutTask = new CancelTask(this);
					locallyScopedConn.getCancelTimer().schedule(timeoutTask,
							this.timeoutInMillis);
				}

				if (!locallyScopedConn.getCatalog().equals(this.currentCatalog)) {
					oldCatalog = locallyScopedConn.getCatalog();
					locallyScopedConn.setCatalog(this.currentCatalog);
				}

				//
				// Check if we have cached metadata for this query...
				//

				Field[] cachedFields = null;

				//是否应用缓存ResultSet
				if (locallyScopedConn.getCacheResultSetMetadata()) {
					cachedMetaData = locallyScopedConn.getCachedMetaData(sql);

					if (cachedMetaData != null) {
						cachedFields = cachedMetaData.fields;
					}
				}

				if (locallyScopedConn.useMaxRows()) {
					// We need to execute this all together
					// So synchronize on the Connection's mutex (because
					// even queries going through there synchronize
					// on the connection
					if (StringUtils.indexOfIgnoreCase(sql, "LIMIT") != -1) { //$NON-NLS-1$
						this.results = locallyScopedConn.execSQL(this, sql,
								this.maxRows, null, this.resultSetType,
								this.resultSetConcurrency,
								doStreaming,
								this.currentCatalog, cachedFields);
					} else {
						if (this.maxRows <= 0) {
							executeSimpleNonQuery(locallyScopedConn,
									"SET OPTION SQL_SELECT_LIMIT=DEFAULT");
						} else {
							executeSimpleNonQuery(locallyScopedConn,
											"SET OPTION SQL_SELECT_LIMIT=" + this.maxRows);
						}

						statementBegins();
						
						this.results = locallyScopedConn.execSQL(this, sql, -1,
								null, this.resultSetType,
								this.resultSetConcurrency,
								doStreaming,
								this.currentCatalog, cachedFields);

						if (oldCatalog != null) {
							locallyScopedConn.setCatalog(oldCatalog);
						}
					}
				} else {
					statementBegins();
					//ConnectionImpl中执行sql语句
					this.results = locallyScopedConn.execSQL(this, sql, -1, null,
							this.resultSetType, this.resultSetConcurrency,
							doStreaming,
							this.currentCatalog, cachedFields);
				}

				if (timeoutTask != null) {
					if (timeoutTask.caughtWhileCancelling != null) {
						throw timeoutTask.caughtWhileCancelling;
					}

					timeoutTask.cancel();
					
					locallyScopedConn.getCancelTimer().purge();
					
					timeoutTask = null;
				}

				synchronized (this.cancelTimeoutMutex) {
					if (this.wasCancelled) {
						SQLException cause = null;
						
						if (this.wasCancelledByTimeout) {
							cause = new MySQLTimeoutException();
						} else {
							cause = new MySQLStatementCancelledException();
						}
						
						resetCancelledState();
						
						throw cause;
					}
				}
			} finally {
				this.statementExecuting.set(false);
				
				if (timeoutTask != null) {
					timeoutTask.cancel();
					
					locallyScopedConn.getCancelTimer().purge();
				}

				if (oldCatalog != null) {
					locallyScopedConn.setCatalog(oldCatalog);
				}
			}

			this.lastInsertId = this.results.getUpdateID();

			if (cachedMetaData != null) {
				locallyScopedConn.initializeResultsMetadataFromCache(sql, cachedMetaData,
						this.results);
			} else {
				if (this.connection.getCacheResultSetMetadata()) {
					locallyScopedConn.initializeResultsMetadataFromCache(sql,
							null /* will be created */, this.results);
				}
			}

			return this.results;
		}
	}

  进入ConnectionImpl.execSQl(..)

