JDBC连接的获取： http://donald-draper.iteye.com/blog/2342011
Mysql负载均衡连接的获取： http://donald-draper.iteye.com/blog/2342089
Mysql主从复制读写分离连接的获取： http://donald-draper.iteye.com/blog/2342108
ConnectionImp创建MysqlIO ： http://donald-draper.iteye.com/blog/2342959
Mysql预编译SQL： http://donald-draper.iteye.com/blog/2342960
MysqlSQL PreparedStatement的查询: http://donald-draper.iteye.com/blog/2343083
MySQL ServerPreparedStatement查询： http://donald-draper.iteye.com/blog/2343124
前面几讲，说过mysql的连接获取，MysqlIO，今天来看一下MySQL的PreparedStatement查询
//ConnectionImpl
protected PreparedStatement clientPrepareStatement(String sql, int resultSetType, int resultSetConcurrency, boolean processEscapeCodesIfNeeded)
throws SQLException
{
checkClosed();
String nativeSql = !processEscapeCodesIfNeeded || !getProcessEscapeCodesForPrepStmts() ? sql : nativeSQL(sql);
com.mysql.jdbc.PreparedStatement pStmt = null;
if(getCachePreparedStatements())
synchronized(cachedPreparedStatementParams)
{
PreparedStatement.ParseInfo pStmtInfo = (PreparedStatement.ParseInfo)cachedPreparedStatementParams.get(nativeSql);
if(pStmtInfo == null)
{
pStmt = PreparedStatement.getInstance(this, nativeSql, database);
PreparedStatement.ParseInfo parseInfo = pStmt.getParseInfo();
if(parseInfo.statementLength < getPreparedStatementCacheSqlLimit())
{
if(cachedPreparedStatementParams.size() >= getPreparedStatementCacheSize())
{
Iterator oldestIter = cachedPreparedStatementParams.keySet().iterator();
long lruTime = 9223372036854775807L;
String oldestSql = null;
do
{
if(!oldestIter.hasNext())
break;
String sqlKey = (String)oldestIter.next();
PreparedStatement.ParseInfo lruInfo = (PreparedStatement.ParseInfo)cachedPreparedStatementParams.get(sqlKey);
if(lruInfo.lastUsed < lruTime)
{
lruTime = lruInfo.lastUsed;
oldestSql = sqlKey;
}
} while(true);
if(oldestSql != null)
cachedPreparedStatementParams.remove(oldestSql);
}
cachedPreparedStatementParams.put(nativeSql, pStmt.getParseInfo());
}
} else
{
pStmtInfo.lastUsed = System.currentTimeMillis();
pStmt = new com.mysql.jdbc.PreparedStatement(this, nativeSql, database, pStmtInfo);
}
}
else
//如果没有缓存，获取PreparedStatement实例
pStmt = PreparedStatement.getInstance(this, nativeSql, database);
pStmt.setResultSetType(resultSetType);
pStmt.setResultSetConcurrency(resultSetConcurrency);
return pStmt;
}
来看PreparedStatement的构造
//PreparedStatement
public class PreparedStatement extends StatementImpl
implements java.sql.PreparedStatement
{
protected static PreparedStatement getInstance(ConnectionImpl conn, String sql, String catalog)
throws SQLException
{
if(!Util.isJdbc4())
return new PreparedStatement(conn, sql, catalog);
else
return (PreparedStatement)Util.handleNewInstance(JDBC_4_PSTMT_3_ARG_CTOR, new Object[] {
conn, sql, catalog
}, conn.getExceptionInterceptor());
}
public PreparedStatement(ConnectionImpl conn, String sql, String catalog)
throws SQLException
{
super(conn, catalog);
batchHasPlainStatements = false;
dbmd = null;
firstCharOfStmt = '\0';
hasLimitClause = false;
isLoadDataQuery = false;
isNull = null;
isStream = null;
numberOfExecutions = 0;
originalSql = null;
parameterStreams = null;
//参数值
parameterValues = (byte[][])null;
//参数类型
parameterTypes = null;
staticSqlStrings = (byte[][])null;
streamConvertBuf = new byte[4096];
streamLengths = null;
tsdf = null;
useTrueBoolean = false;
hasCheckedForRewrite = false;
canRewrite = false;
compensateForOnDuplicateKeyUpdate = false;
