简介
MySQL数据库由后台线程以及一个共享内存区组成。共享内存可以被运行着的后台线程所共享。
数据库实例才是真正用于操作数据库文件的。MySQL数据库实例在操作系统上的表现实际就是一个进程，
是一个单进程多线程架构的数据库。（来自《Mysql技术内幕InnoDB存储引擎》）
上面讲到MySQL数据库在操作系统上的表现是进程，那么连接MySQL的本质就是进程间的通信。常用的进程间通信方式有管道，命名管道，TCP/IP套接字，UNIX域套接字。
TCP/IP套接字是MySQL数据库在任何平台下（指的是不同的操作系统）都可以使用的连接方式，本文也是此对JDBC连接进行详细的讲解。
使用mysql-connector-java-5.1.34.jar的版本
import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
public class SimpleTest {
private final static String url = "jdbc:mysql://localhost/test";
private final static String username = "root";
private final static String password = "123456";
public static void main(String[] args) {
try {
Class.forName("com.mysql.jdbc.Driver");
//建立连接
Connection connection = (Connection) DriverManager.getConnection(url, username, password);
System.out.println("连接成功");
Statement statement = (Statement) connection.createStatement();
//进行查询
ResultSet resultSet = statement.executeQuery("select * from user");
while (resultSet.next()) {
String loginname = resultSet.getString("loginname");
String password = resultSet.getString("password");
System.out.println("loginname = " + loginname + " password = " + password);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e2) {
e2.printStackTrace();
}
}
}
注册驱动
Class.forName("com.mysql.jdbc.Driver");
很多人可能对这句代码都有疑问，怎么上面这行代码就注册驱动了呢？
class.forName()这行代码，有两个作用，一个是类的.class文件加载到jvm中，还有一个是执行类中的static块。
如果对Java中static块什么时候会执行，可阅读https://www.cnblogs.com/jswang/p/7699643.html
果不其然，Driver类中有一个静态块，会java.sql.DriverManager.registerDriver(new Driver());
com.mysql.jdbc.Driver.java
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
//
// Register ourselves with the DriverManager
// static块，执行这行Class.forName("com.mysql.jdbc.Driver");的时候，会调用static块
static {
try {
java.sql.DriverManager.registerDriver(new Driver());
} catch (SQLException E) {
throw new RuntimeException("Can't register driver!");
}
}
/**
* Construct a new driver and register it with DriverManager
*
* @throws SQLException
* if a database error occurs.
*/
public Driver() throws SQLException {
// Required for Class.forName().newInstance()
}
}
java.sql.DriverManager.java
public static synchronized void registerDriver(java.sql.Driver driver)
throws SQLException {
registerDriver(driver, null);
}
registerDriver(driver, null); //注册驱动，进入方法继续看
private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>();
public static synchronized void registerDriver(java.sql.Driver driver,
DriverAction da)
throws SQLException {
/* Register the driver if it has not already been added to our list */
if(driver != null) {
//registeredDrivers是一个List，将驱动信息保存到List中
registeredDrivers.addIfAbsent(new DriverInfo(driver, da));
} else {
// This is for compatibility with the original DriverManager
throw new NullPointerException();
}
println("registerDriver: " + driver);
}
通过上面几步，就完成了数据库驱动的注册。
数据库连接
Connection connection = (Connection) DriverManager.getConnection(url, username, password);
java.sql.DriverManager.java
public static Connection getConnection(String url,
String user, String password) throws SQLException {
java.util.Properties info = new java.util.Properties();
if (user != null) {
info.put("user", user);
}
if (password != null) {
info.put("password", password);
}
//getConnection()才是真正连接的，所以往下看
return (getConnection(url, info, Reflection.getCallerClass()));
}
private static Connection getConnection(
String url, java.util.Properties info, Class<?> caller) throws SQLException {
/*
* When callerCl is null, we should check the application's
* (which is invoking this class indirectly)
* classloader, so that the JDBC driver class outside rt.jar
* can be loaded from here.
*/
ClassLoader callerCL = caller != null ? caller.getClassLoader() : null;
synchronized(DriverManager.class) {
// synchronize loading of the correct classloader.
if (callerCL == null) {
callerCL = Thread.currentThread().getContextClassLoader();
}
}
if(url == null) {
throw new SQLException("The url cannot be null", "08001");
}
println("DriverManager.getConnection(\"" + url + "\")");
// Walk through the loaded registeredDrivers attempting to make a connection.