 

public synchronized ResultSetInternalMethods execSQL(StatementImpl callingStatement, String sql, int maxRows,
			Buffer packet, int resultSetType, int resultSetConcurrency,
			boolean streamResults, String catalog,
			Field[] cachedMetadata,
			boolean isBatch) throws SQLException {

		long queryStartTime = 0;

		int endOfQueryPacketPosition = 0;

		if (packet != null) {
			endOfQueryPacketPosition = packet.getPosition();
		}

		if (getGatherPerformanceMetrics()) {
			queryStartTime = System.currentTimeMillis();
		}

		this.lastQueryFinishedTime = 0; // we're busy!

		if ((getHighAvailability())
				&& (this.autoCommit || getAutoReconnectForPools())
				&& this.needsPing && !isBatch) {
			try {
				pingInternal(false, 0);

				this.needsPing = false;
			} catch (Exception Ex) {
				createNewIO(true);
			}
		}

		try {
			if (packet == null) {
				String encoding = null;

				if (getUseUnicode()) {
					encoding = getEncoding();
				}
				//进入MysqlIO中执行查询操作
				return this.io.sqlQueryDirect(callingStatement, sql,
						encoding, null, maxRows, resultSetType,
						resultSetConcurrency, streamResults, catalog,
						cachedMetadata);
			}

			return this.io.sqlQueryDirect(callingStatement, null, null,
					packet, maxRows, resultSetType,
					resultSetConcurrency, streamResults, catalog,
					cachedMetadata);
		} catch (java.sql.SQLException sqlE) {
			// don't clobber SQL exceptions

			if (getDumpQueriesOnException()) {
				String extractedSql = extractSqlFromPacket(sql, packet,
						endOfQueryPacketPosition);
				StringBuffer messageBuf = new StringBuffer(extractedSql
						.length() + 32);
				messageBuf
						.append("\n\nQuery being executed when exception was thrown:\n");
				messageBuf.append(extractedSql);
				messageBuf.append("\n\n");

				sqlE = appendMessageToException(sqlE, messageBuf.toString(), getExceptionInterceptor());
			}

			if ((getHighAvailability())) {
				this.needsPing = true;
			} else {
				String sqlState = sqlE.getSQLState();

				if ((sqlState != null)
						&& sqlState
								.equals(SQLError.SQL_STATE_COMMUNICATION_LINK_FAILURE)) {
					cleanup(sqlE);
				}
			}

			throw sqlE;
		} catch (Exception ex) {
			if (getHighAvailability()) {
				this.needsPing = true;
			} else if (ex instanceof IOException) {
				cleanup(ex);
			}

			SQLException sqlEx = SQLError.createSQLException(
					Messages.getString("Connection.UnexpectedException"),
					SQLError.SQL_STATE_GENERAL_ERROR, getExceptionInterceptor());
			sqlEx.initCause(ex);
			
			throw sqlEx;
		} finally {
			if (getMaintainTimeStats()) {
				this.lastQueryFinishedTime = System.currentTimeMillis();
			}


			if (getGatherPerformanceMetrics()) {
				long queryTime = System.currentTimeMillis()
						- queryStartTime;

				registerQueryExecutionTime(queryTime);
			}
		}
	}

 

 

进入MysqlIO.sqlQueryDirect(..)中执行生成ResultSet

 

  final ResultSetInternalMethods sqlQueryDirect(StatementImpl callingStatement, String query,
    		String characterEncoding, Buffer queryPacket, int maxRows,
    		int resultSetType, int resultSetConcurrency,
    		boolean streamResults, String catalog, Field[] cachedMetadata)
    throws Exception {
    	this.statementExecutionDepth++;

    	try {
	    	if (this.statementInterceptors != null) {
	    		ResultSetInternalMethods interceptedResults =
	    			invokeStatementInterceptorsPre(query, callingStatement, false);

	    		if (interceptedResults != null) {
	    			return interceptedResults;
	    		}
	    	}

	    	long queryStartTime = 0;
	    	long queryEndTime = 0;

    		String statementComment = this.connection.getStatementComment();
    		
    		if (this.connection.getIncludeThreadNamesAsStatementComment()) {
    			statementComment = (statementComment != null ? statementComment + ", " : "") + "java thread: " + Thread.currentThread().getName();
    		}
    		
	    	if (query != null) {
	    		// We don't know exactly how many bytes we're going to get
	    		// from the query. Since we're dealing with Unicode, the
	    		// max is 2, so pad it (2 * query) + space for headers
	    		int packLength = HEADER_LENGTH + 1 + (query.length() * 2) + 2;

	    		byte[] commentAsBytes = null;

	    		if (statementComment != null) {
	    			commentAsBytes = StringUtils.getBytes(statementComment, null,
	    					characterEncoding, this.connection
	    					.getServerCharacterEncoding(),
	    					this.connection.parserKnowsUnicode(), getExceptionInterceptor());