batchCommandIndex = -1;
if(sql == null)
throw SQLError.createSQLException(Messages.getString("PreparedStatement.0"), "S1009", getExceptionInterceptor());
originalSql = sql;
if(originalSql.startsWith("/* ping */"))
doPingInstead = true;
else
doPingInstead = false;
//获取数据库MetaData
dbmd = connection.getMetaData();
useTrueBoolean = connection.versionMeetsMinimum(3, 21, 23);
//构建Statement的
parseInfo = new ParseInfo(sql, connection, dbmd, charEncoding, charConverter);
initializeFromParseInfo();
compensateForOnDuplicateKeyUpdate = connection.getCompensateOnDuplicateKeyUpdateCounts();
if(conn.getRequiresEscapingEncoder())
charsetEncoder = Charset.forName(conn.getEncoding()).newEncoder();
}
}
构造PreparedStatement完毕，来看一下，如何查询
public ResultSet executeQuery()
throws SQLException
{
checkClosed();
ConnectionImpl locallyScopedConn = connection;
checkForDml(originalSql, firstCharOfStmt);
CachedResultSetMetaData cachedMetadata = null;
synchronized(locallyScopedConn.getMutex())
{
clearWarnings();
boolean doStreaming = createStreamingResultSet();
batchedGeneratedKeys = null;
if(doStreaming && connection.getNetTimeoutForStreamingResults() > 0)
locallyScopedConn.execSQL(this, "SET net_write_timeout=" + connection.getNetTimeoutForStreamingResults(), -1, null, 1003, 1007, false, currentCatalog, null, false);
Buffer sendPacket = fillSendPacket();
if(results != null && !connection.getHoldResultsOpenOverStatementClose() && !holdResultsOpenOverClose)
results.realClose(false);
String oldCatalog = null;
if(!locallyScopedConn.getCatalog().equals(currentCatalog))
{
oldCatalog = locallyScopedConn.getCatalog();
locallyScopedConn.setCatalog(currentCatalog);
}
if(locallyScopedConn.getCacheResultSetMetadata())
cachedMetadata = locallyScopedConn.getCachedMetaData(originalSql);
Field metadataFromCache[] = null;
if(cachedMetadata != null)
metadataFromCache = cachedMetadata.fields;
if(locallyScopedConn.useMaxRows())
{
if(hasLimitClause)
{
//没有分页语句的查询
results = executeInternal(maxRows, sendPacket, createStreamingResultSet(), true, metadataFromCache, false);
} else
{
if(maxRows <= 0)
executeSimpleNonQuery(locallyScopedConn, "SET OPTION SQL_SELECT_LIMIT=DEFAULT");
else
executeSimpleNonQuery(locallyScopedConn, "SET OPTION SQL_SELECT_LIMIT=" + maxRows);
results = executeInternal(-1, sendPacket, doStreaming, true, metadataFromCache, false);
if(oldCatalog != null)
connection.setCatalog(oldCatalog);
}
} else
{
results = executeInternal(-1, sendPacket, doStreaming, true, metadataFromCache, false);
}
if(oldCatalog != null)
locallyScopedConn.setCatalog(oldCatalog);
if(cachedMetadata != null)
locallyScopedConn.initializeResultsMetadataFromCache(originalSql, cachedMetadata, results);
else
if(locallyScopedConn.getCacheResultSetMetadata())
locallyScopedConn.initializeResultsMetadataFromCache(originalSql, null, results);
}
lastInsertId = results.getUpdateID();
return results;
}
来看没有分页语句的查询executeInternal
protected ResultSetInternalMethods executeInternal(int maxRowsToRetrieve, Buffer sendPacket, boolean createStreamingResultSet, boolean queryIsSelectOnly, Field metadataFromCache[], boolean isBatch)
throws SQLException
{
ConnectionImpl locallyScopedConnection;
resetCancelledState();
locallyScopedConnection = connection;
numberOfExecutions++;
if(!doPingInstead)
break MISSING_BLOCK_LABEL_36;
doPingInstead();
return results;
StatementImpl.CancelTask timeoutTask = null;
ResultSetInternalMethods rs;
