Java.sql包中的 java.sql.Driver, jdbc.sql.Connection等提供給程序開發人員統一的開發接口，數據庫提供商提供相應的實現，對程序開發人員來講只要知道這些接口都有哪些方法就可以了。但我們可以深入一些看看到底這裡面都做了那些事， 同時也可以學習其中的編程模式(如Interface模式等)。
1、 Class.forName(String classname) 的源碼為：
public final
class Class implements java.io.Serializable {
...
public static Class forName(String className)
throws ClassNotFoundException {
return forName0(className, true, ClassLoader.getCallerClassLoader());
}
...
}
關於forName0 請自己查看jdk source.
的是把指定的Class裝載到JVM中來。（注意class的裝載、初始化過程）在裝載過程中將執行被裝載類的static塊(如下)
2 sun的JdbcOdbcDriver 源碼：
public class JdbcOdbcDriver extends JdbcOdbcObject
implements JdbcOdbcDriverInterface
{
...
/**
* connect to DB
*/
public synchronized Connection connect(String s, Properties properties)
throws SQLException
{
if(JdbcOdbcObject.isTracing())
JdbcOdbcObject.trace("*Driver.connect (" + s + ")");
if(!acceptsURL(s))
return null;
if(hDbc != 0)
{
disconnect(hDbc);
closeConnection(hDbc);
hDbc = 0;
}
if(!initialize())
{
return null;
}
else
{
JdbcOdbcConnection jdbcodbcconnection = new JdbcOdbcConnection(OdbcApi, hEnv, this);
jdbcodbcconnection.initialize(getSubName(s), properties, DriverManager.getLoginTimeout());
jdbcodbcconnection.setURL(s);
return jdbcodbcconnection;
}
}
static
{
if(JdbcOdbcObject.isTracing())
JdbcOdbcObject.trace("JdbcOdbcDriver class loaded");
JdbcOdbcDriver jdbcodbcdriver = new JdbcOdbcDriver();
try
{
DriverManager.registerDriver(jdbcodbcdriver);
}
catch(SQLException sqlexception)
{
if(JdbcOdbcObject.isTracing())
JdbcOdbcObject.trace("Unable to register driver");
}
}
}
public interface JdbcOdbcDriverInterface
extends Driver
{
...
}
3 連接過程
jdbc.sql.Connection con = DriverManager.getConnection("jdbc:odbc:pubs","sa","");
public class DriverManager {
public static synchronized 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));
}
private static synchronized Connection getConnection(String url,java.util.Properties info,
ClassLoader callerCL) throws SQLException
{
...
Connection result = di.driver.connect(url, info);
...
}
}
4 結構圖：