	    			packLength += commentAsBytes.length;
	    			packLength += 6; // for /*[space] [space]*/
	    		}
			//sendPacket封装数据的包，发送至服务器
	    		if (this.sendPacket == null) {
	    			this.sendPacket = new Buffer(packLength);
	    		} else {
	    			this.sendPacket.clear();
	    		}

	    		this.sendPacket.writeByte((byte) MysqlDefs.QUERY);

	    		if (commentAsBytes != null) {
	    			this.sendPacket.writeBytesNoNull(Constants.SLASH_STAR_SPACE_AS_BYTES);
	    			this.sendPacket.writeBytesNoNull(commentAsBytes);
	    			this.sendPacket.writeBytesNoNull(Constants.SPACE_STAR_SLASH_SPACE_AS_BYTES);
	    		}

	    		if (characterEncoding != null) {
	    			if (this.platformDbCharsetMatches) {
	    				this.sendPacket.writeStringNoNull(query, characterEncoding,
	    						this.connection.getServerCharacterEncoding(),
	    						this.connection.parserKnowsUnicode(),
	    						this.connection);
	    			} else {
	    				if (StringUtils.startsWithIgnoreCaseAndWs(query, "LOAD DATA")) { //$NON-NLS-1$
	    					this.sendPacket.writeBytesNoNull(StringUtils.getBytes(query));
	    				} else {
	    					this.sendPacket.writeStringNoNull(query,
	    							characterEncoding,
	    							this.connection.getServerCharacterEncoding(),
	    							this.connection.parserKnowsUnicode(),
	    							this.connection);
	    				}
	    			}
	    		} else {
	    			this.sendPacket.writeStringNoNull(query);
	    		}
                         //赋值
	    		queryPacket = this.sendPacket;
	    	}

	    	byte[] queryBuf = null;
	    	int oldPacketPosition = 0;

	    	if (needToGrabQueryFromPacket) {
	    		queryBuf = queryPacket.getByteBuffer();

	    		// save the packet position
	    		oldPacketPosition = queryPacket.getPosition();

	    		queryStartTime = getCurrentTimeNanosOrMillis();
	    	}
	    	
	    	if (this.autoGenerateTestcaseScript) {
	    		String testcaseQuery = null;

	    		if (query != null) {
	    			if (statementComment != null) {
	    				testcaseQuery = "/* " + statementComment + " */ " + query;
	    			} else {
	    				testcaseQuery = query;
	    			}
	    		} else {
	    			testcaseQuery = StringUtils.toString(queryBuf, 5,
	    					(oldPacketPosition - 5));
	    		}

	    		StringBuffer debugBuf = new StringBuffer(testcaseQuery.length() + 32);
	    		this.connection.generateConnectionCommentBlock(debugBuf);
	    		debugBuf.append(testcaseQuery);
	    		debugBuf.append(';');
	    		this.connection.dumpTestcaseQuery(debugBuf.toString());
	    	}

	    	// Send query command and sql query string
                //发送查询命与sql查询语句，并得到查询结果(socket处理)
	    	Buffer resultPacket = sendCommand(MysqlDefs.QUERY, null, queryPacket,
	    			false, null, 0);

	    	long fetchBeginTime = 0;
	    	long fetchEndTime = 0;

	    	String profileQueryToLog = null;

	    	boolean queryWasSlow = false;

	    	if (this.profileSql || this.logSlowQueries) {
	    		queryEndTime = System.currentTimeMillis();

	    		boolean shouldExtractQuery = false;

	    		if (this.profileSql) {
	    			shouldExtractQuery = true;
	    		} else if (this.logSlowQueries) {
	    			long queryTime = queryEndTime - queryStartTime;
	    			
	    			boolean logSlow = false;
	    			
	    			if (this.useAutoSlowLog) {
	    				logSlow = queryTime > this.connection.getSlowQueryThresholdMillis();
	    			} else {
	    				logSlow = this.connection.isAbonormallyLongQuery(queryTime);
	    				
	    				this.connection.reportQueryTime(queryTime);
	    			}
	    			
	    			if (logSlow) {
	    				shouldExtractQuery = true;
	    				queryWasSlow = true;
	    			}
	    		}

