JDBC到底是怎么連上數(shù)據(jù)庫的?

2019-11-18 13:59:24

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供稿：網(wǎng)友

　　作者：jdeveloper

java.sql包中的 java.sql.Driver, jdbc.sql.Connection等提供給程序開發(fā)人員統(tǒng)一的開發(fā)接口
數(shù)據(jù)庫提供商提供相應(yīng)的實(shí)現(xiàn)，對程序開發(fā)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里面都做了那些事，同時也可以學(xué)習(xí)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(guān)于forName0 請自己查看jdk source.
目的是把指定的Class裝載到JVM中來。（注重class的裝載、初始化過程）
在裝載過程中將執(zhí)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);
...
}
}

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