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
前面讲过Driver的初始化，单机Server连接的获取，负载均衡连接的获取，今天讲一下主从复制，读写分析连接的获取：
从下面一段代码来看：
//如果url以jdbc:mysql:replication://则调用集群连接获取方法
if(StringUtils.startsWithIgnoreCase(url, "jdbc:mysql:replication://")) return connectReplicationConnection(url, info);
//NonRegisteringDriver
private Connection connectReplicationConnection(String url, Properties info)
throws SQLException
{
Properties parsedProps = parseURL(url, info);
if(parsedProps == null)
return null;
Properties masterProps = (Properties)parsedProps.clone();
Properties slavesProps = (Properties)parsedProps.clone();
slavesProps.setProperty("com.mysql.jdbc.ReplicationConnection.isSlave", "true");
String hostValues = parsedProps.getProperty("HOST");
if(hostValues != null)
{
StringTokenizer st = new StringTokenizer(hostValues, ",");
StringBuffer masterHost = new StringBuffer();
StringBuffer slaveHosts = new StringBuffer();
//Url中第一个host为master，后面为Slave
if(st.hasMoreTokens())
{
String hostPortPair[] = parseHostPortPair(st.nextToken());
if(hostPortPair[0] != null)
masterHost.append(hostPortPair[0]);
if(hostPortPair[1] != null)
{
masterHost.append(":");
masterHost.append(hostPortPair[1]);
}
}
boolean firstSlaveHost = true;
do
{
if(!st.hasMoreTokens())
break;
String hostPortPair[] = parseHostPortPair(st.nextToken());
if(!firstSlaveHost)
slaveHosts.append(",");
else
firstSlaveHost = false;
if(hostPortPair[0] != null)
slaveHosts.append(hostPortPair[0]);
if(hostPortPair[1] != null)
{
slaveHosts.append(":");
slaveHosts.append(hostPortPair[1]);
}
} while(true);
if(slaveHosts.length() == 0)
throw SQLError.createSQLException("Must specify at least one slave host to connect to for master/slave replication load-balancing functionality", "01S00", null);
//MaterHost
masterProps.setProperty("HOST", masterHost.toString());
//SlaveHost
slavesProps.setProperty("HOST", slaveHosts.toString());
}
return new ReplicationConnection(masterProps, slavesProps);
}
我们来看一下ReplicationConnection
public class ReplicationConnection
implements Connection, PingTarget
{
protected Connection currentConnection;//当前连接
protected Connection masterConnection;//主连接
protected Connection slavesConnection;//从连接
public ReplicationConnection(Properties masterProperties, Properties slaveProperties)
throws SQLException
{
NonRegisteringDriver driver = new NonRegisteringDriver();
StringBuffer masterUrl = new StringBuffer("jdbc:mysql://");
StringBuffer slaveUrl = new StringBuffer("jdbc:mysql://");
String masterHost = masterProperties.getProperty("HOST");
//初始化Master与Slave的URL
if(masterHost != null)
masterUrl.append(masterHost);
String slaveHost = slaveProperties.getProperty("HOST");
if(slaveHost != null)
slaveUrl.append(slaveHost);
String masterDb = masterProperties.getProperty("DBNAME");
masterUrl.append("/");
if(masterDb != null)
masterUrl.append(masterDb);
String slaveDb = slaveProperties.getProperty("DBNAME");
slaveUrl.append("/");
if(slaveDb != null)
slaveUrl.append(slaveDb);
slaveProperties.setProperty("roundRobinLoadBalance", "true");
//从Driver获取Master连接
masterConnection = (Connection)driver.connect(masterUrl.toString(), masterProperties);
//从Driver获取Slave连接
slavesConnection = (Connection)driver.connect(slaveUrl.toString(), slaveProperties);
slavesConnection.setReadOnly(true);
//当前连接为masterConnection
currentConnection = masterConnection;
}
public synchronized void setReadOnly(boolean readOnly)
throws SQLException
{
if(readOnly)
{
if(currentConnection != slavesConnection)
switchToSlavesConnection();
} else
if(currentConnection != masterConnection)
switchToMasterConnection();
}
//Master与SLave连接切换
private synchronized void switchToMasterConnection()
throws SQLException
{
swapConnections(masterConnection, slavesConnection);
}
//Slave与Master连接切换
private synchronized void switchToSlavesConnection()
throws SQLException
{
swapConnections(slavesConnection, masterConnection);