	    		if (shouldExtractQuery) {
	    			// Extract the actual query from the network packet
	    			boolean truncated = false;

	    			int extractPosition = oldPacketPosition;

	    			if (oldPacketPosition > this.connection.getMaxQuerySizeToLog()) {
	    				extractPosition = this.connection.getMaxQuerySizeToLog() + 5;
	    				truncated = true;
	    			}

	    			profileQueryToLog = StringUtils.toString(queryBuf, 5,
	    					(extractPosition - 5));

	    			if (truncated) {
	    				profileQueryToLog += Messages.getString("MysqlIO.25"); //$NON-NLS-1$
	    			}
	    		}

	    		fetchBeginTime = queryEndTime;
	    	}
                //封装成ResultSet
	    	ResultSetInternalMethods rs = readAllResults(callingStatement, maxRows, resultSetType,
	    			resultSetConcurrency, streamResults, catalog, resultPacket,
	    			false, -1L, cachedMetadata);

	    	if (queryWasSlow && !this.serverQueryWasSlow /* don't log slow queries twice */) {
	    		StringBuffer mesgBuf = new StringBuffer(48 +
	    				profileQueryToLog.length());

	    		mesgBuf.append(Messages.getString("MysqlIO.SlowQuery",
	    				new Object[] {Long.valueOf(this.slowQueryThreshold),
	    				queryTimingUnits,
	    				Long.valueOf(queryEndTime - queryStartTime)}));
	    		mesgBuf.append(profileQueryToLog);

	    		ProfilerEventHandler eventSink = ProfilerEventHandlerFactory.getInstance(this.connection);

	    		eventSink.consumeEvent(new ProfilerEvent(ProfilerEvent.TYPE_SLOW_QUERY,
	    				"", catalog, this.connection.getId(), //$NON-NLS-1$
	    				(callingStatement != null) ? callingStatement.getId() : 999,
	    						((ResultSetImpl)rs).resultId, System.currentTimeMillis(),
	    						(int) (queryEndTime - queryStartTime), queryTimingUnits, null,
	    						new Throwable(), mesgBuf.toString()));

	    		if (this.connection.getExplainSlowQueries()) {
	    			if (oldPacketPosition < MAX_QUERY_SIZE_TO_EXPLAIN) {
	    				explainSlowQuery(queryPacket.getBytes(5,
	    						(oldPacketPosition - 5)), profileQueryToLog);
	    			} else {
	    				this.connection.getLog().logWarn(Messages.getString(
	    						"MysqlIO.28") //$NON-NLS-1$
	    						+MAX_QUERY_SIZE_TO_EXPLAIN +
	    						Messages.getString("MysqlIO.29")); //$NON-NLS-1$
	    			}
	    		}
	    	}

	    	if (this.logSlowQueries) {

	    		ProfilerEventHandler eventSink = ProfilerEventHandlerFactory.getInstance(this.connection);

	    		if (this.queryBadIndexUsed && this.profileSql) {
	    			eventSink.consumeEvent(new ProfilerEvent(
	    					ProfilerEvent.TYPE_SLOW_QUERY, "", catalog, //$NON-NLS-1$
	    					this.connection.getId(),
	    					(callingStatement != null) ? callingStatement.getId()
	    							: 999, ((ResultSetImpl)rs).resultId,
	    							System.currentTimeMillis(),
	    							(queryEndTime - queryStartTime), this.queryTimingUnits,
	    							null,
	    							new Throwable(),
	    							Messages.getString("MysqlIO.33") //$NON-NLS-1$
	    							+profileQueryToLog));
	    		}

	    		if (this.queryNoIndexUsed && this.profileSql) {
	    			eventSink.consumeEvent(new ProfilerEvent(
	    					ProfilerEvent.TYPE_SLOW_QUERY, "", catalog, //$NON-NLS-1$
	    					this.connection.getId(),
	    					(callingStatement != null) ? callingStatement.getId()
	    							: 999, ((ResultSetImpl)rs).resultId,
	    							System.currentTimeMillis(),
	    							(queryEndTime - queryStartTime), this.queryTimingUnits,
	    							null,
	    							new Throwable(),
	    							Messages.getString("MysqlIO.35") //$NON-NLS-1$
	    							+profileQueryToLog));
	    		}
	    		