if(locallyScopedConnection.getEnableQueryTimeouts() && timeoutInMillis != 0 && locallyScopedConnection.versionMeetsMinimum(5, 0, 0))
{
timeoutTask = new StatementImpl.CancelTask(this, this);
//连接定时任务执行器Timer，等待timeoutInMillis毫秒后，执行查询定时任务timeoutTask
ConnectionImpl.getCancelTimer().schedule(timeoutTask, timeoutInMillis);
}
//执行查询，并返回结果集
rs = locallyScopedConnection.execSQL(this, null, maxRowsToRetrieve, sendPacket, resultSetType, resultSetConcurrency, createStreamingResultSet, currentCatalog, metadataFromCache, isBatch);
if(timeoutTask != null)
{
timeoutTask.cancel();
if(timeoutTask.caughtWhileCancelling != null)
throw timeoutTask.caughtWhileCancelling;
timeoutTask = null;
}
synchronized(cancelTimeoutMutex)
{
if(wasCancelled)
{
SQLException cause = null;
if(wasCancelledByTimeout)
cause = new MySQLTimeoutException();
else
cause = new MySQLStatementCancelledException();
resetCancelledState();
throw cause;
}
}
if(timeoutTask != null)
timeoutTask.cancel();
break MISSING_BLOCK_LABEL_242;
Exception exception1;
exception1;
if(timeoutTask != null)
timeoutTask.cancel();
throw exception1;
return rs;
NullPointerException npe;
npe;
checkClosed();
throw npe;
}
我们来看一下这一段都做了些什么？
if(locallyScopedConnection.getEnableQueryTimeouts() && timeoutInMillis != 0 && locallyScopedConnection.versionMeetsMinimum(5, 0, 0))
{
timeoutTask = new StatementImpl.CancelTask(this, this);
//连接定时任务执行器Timer，等待timeoutInMillis毫秒后，执行查询定时任务timeoutTask
ConnectionImpl.getCancelTimer().schedule(timeoutTask, timeoutInMillis);
}
//StatementImpl
public class StatementImpl
implements com.mysql.jdbc.Statement
{
class CancelTask extends TimerTask
{
public void run()
{
Thread cancelThread = new Thread() {
public void run()
{
com.mysql.jdbc.Connection cancelConn = null;
Statement cancelStmt = null;
try
{
synchronized(cancelTimeoutMutex)
{
//复制connection
cancelConn = connection.duplicate();
//创建Statement
cancelStmt = cancelConn.createStatement();
cancelStmt.execute("KILL QUERY " + connectionId);
toCancel.wasCancelled = true;
toCancel.wasCancelledByTimeout = true;
}
}
catch(SQLException sqlEx)
{
caughtWhileCancelling = sqlEx;
}
catch(NullPointerException npe) { }
finally
{
if(cancelStmt != null)
try
{
cancelStmt.close();
}
catch(SQLException sqlEx)
{
throw new RuntimeException(sqlEx.toString());
}
if(cancelConn != null)
try
{
cancelConn.close();
}
catch(SQLException sqlEx)
{
throw new RuntimeException(sqlEx.toString());
}
}
}
};
cancelThread.start();
}
long connectionId;
SQLException caughtWhileCancelling;
StatementImpl toCancel;
CancelTask(StatementImpl cancellee)
throws SQLException
{
connectionId = 0L;
caughtWhileCancelling = null;
connectionId = connection.getIO().getThreadId();
toCancel = cancellee;
}
}
}
//创建Statement
cancelStmt = cancelConn.createStatement();
//ConnectionImpl
public Statement createStatement()
throws SQLException
{
return createStatement(1003, 1007);
}
public Statement createStatement(int resultSetType, int resultSetConcurrency)
throws SQLException
{
checkClosed();
StatementImpl stmt = new StatementImpl(this, database);
stmt.setResultSetType(resultSetType);
stmt.setResultSetConcurrency(resultSetConcurrency);
return stmt;
}
//连接定时任务执行器Timer，等待timeoutInMillis毫秒后，执行查询定时任务timeoutTask
ConnectionImpl.getCancelTimer().schedule(timeoutTask, timeoutInMillis);
//ConnectionImpl
protected static Timer getCancelTimer()
{
//private static Timer cancelTimer;
return cancelTimer;
