一般获取数据库连接的程序
Class.forName("com.mysql.jdbc.Driver");
final Connection connection = （Connection）DriverManager.getConnection("jdbc:mysql://localhost:3306/testDB","guoxiaoming","guoxiaoming");
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注册mysql驱动类下次再说，目前重点介绍Connection的建立
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public interface Connection extends Wrapper {
JDK的Connection提供了一种标准，与特定数据库的连接（会话）。在连接上下文中执行 SQL 语句并返回结果。
该Connection接口被数据库驱动类实现，保存有数据库连接中的IO类。
JDBC当中的DriverManager类封装了获取Connection对象的统一方法
public static Connection getConnection(String url, String user, String password) throws SQLException {
java.util.Properties info = new java.util.Properties();
// Gets the classloader of the code that called this method, may
// be null.
ClassLoader callerCL = DriverManager.getCallerClassLoader();
if (user != null) {
info.put("user", user);
}
if (password != null) {
info.put("password", password);
}
return (getConnection(url, info, callerCL));
}
进入getConnection（url，info，callerCL）方法查看可以看到，
Connection result = di.driver.connect(url, info);
代码最终获取了Connection对象
对应的driver驱动类实现，在jdbc当中
public class NonRegisteringReplicationDriver extends NonRegisteringDriver {
public NonRegisteringReplicationDriver() throws SQLException {
super();
}
/*
* (non-Javadoc)
*
* @see java.sql.Driver#connect(java.lang.String, java.util.Properties)
*/
public Connection connect(String url, Properties info) throws SQLException {
return connectReplicationConnection(url, info);
}
}
看到connectReplicationConnection(url,info)方法在父类NonRegisteringDriver类当中
return new ReplicationConnection(masterProps, slavesProps);
看到该类
public ReplicationConnection(Properties masterProperties,
Properties slaveProperties) throws SQLException {
this.driver = new NonRegisteringDriver();
this.slaveProperties = slaveProperties;
this.masterProperties = masterProperties;
this.initializeMasterConnection();
this.initializeSlaveConnection();
this.currentConnection = this.masterConnection;
}
初始化了两个链接，一个是masterConnection 一个是slaveConnection
看注释
/** * Connection that opens two connections, one two a replication master, and * another to one or more slaves, and decides to use master when the connection * is not read-only, and use slave(s) when the connection is read-only. * * @version $Id: ReplicationConnection.java,v 1.1.2.1 2005/05/13 18:58:38 * mmatthews Exp $ */
我们最终看到在ConnectionImpl类当中
protected static Connection getInstance(String hostToConnectTo,
int portToConnectTo, Properties info, String databaseToConnectTo,
String url) throws SQLException {
if (!Util.isJdbc4()) {
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);
}
实例化了该类的一个子类
public class JDBC4Connection extends ConnectionImpl
通过构造方法
public JDBC4Connection(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url) throws SQLException {
super(hostToConnectTo, portToConnectTo, info, databaseToConnectTo, url);
// TODO Auto-generated constructor stub
}
在其父类中
protected ConnectionImpl(String hostToConnectTo, int portToConnectTo, Properties info,
String databaseToConnectTo, String url)
throws SQLException {
this.connectionCreationTimeMillis = System.currentTimeMillis();
if (databaseToConnectTo == null) {
databaseToConnectTo = "";
}
重点关于方法
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()) {
connectOneTryOnly(isForReconnect, mergedProps);
return;
}
connectWithRetries(isForReconnect, mergedProps);
}
}
最终我们看到在coreConnect方法中实现了具体的链接
private void coreConnect(Properties mergedProps) throws SQLException,
IOException {
int newPort = 3306;
String newHost = "localhost";
String protocol = mergedProps.getProperty(NonRegisteringDriver.PROTOCOL_PROPERTY_KEY);
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;
this.io = new MysqlIO(newHost, newPort,
mergedProps, getSocketFactoryClassName(),
getProxy(), getSocketTimeout(),
this.largeRowSizeThreshold.getValueAsInt());
this.io.doHandshake(this.user, this.password,
this.database);
}
在new MysqlIO类当中的构造方法中实现
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);
this.sendPacket = new Buffer(INITIAL_PACKET_SIZE);
this.port = port;
this.host = host;
this.socketFactoryClassName = socketFactoryClassName;
this.socketFactory = createSocketFactory();
this.exceptionInterceptor = this.connection.getExceptionInterceptor();
try {
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();
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);
}
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());
}
}
this.mysqlConnection = this.socketFactory.connect(this.host,this.port, props);
这样就返回了Socket对象
在StandardSocketFactory类当中
if (this.host != null) {
if (!(wantsLocalBind || wantsTimeout || needsConfigurationBeforeConnect)) {
InetAddress[] possibleAddresses = InetAddress
.getAllByName(this.host);
Throwable caughtWhileConnecting = null;
// Need to loop through all possible addresses, in case
// someone has IPV6 configured (SuSE, for example...)
for (int i = 0; i < possibleAddresses.length; i++) {
try {
this.rawSocket = new Socket(possibleAddresses[i],
port);
configureSocket(this.rawSocket, props);
break;
} catch (Exception ex) {
caughtWhileConnecting = ex;
}
}
if (rawSocket == null) {
unwrapExceptionToProperClassAndThrowIt(caughtWhileConnecting);
}
} else {
// must explicitly state this due to classloader issues
// when running on older JVMs :(
try {
InetAddress[] possibleAddresses = InetAddress
.getAllByName(this.host);
Throwable caughtWhileConnecting = null;
Object localSockAddr = null;
Class<?> inetSocketAddressClass = null;
Constructor<?> addrConstructor = null;
try {
inetSocketAddressClass = Class
.forName("java.net.InetSocketAddress");
addrConstructor = inetSocketAddressClass
.getConstructor(new Class[] {
InetAddress.class, Integer.TYPE });
if (wantsLocalBind) {
localSockAddr = addrConstructor
.newInstance(new Object[] {
InetAddress
.getByName(localSocketHostname),
new Integer(0 /*
* use ephemeral
* port
*/) });
}
} catch (Throwable ex) {
unwrapExceptionToProperClassAndThrowIt(ex);
}
// Need to loop through all possible addresses, in case
// someone has IPV6 configured (SuSE, for example...)
for (int i = 0; i < possibleAddresses.length; i++) {
try {
this.rawSocket = new Socket();
configureSocket(this.rawSocket, props);
Object sockAddr = addrConstructor
.newInstance(new Object[] {
possibleAddresses[i],
Integer.valueOf(port) });
// bind to the local port if not using the ephemeral port
if (localSockAddr != null) {
socketBindMethod.invoke(rawSocket,
new Object[] { localSockAddr });
}
connectWithTimeoutMethod.invoke(rawSocket,
new Object[] { sockAddr,
Integer.valueOf(connectTimeout) });
break;
} catch (Exception ex) {
this.rawSocket = null;
caughtWhileConnecting = ex;
}
}
if (this.rawSocket == null) {
unwrapExceptionToProperClassAndThrowIt(caughtWhileConnecting);
}
} catch (Throwable t) {
unwrapExceptionToProperClassAndThrowIt(t);
}
}
return this.rawSocket;
}
针对host可能对应多个ip的可能性，连接到其中一个ip之后就break退出