	    		if (this.serverQueryWasSlow && this.profileSql) {
	    			eventSink.consumeEvent(new ProfilerEvent(
	    					ProfilerEvent.TYPE_SLOW_QUERY, "", catalog, //$NON-NLS-1$
	    					this.connection.getId(),
	    					(callingStatement != null) ? callingStatement.getId()
	    							: 999, ((ResultSetImpl)rs).resultId,
	    							System.currentTimeMillis(),
	    							(queryEndTime - queryStartTime), this.queryTimingUnits,
	    							null,
	    							new Throwable(),
	    							Messages.getString("MysqlIO.ServerSlowQuery") //$NON-NLS-1$
	    							+profileQueryToLog));
	    		}
	    	}

	    	if (this.profileSql) {
	    		fetchEndTime = getCurrentTimeNanosOrMillis();

	    		ProfilerEventHandler eventSink = ProfilerEventHandlerFactory.getInstance(this.connection);

	    		eventSink.consumeEvent(new ProfilerEvent(ProfilerEvent.TYPE_QUERY,
	    				"", catalog, this.connection.getId(), //$NON-NLS-1$
	    				(callingStatement != null) ? callingStatement.getId() : 999,
	    						((ResultSetImpl)rs).resultId, System.currentTimeMillis(),
	    						(queryEndTime - queryStartTime), this.queryTimingUnits,
	    						null,
	    						new Throwable(), profileQueryToLog));

	    		eventSink.consumeEvent(new ProfilerEvent(ProfilerEvent.TYPE_FETCH,
	    				"", catalog, this.connection.getId(), //$NON-NLS-1$
	    				(callingStatement != null) ? callingStatement.getId() : 999,
	    						((ResultSetImpl)rs).resultId, System.currentTimeMillis(),
	    						(fetchEndTime - fetchBeginTime), this.queryTimingUnits,
	    						null,
	    						new Throwable(), null));
	    	}

	    	if (this.hadWarnings) {
	    		scanForAndThrowDataTruncation();
	    	}

	    	if (this.statementInterceptors != null) {
	    		ResultSetInternalMethods interceptedResults = invokeStatementInterceptorsPost(
	    				query, callingStatement, rs, false, null);

	    		if (interceptedResults != null) {
	    			rs = interceptedResults;
	    		}
	    	}

	    	return rs;
    	} catch (SQLException sqlEx) {
    		if (this.statementInterceptors != null) {
	    		invokeStatementInterceptorsPost(
	    				query, callingStatement, null, false, sqlEx); // we don't do anything with the result set in this case
    		}
    		
    		if (callingStatement != null) {
    			synchronized (callingStatement.cancelTimeoutMutex) {
	    			if (callingStatement.wasCancelled) {
						SQLException cause = null;
						
						if (callingStatement.wasCancelledByTimeout) {
							cause = new MySQLTimeoutException();
						} else {
							cause = new MySQLStatementCancelledException();
						}
						
						callingStatement.resetCancelledState();
						
						throw cause;
					}
    			}
    		}
    		
    		throw sqlEx;
    	} finally {
    		this.statementExecutionDepth--;
    	}
    }

 MysqlIO.readAllResults(..)处理生成ResultSet

 ResultSetImpl readAllResults(StatementImpl callingStatement, int maxRows,
        int resultSetType, int resultSetConcurrency, boolean streamResults,
        String catalog, Buffer resultPacket, boolean isBinaryEncoded,
        long preSentColumnCount, Field[] metadataFromCache)
        throws SQLException {
        //设置指针
        resultPacket.setPosition(resultPacket.getPosition() - 1);

        //读取第一条数据
        ResultSetImpl topLevelResultSet = readResultsForQueryOrUpdate(callingStatement,
                maxRows, resultSetType, resultSetConcurrency, streamResults,
                catalog, resultPacket, isBinaryEncoded, preSentColumnCount,
                metadataFromCache);

        ResultSetImpl currentResultSet = topLevelResultSet;

        boolean checkForMoreResults = ((this.clientParam &
            CLIENT_MULTI_RESULTS) != 0);

        boolean serverHasMoreResults = (this.serverStatus &
            SERVER_MORE_RESULTS_EXISTS) != 0;