// Remember the first exception that gets raised so we can reraise it.
SQLException reason = null;
//重点
//registeredDrivers是上一步注册的数据库驱动信息
for(DriverInfo aDriver : registeredDrivers) {
// If the caller does not have permission to load the driver then
// skip it.
if(isDriverAllowed(aDriver.driver, callerCL)) {
try {
println(" trying " + aDriver.driver.getClass().getName());
//重点中的重点，connect()才是真正与数据库服务器建立连接的
Connection con = aDriver.driver.connect(url, info);
if (con != null) {
// Success!
println("getConnection returning " + aDriver.driver.getClass().getName());
return (con);
}
} catch (SQLException ex) {
if (reason == null) {
reason = ex;
}
}
} else {
println(" skipping: " + aDriver.getClass().getName());
}
}
// if we got here nobody could connect.
if (reason != null) {
println("getConnection failed: " + reason);
throw reason;
}
println("getConnection: no suitable driver found for "+ url);
throw new SQLException("No suitable driver found for "+ url, "08001");
}
java.sql.Driver.java 是一个接口，原生的Java本身并没有实现，mysql-connector-java-5.1.34.jar包下面有它的实现类，NonRegisteringDriver。
Connection connect(String url, java.util.Properties info)
throws SQLException;
com.mysql.jdbc.NonRegisteringDriver.java
public java.sql.Connection connect(String url, Properties info) throws SQLException {
if (url != null) {
if (StringUtils.startsWithIgnoreCase(url, LOADBALANCE_URL_PREFIX)) {
return connectLoadBalanced(url, info);
} else if (StringUtils.startsWithIgnoreCase(url, REPLICATION_URL_PREFIX)) {
return connectReplicationConnection(url, info);
}
}
Properties props = null;
if ((props = parseURL(url, info)) == null) {
return null;
}
if (!"1".equals(props.getProperty(NUM_HOSTS_PROPERTY_KEY))) {
return connectFailover(url, info);
}
//前面都是一些判断之类
//重点是下面一行代码
try {
Connection newConn = com.mysql.jdbc.ConnectionImpl.getInstance(host(props), port(props), props, database(props), url);
return newConn;
} catch (SQLException sqlEx) {
// Don't wrap SQLExceptions, throw
// them un-changed.
throw sqlEx;
} catch (Exception ex) {
SQLException sqlEx = SQLError.createSQLException(
Messages.getString("NonRegisteringDriver.17") + ex.toString() + Messages.getString("NonRegisteringDriver.18"),
SQLError.SQL_STATE_UNABLE_TO_CONNECT_TO_DATASOURCE, null);
sqlEx.initCause(ex);
throw sqlEx;
}
}
com.mysql.jdbc.ConnectionImpl.java
protected static Connection getInstance(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url)
throws SQLException {
if (!Util.isJdbc4()) {
//重点
return new ConnectionImpl(hostToConnectTo, portToConnectTo, info, databaseToConnectTo, url);
}
return (Connection) Util.handleNewInstance(JDBC_4_CONNECTION_CTOR, new Object[] { hostToConnectTo, Integer.valueOf(portToConnectTo), info,
databaseToConnectTo, url }, null);
}
//执行完这个构造函数，程序就返回Connectin了，但是我们还没有看到是如何建立连接，有点失望了
public ConnectionImpl(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url) throws SQLException {
this.connectionCreationTimeMillis = System.currentTimeMillis();
if (databaseToConnectTo == null) {
databaseToConnectTo = "";
}
// Stash away for later, used to clone this connection for Statement.cancel and Statement.setQueryTimeout().
//
this.origHostToConnectTo = hostToConnectTo;
this.origPortToConnectTo = portToConnectTo;
this.origDatabaseToConnectTo = databaseToConnectTo;
try {
Blob.class.getMethod("truncate", new Class[] { Long.TYPE });
this.isRunningOnJDK13 = false;
} catch (NoSuchMethodException nsme) {
this.isRunningOnJDK13 = true;
}
this.sessionCalendar = new GregorianCalendar();
this.utcCalendar = new GregorianCalendar();
this.utcCalendar.setTimeZone(TimeZone.getTimeZone("GMT"));
//
// Normally, this code would be in initializeDriverProperties, but we need to do this as early as possible, so we can start logging to the 'correct'
// place as early as possible...this.log points to 'NullLogger' for every connection at startup to avoid NPEs and the overhead of checking for NULL at
// every logging call.