}
从上面这一段可以看出，如果延时查询的话，就创建StatementImpl.CancelTask（TimeTask）定时任务，并由ConnectionImpl的cancelTimer（Timer）去调度。
回到executeInternal方法，
来看执行查询，返回结果集，这个时调用ConnectionImpl的execSQL
//ConnectionImpl
ResultSetInternalMethods execSQL(StatementImpl callingStatement, String sql, int maxRows, Buffer packet, int resultSetType, int resultSetConcurrency, boolean streamResults,
String catalog, Field cachedMetadata[], boolean isBatch)
throws SQLException
{
Object obj = mutex;
JVM INSTR monitorenter ;
long queryStartTime;
int endOfQueryPacketPosition;
queryStartTime = 0L;
endOfQueryPacketPosition = 0;
if(packet != null)
endOfQueryPacketPosition = packet.getPosition();
if(getGatherPerformanceMetrics())
queryStartTime = System.currentTimeMillis();
lastQueryFinishedTime = 0L;
if(!failedOver || !autoCommit || isBatch || !shouldFallBack() || executingFailoverReconnect)
break MISSING_BLOCK_LABEL_151;
executingFailoverReconnect = true;
//创建MysqlIO，这个我们在前面ServerPrepareStatement中讲过
createNewIO(true);
String connectedHost = io.getHost();
if(connectedHost != null && hostList.get(0).equals(connectedHost))
{
failedOver = false;
queriesIssuedFailedOver = 0L;
setReadOnlyInternal(false);
}
if((getHighAvailability() || failedOver) && (autoCommit || getAutoReconnectForPools()) && needsPing && !isBatch)
try
{
pingInternal(false, 0);
needsPing = false;
}
catch(Exception Ex)
{
createNewIO(true);
}
ResultSetInternalMethods resultsetinternalmethods1;
if(packet != null)
break MISSING_BLOCK_LABEL_267;
String encoding = null;
if(getUseUnicode())
encoding = getEncoding();
//关键在这一句MysqlIO执行查询
resultsetinternalmethods1 = io.sqlQueryDirect(callingStatement, sql, encoding, null, maxRows, resultSetType, resultSetConcurrency, streamResults, catalog, cachedMetadata);
return resultsetinternalmethods1;
ResultSetInternalMethods resultsetinternalmethods;
try
{
resultsetinternalmethods = io.sqlQueryDirect(callingStatement, null, null, packet, maxRows, resultSetType, resultSetConcurrency, streamResults, catalog, cachedMetadata);
}
return resultsetinternalmethods;
}
来看MysqlIO执行查询
//MysqlIO
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
{
statementExecutionDepth++;
//返回结果集
ResultSetInternalMethods resultsetinternalmethods;
if(statementInterceptors == null)
break MISSING_BLOCK_LABEL_47;
//拦截器处理
ResultSetInternalMethods interceptedResults = invokeStatementInterceptorsPre(query, callingStatement);
if(interceptedResults == null)
break MISSING_BLOCK_LABEL_47;
resultsetinternalmethods = interceptedResults;
statementExecutionDepth--;
return resultsetinternalmethods;
ResultSetInternalMethods resultsetinternalmethods1;
long queryStartTime = 0L;
long queryEndTime = 0L;
if(query != null)
{
int packLength = 5 + query.length() * 2 + 2;
String statementComment = connection.getStatementComment();
byte commentAsBytes[] = null;
if(statementComment != null)
{
commentAsBytes = StringUtils.getBytes(statementComment, null, characterEncoding, connection.getServerCharacterEncoding(), connection.parserKnowsUnicode(), getExceptionInterceptor());
packLength += commentAsBytes.length;
packLength += 6;
}
if(sendPacket == null)
sendPacket = new Buffer(packLength);
else
sendPacket.clear();
sendPacket.writeByte((byte)3);
if(commentAsBytes != null)
{
//将注释添加的查询包中
sendPacket.writeBytesNoNull(Constants.SLASH_STAR_SPACE_AS_BYTES);
sendPacket.writeBytesNoNull(commentAsBytes);
sendPacket.writeBytesNoNull(Constants.SPACE_STAR_SLASH_SPACE_AS_BYTES);