        //
        // TODO: We need to support streaming of multiple result sets
        //
        if (serverHasMoreResults && streamResults) {
            //clearInputStream();
//
            //throw SQLError.createSQLException(Messages.getString("MysqlIO.23"), //$NON-NLS-1$
                //SQLError.SQL_STATE_DRIVER_NOT_CAPABLE);
        	if (topLevelResultSet.getUpdateCount() != -1) {
        		tackOnMoreStreamingResults(topLevelResultSet);
        	}
        	
        	reclaimLargeReusablePacket();
        	
        	return topLevelResultSet;
        }

        boolean moreRowSetsExist = checkForMoreResults & serverHasMoreResults;

        while (moreRowSetsExist) {
        	Buffer fieldPacket = checkErrorPacket();
            fieldPacket.setPosition(0);

            ResultSetImpl newResultSet = readResultsForQueryOrUpdate(callingStatement,
                    maxRows, resultSetType, resultSetConcurrency,
                    streamResults, catalog, fieldPacket, isBinaryEncoded,
                    preSentColumnCount, metadataFromCache);

            currentResultSet.setNextResultSet(newResultSet);

            currentResultSet = newResultSet;

            moreRowSetsExist = (this.serverStatus & SERVER_MORE_RESULTS_EXISTS) != 0;
        }

        if (!streamResults) {
            clearInputStream();
        }

        reclaimLargeReusablePacket();

        return topLevelResultSet;
    }

=============================
 protected final ResultSetImpl readResultsForQueryOrUpdate(
        StatementImpl callingStatement, int maxRows, int resultSetType,
        int resultSetConcurrency, boolean streamResults, String catalog,
        Buffer resultPacket, boolean isBinaryEncoded, long preSentColumnCount,
        Field[] metadataFromCache) throws SQLException {
        long columnCount = resultPacket.readFieldLength();

        if (columnCount == 0) {
            return buildResultSetWithUpdates(callingStatement, resultPacket);
        } else if (columnCount == Buffer.NULL_LENGTH) {
            String charEncoding = null;

            if (this.connection.getUseUnicode()) {
                charEncoding = this.connection.getEncoding();
            }

            String fileName = null;

            if (this.platformDbCharsetMatches) {
                fileName = ((charEncoding != null)
                    ? resultPacket.readString(charEncoding, getExceptionInterceptor())
                    : resultPacket.readString());
            } else {
                fileName = resultPacket.readString();
            }

            return sendFileToServer(callingStatement, fileName);
        } else {
            //获取结果集
            com.mysql.jdbc.ResultSetImpl results = getResultSet(callingStatement,
                    columnCount, maxRows, resultSetType, resultSetConcurrency,
                    streamResults, catalog, isBinaryEncoded,
                    metadataFromCache);

            return results;
        }
    }

=========================
    //对数据进行解析封装生成结果集
    protected ResultSetImpl getResultSet(StatementImpl callingStatement,
        long columnCount, int maxRows, int resultSetType,
        int resultSetConcurrency, boolean streamResults, String catalog,
        boolean isBinaryEncoded, Field[] metadataFromCache)
        throws SQLException {
        Buffer packet; // The packet from the server
        //字段数组
        Field[] fields = null;

        // Read in the column information

        if (metadataFromCache == null /* we want the metadata from the server */) {
            fields = new Field[(int) columnCount];

            for (int i = 0; i < columnCount; i++) {
            	Buffer fieldPacket = null;

                //循环处理
                fieldPacket = readPacket();
                fields[i] = unpackField(fieldPacket, false);
            }
        } else {
        	for (int i = 0; i < columnCount; i++) {
        		skipPacket();
        	}
        }
         //
        packet = reuseAndReadPacket(this.reusablePacket);
        
        readServerStatusForResultSets(packet);

		//
		// Handle cursor-based fetch first
		//

		if (this.connection.versionMeetsMinimum(5, 0, 2)
				&& this.connection.getUseCursorFetch()
				&& isBinaryEncoded
				&& callingStatement != null
				&& callingStatement.getFetchSize() != 0
				&& callingStatement.getResultSetType() == ResultSet.TYPE_FORWARD_ONLY) {
			ServerPreparedStatement prepStmt = (com.mysql.jdbc.ServerPreparedStatement) callingStatement;

			boolean usingCursor = true;