//
// We will reset this to the configured logger during properties initialization.
//
this.log = LogFactory.getLogger(getLogger(), LOGGER_INSTANCE_NAME, getExceptionInterceptor());
// We store this per-connection, due to static synchronization issues in Java's built-in TimeZone class...
this.defaultTimeZone = Util.getDefaultTimeZone();
this.isClientTzUTC = "GMT".equalsIgnoreCase(this.defaultTimeZone.getID());
this.openStatements = new HashMap<Statement, Statement>();
if (NonRegisteringDriver.isHostPropertiesList(hostToConnectTo)) {
Properties hostSpecificProps = NonRegisteringDriver.expandHostKeyValues(hostToConnectTo);
Enumeration<?> propertyNames = hostSpecificProps.propertyNames();
while (propertyNames.hasMoreElements()) {
String propertyName = propertyNames.nextElement().toString();
String propertyValue = hostSpecificProps.getProperty(propertyName);
info.setProperty(propertyName, propertyValue);
}
} else {
if (hostToConnectTo == null) {
this.host = "localhost";
this.hostPortPair = this.host + ":" + portToConnectTo;
} else {
this.host = hostToConnectTo;
if (hostToConnectTo.indexOf(":") == -1) {
this.hostPortPair = this.host + ":" + portToConnectTo;
} else {
this.hostPortPair = this.host;
}
}
}
//端口
this.port = portToConnectTo;
//数据库名称
this.database = databaseToConnectTo;
//URL
this.myURL = url;
this.user = info.getProperty(NonRegisteringDriver.USER_PROPERTY_KEY);
this.password = info.getProperty(NonRegisteringDriver.PASSWORD_PROPERTY_KEY);
//用户名和密码
if ((this.user == null) || this.user.equals("")) {
this.user = "";
}
if (this.password == null) {
this.password = "";
}
this.props = info;
initializeDriverProperties(info);
if (getUseUsageAdvisor()) {
this.pointOfOrigin = LogUtils.findCallingClassAndMethod(new Throwable());
} else {
this.pointOfOrigin = "";
}
try {
this.dbmd = getMetaData(false, false);
initializeSafeStatementInterceptors();
//重点
createNewIO(false);
unSafeStatementInterceptors();
} catch (SQLException ex) {
cleanup(ex);
// don't clobber SQL exceptions
throw ex;
} catch (Exception ex) {
cleanup(ex);
StringBuffer mesg = new StringBuffer(128);
if (!getParanoid()) {
mesg.append("Cannot connect to MySQL server on ");
mesg.append(this.host);
mesg.append(":");
mesg.append(this.port);
mesg.append(".\n\n");
mesg.append("Make sure that there is a MySQL server ");
mesg.append("running on the machine/port you are trying ");
mesg.append("to connect to and that the machine this software is running on ");
mesg.append("is able to connect to this host/port (i.e. not firewalled). ");
mesg.append("Also make sure that the server has not been started with the --skip-networking ");
mesg.append("flag.\n\n");
} else {
mesg.append("Unable to connect to database.");
}
SQLException sqlEx = SQLError.createSQLException(mesg.toString(), SQLError.SQL_STATE_COMMUNICATION_LINK_FAILURE, getExceptionInterceptor());
sqlEx.initCause(ex);
throw sqlEx;
}
NonRegisteringDriver.trackConnection(this);
}
//接着继续看咯
public void createNewIO(boolean isForReconnect) throws SQLException {
synchronized (getConnectionMutex()) {
// Synchronization Not needed for *new* connections, but defintely for connections going through fail-over, since we might get the new connection up
// and running *enough* to start sending cached or still-open server-side prepared statements over to the backend before we get a chance to
// re-prepare them...