}
if(characterEncoding != null)
{
//如果有编码信息，则将查询编码后，组装到包中
if(platformDbCharsetMatches)
sendPacket.writeStringNoNull(query, characterEncoding, connection.getServerCharacterEncoding(), connection.parserKnowsUnicode(), connection);
else
if(StringUtils.startsWithIgnoreCaseAndWs(query, "LOAD DATA"))
sendPacket.writeBytesNoNull(query.getBytes());
else
sendPacket.writeStringNoNull(query, characterEncoding, connection.getServerCharacterEncoding(), connection.parserKnowsUnicode(), connection);
} else
{
sendPacket.writeStringNoNull(query);
}
queryPacket = sendPacket;
}
byte queryBuf[] = null;
int oldPacketPosition = 0;
if(needToGrabQueryFromPacket)
{
queryBuf = queryPacket.getByteBuffer();
oldPacketPosition = queryPacket.getPosition();
queryStartTime = getCurrentTimeNanosOrMillis();
}
if(autoGenerateTestcaseScript)
{
String testcaseQuery = null;
if(query != null)
testcaseQuery = query;
else
testcaseQuery = new String(queryBuf, 5, oldPacketPosition - 5);
StringBuffer debugBuf = new StringBuffer(testcaseQuery.length() + 32);
connection.generateConnectionCommentBlock(debugBuf);
debugBuf.append(testcaseQuery);
debugBuf.append(';');
connection.dumpTestcaseQuery(debugBuf.toString());
}
//MysqlIO发送查询包到Server，获取返回结果
Buffer resultPacket = sendCommand(3, null, queryPacket, false, null, 0);
long fetchBeginTime = 0L;
long fetchEndTime = 0L;
String profileQueryToLog = null;
boolean queryWasSlow = false;
if(profileSql || logSlowQueries)
{
queryEndTime = System.currentTimeMillis();
boolean shouldExtractQuery = false;
if(profileSql)
shouldExtractQuery = true;
else
if(logSlowQueries)
{
long queryTime = queryEndTime - queryStartTime;
boolean logSlow = false;
if(useAutoSlowLog)
{
logSlow = queryTime > (long)connection.getSlowQueryThresholdMillis();
} else
{
logSlow = connection.isAbonormallyLongQuery(queryTime);
connection.reportQueryTime(queryTime);
}
if(logSlow)
{
shouldExtractQuery = true;
queryWasSlow = true;
}
}
if(shouldExtractQuery)
{
boolean truncated = false;
int extractPosition = oldPacketPosition;
if(oldPacketPosition > connection.getMaxQuerySizeToLog())
{
extractPosition = connection.getMaxQuerySizeToLog() + 5;
truncated = true;
}
profileQueryToLog = new String(queryBuf, 5, extractPosition - 5);
if(truncated)
profileQueryToLog = profileQueryToLog + Messages.getString("MysqlIO.25");
}
fetchBeginTime = queryEndTime;
}
//从中resultPacket，获取返回结果
ResultSetInternalMethods rs = readAllResults(callingStatement, maxRows, resultSetType, resultSetConcurrency, streamResults, catalog, resultPacket, false, -1L, cachedMetadata);
if(queryWasSlow && !serverQueryWasSlow)
{
StringBuffer mesgBuf = new StringBuffer(48 + profileQueryToLog.length());
mesgBuf.append(Messages.getString("MysqlIO.SlowQuery", new Object[] {
new Long(slowQueryThreshold), queryTimingUnits, new Long(queryEndTime - queryStartTime)
}));
mesgBuf.append(profileQueryToLog);
ProfilerEventHandler eventSink = ProfilerEventHandlerFactory.getInstance(connection);
eventSink.consumeEvent(new ProfilerEvent((byte)6, "", catalog, connection.getId(), callingStatement == null ? 999 : callingStatement.getId(), ((ResultSetImpl)rs).resultId, System.currentTimeMillis(), (int)(queryEndTime - queryStartTime), queryTimingUnits, null, new Throwable(), mesgBuf.toString()));
if(connection.getExplainSlowQueries())
if(oldPacketPosition < 1048576)
explainSlowQuery(queryPacket.getBytes(5, oldPacketPosition - 5), profileQueryToLog);