			//
			// Server versions 5.0.5 or newer will only open
			// a cursor and set this flag if they can, otherwise
			// they punt and go back to mysql_store_results() behavior
			//

			if (this.connection.versionMeetsMinimum(5, 0, 5)) {
				usingCursor = (this.serverStatus &
						SERVER_STATUS_CURSOR_EXISTS) != 0;
			}

			if (usingCursor) {
				RowData rows = new RowDataCursor(
					this,
					prepStmt,
					fields);

				ResultSetImpl rs = buildResultSetWithRows(
					callingStatement,
					catalog,
					fields,
					rows, resultSetType, resultSetConcurrency, isBinaryEncoded);

				if (usingCursor) {
		        	rs.setFetchSize(callingStatement.getFetchSize());
		        }

				return rs;
			}
		}

        RowData rowData = null;

        if (!streamResults) {
            //封装成RowData的数据
            rowData = readSingleRowSet(columnCount, maxRows,
                    resultSetConcurrency, isBinaryEncoded,
                    (metadataFromCache == null) ? fields : metadataFromCache);
        } else {
            rowData = new RowDataDynamic(this, (int) columnCount,
            		(metadataFromCache == null) ? fields : metadataFromCache,
                    isBinaryEncoded);
            this.streamingData = rowData;
        }

        //创建ResultSetImpl对象
        ResultSetImpl rs = buildResultSetWithRows(callingStatement, catalog,
        		(metadataFromCache == null) ? fields : metadataFromCache,
            rowData, resultSetType, resultSetConcurrency, isBinaryEncoded);



        return rs;
    }
==================================
   //对rowData的封装
   private RowData readSingleRowSet(long columnCount, int maxRows,
        int resultSetConcurrency, boolean isBinaryEncoded, Field[] fields)
        throws SQLException {
        RowData rowData;
        ArrayList rows = new ArrayList();

        boolean useBufferRowExplicit = useBufferRowExplicit(fields);

        // Now read the data
        //读取数据
        ResultSetRow row = nextRow(fields, (int) columnCount, isBinaryEncoded,
                resultSetConcurrency, false, useBufferRowExplicit, false, null);

        int rowCount = 0;

        if (row != null) {
            rows.add(row);
            rowCount = 1;
        }

        while (row != null) {
                //读取全部数据，封装至list
        	row = nextRow(fields, (int) columnCount, isBinaryEncoded,
                    resultSetConcurrency, false, useBufferRowExplicit, false, null);

            if (row != null) {
            	if ((maxRows == -1) || (rowCount < maxRows)) {
            		rows.add(row);
            		rowCount++;
            	}
            }
        }

        rowData = new RowDataStatic(rows);

        return rowData;
    }

=============================
   //创建ResultSetImpl对象
    private com.mysql.jdbc.ResultSetImpl buildResultSetWithRows(
        StatementImpl callingStatement, String catalog,
        com.mysql.jdbc.Field[] fields, RowData rows, int resultSetType,
        int resultSetConcurrency, boolean isBinaryEncoded)
        throws SQLException {
        ResultSetImpl rs = null;
 
        //根据所传的resultSet常量参数生成相应模式的ResultSetImpl
        switch (resultSetConcurrency) {
        case java.sql.ResultSet.CONCUR_READ_ONLY:
            rs = com.mysql.jdbc.ResultSetImpl.getInstance(catalog, fields, rows,
                    this.connection, callingStatement, false);

            if (isBinaryEncoded) {
                rs.setBinaryEncoded();
            }

            break;

        case java.sql.ResultSet.CONCUR_UPDATABLE:
            rs = com.mysql.jdbc.ResultSetImpl.getInstance(catalog, fields, rows,
                    this.connection, callingStatement, true);

            break;

        default:
            return com.mysql.jdbc.ResultSetImpl.getInstance(catalog, fields, rows,
                this.connection, callingStatement, false);
        }

        rs.setResultSetType(resultSetType);
        rs.setResultSetConcurrency(resultSetConcurrency);

        return rs;
    }