}
//切换连接
private synchronized void swapConnections(Connection switchToConnection, Connection switchFromConnection)
throws SQLException
{
String switchFromCatalog = switchFromConnection.getCatalog();
String switchToCatalog = switchToConnection.getCatalog();
if(switchToCatalog != null && !switchToCatalog.equals(switchFromCatalog))
switchToConnection.setCatalog(switchFromCatalog);
else
if(switchFromCatalog != null)
switchToConnection.setCatalog(switchFromCatalog);
boolean switchToAutoCommit = switchToConnection.getAutoCommit();
boolean switchFromConnectionAutoCommit = switchFromConnection.getAutoCommit();
if(switchFromConnectionAutoCommit != switchToAutoCommit)
switchToConnection.setAutoCommit(switchFromConnectionAutoCommit);
int switchToIsolation = switchToConnection.getTransactionIsolation();
int switchFromIsolation = switchFromConnection.getTransactionIsolation();
if(switchFromIsolation != switchToIsolation)
switchToConnection.setTransactionIsolation(switchFromIsolation);
currentConnection = switchToConnection;
}
//回滚
public synchronized void rollback()
throws SQLException
{
currentConnection.rollback();
}
public synchronized void rollback(Savepoint savepoint)
throws SQLException
{
currentConnection.rollback(savepoint);
}
//设置是否自动提交
public synchronized void setAutoCommit(boolean autoCommit)
throws SQLException
{
currentConnection.setAutoCommit(autoCommit);
}
public PreparedStatement prepareStatement(String sql)
throws SQLException
{
PreparedStatement pstmt = currentConnection.prepareStatement(sql);
((com.mysql.jdbc.Statement)pstmt).setPingTarget(this);
return pstmt;
}
public CallableStatement prepareCall(String sql)
throws SQLException
{
return currentConnection.prepareCall(sql);
}
}
总结：
从上面可以看出，主从集群的连接获取，首先解析url分离出Mater host和Slave host，第一个为Master，后面为Slave，NonRegisteringDriver创建复制连接时，返回的是一个ReplicationConnection，而ReplicationConnection内有三个连接分别为，currentConnection，masterConnection，slavesConnection，
这三个连接实际上是ConnectionImpl；默认情况下currentConnection为masterConnection，当我们设置readonly为true时，切换到slavesConnection，为false，切换到masterConnection；；ReplicationConnection的相关方法的实现，实际上是调用ConnectionImpl的相应方法。
//NonRegisteringReplicationDriver
public class NonRegisteringReplicationDriver extends NonRegisteringDriver
{
public NonRegisteringReplicationDriver()
throws SQLException
{
}
public Connection connect(String url, Properties info)
throws SQLException
{
Properties parsedProps = parseURL(url, info);
if(parsedProps == null)
return null;
Properties masterProps = (Properties)parsedProps.clone();
Properties slavesProps = (Properties)parsedProps.clone();
slavesProps.setProperty("com.mysql.jdbc.ReplicationConnection.isSlave", "true");
String hostValues = parsedProps.getProperty("HOST");
if(hostValues != null)
{
StringTokenizer st = new StringTokenizer(hostValues, ",");
StringBuffer masterHost = new StringBuffer();
StringBuffer slaveHosts = new StringBuffer();
if(st.hasMoreTokens())
{
String hostPortPair[] = parseHostPortPair(st.nextToken());
if(hostPortPair[0] != null)
masterHost.append(hostPortPair[0]);
if(hostPortPair[1] != null)
{
masterHost.append(":");
masterHost.append(hostPortPair[1]);
}
}
boolean firstSlaveHost = true;
do
{
if(!st.hasMoreTokens())
break;
String hostPortPair[] = parseHostPortPair(st.nextToken());
if(!firstSlaveHost)
slaveHosts.append(",");
else
firstSlaveHost = false;
if(hostPortPair[0] != null)
slaveHosts.append(hostPortPair[0]);
if(hostPortPair[1] != null)
{
slaveHosts.append(":");
slaveHosts.append(hostPortPair[1]);
}
} while(true);
if(slaveHosts.length() == 0)
throw SQLError.createSQLException("Must specify at least one slave host to connect to for master/slave replication load-balancing functionality", "01S00", null);
masterProps.setProperty("HOST", masterHost.toString());
slavesProps.setProperty("HOST", slaveHosts.toString());
}
return new ReplicationConnection(masterProps, slavesProps);
}
}