else
connection.getLog().logWarn(Messages.getString("MysqlIO.28") + 1048576 + Messages.getString("MysqlIO.29"));
}
if(logSlowQueries)
{
ProfilerEventHandler eventSink = ProfilerEventHandlerFactory.getInstance(connection);
if(queryBadIndexUsed)
eventSink.consumeEvent(new ProfilerEvent((byte)6, "", catalog, connection.getId(), callingStatement == null ? 999 : callingStatement.getId(), ((ResultSetImpl)rs).resultId, System.currentTimeMillis(), queryEndTime - queryStartTime, queryTimingUnits, null, new Throwable(), Messages.getString("MysqlIO.33") + profileQueryToLog));
if(queryNoIndexUsed)
eventSink.consumeEvent(new ProfilerEvent((byte)6, "", catalog, connection.getId(), callingStatement == null ? 999 : callingStatement.getId(), ((ResultSetImpl)rs).resultId, System.currentTimeMillis(), queryEndTime - queryStartTime, queryTimingUnits, null, new Throwable(), Messages.getString("MysqlIO.35") + profileQueryToLog));
if(serverQueryWasSlow)
eventSink.consumeEvent(new ProfilerEvent((byte)6, "", catalog, connection.getId(), callingStatement == null ? 999 : callingStatement.getId(), ((ResultSetImpl)rs).resultId, System.currentTimeMillis(), queryEndTime - queryStartTime, queryTimingUnits, null, new Throwable(), Messages.getString("MysqlIO.ServerSlowQuery") + profileQueryToLog));
}
if(profileSql)
{
fetchEndTime = getCurrentTimeNanosOrMillis();
ProfilerEventHandler eventSink = ProfilerEventHandlerFactory.getInstance(connection);
eventSink.consumeEvent(new ProfilerEvent((byte)3, "", catalog, connection.getId(), callingStatement == null ? 999 : callingStatement.getId(), ((ResultSetImpl)rs).resultId, System.currentTimeMillis(), queryEndTime - queryStartTime, queryTimingUnits, null, new Throwable(), profileQueryToLog));
eventSink.consumeEvent(new ProfilerEvent((byte)5, "", catalog, connection.getId(), callingStatement == null ? 999 : callingStatement.getId(), ((ResultSetImpl)rs).resultId, System.currentTimeMillis(), fetchEndTime - fetchBeginTime, queryTimingUnits, null, new Throwable(), null));
}
if(hadWarnings)
scanForAndThrowDataTruncation();
if(statementInterceptors != null)
{
ResultSetInternalMethods interceptedResults = invokeStatementInterceptorsPost(query, callingStatement, rs);
if(interceptedResults != null)
rs = interceptedResults;
}
resultsetinternalmethods1 = rs;
statementExecutionDepth--;
return resultsetinternalmethods1;
}
//从缓冲区，去除结果集
ResultSetImpl readAllResults(StatementImpl callingStatement, int maxRows, int resultSetType, int resultSetConcurrency, boolean streamResults, String catalog, Buffer resultPacket,
boolean isBinaryEncoded, long preSentColumnCount, Field metadataFromCache[])
throws SQLException
{
resultPacket.setPosition(resultPacket.getPosition() - 1);
ResultSetImpl topLevelResultSet = readResultsForQueryOrUpdate(callingStatement, maxRows, resultSetType, resultSetConcurrency, streamResults, catalog, resultPacket, isBinaryEncoded, preSentColumnCount, metadataFromCache);
ResultSetImpl currentResultSet = topLevelResultSet;
boolean checkForMoreResults = (clientParam & 131072L) != 0L;
boolean serverHasMoreResults = (serverStatus & 8) != 0;
if(serverHasMoreResults && streamResults)
{
if(topLevelResultSet.getUpdateCount() != -1L)
tackOnMoreStreamingResults(topLevelResultSet);
reclaimLargeReusablePacket();
return topLevelResultSet;
}
for(boolean moreRowSetsExist = checkForMoreResults & serverHasMoreResults; moreRowSetsExist; moreRowSetsExist = (serverStatus & 8) != 0)