Properties mergedProps = exposeAsProperties(this.props);
if (!getHighAvailability()) {
//重点，进去看看
connectOneTryOnly(isForReconnect, mergedProps);
return;
}
connectWithRetries(isForReconnect, mergedProps);
}
}
//重点
private void coreConnect(Properties mergedProps) throws SQLException, IOException {
int newPort = 3306;
String newHost = "localhost";
String protocol = mergedProps.getProperty(NonRegisteringDriver.PROTOCOL_PROPERTY_KEY);
//在这里，似乎看到了，快要建立连接了，protocol判断是使用哪种协议进行通信的了，tcp/ip套接字，pipe管道，还是其他
if (protocol != null) {
// "new" style URL
if ("tcp".equalsIgnoreCase(protocol)) {
newHost = normalizeHost(mergedProps.getProperty(NonRegisteringDriver.HOST_PROPERTY_KEY));
newPort = parsePortNumber(mergedProps.getProperty(NonRegisteringDriver.PORT_PROPERTY_KEY, "3306"));
} else if ("pipe".equalsIgnoreCase(protocol)) {
setSocketFactoryClassName(NamedPipeSocketFactory.class.getName());
String path = mergedProps.getProperty(NonRegisteringDriver.PATH_PROPERTY_KEY);
if (path != null) {
mergedProps.setProperty(NamedPipeSocketFactory.NAMED_PIPE_PROP_NAME, path);
}
} else {
// normalize for all unknown protocols
newHost = normalizeHost(mergedProps.getProperty(NonRegisteringDriver.HOST_PROPERTY_KEY));
newPort = parsePortNumber(mergedProps.getProperty(NonRegisteringDriver.PORT_PROPERTY_KEY, "3306"));
}
} else {
String[] parsedHostPortPair = NonRegisteringDriver.parseHostPortPair(this.hostPortPair);
newHost = parsedHostPortPair[NonRegisteringDriver.HOST_NAME_INDEX];
newHost = normalizeHost(newHost);
if (parsedHostPortPair[NonRegisteringDriver.PORT_NUMBER_INDEX] != null) {
newPort = parsePortNumber(parsedHostPortPair[NonRegisteringDriver.PORT_NUMBER_INDEX]);
}
}
this.port = newPort;
this.host = newHost;
// reset max-rows to default value
this.sessionMaxRows = -1;
//重点中的重点，进去看看咯
this.io = new MysqlIO(newHost, newPort, mergedProps, getSocketFactoryClassName(), getProxy(), getSocketTimeout(),
this.largeRowSizeThreshold.getValueAsInt());
//重点，建立好连接之后，需要验证密码之类
this.io.doHandshake(this.user, this.password, this.database);
if (versionMeetsMinimum(5, 5, 0)) {
// error messages are returned according to character_set_results which, at this point, is set from the response packet
this.errorMessageEncoding = this.io.getEncodingForHandshake();
}
}
com.mysql.jdbc.MysqlIO.java
public MysqlIO(String host, int port, Properties props, String socketFactoryClassName, MySQLConnection conn, int socketTimeout,
int useBufferRowSizeThreshold) throws IOException, SQLException {
this.connection = conn;
if (this.connection.getEnablePacketDebug()) {
this.packetDebugRingBuffer = new LinkedList<StringBuffer>();
}
this.traceProtocol = this.connection.getTraceProtocol();
this.useAutoSlowLog = this.connection.getAutoSlowLog();
this.useBufferRowSizeThreshold = useBufferRowSizeThreshold;
this.useDirectRowUnpack = this.connection.getUseDirectRowUnpack();
this.logSlowQueries = this.connection.getLogSlowQueries();
this.reusablePacket = new Buffer(INITIAL_PACKET_SIZE);
//发送包
this.sendPacket = new Buffer(INITIAL_PACKET_SIZE);
//端口和主机名
this.port = port;
this.host = host;
this.socketFactoryClassName = socketFactoryClassName;
//套接字工厂
this.socketFactory = createSocketFactory();
this.exceptionInterceptor = this.connection.getExceptionInterceptor();
try {
//套接字连接，到这里，终于看到连接了
this.mysqlConnection = this.socketFactory.connect(this.host, this.port, props);
if (socketTimeout != 0) {
try {
this.mysqlConnection.setSoTimeout(socketTimeout);
} catch (Exception ex) {
/* Ignore if the platform does not support it */
}
}
this.mysqlConnection = this.socketFactory.beforeHandshake();
//输入流
if (this.connection.getUseReadAheadInput()) {
this.mysqlInput = new ReadAheadInputStream(this.mysqlConnection.getInputStream(), 16384, this.connection.getTraceProtocol(),
this.connection.getLog());
} else if (this.connection.useUnbufferedInput()) {
this.mysqlInput = this.mysqlConnection.getInputStream();
