ion() methods.
private static Connection getConnection(
String url, java.util.Properties info, ClassLoader callerCL) throws SQLException {
java.util.Vector drivers = null;
/*
* 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.
*/
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 + "\")");
if (!initialized) {
initialize();
}
synchronized (DriverManager.class){
// use the readcopy of drivers
drivers = readDrivers;
}
// Walk through the loaded drivers attempting to make a connection.
// Remember the first exception that gets raised so we can reraise it.
SQLException reason = null;
for (int i = 0; i < drivers.size(); i++) {
DriverInfo di = (DriverInfo)drivers.elementAt(i);
// If the caller does not have permission to load the driver then
// skip it.
if ( getCallerClass(callerCL, di.driverClassName ) != di.driverClass ) {
println(" skipping: " + di);
continue;
}
try {
println(" trying " + di);
Connection result = di.driver.connect(url, info);
if (result != null) {
// Success!
println("getConnection returning " + di);
return (result);
}
} catch (SQLException ex) {
if (reason == null) {
reason = ex;
}
}
}
// 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");
} 这个函数代码比较多，但是我们关注的核心代码就一句：
Connection result = di.driver.connect(url, info);
其中di就是我们前面加载驱动后DriverManager的成员变量readDrivers包含的一个对象，也就是调用com.mysql.jdbc.driver的connect函数，但是从上面该类代码可知，它只包含一个构造函数和静态代码段，connect函数从何而来？
别忘了com.mysql.jdbc.driver继承自NonRegisteringDriver，这也是MySQL驱动下的一个类，进入该类，找到connect函数：
package com.mysql.jdbc;
/***省略引用和注释***/
public class NonRegisteringDriver implements java.sql.Driver {
/***省略其他函数和注释***/
public java.sql.Connection connect(String url, Properties info)
throws SQLException {
Properties props = null;
if ((props = parseURL(url, info)) == null) {
return null;
}
try {
Connection newConn = new com.mysql.jdbc.Connection(host(props),
port(props), props, database(props), url, this);
return newConn;
} catch (SQLException sqlEx) {
// Don't wrap SQLExceptions, throw
// them un-changed.
throw sqlEx;
} catch (Exception ex) {
throw new SQLException(Messages
.getString("NonRegisteringDriver.17") //$NON-NLS-1$
+ ex.toString()
+ Messages.getString("NonRegisteringDriver.18"), //$NON-NLS-1$
SQLError.SQL_STATE_UNABLE_TO_CONNECT_TO_DATASOURCE);
}
}
}
因为NonRegisteringDriver也是java.sql.Driver的实现，返回的也是JDBC中Connection的实现，所以如上面向接口编程，即可从DriverManager中得到MySQL的Connection。
总结
JDBC的分析介绍到此结束，如果有兴趣大家可以看一下其他数据库驱动的源码，因为都是根据JDBC而来，所以大都大同小异。