{
Buffer fieldPacket = checkErrorPacket();
fieldPacket.setPosition(0);
//读取结果集
ResultSetImpl newResultSet = readResultsForQueryOrUpdate(callingStatement, maxRows, resultSetType, resultSetConcurrency, streamResults, catalog, fieldPacket, isBinaryEncoded, preSentColumnCount, metadataFromCache);
currentResultSet.setNextResultSet(newResultSet);
currentResultSet = newResultSet;
}
if(!streamResults)
clearInputStream();
reclaimLargeReusablePacket();
return topLevelResultSet;
}
总结：
PreparedStatement执行查询，实际上是通过ConnectionImpl的execSQL，而ConnectionImpl的执行查询，实际上是通过MysqlIO，MysqlIO执行查询，就是将Sql查询，组成Mysql的查询包，通过socket的发送给Server，Server返回查询结果缓存区，然后MysqlIO将结果缓存区转换为ResultSetInternalMethods（ResultSetImpl），就是我们需要的结果集，即ResultSet。
public class ResultSetImpl
implements ResultSetInternalMethods
{
public float getFloat(int columnIndex)
throws SQLException
{
if(!isBinaryEncoded)
{
String val = null;
//获取columnIndex对应的String值
val = getString(columnIndex);
//将String转换为Float
return getFloatFromString(val, columnIndex);
} else
{
return getNativeFloat(columnIndex);
}
}
public float getFloat(String columnName)
throws SQLException
{
return getFloat(findColumn(columnName));
}
//获取columnIndex对应的String值
public String getString(int columnIndex)
throws SQLException
{
String stringVal = getStringInternal(columnIndex, true);
if(padCharsWithSpace && stringVal != null)
{
Field f = fields[columnIndex - 1];
if(f.getMysqlType() == 254)
{
int fieldLength = (int)f.getLength() / f.getMaxBytesPerCharacter();
int currentLength = stringVal.length();
if(currentLength < fieldLength)
{
StringBuffer paddedBuf = new StringBuffer(fieldLength);
paddedBuf.append(stringVal);
int difference = fieldLength - currentLength;
paddedBuf.append(EMPTY_SPACE, 0, difference);
stringVal = paddedBuf.toString();
}
}
}
return stringVal;
}
}
//ResultSetInternalMethods
public interface ResultSetInternalMethods
extends ResultSet
{
public abstract ResultSetInternalMethods copy()
throws SQLException;
public abstract boolean reallyResult();
public abstract Object getObjectStoredProc(int i, int j)
throws SQLException;
public abstract Object getObjectStoredProc(int i, Map map, int j)
throws SQLException;
public abstract Object getObjectStoredProc(String s, int i)
throws SQLException;
public abstract Object getObjectStoredProc(String s, Map map, int i)
throws SQLException;
public abstract String getServerInfo();
public abstract long getUpdateCount();
public abstract long getUpdateID();
public abstract void realClose(boolean flag)
throws SQLException;
public abstract void setFirstCharOfQuery(char c);
public abstract void setOwningStatement(StatementImpl statementimpl);
public abstract char getFirstCharOfQuery();
public abstract void clearNextResult();
public abstract ResultSetInternalMethods getNextResultSet();
public abstract void setStatementUsedForFetchingRows(PreparedStatement preparedstatement);
public abstract void setWrapperStatement(Statement statement);
public abstract void buildIndexMapping()
throws SQLException;
public abstract void initializeWithMetadata()
throws SQLException;
public abstract void redefineFieldsForDBMD(Field afield[]);
public abstract void populateCachedMetaData(CachedResultSetMetaData cachedresultsetmetadata)
throws SQLException;
public abstract void initializeFromCachedMetaData(CachedResultSetMetaData cachedresultsetmetadata);
}