} else {
this.mysqlInput = new BufferedInputStream(this.mysqlConnection.getInputStream(), 16384);
}
//输出流
this.mysqlOutput = new BufferedOutputStream(this.mysqlConnection.getOutputStream(), 16384);
this.isInteractiveClient = this.connection.getInteractiveClient();
this.profileSql = this.connection.getProfileSql();
this.autoGenerateTestcaseScript = this.connection.getAutoGenerateTestcaseScript();
this.needToGrabQueryFromPacket = (this.profileSql || this.logSlowQueries || this.autoGenerateTestcaseScript);
if (this.connection.getUseNanosForElapsedTime() && Util.nanoTimeAvailable()) {
this.useNanosForElapsedTime = true;
this.queryTimingUnits = Messages.getString("Nanoseconds");
} else {
this.queryTimingUnits = Messages.getString("Milliseconds");
}
if (this.connection.getLogSlowQueries()) {
calculateSlowQueryThreshold();
}
} catch (IOException ioEx) {
throw SQLError.createCommunicationsException(this.connection, 0, 0, ioEx, getExceptionInterceptor());
}
}
com.mysql.jdbc.SocketFactory.java
Socket connect(String host, int portNumber, Properties props) throws SocketException, IOException;
com.mysql.jdbc.StandardSocketFactory.java
//终于看到底层，我们熟悉的Socket连接了
public Socket connect(String hostname, int portNumber, Properties props) throws SocketException, IOException {
if (props != null) {
this.host = hostname;
this.port = portNumber;
String localSocketHostname = props.getProperty("localSocketAddress");
InetSocketAddress localSockAddr = null;
if (localSocketHostname != null && localSocketHostname.length() > 0) {
localSockAddr = new InetSocketAddress(InetAddress.getByName(localSocketHostname), 0);
}
String connectTimeoutStr = props.getProperty("connectTimeout");
int connectTimeout = 0;
if (connectTimeoutStr != null) {
try {
connectTimeout = Integer.parseInt(connectTimeoutStr);
} catch (NumberFormatException nfe) {
throw new SocketException("Illegal value '" + connectTimeoutStr + "' for connectTimeout");
}
}
if (this.host != null) {
InetAddress[] possibleAddresses = InetAddress.getAllByName(this.host);
if (possibleAddresses.length == 0) {
throw new SocketException("No addresses for host");
}
// save last exception to propagate to caller if connection fails
SocketException lastException = null;
// Need to loop through all possible addresses. Name lookup may return multiple addresses including IPv4 and IPv6 addresses. Some versions of
// MySQL don't listen on the IPv6 address so we try all addresses.
for (int i = 0; i < possibleAddresses.length; i++) {
try {
this.rawSocket = createSocket(props);
configureSocket(this.rawSocket, props);
InetSocketAddress sockAddr = new InetSocketAddress(possibleAddresses[i], this.port);
// bind to the local port if not using the ephemeral port
if (localSockAddr != null) {
//绑定端口
this.rawSocket.bind(localSockAddr);
}
//正式与数据库服务器建立连接
this.rawSocket.connect(sockAddr, getRealTimeout(connectTimeout));
break;
} catch (SocketException ex) {
lastException = ex;
resetLoginTimeCountdown();
this.rawSocket = null;
}
}
if (this.rawSocket == null && lastException != null) {
throw lastException;
}
resetLoginTimeCountdown();
return this.rawSocket;
}
}
throw new SocketException("Unable to create socket");
}
到这里，终于是与数据库服务器建立了连接。
建立好接连之后，还要继续通信吧。那接着继续看呗
com.mysql.jdbc.MysqlIO.java
有兴趣的看看吧，这个方法有点长
void doHandshake(String user, String password, String database) throws SQLException {
//里面有一个重要的方法是，给数据库服务器发送包，与服务器进行通信
send(packet, packet.getPosition());
}
private final void send(Buffer packet, int packetLen) throws SQLException {
try {
if (this.maxAllowedPacket > 0 && packetLen > this.maxAllowedPacket) {
throw new PacketTooBigException(packetLen, this.maxAllowedPacket);
}
if ((this.serverMajorVersion >= 4)
&& (packetLen - HEADER_LENGTH >= this.maxThreeBytes || (this.useCompression && packetLen - HEADER_LENGTH >= this.maxThreeBytes
- COMP_HEADER_LENGTH))) {
sendSplitPackets(packet, packetLen);
} else {
this.packetSequence++;
Buffer packetToSend = packet;
packetToSend.setPosition(0);
packetToSend.writeLongInt(packetLen - HEADER_LENGTH);
packetToSend.writeByte(this.packetSequence);
if (this.useCompression) {
this.compressedPacketSequence++;
int originalPacketLen = packetLen;
packetToSend = compressPacket(packetToSend, 0, packetLen);
packetLen = packetToSend.getPosition();
if (this.traceProtocol) {
StringBuffer traceMessageBuf = new StringBuffer();
traceMessageBuf.append(Messages.getString("MysqlIO.57"));
traceMessageBuf.append(getPacketDumpToLog(packetToSend, packetLen));
traceMessageBuf.append(Messages.getString("MysqlIO.58"));
traceMessageBuf.append(getPacketDumpToLog(packet, originalPacketLen));
this.connection.getLog().logTrace(traceMessageBuf.toString());
}
} else {
if (this.traceProtocol) {
StringBuffer traceMessageBuf = new StringBuffer();
traceMessageBuf.append(Messages.getString("MysqlIO.59"));
traceMessageBuf.append("host: '");
traceMessageBuf.append(this.host);
traceMessageBuf.append("' threadId: '");
traceMessageBuf.append(this.threadId);
traceMessageBuf.append("'\n");
traceMessageBuf.append(packetToSend.dump(packetLen));
this.connection.getLog().logTrace(traceMessageBuf.toString());
}
}
//终于把数据写到输出流中，这样子就完成通信了
this.mysqlOutput.write(packetToSend.getByteBuffer(), 0, packetLen);
this.mysqlOutput.flush();
}
if (this.enablePacketDebug) {
enqueuePacketForDebugging(true, false, packetLen + 5, this.packetHeaderBuf, packet);
}
//
// Don't hold on to large packets
//
if (packet == this.sharedSendPacket) {
reclaimLargeSharedSendPacket();
}
if (this.connection.getMaintainTimeStats()) {
this.lastPacketSentTimeMs = System.currentTimeMillis();
}
} catch (IOException ioEx) {
throw SQLError.createCommunicationsException(this.connection, this.lastPacketSentTimeMs, this.lastPacketReceivedTimeMs, ioEx,
getExceptionInterceptor());
}
}
总结一下上面的步骤吧。
上面的结果是拿到了Connection接口，实际也就是它的实现类ConnectionImpl类。而ConnectionImpl类的成员变量io，也是MysqlIO类，而MysqlIO类就具备了与数据库服务器进行通信的能力了。
执行SQL语句
//这一步就不看
Statement statement = (Statement) connection.createStatement();
//看看是怎么执行SQL语句的吧
ResultSet resultSet = statement.executeQuery("select * from user");
com.mysql.jdbc.StatementImpl.java
public java.sql.ResultSet executeQuery(String sql) throws SQLException {
//方法挺长，重点有一行代码
this.results = locallyScopedConn.execSQL(this, sql, this.maxRows, null, this.resultSetType, this.resultSetConcurrency, doStreaming,
this.currentCatalog, cachedFields);
}
com.mysql.jdbc.ConnectionImpl.java
又是这个熟悉的类哈
public ResultSetInternalMethods execSQL(StatementImpl callingStatement, String sql, int maxRows, Buffer packet, int resultSetType,
int resultSetConcurrency, boolean streamResults, String catalog, Field[] cachedMetadata, boolean isBatch) throws SQLException {
synchronized (getConnectionMutex()) {
//
// Fall-back if the master is back online if we've issued queriesBeforeRetryMaster queries since we failed over
//
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();
}
//重点
return this.io.sqlQueryDirect(callingStatement, sql, encoding, null, maxRows, resultSetType, resultSetConcurrency, streamResults, catalog,
cachedMetadata);
}
//重点
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);
}
}
}
}
com.mysql.jdbc.MysqlIO.java 也是熟悉的类呀
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 {
//又是好长的代码呀
//只看关键的代码吧
// Send query command and sql query string
Buffer resultPacket = sendCommand(MysqlDefs.QUERY, null, queryPacket, false, null, 0);
}
//最终还是调用send（）与数据库服务器通信
final Buffer sendCommand(int command, String extraData, Buffer queryPacket, boolean skipCheck, String extraDataCharEncoding, int timeoutMillis)
throws SQLException {
this.commandCount++;
//
// We cache these locally, per-command, as the checks for them are in very 'hot' sections of the I/O code and we save 10-15% in overall performance by
// doing this...
//
this.enablePacketDebug = this.connection.getEnablePacketDebug();
this.readPacketSequence = 0;
int oldTimeout = 0;
if (timeoutMillis != 0) {
try {
oldTimeout = this.mysqlConnection.getSoTimeout();
this.mysqlConnection.setSoTimeout(timeoutMillis);
} catch (SocketException e) {
throw SQLError.createCommunicationsException(this.connection, this.lastPacketSentTimeMs, this.lastPacketReceivedTimeMs, e,
getExceptionInterceptor());
}
}
try {
checkForOutstandingStreamingData();
// Clear serverStatus...this value is guarded by an external mutex, as you can only ever be processing one command at a time
this.oldServerStatus = this.serverStatus;
this.serverStatus = 0;
this.hadWarnings = false;
this.warningCount = 0;
this.queryNoIndexUsed = false;
this.queryBadIndexUsed = false;
this.serverQueryWasSlow = false;
//
// Compressed input stream needs cleared at beginning of each command execution...
//
if (this.useCompression) {
int bytesLeft = this.mysqlInput.available();
if (bytesLeft > 0) {
this.mysqlInput.skip(bytesLeft);
}
}
try {
clearInputStream();
//
// PreparedStatements construct their own packets, for efficiency's sake.
//
// If this is a generic query, we need to re-use the sending packet.
//
if (queryPacket == null) {
int packLength = HEADER_LENGTH + COMP_HEADER_LENGTH + 1 + ((extraData != null) ? extraData.length() : 0) + 2;
if (this.sendPacket == null) {
this.sendPacket = new Buffer(packLength);
}
this.packetSequence = -1;
this.compressedPacketSequence = -1;
this.readPacketSequence = 0;
this.checkPacketSequence = true;
this.sendPacket.clear();
this.sendPacket.writeByte((byte) command);
if ((command == MysqlDefs.INIT_DB) || (command == MysqlDefs.CREATE_DB) || (command == MysqlDefs.DROP_DB) || (command == MysqlDefs.QUERY)
|| (command == MysqlDefs.COM_PREPARE)) {
if (extraDataCharEncoding == null) {
this.sendPacket.writeStringNoNull(extraData);
} else {
this.sendPacket.writeStringNoNull(extraData, extraDataCharEncoding, this.connection.getServerCharset(),
this.connection.parserKnowsUnicode(), this.connection);
}
} else if (command == MysqlDefs.PROCESS_KILL) {
long id = Long.parseLong(extraData);
this.sendPacket.writeLong(id);
}
send(this.sendPacket, this.sendPacket.getPosition());
} else {
this.packetSequence = -1;
this.compressedPacketSequence = -1;
//最终还是调用send（）与数据库服务器通信
send(queryPacket, queryPacket.getPosition()); // packet passed by PreparedStatement
}
} catch (SQLException sqlEx) {
// don't wrap SQLExceptions
throw sqlEx;
} catch (Exception ex) {
throw SQLError.createCommunicationsException(this.connection, this.lastPacketSentTimeMs, this.lastPacketReceivedTimeMs, ex,
getExceptionInterceptor());
}
Buffer returnPacket = null;
if (!skipCheck) {
if ((command == MysqlDefs.COM_EXECUTE) || (command == MysqlDefs.COM_RESET_STMT)) {
this.readPacketSequence = 0;
this.packetSequenceReset = true;
}
returnPacket = checkErrorPacket(command);
}
return returnPacket;
} catch (IOException ioEx) {
throw SQLError.createCommunicationsException(this.connection, this.lastPacketSentTimeMs, this.lastPacketReceivedTimeMs, ioEx,
getExceptionInterceptor());
} finally {
if (timeoutMillis != 0) {
try {
this.mysqlConnection.setSoTimeout(oldTimeout);
} catch (SocketException e) {
throw SQLError.createCommunicationsException(this.connection, this.lastPacketSentTimeMs, this.lastPacketReceivedTimeMs, e,
getExceptionInterceptor());
}
}
}
}
到这里为止，我们讲到整个过程了，代码太多，也比较难表达，希望能够帮到你们吧，我也是第一次读这些代码，还是很熟悉。
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